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• Range size and cellular markers in the dentate gyrus were assessed in wild voles. • Voles with larger home ranges had more cell proliferation in the dentate gyrus. • Voles with larger home ranges had more pyknotic cells in the dentate gyrus. • There was no correlation between range size and a marker of neurogenesis (DCX). Neurogenesis occurs throughout adulthood within the dentate gyrus, and evidence indicates that these new neurons play a critical role in both spatial and social memory. However, a vast majority of past research on adult neurogenesis has involved experiments with captive mice and rats, making the generalizability of results to natural settings questionable. We assessed the connection between adult neurogenesis and memory by measuring the home range size of wild-caught, free-ranging meadow voles (Microtus pennsylvanicus). Adult male voles (n = 18) were captured, fitted with radio collars, and released back into their natural habitat, where each vole's home range was assessed using 40 radio-telemetry fixes over the course of 5 evenings. Voles were then recaptured, and brain tissue was collected. Cellular markers of cell proliferation (pHisH3, Ki67), neurogenesis (DCX), and pyknosis were labeled on histological sections and then quantified using either fluorescent or light microscopy. Voles with larger home ranges had significantly higher pHisH3+ cell densities within the granule cell layer and subgranular zone (GCL + SGZ) of the dentate gyrus and higher Ki67+ cell densities in the dorsal GCL + SGZ. Voles with larger ranges also had significantly higher pyknotic cell densities in the entire GCL + SGZ and in the dorsal GCL + SGZ. These results support the hypothesis that cell proliferation and cell death within the hippocampus are involved with spatial memory formation. However, a marker of neurogenesis (DCX+) was not correlated with range size, suggesting that there may be selective cellular turnover in the dentate gyrus when a vole is ranging through its environment. [ABSTRACT FROM AUTHOR]

• D1R expression was higher in the PCL of PD vs. sham animals in the cerebellum. • D1R expression was higher in the GCL of PD vs. sham animals in the cerebellum. • There were few differences in D2R expression in PD vs. sham animals in GCL or PCL. Parkinson's Disease (PD) is a neurodegenerative disease with loss of dopaminergic neurons in the nigrostriatal pathway resulting in basal ganglia (BG) dysfunction. This is largely why much of the preclinical and clinical research has focused on pathophysiological changes in these brain areas in PD. The cerebellum is another motor area of the brain. Yet, if and how this brain area responds to PD therapy and contributes to maintaining motor function fidelity in the face of diminished BG function remains largely unanswered. Limited research suggests that dopaminergic signaling exists in the cerebellum with functional dopamine receptors, tyrosine hydroxylase (TH) and dopamine transporters (DATs); however, much of this information is largely derived from healthy animals and humans. Here, we identified the location and relative expression of dopamine 1 receptors (D1R) and dopamine 2 receptors (D2R) in the cerebellum of a hemi-parkinsonian male rat model of PD. D1R expression was higher in PD animals compared to sham animals in both hemispheres in the purkinje cell layer (PCL) and granule cell layer (GCL) of the cerebellar cortex. Interestingly, D2R expression was higher in PD animals than sham animals mostly in the posterior lobe of the PCL, but no discernible pattern of D2R expression was seen in the GCL between PD and sham animals. To our knowledge, we are the first to report these findings, which may lay the foundation for further interrogation of the role of the cerebellum in PD therapy and/or pathophysiology. [ABSTRACT FROM AUTHOR]

• Neurons segmented automatically in phase contrast CT of postmortem brain tissue. • Optimal transport analysis quantifies morphometric differences between samples. • Cytoarchitecture in granular cell layer differs in MS and control group. • Nuclei of granular cell neurons in human cerebellum become more compact in MS. We investigate structural properties of neurons in the granular layer of human cerebellum with respect to their involvement in multiple sclerosis (MS). To this end we analyze data recorded by X-ray phase contrast tomography from tissue samples collected post mortem from a MS and a healthy control group. Using automated segmentation and histogram analysis based on optimal transport theory (OT) we find that the distributions representing nuclear structure in the granular layer move to a more compact nuclear state, i.e. smaller, denser and more heterogeneous nuclei in MS. We have previously made a similar observation for neurons of the dentate gyrus in Alzheimer's disease, suggesting that more compact structure of neuronal nuclei which we attributed to increased levels of heterochromatin, may possibly represent a more general phenomenon of cellular senescence associated with neurodegeneration. [ABSTRACT FROM AUTHOR]

• Regional differences in glial response at late phase after global hypoxia–ischemia. • Glassy large gemistocytes emerge upon removal of dead neurons in striate cortex. • CHI3L1+/GFAP+/S100β+ coexpressing gemistocytes in striate cortex, not in cerebellum. • Abundant IBA1+/CD68+/CHIT1+ macrophages at late posthypoxia phase in striate cortex. • CD68-/CHIT1-complex IBA1+ microglia at late posthypoxia phase in cerebellar cortex. Here, we studied the neuroinflammation- and ischemia-related glial markers chitotriosidase 1 (CHIT1) and chitinase-3-like protein 1 (CHI3L1, alias YKL-40) in the human striate cortex and cerebellum at different time points after global hypoxic-ischemic brain injury (HIBI). Both regions differ considerably in their glial cell population but are supplied by the posterior circulation. CHIT1 and CHI3L1 expression was compared to changes in microglial (IBA1, CD68), astrocytic (GFAP, S100β), and neuronal markers (H&E, neurofilament heavy chain, NfH; calretinin, CALR) using immunohistochemistry and multiple-label immunofluorescence. Initial striatal cortical and cerebellar Purkinje cell damage, detectable already 1/2 d after HIBI, led to delayed neuronal death, whereas loss of cerebellar NfH-positive stellate and CALR-positive granule cells was variable. During the first week post-HIBI, a transient reduction of IBA1-positive microglia was observed in both regions, and fragmented/clasmatodendritic cerebellar Bergmann glia appeared. In long-term survivors, both brain regions displayed high densities of activated IBA1-positive cells and CD68-positive macrophages, which showed CHIT1 co-localization in the striate cortex. Furthermore, enlarged GFAP- and S100β-positive astroglia emerged in both regions around 9–10 d post-HIBI, i.e., along with clearance of dead neurons from the neuropil, although GFAP-/S100β-positive gemistocytic astrocytes that co-expressed CHI3L1 were found only in the striate cortex. Thus, only GFAP-/S100β-positive astrocytes in the striate cortex, but not cerebellar Bergmann glia, differentiated into CHI3L1-positive gemistocytes. CHIT1 was co-expressed almost entirely in macrophages in the striate cortex and not cerebellum of long-term survivors, thereby indicating that CHIT1 and CHI3L1 could be valuable biomarkers for monitoring the outcome of global HIBI. [ABSTRACT FROM AUTHOR]

• 3DEM reveals dendrite diameter and spine density correlate with microtubule number. • In thick dendrites, microtubules support both dendritic branches and spines. • In thin unbranched dendrites, microtubules need only support local dendritic spines. • Existing dendritic microtubules are sufficient to supply synapses after plasticity. • Resources are delivered to and from dendrites in proportion to synapse load. Microtubules deliver essential resources to and from synapses. Three-dimensional reconstructions in rat hippocampus reveal a sampling bias regarding spine density that needs to be controlled for dendrite caliber and resource delivery based on microtubule number. The strength of this relationship varies across dendritic arbors, as illustrated for area CA1 and dentate gyrus. In both regions, proximal dendrites had more microtubules than distal dendrites. For CA1 pyramidal cells, spine density was greater on thicker than thinner dendrites in stratum radiatum , or on the more uniformly thin terminal dendrites in stratum lacunosum moleculare. In contrast, spine density was constant across the cone shaped arbor of tapering dendrites from dentate granule cells. These differences suggest that thicker dendrites supply microtubules to subsequent dendritic branches and local dendritic spines, whereas microtubules in thinner dendrites need only provide resources to local spines. Most microtubules ran parallel to dendrite length and associated with long, presumably stable mitochondria, which occasionally branched into lateral dendritic branches. Short, presumably mobile, mitochondria were tethered to microtubules that bent and appeared to direct them into a thin lateral branch. Prior work showed that dendritic segments with the same number of microtubules had elevated resources in subregions of their dendritic shafts where spine synapses had enlarged, and spine clusters had formed. Thus, additional microtubules were not required for redistribution of resources locally to growing spines or synapses. These results provide new understanding about the potential for microtubules to regulate resource delivery to and from dendritic branches and locally among dendritic spines. [ABSTRACT FROM AUTHOR]

• Cognitive deficits were induced following short-term CPZ exposure in mice. • NPCs/NGCs but not NSCs in the hippocampus were decreased by CPZ exposure. • STAT3 was activated in NSCs but not in NPCs/NGCs by CPZ exposure. • Subsequent CPZ exposure increased BrdU+ NSCs but not BrdU+ NPCs/NGCs. • Differentiation of NSCs into NPCs may be inhibited by CPZ exposure. Recent studies have emphasized that adult hippocampal neurogenesis impairment may be associated with cognitive problems. Because cuprizone (CPZ), a copper-chelating reagent, was shown to decrease the production of new neurons, we aimed to further understand the involvement of adult hippocampal neurogenesis impairment in cognitive function by using a short-term (2-week) CPZ exposure paradigm. The CPZ-fed mice showed cognitive deficits, i.e., impaired sensorimotor gating and reduced social novelty preference, compared to normal-fed mice. Although a long-term (e.g., 5-week) CPZ exposure paradigm was found to cause demyelination, we encountered that the labeling for myelin in the hippocampus was unaffected by 2-week CPZ exposure. The densities of neuronal progenitor cells (NPCs) and newborn granule cells (NGCs) were lower in CPZ-fed mice than in normal-fed mice, while those of neural stem cells (NSCs) were comparable between groups. We then examined whether short-term CPZ exposure might induce activation of signal transducer and activator of transcription 3 (STAT3), which plays a major role in cytokine receptor signaling. The densities of phosphorylated STAT3-positive (pSTAT3+) NSCs were higher in CPZ-fed mice than in normal-fed mice, while those of pSTAT3+ NPCs/NGCs were very low in both groups. Interestingly, the densities of bromodeoxyuridine-positive (BrdU+) NSCs were higher in CPZ-fed mice than in normal-fed mice 2 weeks after BrdU injection, while those of BrdU+ NPCs/NGCs were lower in CPZ-fed mice than in normal-fed mice. These findings suggest that short-term CPZ exposure inhibits differentiation of NSCs into NPCs via activation of STAT3, which may in part underlie cognitive deficits. [ABSTRACT FROM AUTHOR]

