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Proinflammatory cytokines are implicated in promoting neurodegeneration in multiple sclerosis (MS) by affecting excitatory and inhibitory transmission at central synapses. Conversely, the synaptic effects of anti-inflammatory molecules remain underexplored, despite their potential neuroprotective properties and their presence in the cerebrospinal fluid (CSF) of patients. In a study involving 184 newly diagnosed relapsing-remitting (RR)-MS patients, we investigated whether CSF levels of the anti-inflammatory interleukin (IL)-10 were linked to disease severity and neurodegeneration measures. Additionally, we examined IL-10 impact on synaptic transmission in striatal medium spiny neurons and its role in counteracting inflammatory synaptopathy induced by IL-1β in female C57BL/6 mice with experimental autoimmune encephalomyelitis (EAE). Our findings revealed a significant positive correlation between IL-10 CSF levels and changes in EDSS (Expanded Disability Status Scale) scores one year after MS diagnosis. Moreover, IL-10 levels in the CSF were positively correlated with volumes of specific subcortical brain structures, such as the nucleus caudate. In both MS patients' CSF and EAE mice striatum, IL-10 and IL-1β expressions were upregulated, suggesting possible antagonistic effects of these cytokines. Notably, IL-10 exhibited the ability to decrease glutamate transmission, increase GABA transmission in the striatum, and reverse IL-1β-induced abnormal synaptic transmission in EAE. In conclusion, our data suggest that IL-10 exerts direct neuroprotective effects in MS patients by modulating both excitatory and inhibitory transmission and attenuating IL-1β-induced inflammatory synaptopathy. These findings underscore the potential therapeutic significance of IL-10 in mitigating neurodegeneration in MS. [ABSTRACT FROM AUTHOR]

Paraventricular thalamus (PVT) plays important roles in the regulation of emotion and motivation through connecting many brain structures including the midbrain and the limbic system. Although acetylcholine (ACh) neurons of the midbrain were reported to send projections to PVT, little is known about how cholinergic signaling regulates PVT neurons. Here, we used both RNAscope and slice patch‐clamp recordings to characterize cholinergic receptor expression and ACh modulation of PVT neurons in mice. We found ACh excited a majority of anterior PVT (aPVT) neurons but predominantly inhibited posterior PVT (pPVT) neurons. Compared to pPVT with more inhibitory M2 receptors, aPVT expressed higher levels of all excitatory receptor subtypes including nicotinic α4, α7, and muscarinic M1 and M3. The ACh‐induced excitation was mimicked by nicotine and antagonized by selective blockers for α4β2