• DGCs express sAHP-mediating currents associated with a burst-like phenotype. • The sAHP-mediating current is carried by at least Kv7 and Kir6 channels. • Perforant path-dentate gyrus LTP is amplified by blocking sAHP-mediating currents. The slow afterhyperpolarizing potential (sAHP) can silence a neuron for hundreds of milliseconds. Thereby, the sAHP determines the discharge behavior of many types of neurons. In dentate granule cells (DGCs), serving as a filter into the hippocampal network, mostly tonic or adapting discharge properties have been described. As under standard whole-cell recording conditions the sAHP is inhibited, we reevaluated the intrinsic functional phenotype of DGCs and the conductances underlying the sAHP, using gramicidine-perforated patch-clamp technique. We found that in 97/113 (86%) of the DGCs, a burst of action potentials (APs) to excitation ended by a large sAHP, despite continued depolarization. This result suggests that burst-like firing is the default functional phenotype of DGCs and that sAHPs are important for it. Indeed, burst-like firing DGCs showed a significantly higher sAHP-current (I sAHP) amplitude compared to spike-frequency adapting cells (16/113 = 14%). The I sAHP was mediated by K v 7 and K ir 6 channels by pharmacological inhibition using XE991 and tolbutamide, although heterogeneously among DGCs. The percent inhibition of I sAHP by these compounds also correlated with the AP number and AP burst length. Application of 100 µM nickel after XE991 and tolbutamide detected a third conductance contributing to burst-like firing and the sAHP, most likely mediated by T-type calcium channels. Lastly, medial perforant path-dentate gyrus long-term potentiation was amplified by XE991 and tolbutamide. In conclusion, the sAHP shapes intrinsic burst-like firing which, under physiological circumstances, could be controlled via cholinergic afferents and ATP metabolism. [ABSTRACT FROM AUTHOR]

• Purkinje cells are born early in cerebellar development and they orchestrate the formation of a transient circuit. • Granule cells are born later and reorganize cerebellar connectivity and shape cerebellar morphology. • Cerebellar function is dependent upon Purkinje cell- and granule cell-mediated developmental processes. • Impairments during cerebellar development can lead to a wide range of neurological and neuropsychiatric conditions. • The relationship between abnormal cerebellar circuit formation and specific functional deficits remains unresolved. Cerebellar development has a remarkably protracted morphogenetic timeline that is coordinated by multiple cell types. Here, we discuss the intriguing cellular consequences of interactions between inhibitory Purkinje cells and excitatory granule cells during embryonic and postnatal development. Purkinje cells are central to all cerebellar circuits, they are the first cerebellar cortical neurons to be born, and based on their cellular and molecular signaling, they are considered the master regulators of cerebellar development. Although rudimentary Purkinje cell circuits are already present at birth, their connectivity is morphologically and functionally distinct from their mature counterparts. The establishment of the Purkinje cell circuit with its mature firing properties has a temporal dependence on cues provided by granule cells. Granule cells are the latest born, yet most populous, neuronal type in the cerebellar cortex. They provide a combination of mechanical, molecular and activity-based cues that shape the maturation of Purkinje cell structure, connectivity and function. We propose that the wiring of Purkinje cells for function falls into two developmental phases: an initial phase that is guided by intrinsic mechanisms and a later phase that is guided by dynamically-acting cues, some of which are provided by granule cells. In this review, we highlight the mechanisms that granule cells use to help establish the unique properties of Purkinje cell firing. [ABSTRACT FROM AUTHOR]

• Lugaro cells form interconnected somatodendritic meshwork beneath Purkinje cells of given aldolase C-defined compartments. • Somatodendritic elements of LCs receive a variety of excitatory, inhibitory, and modulatory inputs. • LCs project a dense lattice of ascending and transverse axons that innervates molecular layer interneurons and Golgi cells. • Thus, LCs can effectively disinhibit cerebellar cortical activities as an interneuron-selective interneuron. Purkinje cells (PCs) are principal cerebellar neurons, and several classes of interneurons modulate their activity. Lugaro cells (LCs) are one such inhibitory interneuron with distinctive cytology and location, but still most enigmatic among cerebellar neurons. Here we serendipitously produced a novel transgenic mouse line, where a half of Yellow Cameleon (YC)(+) cells in the cerebellar cortex were judged to be LCs, and YC(+) LCs were estimated to constitute one-third of the total LC populations. Neurochemically, two-thirds of YC(+) LCs were dually GABAergic/glycinergic, with the rest being GABAergic. Beneath the PC layer, they extended a sheet of somatodendritic meshwork interconnected with neighboring LCs by adherens junctions, and received various inputs from climbing fibers, mossy fibers, granule cell axons, recurrent PC axons, Golgi cell axons, LC axons, and serotonergic fibers. Intriguingly, somatodendritic elements of individual LCs preferentially extended within a given cerebellar compartment defined by aldolase C expression. In turn, YC(+) LCs projected a dense lattice of ascending and transverse axons to the molecular layer, and innervated molecular layer interneurons (basket and stellate cells) and Golgi cells, but not PCs. Of note, ascending axons profusely innervated individual targets within a cerebellar compartment, while transverse axons ran across several compartments and innervated targets sparsely. This unique circuit configuration highlights that LCs integrate various excitatory, inhibitory, and modulatory inputs coming to the belonging cerebellar compartment and that, as an interneuron-selective interneuron, LCs can effectively disinhibit cerebellar cortical activities in a compartment-dependent manner through inhibition of inhibitory interneurons selectively targeting PCs and granule cells. [ABSTRACT FROM AUTHOR]

• Regular structures of cerebellar neural networks are formed through dynamic processes during postnatal development. • This review summarizes developmental processes in the cerebellum regulated by extracellular signaling. • Many processes indeed rely on extracellular signaling via synaptic transmission or secreted/cell adhesion molecules. • Extracellular signaling may spatiotemporally coordinate different processes to form organized cerebellar networks. The cerebellum forms regular neural network structures consisting of a few major types of neurons, such as Purkinje cells, granule cells, and molecular layer interneurons, and receives two major inputs from climbing fibers and mossy fibers. Its regular structures consist of three well-defined layers, with each type of neuron designated to a specific location and forming specific synaptic connections. During the first few weeks of postnatal development in rodents, the cerebellum goes through dynamic changes via proliferation, migration, differentiation, synaptogenesis, and maturation, to create such a network structure. The development of this organized network structure presumably relies on the communication between developing elements in the network, including not only individual neurons, but also their dendrites, axons, and synapses. Therefore, it is reasonable that extracellular signaling via synaptic transmission, secreted molecules, and cell adhesion molecules, plays important roles in cerebellar network development. Although it is not yet clear as to how overall cerebellar development is orchestrated, there is indeed accumulating lines of evidence that extracellular signaling acts toward the development of individual elements in the cerebellar networks. In this article, we introduce what we have learned from many studies regarding the extracellular signaling required for cerebellar network development, including our recent study suggesting the importance of unbiased synaptic inputs from parallel fibers. [ABSTRACT FROM AUTHOR]

• In newborn adult hippocampal neurons, FGFR signaling through FRS is required to promote proximal dendrite length. • In contrast, FGFRs are required to inhibit distal dendrite length through PLCγ in newborn adult hippocampal neurons. • FGFRs through as yet unidentified mediators promote or counterbalance inhibition of dendrite length by FGFR-PLCγ. Fibroblast Growth Factor Receptors (FGFRs) play crucial roles in promoting dendrite growth and branching during development. In mice, three FGFR genes, Fgfr1 , Fgfr2 , and Fgfr3 , remain expressed in the adult neurogenic niche of the hippocampal dentate gyrus. However, the function of FGFRs in the dendritic maturation of adult-born neurons remains largely unexplored. Here, using conditional alleles of Fgfr1, Fgfr2, and Fgfr3 as well as Fgfr1 alleles lacking binding sites for Phospholipase-Cγ (PLCγ) and FGF Receptor Substrate (FRS) proteins, we test the requirement for FGFRs in dendritogenesis of adult-born granule cells. We find that deleting all three receptors results in a small decrease in proximal dendrite elaboration. In contrast, specifically mutating Tyr766 in FGFR1 (a PLCγ binding site) in an Fgfr2;Fgfr3 deficient background results in a dramatic increase of overall dendrite elaboration, while blocking FGFR1-FRS signaling causes proximal dendrite deficits and, to a lesser extent than Tyr766 mutants, increases distal dendrite elaboration. These findings reveal unexpectedly complex roles for FGFRs and their intracellular mediators in regulating proximal and distal dendrite elaboration, with the most notable role in suppressing distal elaboration through the PLCγbinding site. [ABSTRACT FROM AUTHOR]

• TLE related pathology in MEA influences neuron loss and gliosis in the hippocampus. • The CA1c region is the most susceptible of the three subdivisions of CA1. • Intervention in MEA with d -serine mitigated hippocampal pathology. • Entrainment of the hippocampus in TLE is mediated via the temporoammonic pathway. • This work is of relevance to TLE-related neurodegeneration and neuroinflammation. Entrainment of the hippocampus by the medial entorhinal area (MEA) in Temporal Lobe Epilepsy (TLE), the most common type of drug-resistant epilepsy in adults, is believed to be mediated primarily through the perforant pathway (PP), which connects stellate cells in layer (L) II of the MEA with granule cells of the dentate gyrus (DG) to drive the hippocampal tri-synaptic circuit. Using immunohistochemistry, high-resolution confocal microscopy and the rat pilocarpine model of TLE, we show here that the lesser known temporoammonic pathway (TAP) plays a significant role in transferring MEA pathology to the CA1 region of the hippocampus independently of the PP. The pathology observed was region-specific and restricted primarily to the CA1c subfield of the hippocampus. As shown previously, daily intracranial infusion of d -serine (100 μm), an antagonist of GluN3-containing triheteromeric N-Methyl d -aspartate receptors (t -NMDARs), into the MEA prevented loss of LIII neurons and epileptogenesis. This intervention in the MEA led to the rescue of hippocampal CA1 neurons that would have otherwise perished in the epileptic animals, and down regulation of the expression of astrocytes and microglia thereby mitigating the effects of neuroinflammation. Interestingly, these changes were not observed to a similar extent in other regions of vulnerability like the hilus, DG or CA3, suggesting that the pathology manifest in CA1 is driven predominantly through the TAP. This work highlights TAP's role in the entrainment of the hippocampus and identifies specific areas for therapeutic intervention in dealing with TLE. [ABSTRACT FROM AUTHOR]

• Parvalbumin expression shows etiology-related difference in temporal lobe epilepsy. • Sprouting of parvalbumin-positive axons are found in the dentate molecular layer. • Ectopic parvalbumin-positive neurons are characteristics of hippocampal sclerosis. • Targets of parvalbumin-positive axon terminals are changed in hippocampal sclerosis. In the present study, we examined parvalbumin-immunoreactive cells and axons in the dentate gyrus of surgically resected tissues of therapy-resistant temporal lobe epilepsy (TLE) patients with different etiologies. Based on MRI results, five groups of patients were formed: (1) hippocampal sclerosis (HS), (2) malformation of cortical development, (3) malformation of cortical development + HS, (4) tumor-induced TLE, (5) patients with negative MRI result. Four control samples were also included in the study. Parvalbumin-immunoreactive cells were observed mostly in subgranular location in the dentate hilus in controls, in tumor-induced TLE, in malformation of cortical development and in MR-negative cases. In patients with HS, significant decrease in the number of hilar parvalbumin-immunoreactive cells and large numbers of ectopic parvalbumin-containing neurons were detected in the dentate gyrus' molecular layer. The ratio of ectopic/normally-located cells was significantly higher in HS than in other TLE groups. In patients with HS, robust sprouting of parvalbumin-immunoreactive axons were frequently visible in the molecular layer. The extent of sprouting was significantly higher in TLE patients with HS than in other groups. Strong sprouting of parvalbumin-immunoreactive axons were frequently observed in patients who had childhood febrile seizure. Significant correlation was found between the level of sprouting of axons and the ratio of ectopic/normally-located parvalbumin-containing cells. Electron microscopy demonstrated that sprouted parvalbumin-immunoreactive axons terminate on proximal and distal dendritic shafts as well as on dendritic spines of granule cells. Our results indicate alteration of target profile of parvalbumin-immunoreactive neurons in HS that contributes to the known synaptic remodeling in TLE. [ABSTRACT FROM AUTHOR]

• Prrrt2 −/− mice exhibit paroxysmal dystonia with face validity. • Prrt2 transcripts reside in granule cells but not Purkinje cells or interneurons within cerebellar cortex. • In the cerebellar molecular layer, Prrt2 −/− mice have increased numbers of docked vesicles but decreased total vesicles. • In Prrt2 −/− mice, we found reduced parallel fiber facilitation at parallel fiber-Purkinje cell synapses. PRRT2 loss-of-function mutations have been associated with familial paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions and choreoathetosis, and benign familial infantile seizures. Dystonia is the foremost involuntary movement disorder manifest by patients with PKD. Using a lacZ reporter and quantitative reverse-transcriptase PCR, we mapped the temporal and spatial distribution of Prrt2 in mouse brain and showed the highest levels of expression in cerebellar cortex. Further investigation into PRRT2 localization within the cerebellar cortex revealed that Prrt2 transcripts reside in granule cells but not Purkinje cells or interneurons within cerebellar cortex, and PRRT2 is presynaptically localized in the molecular layer. Analysis of synapses in the cerebellar molecular layer via electron microscopy showed that Prrt2 −/− mice have increased numbers of docked vesicles but decreased vesicle numbers overall. In addition to impaired performance on several motor tasks, approximately 5% of Prrt2 −/− mice exhibited overt PKD with clear face validity manifest as dystonia. In Prrt2 mutants, we found reduced parallel fiber facilitation at parallel fiber-Purkinje cell synapses, reduced Purkinje cell excitability, and normal cerebellar nuclear excitability, establishing a potential mechanism by which altered cerebellar activity promotes disinhibition of the cerebellar nuclei, driving motor abnormalities in PKD. Overall, our findings replicate, refine, and expand upon previous work with PRRT2 mouse models, contribute to understanding of paroxysmal disorders of the nervous system, and provide mechanistic insight into the role of cerebellar cortical dysfunction in dystonia. [ABSTRACT FROM AUTHOR]

• Draxin knockout resulted in fewer proliferative cells in the subgranular zone (SGZ). • Draxin knockout did not affect the cell cycle duration of SGZ cells. • Draxin -deficient mice displayed enhanced neuronal differentiation in the SGZ. • Lrp6 was expressed in granule cell progenitors. The hippocampus is characterized by the presence of life-long neurogenesis. To elucidate the molecular mechanism regulating hippocampal neurogenesis, we studied the functions of the chemorepellent Draxin in neuronal proliferation and differentiation in the postnatal dentate gyrus. The present in vivo cell labeling and fate tracking analyses revealed enhanced differentiation of hippocampal neural stem and progenitor cells (hNSPCs) in the subgranular zone (SGZ) of Draxin -deficient mice. We observed a reduction in the number of BrdU-pulse labeled or Ki-67 immunopositive SGZ cells in the mutant mice. However, Draxin deficiency did not affect cell cycle duration of SGZ cells. In situ hybridization analysis indicated that the receptor component of the canonical Wnt pathway, Lrp6, is expressed in SGZ cells, including Nestin and Sox2 double-positive hNSPCs. Taken together with the previous finding that Draxin interacts physically with Lrp6, we postulate that Draxin plays a pivotal role in the regulation of Wnt-driven hNSPC differentiation to modulate the rate of neuronal differentiation in the progenitor population. [ABSTRACT FROM AUTHOR]

• Mice trained in a single-trial olfactory fear conditioning task maintain associative memory for at least two weeks. • Both hippocampal and olfactory granule cells express c-Fos mainly during fear memory retrieval but not during acquisition. • In the dentate gyrus, retrieval-induced c-Fos expression is limited to the suprapyramidal blade. • Adult-born olfactory neurons show little c-Fos activity during acquisition and retrieval of odor-associated fear memory. The production of new neurons and their incorporation into preexisting neuronal circuits occur throughout adulthood in the olfactory bulb and the hippocampal dentate gyrus of the mammalian brain. To determine whether the adult-born neurons are engaged in the acquisition and retrieval of olfactory associative memory, we developed and validated a single-trial olfactory fear conditioning protocol in mice which allows to detect activation of newborn neurons during a specific episode of memory acquisition. Using c-Fos mapping of neuronal activity, we then examined the activation of new and preexisting neurons during training and testing sessions. We found that a single trial of olfactory fear conditioning did not lead to a significant increase in the number of c-Fos-positive granule cells (GCs) of the olfactory bulb and the dentate gyrus. However, the activity of these two cell populations was dramatically increased during memory retrieval. Activation of neurons in the dentate gyrus during memory retrieval was observed mainly in the suprapyramidal blade. In the olfactory bulb, 1.6–2.7% of newborn GCs marked with thymidine analogues (2, 4, and 6 weeks old) expressed c-Fos during memory retrieval, while in the dentate gyrus no newborn neurons were found among the c-Fos-positive cells. These data are consistent with the hypothesis that adult-born GCs of the olfactory bulb are less involved in odor-cued associative fear memory than in odor-cued operant behavior memory. [ABSTRACT FROM AUTHOR]

In the adult hippocampal dentate gyrus (DG), the majority of newly generated cells are eliminated by apoptotic mechanisms. The apoptosis repressor with caspase recruitment domain (ARC), encoded by the Nol3 gene, is a potent and multifunctional death repressor that inhibits both death receptor and mitochondrial apoptotic signaling. The aim of the present study was to parse the role of ARC in the development of new granule cell neurons. Nol3 gene expression as revealed by in situ hybridization is present in the entire dentate granule cell layer. Moreover, a comparison of Nol3 expression between FACS-sorted Sox2-positive neural stem cells and Doublecortin (DCX)-positive immature neurons demonstrates upregulation of Nol3 during neurogenesis. Using ARC-deficient mice, we show that proliferation and survival of BrdU birth-dated cells are strongly reduced in the absence of ARC while neuronal-glial fate choice is not affected. Both the number of DCX-positive cells and the number of calretinin (CR)-positive immature postmitotic neurons are reduced in the hippocampus of ARC−/− mice. ARC knockout is not associated with increased numbers of microglia or with microglia activation. However, hippocampal brain-derived neurotrophic factor (BDNF) protein content is significantly increased in ARC−/− mice, possibly representing a compensatory response. Collectively, our results suggest that ARC plays a critical cell-autonomous role in preventing cell death during adult granule cell neogenesis. • Reduced net hippocampal neurogenesis in ARC−/− mice • ARC knockout not associated with increased microglia density or activation • Increased BDNF concentrations in microdissected left hippocampus of ARC−/− mice [ABSTRACT FROM AUTHOR]

Exposure to commonly used anesthetics is associated with widespread neuroapoptosis in neonatal animals. Vulnerability of developing hippocampal dentate gyrus granule cells to anesthetic neurotoxicity peaks approximately 2 weeks after cell birth, as measured by bromodeoxyuridine birth dating, regardless of the age of the animal. The present study examined whether the vulnerable window can be further characterized by utilizing a transgenic approach. Proopiomelanocortin enhanced green fluorescent protein (POMC-EGFP) mice (postnatal day 21) were exposed to 3% sevoflurane for 6 h. Following exposure, cleaved caspase 3, expression of EGFP and differential maturational markers were quantified and compared with unanesthetized littermates. Electrophysiological properties of EGFP+ and EGFP− cells in the subgranular zone and the inner half of the granule cell layer were recorded by whole-cell patch-clamp. We found that sevoflurane significantly increased apoptosis of POMC-EGFP+ granule cells that accounted for approximate 1/3 of all apoptotic cells in dentate gyrus. Apoptotic EGFP− granule cells more frequently expressed the immature neuronal marker calretinin (75.4% vs 45.0%, P < 0.001) and less frequently the late progenitor marker NeuroD1 (21.9% vs 87.9%, P < 0.001) than EGFP+ granule cells. Although EGFP− granule cells were more mature in immunostaining than EGFP+ granule cells, their electrophysiological properties partially overlapped in terms of input resistance, resting membrane potential and action potential amplitude. Our results revealed the POMC stage, when GABA acts as an excitatory neurotransmitter, only partly captures susceptibility to anesthetic neurotoxicity, suggesting the vulnerable window of anesthesia-induced neuroapoptosis extends from the end of POMC+ stage to the post-POMC+ stage when depolarizing glutamatergic inputs emerge. • Sevoflurane increased apoptosis of POMC-EGFP+ granule cells in DG by seven-fold. • About one third of sevoflurane-induced apoptotic granule cells were POMC-EGFP+. • POMC-EGFP was not the exclusive marker predicting anesthesia-induced apoptosis. • The post-POMC+ stage covered the majority of apoptotic cells induced by anesthesia. [ABSTRACT FROM AUTHOR]

Prescription opioid abuse is a serious public health issue. Recently, we showed that female and male Sprague–Dawley rats acquire conditioned place preference (CPP) to the mu opioid receptor agonist oxycodone. Anatomical analysis of the hippocampus from these rats unveiled sex differences in the opioid system in a way that would support excitation and opiate associative learning processes especially in females. In this study, we examined the expression and protein densities of opioid, plasticity, stress and related kinase and signaling molecules in the hippocampus of female and male rats following oxycodone CPP. Oxycodone CPP females have: a) increases in ARC (activity regulated cytoskeletal-associated protein)-immunoreactivity (ir) in CA3 pyramidal cells; b) decreases in Npy (neuropeptide Y) gene expression in the medial hippocampus but higher numbers of NPY-containing hilar interneurons compared to males; c) increases in Crhr2 (corticotropin releasing factor receptor 2) expression in CA2/3; d) increases in Akt1 (AKT serine/threonine kinase 1) expression in medial hippocampus; and e) decreases in phosphorylated MAPK (mitogen activated protein kinase)-ir in CA1 and dentate gyrus. Oxycodone CPP males have: a) increases in Bdnf (brain derived-neurotrophic factor) expression, which is known to be produced in granule cells, relative to females; b) elevated Mapk1 expression and pMAPK-ir in the dentate hilus which harbors newly generated granule cells; and c) increases in CRHR1-ir in CA3 pyramidal cell soma. These sex-specific changes in plasticity, stress and kinase markers in hippocampal circuitry parallel previously observed sex differences in the opioid system after oxycodone CPP. Unlabelled Image • Hippocampal gene expression and protein levels vary depending on sex after oxycodone (Oxy) conditioned place preference (CPP) • After Oxy CPP, Npy mRNA expression decreases but a subset of NPY-labeled cells increases in the dentate gyrus (DG) in females • In CA3, plasticity and stress markers differentially increase in Oxy CPP females (ARC, Crhr2) and males (Arc , CRHR1) • After Oxy CPP, signaling kinases (Akt1 , pAKT, pMAPK) change in opposite directions in females and males in CA1 and DG • Differences in signaling, kinase, and stress markers suggest sex-specific hippocampal pathways for opioid-associated learning [ABSTRACT FROM AUTHOR]

Neuroinflammation plays an important role in epileptic disorders. Toll-like receptors (TLRs) are the key signal transduction tools by which neuroinflammation may promote epileptogenesis. Depending on the stimulus nature, TLRs may engage a distinct signaling pathway. We examined the impact of early minor activation of TLR4 and TLR2 on the severity of seizure in the pilocarpine rat model of temporal lobe epilepsy (TLE). One μg of Lipopolysaccharides (LPS), Monophosphoryl lipid A (MPL), Pam3Cysor or vehicles were microinjected into the right lateral ventricle of the male Wistar rats. 24 h later, seizures were induced by intraperitoneal injection of pilocarpine, and seizure-related behaviors were monitored. 24 h after seizure induction, the hippocampal level of pro/anti-inflammatory mediators and electrophysiological properties of the dentate gyrus (DG) granular cells were investigated by western blot and whole cell patch clamp techniques, respectively. Pretreatment with TLR ligands resulted in decreased seizure severity, lower hippocampal pro-inflammatory (IL-1β and IL-6) cytokines and higher anti-inflammatory (IL-10 and TGF- β) mediators in the pilocarpine-treated rats. Pilocarpine induced profound hyperexcitability in the DG granule cells accompanied by potentiated excitatory postsynaptic currents (EPSCs) and dampened inhibitory postsynaptic currents (IPSCs), in contrast to the control group. However, pretreatment with TLR ligands preserved almost normal excitability and synaptic transmission against the pilocarpine. In conclusion, early activation of TLR4 and TLR2, probably through preserving normal hippocampal cytokine profile and neuronal function attenuates seizure severity in the rat model of TLE. • Pilocarpine induced neuroinflammation and neuronal hyper-excitability. • Pretreatment with TLR ligands dampened neuroinflammation and attenuated the seizure severity. • Preconditioning through TLRs normalized neuronal excitability and synaptic transmissions. [ABSTRACT FROM AUTHOR]

Highlights • Physiological odorant processing in vivo at olfactory bulb level is open to debate. • Olfactory bulb reveals specific optical imaging patterns of glomerular activation in GCaMP2 mouse. • In vivo -activation of GABAergic receptors confine the signal transduction along mitral cell secondary dendrite. • The mitral-granual-reciprocal synapses should work during odor-evoked response in physiological situation. Abstract The olfactory circuitry in mice involves a well-characterized, vertical receptor type-specific organization, but the localized inhibitory effect from granule cells on action potentials that propagate laterally in secondary dendrites of mitral cell remains open to debate. To understand the functional dynamics of the lateral (horizontal) circuits, we analyzed odor-induced signaling using transgenic mice expressing a genetically encoded Ca2+ indicator specifically in mitral/tufted and some juxtaglomerular cells. Optical imaging of the dorsal olfactory bulb (dOB) revealed specific patterns of glomerular activation in response to odor presentation or direct electric stimulation of the olfactory nerve (ON). Application of a mixture of ionotropic and metabotropic glutamate receptor antagonists onto the exposed dOB completely abolished the responses to direct stimulation of the ON as well as discrete odor-evoked glomerular responses patterns, while a spatially more widespread response component increased and expanded into previously nonresponsive regions. To test whether the widespread odor response component represented signal propagation along mitral cell secondary dendrites, an NMDA receptor antagonist alone was applied to the dOB and was found to also increase and expand odor-evoked response patterns. Finally, with dOB excitatory synaptic transmission completely blocked, application of 1 mM muscimol (a GABA A receptor agonist) to a circumscribed volume in the deep external plexiform layer (EPL) induced an odor non-responsive area. These results indicate that odor stimulation can activate olfactory reciprocal synapses and control lateral interactions among olfactory glomerular modules along a wide range of mitral cell secondary dendrites by modulating the inhibitory effect from granule cells. [ABSTRACT FROM AUTHOR]

Dentate granule cells (DGCs) play important roles in cognitive processes. Knowledge about how growth factors such as FGFs and neurotrophins contribute to the maturation and synaptogenesis of DGCs is limited. Here, using brain-specific and germline mouse mutants we show that a module of neurotrophin and FGF signaling, the FGF Receptor Substrate (FRS) family of intracellular adapters, FRS2 and FRS3, are together required for postnatal brain development. In the hippocampus, FRS promotes dentate gyrus morphogenesis and DGC maturation during developmental neurogenesis, similar to previously published functions for both neurotrophins and FGFs. Consistent with a role in DGC maturation, two-photon imaging revealed that Frs2,3 -double mutants have reduced numbers of dendritic branches and spines in DGCs. Functional analysis further showed that double-mutant mice exhibit fewer excitatory synaptic inputs onto DGCs. These observations reveal roles for FRS adapters in DGC maturation and synaptogenesis and suggest that FRS proteins may act as an important node for FGF and neurotrophin signaling in postnatal hippocampal development. [ABSTRACT FROM AUTHOR]

The tyrosine kinases of the Syk family are essential components of the well-characterized immunoreceptor ITAM-based signaling pathway. However, ITAM-based signaling typically does not function in isolation. Instead, it is enmeshed in the molecular network controlling cellular adhesion and chemotaxis. Consistent with the increasing number of data involving ITAM-bearing molecules in neuronal functions, we previously depicted a role for Syk kinases in the establishment of neuronal connectivity. In the developing cerebellum, we found that Syk is essentially expressed in the granule cells (GC) and more importantly, phosphorylated on tyrosine residues representative of an active form of the kinase in tangentially migrating GC. In light of these findings, experiments were performed to establish the implication of Syk in this process. We showed that Syk state of phosphorylation is spatiotemporally regulated during GC ontogeny. Moreover, the analysis of external granular layer microexplants treated with a Syk pharmacological inhibitor together with the quantification of ectopic GC in Syk +/− ; ZAP-70 −/− mutant mice brought evidence of a requirement of Syk in GC tangential migration. Syk phosphorylation was induced by EphB2 engagement and locally turned down by a not yet identified factor that could in part explain the restricted pattern of Syk phosphorylation observed along GC migratory route. Whereas Syk kinase activity appeared not essential for ephrin/Eph-mediated axon extension, it might provide polarization signals required for proper nucleus translocation during GC migration. In conclusion, Syk kinase acts downstream of receptors controlling GC tangential migration. [ABSTRACT FROM AUTHOR]

Objective: In experimental models of temporal lobe epilepsy (TLE), brain neurons manifest multiple changes in intrinsic excitability that contribute to neuronal network hyperexcitability. We have investigated whether the intrinsic firing response gain, quantified by the slope of the function relating the number of evoked spikes (Ns) to input excitatory current intensity (I), is modified in principal rat hippocampal neurons in the pilocarpine-status epilepticus (SE) model of TLE. Methods: Intracellular recordings were made in CA3 and CA1 pyramidal cells (PCs) and dentate granule cells (GCs) in acute hippocampal slices obtained 7–36 days after pilocarpine-SE. Firing response gains were determined empirically from Ns/I relationships and compared to other measured neuronal properties. Results: The firing response gain in all three types of principal neurons, particularly in CA3 PCs, was markedly multiplied following pilocarpine-SE. Analyses of persistent changes in active and passive properties of CA3 PCs suggested that this increase is multifactorial in origin, the major factors being a reduction in amplitude of the slow afterhyperpolarization and an increase in the fraction of bursting neurons. Significance: Here we show that pilocarpine-SE causes multiplication of the firing response gain in the three principal neurons in the hippocampal trisynaptic pathway. This alteration undoubtedly would contribute to hippocampal hyperexcitability in SE-induced TLE. [ABSTRACT FROM AUTHOR]

Wntless (Wls) is implicated in the Wnt signaling pathway by regulating the secretion of Wnt molecules. During brain development, Wls is expressed in the isthmic organizer (ISO) and rhombic lip (RL). Wls regulates Wnt1 secretion at the ISO which is required to induce midbrain–hindbrain structures. However, Wls function in the RL is not known. Here, we employed Nestin -cre to delete Wls specifically in the RL during mid-gestation. The loss-of- Wls leads to an abnormal RL during development and cerebellar vermis hypoplasia at birth. The Wls conditional knockout (cKO) has rudimentary foliation with an absence of Bergmann glia fibers in the external germinal layer (EGL). The Wls -cKO cerebellum also exhibits ectopia of several cell types and aberrations in granule cell organization. Finally, there is a loss of 85% of unipolar brush cells. From these findings, Wls-expressing cells in the rhombic lip are implicated in the orchestration of cerebellar development. [ABSTRACT FROM AUTHOR]

Population-based studies have demonstrated that children with a history of febrile seizure (FS) perform better than age-matched controls at hippocampus-dependent memory tasks. Here, we report that FSs induce two distinct structural reorganizations in the hippocampus and bidirectionally modify future learning abilities in an age-dependent manner. Compared with age-matched controls, adult mice that had experienced experimental FSs induced by hyperthermia (HT) on postnatal day 14 (P14-HT) performed better in a cognitive task that requires dentate granule cells (DGCs). The enhanced memory performance correlated with an FS-induced persistent increase in the density of large mossy fiber terminals (LMTs) of the DGCs. The memory enhancement was not observed in mice that had experienced HT-induced seizures at P11 which exhibited abnormally located DGCs in addition to the increased LMT density. The ectopic DGCs of the P11-HT mice were abolished by the diuretic bumetanide, and this pharmacological treatment unveiled the masked memory enhancement. Thus, this work provides a novel basis for age-dependent structural plasticity in which FSs influence future brain function. [ABSTRACT FROM AUTHOR]

Transient receptor potential canonical channel-6 (TRPC6) forms Ca 2+ -permeable non-selective cation channels in neurons. Although TRPC6 plays an important role in neurite outgrowth and neuronal survival during development, TRPC6 expression profiles available to identify distinctive hippocampal neuronal damage and hippocampal excitability in epilepsy are less defined. As compared to normal animals, TRPC6 expression was down-regulated in chronic epileptic rats showing spontaneous recurrent seizures. TRPC6 knockdown increased seizure susceptibility, excitability ratio and paired-pulse inhibition in the dentate gyrus (DG) of normal animals. Furthermore, TRPC6 knockdown promoted programed neuronal necrosis in dentate granule cells, but prevented it in CA1 and CA3 neurons following status epilepticus. The present data suggest for the first time that TRPC6 may inhibit seizure susceptibility and neuronal vulnerability in the rat DG. [ABSTRACT FROM AUTHOR]

Olfactory bulb granule cells (GCs) are axon-less, inhibitory interneurons that regulate the activity of the excitatory output neurons, the mitral and tufted cells, through reciprocal dendrodendritic synapses located on GC spines. These contacts are established in the distal apical dendritic compartment, while GC basal dendrites and more proximal apical segments bear spines that receive glutamatergic inputs from the olfactory cortices. This synaptic connectivity is vital to olfactory circuit function and is remodeled during development, and in response to changes in sensory activity and lifelong GC neurogenesis. Manipulations that alter levels of the neurotrophin brain-derived neurotrophic factor (BDNF) in vivo have significant effects on dendritic spine morphology, maintenance and activity-dependent plasticity for a variety of CNS neurons, yet little is known regarding BDNF effects on bulb GC spine maturation or maintenance. Here we show that, in vivo , sustained bulbar over-expression of BDNF in transgenic mice produces a marked increase in GC spine density that includes an increase in mature spines on their apical dendrites. Morphometric analysis demonstrated that changes in spine density were most notable in the distal and proximal apical domains, indicating that multiple excitatory inputs are potentially modified by BDNF. Our results indicate that increased levels of endogenous BDNF can promote the maturation and/or maintenance of dendritic spines on GCs, suggesting a role for this factor in modulating GC functional connectivity within adult olfactory circuitry. [ABSTRACT FROM AUTHOR]

Aversive experiences in early life are thought to dispose to psychopathologies such as mood or anxiety disorders. In a two-hit stress model, we assessed the effects of juvenile and/or adult stress on the 5-HT-mediated modulation of synaptic inhibition of ventral dentate gyrus granule cells. Combined but not single stress exposure led to a significant reduction in activity and increased anxiety-like behavior. Similarly, the 5-HT1A receptor-mediated inhibition of evoked inhibitory postsynaptic currents (IPSCs) of granule cells was only reduced in single stress exposed animals. This was also true for the number of granule cells responding with a 5-HT3 receptor-dependent burst of miniature IPSCs. 5-HT3 receptors are expressed on cholecystokinin (CCK)+ basket cells in the hippocampus. In fact, we observed a reduction of steady-state mRNA levels of CCK+ basket cell markers after single juvenile or adult stress and partial recovery after combined stress, thus matching the electrophysiological findings. Adaptive changes in 5-HT-mediated modulation of synaptic inhibition and CCK+ basket cells in the DG may help to maintain normal levels of anxiety after single juvenile or adult stress exposure, as indicated by the increased anxiety that accompanies the loss of this regulation upon combined stress. [ABSTRACT FROM AUTHOR]

Structural changes that alter hippocampal functional circuitry are implicated in learning impairments, mood disorders and epilepsy. Reorganization of mossy fiber (MF) axons from dentate granule cells is one such form of plasticity. Increased neurotrophin signaling is proposed to underlie MF plasticity, and there is evidence to support a mechanistic role for brain-derived neurotrophic factor (BDNF) in this process. Transgenic mice overexpressing BDNF in the forebrain under the α-calcium/calmodulin-dependent protein kinase II promoter (TgBDNF mice) exhibit spatial learning deficits at 2–3 months of age, followed by the emergence of spontaneous seizures at ∼6 months. These behavioral changes suggest that chronic increases in BDNF progressively disrupt hippocampal functional organization. To determine if the dentate MF pathway is structurally altered in this strain, the present study employed Timm staining and design-based stereology to compare MF distribution and projection volumes in transgenic and wild-type mice at 2–3 months, and at 6–7 months. Mice in the latter age group were assessed for seizure vulnerability with a low dose of pilocarpine given 2 h before euthanasia. At 2–3 months, TgBDNF mice showed moderate expansion of CA3-projecting MFs (∼20%), with increased volumes measured in the suprapyramidal (SP-MF) and intra/infrapyramidal (IIP-MF) compartments. At 6–7 months, a subset of transgenic mice exhibited increased seizure susceptibility, along with an increase in IIP-MF volume (∼30%). No evidence of MF sprouting was seen in the inner molecular layer. Additional stereological analyses demonstrated significant increases in molecular layer (ML) volume in TgBDNF mice at both ages, as well as an increase in granule cell number by 8 months of age. Collectively, these results indicate that sustained increases in endogenous BDNF modify dentate structural organization over time, and may thereby contribute to the development of pro-epileptic circuitry. [ABSTRACT FROM AUTHOR]

The islands of Calleja (IC) are dense clusters of cells localized within the ventral striatum. The IC have been described as variable in both number and localization from animal-to-animal, however, a quantitative investigation of this variability is unavailable. Further, it is presently unknown whether the IC occupy select areas of the olfactory tubercle (OT), the ventral striatum structure which possesses the IC in mice. To address these questions, we examined the IC of adult C57bl/6 mice. As previously noted, we found substantial inter-hemispheric and inter-mouse variations in the total number of IC. While the IC were observed in all three cell layers of the OT, the bulk of IC occupied layer iii. The span of the IC along the anterior–posterior and medial–lateral axes of the OT was variant. Further, localizations of the IC within the OT also differed across animals. Notably, the probability of observing an IC in the medial OT was greater than that of observing one in the lateral. These data provide a fundamental characterization of both differences and similarities regarding the IC in mice and will be informative for future in vivo studies seeking to perturb and possibly record from the IC. Further, we predict that inter-animal diversity in the IC may be a mechanism for inter-animal differences in behavior, especially reward-related and motivational behaviors. [ABSTRACT FROM AUTHOR]

Alterations in hippocampal neurogenesis affect spatial learning, though, the relative contributions of cell proliferation and cell survival on this process are poorly understood. The current study utilized mu opioid receptor (MOR-1) knockout (KO) mice on two background strains, C57BL/6 and 129S6, to assess cell survival as well as determine the impact on spatial learning using the Morris water maze. These experiments were designed to extend prior work showing that both C57BL/6 and 129S6 MOR-1 KO mice have an increased number of proliferating cells in the dentate gyrus (DG) when compared to wild-type (WT) mice. The current study indicates that newly born neurons in the DG of C57BL/6 MOR-1 KO mice exhibit enhanced survival when compared to WT mice, while new neurons in the DG of 129S6 MOR-1 KO mice do not. In addition, C57BL/6 MOR-1 KO mice have a lower number of apoptotic cells in the DG compared to WT mice while, in contrast, 129S6 MOR-1 KO mice have a higher number of apoptotic cells in this region. These alterations collectively contribute to an increase in the granule cell number in the DG of C57BL/6 MOR-1 KO mice, while the total number of granule cells in 129S6 MOR-1 KO mice is unchanged. Thus, although C57BL/6 and 129S6 MOR-1 KO mice both exhibit increased cell proliferation in the DG, the impact of the MOR-1 mutation on cell survival differs between strains. Furthermore, the decrease in DG cell survival displayed by 129S6 MOR-1 KO mice is correlated with functional deficits in spatial learning, suggesting that MOR-1-dependent alterations in the survival of new neurons in the DG, and not MOR-1-dependent changes in proliferation of progenitor cells in the DG, is important for spatial learning. [ABSTRACT FROM AUTHOR]

The generation of new neurons in the dentate gyrus of the adult brain has been demonstrated in many species including humans and is suggested to have functional relevance for learning and memory. The wake promoting drug modafinil has popularly been categorized as a so-called neuroenhancer due to its positive effects on cognition. We here show that short- and long-term treatment with modafinil differentially effects hippocampal neurogenesis. We used different thymidine analogs (5-bromo-2-deoxyuridine (BrdU), chlorodeoxyuridine (CldU), iododeoxyuridine (IdU)) and labeling protocols to investigate distinct regulative events during hippocampal neurogenesis, namely cell proliferation and survival. Eight-week-old mice that were treated with modafinil (64 mg/kg, i.p.) every 24 h for 4 days show increased proliferation in the dentate gyrus indicated by BrdU-labeling and more newborn granule cells 3 weeks after treatment. Short-term treatment for 4 days also enhanced the number of postmitotic calretinin-expressing progenitor cells that were labeled with BrdU 1 week prior to treatment indicating an increased survival of new born immature granule cells. Interestingly, long-term treatment for 14 days resulted in an increased number of newborn Prox1 + granule cells, but we could not detect an additive effect of the prolonged treatment on proliferation and survival of newborn cells. Moreover, daily administration for 14 days did not influence the number of proliferating cells in the dentate gyrus. Together, modafinil has an acute impact on precursor cell proliferation as well as survival but loses this ability during longer treatment durations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Synthesis of new 1,5-benzodiazepine derivatives. [•] Use of patch-clamp technique on rat cerebellar granule cells in culture. [•] 1,5-Benzodiazepine derivatives modulate chloride currents activated by GABA. [•] Comparison between 1,4- and 1,5-benzodiazepines effects on GABAA receptor. [ABSTRACT FROM AUTHOR]

Abstract: We have previously shown that the first-paced mating encounter increases the number of newborn cells in the granule cell layer (Gra; also known as internal cell layer, ICL) of the accessory olfactory bulb (AOB) in the adult female rat (Corona et al., 2011). In the present study we evaluated if repetition of the stimulus (paced mating) could increase the arrival of more newborn neurons in the olfactory bulb generated during the first session of paced sexual contact. Sexually naive female rats were bilaterally ovariectomized, hormonally supplemented with estradiol (E2) and progesterone (P) and randomly assigned to one of four groups: (1) without sexual contact, (2) one session of paced mating, (3) four sessions of paced mating, and (4) four sessions of non-paced mating. We also included a group of gonadally intact females. On the first day of the experiment, all females were i.p. injected with the marker of DNA synthesis bromodeoxyuridine and were killed 16days later. Blood was collected at sacrifice to determine the plasma levels of E2 and P. The number of newborn neurons that arrived at the ICL of the AOB and the Gra of the main olfactory bulb (MOB) increased, relative to all other groups, only in the group that repeatedly mated under pacing conditions. No differences were found in E2 and P levels between supplemented groups indicating that our results are not influenced by changes in hormone concentrations. We suggest that repeated paced mating promotes the arrival of more newborn neurons in the AOB and MOB. [Copyright &y& Elsevier]

Abstract: Doublecortin (DCX) is a microtubule-associated protein that is critical for neuronal migration and the development of the cerebral cortex. In the adult, it is expressed in newborn neurons in the subventricular and subgranular zones, but not in the mature neurons of the cerebral cortex. By contrast, neurogenesis and neuronal migration of cells in the cerebellum continue into early postnatal life; migration of one class of cerebellar interneuron, unipolar brush cells (UBCs), may continue into adulthood. To explore the possibility of continued neuronal migration in the adult cerebellum, closely spaced sections through the brainstem and cerebellum of adult (3–16 months old) Sprague–Dawley rats were immunolabeled for DCX. Neurons immunoreactive (ir) to DCX were present in the granular cell layer of the vestibulocerebellum, most densely in the transition zone (tz), the region between the flocculus (FL) and ventral paraflocculus (PFL), as well as in the dorsal cochlear nucleus (DCN). These DCX-ir cells had the morphological appearance of UBCs with oval somata and a single dendrite ending in a brush. There were many examples of colocalization of DCX with Eps8 or calretinin, UBC markers. We also identified DCX-ir elements along the fourth ventricle and its lateral recess that had labeled somata but lacked the dendritic structure characteristic of UBCs. Labeled UBCs were seen in nearby white matter. These results suggest that there may be continued neurogenesis and/or migration of UBCs in the adult. Another possibility is that UBCs maintain DCX expression even after migration and maturation, reflecting a role of DCX in adult neuronal plasticity in addition to a developmental role in migration. [Copyright &y& Elsevier]

Abstract: Epilepsy is known to influence hippocampal dentate granule cell (DGC) layer neurogenesis. In young adult rats, status epilepticus (SE) increases the number DGC newly borne cells and basal dendrites (BD), which persist at long-term. In contrast, little is known on whether these phenomena occur in elderly epileptic animals. In the present study, we compare DGC proliferation and the incidence of BD in young and aged pilocarpine-treated rats. Three epileptic groups were considered: Young animals given pilocarpine at 3 months of age. Aged animals treated with pilocarpine at 3 months of age that were sacrificed at 17–20 months. Aged animals that had pilocarpine and developed SE at 20 months, being sacrificed 2 months later. Nine days prior to sacrifice, animals underwent swimming sessions in the Morris water maze as a protocol for the development of hippocampal neurogenesis. We found a higher incidence of newly born DGC cells in young as compared to aged epileptic animals (P<0.001). This later group however, was not homogeneous. While a significant increase in DGC neurogenesis was observed when aged animals with long lasting epilepsy were compared to non-epileptic controls (P<0.01), this has not been recorded in aged animals that had epilepsy for only 2 months (P>0.05). When the number of DGC containing BD was considered, a significantly higher incidence was observed in young as compared to aged epileptic rats (P=0.001). Animals in this later group virtually lacked BD in newly formed dentate gyrus (DG) cells. Based on these results we conclude that plastic changes during epileptogenesis and the development of a pathological substrate in young animals is associated with DGC proliferation and the emergence of BD. As aging occurs, DGC neurogenesis can still be induced in rats with a long-term history of epilepsy but the emergence of BD is markedly reduced. [Copyright &y& Elsevier]

Abstract: The mammalian main olfactory bulb (MOB) receives a dense noradrenergic innervation from the pontine nucleus locus coeruleus that is important for neonatal odor preference learning and odor processing in mature animals. Modulation of GABAergic granule cells (GCs) is thought to play a key role in the net functional impact of norepinephrine (NE) release in the MOB, yet there are few direct studies of the influence of NE on these cells. In the present study we investigated noradrenergic modulation of GC excitability using electrophysiological approaches in rat MOB slices. A moderate concentration of NE (10 μM) and the α1 receptor agonist phenylephrine (10 μM) depolarized and increased spontaneous or current injection-evoked spiking in GCs. By contrast, low NE concentrations (0.1–1.0 μM) or the α2 receptor agonist clonidine (Clon, 10 μM) hyperpolarized and decreased the discharge of GCs. The effects of NE (10 μM) were blocked by antagonism of α1 and α2 receptors. Inhibitory effects of low NE concentrations were blocked or converted to excitatory responses by α2 receptor blockade, whereas excitatory effects of the moderate NE concentration were converted to inhibitory responses after α1 receptor blockade. NE (10 μM) and phenylephrine elicited inward currents that reversed near the potassium equilibrium potential. The effects of NE and phenylephrine were associated with increased membrane input resistance. Clonidine elicited an outward current associated with decreased membrane input resistance that reversed near the potassium equilibrium potential. These results indicate that α1 and α2 receptor activation exert opposing effects on GC excitability. Low concentrations of NE acting via α2 receptors suppress GC excitability, while higher concentrations of NE acting at α1 receptors increase GC excitability. These findings are consistent with recent findings that α1 and α2 receptor activation increase and decrease, respectively, GABAergic inhibition of mitral cells. The differential affinities of α1 and α2 noradrenergic receptor subtypes may allow for differential modulation of GABA release and olfactory processing as a function of the level of NE release, which in turn, is regulated by behavioral state. [Copyright &y& Elsevier]

Abstract: The brain generates many rhythmic activities, and the olivo-cerebellar system is not an exception. In recent years, the cerebellum has revealed activities ranging from low frequency to very high-frequency oscillations. These rhythms depend on the brain functional state and are typical of certain circuit sections or specific neurons. Interestingly, the granular layer, which gates sensorimotor and cognitive signals to the cerebellar cortex, can also sustain low frequency (7–25 Hz) and perhaps higher-frequency oscillations. In this review we have considered (i) how these oscillations are generated in the granular layer network depending on intrinsic electroresponsiveness and circuit connections, (ii) how these oscillations are correlated with those in other cerebellar circuit sections, and (iii) how the oscillating cerebellum communicates with extracerebellar structures. It is suggested that the granular layer can generate oscillations that integrate well with those generated in the inferior olive, in deep-cerebellar nuclei and in Purkinje cells. These rhythms, in turn, might play a role in cognition and memory consolidation by interacting with the mechanisms of long-term synaptic plasticity. [Copyright &y& Elsevier]

Abstract: Increasing evidence implicates the c-Jun NH2-terminal kinase (JNK) pathway in the regulation of apoptosis in neurodegenerative diseases. In this study, we examined the neuroprotective effect of SP600125, a selective JNK inhibitor, in cerebellar granule cells (CGNs) deprived of serum and potassium (S/K withdrawal). S/K withdrawal-induced apoptosis occurs via activation of multiple pro-apoptotic pathways, including re-entry into the cell cycle, activation of glycogen synthase kinase-3 beta (GSK-3β), cyclin-dependent kinase 5 (cdk5/p35) breakdown, formation of cdk5/p25 and JNK activation. Here we demonstrate that SP600125 is able to inhibit all these pro-apoptotic pathways via the inhibition of JNK. Further, we found that JNK inhibition maintains the phosphorylation/activation of Akt after S/K withdrawal. For further confirmation of this result, we studied several targets downstream of Akt including GSK-3β, p-FOXO1, p-CREB and p35. In addition, the specific PI3K/Akt inhibitor LY294002 greatly diminished the antiapoptotic effects of SP600125 upon S/K withdrawal, confirming that Akt is involved in the neuroprotection achieved by SP600125. These results suggest that the maintenance of the PI3-kinase/Akt pathway by inhibition of JNK contributes to the prevention of apoptosis in rat cerebellar granule neurons mediated by S/K withdrawal. Furthermore, we propose that JNK may regulate the cell cycle re-entry by a novel mechanism that involves Akt, GSK-3β and Rb phosphorylation. [Copyright &y& Elsevier]

Abstract: The mechanism involved in neuronal apoptosis is largely unknown. Studies performed on neuronal cell cultures provide information about the pathways which orchestrate the process of neuronal loss and potential drugs for the treatment of neurological disorders. In the present study we select resveratrol, a natural antioxidant, as a potential drug for the treatment of neurodegenerative diseases. We evaluate the neuroprotective effects of resveratrol in two apoptotic models in rat cerebellar granule neurons (CGNs): the inhibition of mitochondrial complex I using 1-methyl-4-phenylpyridinium (MPP+) (an in vitro model of Parkinson’s disease) and serum potassium withdrawal. We study the role of the mammalian silent information regulator 2 (SIRT1) in the process of neuroprotection mediated by resveratrol. Because recent studies have demonstrated that SIRT1 is involved in cell survival and has antiaging properties, we also measured changes in the expression of this protein after the addition of these two apoptotic stimuli. MPP+-induced loss of cell viability and apoptosis in CGNs was prevented by the addition of RESV (1 μM to 100 μM). However, the neuroprotective effects were not mediated by the activation of SIRT1, since sirtinol—an inhibitor of this enzyme—did not attenuate them. Furthermore MPP+ decreases the protein expression of SIRT1. RESV did not prevent serum potassium withdrawal–induced apoptosis although it did completely attenuate oxidative stress production by these apoptotic stimuli. Furthermore, serum potassium withdrawal increases the expression of SIRT1. Our results indicate that the antiapoptotic effects of RESV in MPP+ are independent of the stimulation of SIRT1 and depend on its antioxidant properties. Furthermore, because SIRT1 is involved in neuronal survival depending on the apoptotic stimuli, changes in the expression of SIRT1 could be involved in the regulation of the apoptotic route. [Copyright &y& Elsevier]

Abstract: It has been shown that Wallerian degeneration, an anterograde degeneration of transected axons, is markedly delayed in a mutant mouse called slow Wallerian degeneration (Wld S ). These mice also show resistance to axonal degeneration caused by microtubule depolymerizing drugs, suggesting that axonal microtubules are stabilized. Here, we have focused on tubulin acetylation, a post-translational modification associated with microtubule stability. We found that the basal level of microtubule acetylation was increased in cultured cerebellar granule cells from Wld S mice. Nicotinamide but not 3-aminobenzamide, an inhibitor for poly(ADP)ribose polymerase, enhanced tubulin acetylation and resistance to axonal degeneration in cultured cerebellar granule cells from wild-type (WT) mice, suggesting that mammalian Sir2-related protein (SIRT) 2, a nicotinamide adenine dinucleotide (NAD)–dependent tubulin deacetylase, could modulate resistance to axonal degeneration. Indeed, the levels of NAD and SIRT2 were decreased in the cytoplasm from Wld S granule cells. Moreover, SIRT2 overexpression abrogated microtubule hyperacetylation and resistance to axonal degeneration in these cells. Conversely, SIRT2 knockdown by using a lentiviral vector expressing small interfering RNA, enhanced microtubule acetylation and resistance to axonal degeneration in WT granule cells. Taken together, these results suggest that SIRT2-mediated tubulin deacetylation is involved in both microtubule hyperacetylation and resistance to axonal degeneration in Wld S granule cells. [Copyright &y& Elsevier]

Abstract: The biochemical pathways involved in neuronal cell death in Parkinson’s disease are not completely characterized. Mitochondrial dysfunction, specifically alteration of the mitochondrial complex I, is the primary target of the parkinsonian neurotoxin 1-methyl-4-phenylpyridinium (MPP+) induced apoptosis in neurons. In the present study, we examine the role of caspase-dependent and -independent routes in MPP+-induced apoptosis in rat cerebellar granule neurons (CGNs). We show a distinct increase in the expression of the cell cycle proteins cyclin D, cyclin E, cdk2, cdk4 and the transcription factor E2F-1 following a MPP+ treatment of CGNs. Flavopiridol (FLAV), a broad inhibitor of cyclin-dependent kinases (CDKs), attenuated the neurotoxic effects of MPP+ and significantly attenuates apoptosis mediated by MPP+ 200 μM. Likewise, the antioxidant vitamin E (vit E) increases neuronal cell viability and attenuates apoptosis induced by MPP+. Moreover, the expression levels of cyclin D and E2F-1 induced by this parkinsonian neurotoxin were also attenuated by vit E. Since, the broad-spectrum caspase inhibitor zVAD-fmk did not attenuate MPP+-induced apoptosis in CGNs, our data provide a caspase-independent mechanism mediated by neuronal reentry in the cell cycle and increased expression of the pro-apoptotic transcription factor E2F-1. Our results also suggest a potential role of oxidative stress in neuronal reentry in the cell cycle mediated by MPP+. Finally, our data further support the therapeutic potential of flavopiridol, for the treatment of Parkinson’s disease. [Copyright &y& Elsevier]

Abstract: Epidermal growth factor receptor pathway substrate 8 (Eps8) is a widely expressed multidomain signaling protein that coordinates two disparate GTPase-dependent mechanisms: actin reorganization via Ras/Rac pathways and receptor trafficking via Rab5. Expression of Eps8, the gene encoding the founding member of the Eps8 family of proteins, was found in cerebellum by virtual Northern analysis and in situ hybridization. Because the cerebellum has a well-known cellular architecture and is a favored model to study synaptic plasticity and actin dynamics, we sought to analyze Eps8 localization in rat cerebellar neurons and synapses by light and electron microscopy. Specificity of Eps8-antibody was demonstrated by immunoblots and in brain sections. In cerebellum, unipolar brush cells (UBCs) were densely Eps8 immunopositive and granule cells were moderately immunostained. In both types of neuron immunoreaction product was localized to the somatodendritic and axonal compartments. Postsynaptic immunostained foci were demonstrated in the glomeruli in correspondence of the synapses formed by mossy fiber terminals with granule cell and UBC dendrites. These foci appeared especially evident in the UBC brush, which contains an extraordinary postsynaptic apparatus of actin microfilaments facing synaptic junctions of the long and segmented varieties. Eps8 immunoreactivity was conspicuously absent in Purkinje cells and their actin-rich dendritic spines, in all types of inhibitory interneurons of the cerebellum, cerebellar nuclei neurons, and astrocytes. In conclusion, Eps8 protein in cerebellum is expressed exclusively by excitatory cortical interneurons and is intracellularly compartmentalized in a cell-class specific manner. This is the first demonstration of the presence of a member of the Eps8 protein family in UBCs and its enrichment at postsynaptic sites. [Copyright &y& Elsevier]

Abstract: Hyperammonemia is responsible for many of the neurological alterations in patients with hepatic encephalopathy by mechanisms that remain unclear. Hyperammonemia alters phosphorylation of brain protein kinase C substrates and impairs N-methyl-d-aspartate (NMDA) receptor-associated signal transduction. The aim of this work was to analyze, in rat cerebellar neurons in culture, the effects of ammonia exposure on NMDA receptor phosphorylation, MK801 binding and surface expression. Ammonia reduces MK801 binding to NMDA receptors and the surface expression of the NR1 and NR2A subunits. As phosphorylation of serines in the NR1 C1 cassette has been implied in receptor trafficking, we assessed whether hyperammonemia alters phosphorylation of these serines. Basal phosphorylation of serines 890, 896 and 897 was increased in neurons exposed to ammonia, while NMDA-induced phosphorylation of S896 and S897 was reduced. Exposure to ammonia also increased basal phosphorylation of Akt but reduced NMDA and BDNF stimulation of Akt phosphorylation. These results suggest that alterations in receptor surface expression and possibly the phosphorylation state of the NR1 subunit of NMDA receptors may contribute to the impairment by ammonia of signal transduction pathways modulated by NMDA receptors. [Copyright &y& Elsevier]

Abstract: Neurogenesis is a constitutive activity in the adult dentate gyrus whereby new cells are created in the subgranular zone, before becoming neurons in the dentate gyrus granule cell layer. New granule cells are thought to migrate from the subgranular zone outwards to the edge of the cell layer as they mature. In these experiments we examined the dendritic morphology of granule cells in the subgranular zone, and the inner and outer regions of the granule cell zone in Sprague–Dawley rats with low and high rates of neurogenesis. In animals with lower rates of neurogenesis, the number of primary dendrites, degree of dendritic complexity and total dendritic length was lowest in cells located in the subgranular zone, higher in inner granule cell zone neurons, and highest in outer granule cell zone granule cells. Subgranular zone granule cells typically extended one primary dendrite and had a simple, immature dendritic tree, while granule cells in the outer granule cell zone had an increased number of primary dendrites, greater dendritic complexity, and greater total dendritic length. Animals that engaged in voluntary exercise showed increased neurogenesis, and the proportion of cells with one or two primary dendrites was increased in all of the granule cell zones. Despite having fewer primary processes, these cells showed enhanced dendritic complexity and an overall increase in their total dendritic length. These results indicate that granule cell dendritic morphology may be indicative of the age and position of a cell in the granule cell layer, but that in animals with increased rates of neurogenesis, the proportion of cells exhibiting what is considered an immature phenotype is increased throughout the all regions of the dentate gyrus cell layer. [Copyright &y& Elsevier]

The development of the dendritic tree of a neuron is a complex process which is thought to be regulated strongly by signals from afferent fibers. In particular the synaptic activity of afferent fibers and activity-dependent signaling by neurotrophic factors are thought to affect dendritic growth. We have studied Purkinje cell dendritic arbor development in organotypic cultures under suppression of glutamate-mediated excitatory neurotransmission, achieved with multiple combinations of blockers of glutamate receptors. Despite the presence of either single receptor blockers or combinations of blockers predicted to fully suppress glutamate-mediated excitatory neurotransmission Purkinje cell dendritic arbors developed similar to those of control cultures. Furthermore, Purkinje cell dendritic arbors in organotypic cultures from brain-derived neurotrophic factor (BDNF) knockout mice or after pharmacological blockade of trk-receptors also developed in a way similar to control cultures. Our results demonstrate that during the stage of rapid dendritic arbor growth signals from afferent fibers are of minor importance for Purkinje cell dendritic development because a seemingly normal Purkinje cell dendritic tree developed in the absence of excitatory neurotransmission and BDNF signaling. Our results suggest that many aspects of Purkinje cell dendritic development can be achieved by an intrinsic growth program. [Copyright &y& Elsevier]

Granule cell activity in cerebellar cortex directly excites Purkinje cells via parallel fibers, but it also inhibits Purkinje cells via cerebellar cortical interneurons. This contribution of inhibitory interneurons to cerebellar cortical processing remains poorly understood. In the present study we examined the response properties of stellate cells in vitro to input patterns that may result from granule cell activity in vivo. We constructed input waveforms that represented the sum of inputs from all individual synapses and applied these waveforms to the soma of stellate cells during whole cell recordings in acute brain slices. The stimulus waveforms contained fluctuations in a broad range of frequencies and were applied at different amplitudes. To determine the contribution of synaptic shunting to stellate cell spike responses we applied the same input waveforms either as a simulated synaptic conductance using dynamic clamping or as a direct current injection stimulus. Only the dynamic clamp stimulus has the shunting properties of real synapses, i.e. leads to different-sized synaptic current as a function of membrane potential. We found that stellate cells spike with millisecond precision in response to fast temporal fluctuations in the total synaptic input. Transient increases in excitatory input frequency led to pronounced stellate cell spike responses, indicating that this pathway may be very responsive to even small assemblies of co-activated granule cells. This was observed regardless of whether the input waveform was applied as a conductance with dynamic clamping, or as a direct current injection. Thus the shunting properties of a conductance input did not play a major role in determining the control of precisely timed spiking. In contrast, a more tonic increase in excitatory conductance did not lead to a sustained spike response as obtained with prolonged positive current injection. However, even with tonic current injection the precision of spiking was lost, as previously observed. Overall, the synaptic response function of stellate cells suggests that this cell type may pick out transients in granule cell activity, and may generate precisely timed inhibition of Purkinje cells during behavior. [Copyright &y& Elsevier]

The aim of the present research was to ascertain the presence of sex differences in the hippocampal dentate gyrus of the guinea-pig, a long-gestation rodent which gives birth to mature young and whose brain is at a more advanced stage of maturation at birth than that of the rat and mouse. The brains of neonatal (15–16 days old) and prepubescent (45–46 days old) male and female guinea pigs were Golgi–Cox stained. Granule cells were sampled from the upper (suprapyramidal) and lower (infrapyramidal) blade of the septal dentate gyrus and their dendritic tree and soma were measured. The analysis was conducted separately on granule cells with soma in the superficial (superficial granule cells) and deep (deep granule cells) half of the granule cell layer.Numerous sex differences were found in the upper blade of the dentate gyrus. Neonatal males had more dendritic branches than females in the innermost dendritic tree of both superficial and deep granule cells, but females had more branches over the middle/outer dendritic tree and a longer dendritic length. In prepubescent animals, the sex difference in the middle dendritic tree of the superficial granule cells changed direction, with males having more branches than females. In the deep granule cells, the sex differences were similar to those in neonatal animals. In both granule cell types, the dendritic length was similar in the two sexes. While no sex differences were found in dendritic spine density in neonatal animals, in prepubescent animals spine density was greater in females. In the lower blade the granule cells showed very few sex differences in both neonatal and prepubescent animals.This study shows wide dynamically changing sex differences in the granule cells located in the upper blade of the septal dentate gyrus, but almost no differences in the lower blade. These results demonstrate that sex differences are not ubiquitous in the dentate gyrus and suggest that the lower blade, unlike the upper blade, might be involved in non-sexually dimorphic behaviors. [Copyright &y& Elsevier]

To investigate developmental changes in neurosteroid modulation of GABAA receptors, whole-cell currents were elicited by applying GABA with allopregnanolone or pregnenolone sulfate (PS) to dentate granule cells (DGCs), acutely isolated from 7–14-day-old and adult rats. GABA evoked larger currents from dentate granule cells acutely isolated from adult rats (adult DGCs) than from neonatal DGCs, due to increased efficacy (1662±267 pA in adult DGCs versus 1094±198 pA in neonatal DGCs, P=0.004), and current density (0.072±0.01 pA/μm2 in neonatal rat DGCs to 0.178±0.02 pA/μm2 in adult DGCs), but unchanged potency (EC50 was 18.5±2 μM in adult DGCs, and 26.6±7.9 μM in neonatal DGCs, P=0.21). Allopregnanolone sensitivity of GABAA receptor currents increased during development due to an increased potency (21.1±4.7 nM in adult DGCs versus 94.6±9 nM in neonatal DGCs, P=0.0002). The potency and efficacy of PS inhibition of GABAA receptor currents were remained unchanged during development (13±6 μM and 13.2±5.9 μM, P=0.71 and 85.5%±3.5% and 83.6%±0.8%, P=0.29, respectively). To investigate possible mechanism of developmental changes in GABAA receptor properties, in situ hybridization for α1, α4 and γ2 subunit mRNAs was performed in dentate gyrus of the two age groups. Qualitatively, α1 subunit mRNA was expressed at low levels in neonatal rats while it was well expressed in adult rats. The α4 and γ2 subunits were well expressed in the dentate gyrus of adult and neonatal rats. Immunohistochemical staining for α1 subunit in hippocampal slices from neonatal and adult rats was examined under confocal laser scanning microscope. This demonstrated that cell bodies and dendrites of granule cells are moderately positive for the α1 staining in adult rats but weakly so in neonatal rats. Higher-magnification images demonstrate large number of clusters of α1-subunit in the cell bodies of dentate granule cells of adult rat but rare clusters in granule cells of neonatal rats.Maturation of GABAA receptors in DGCs is characterized by increased number of GABAA receptors that are more sensitive to endogenous neurosteroid allopregnanolone, which might be related to increased expression of α1 subunit. [Copyright &y& Elsevier]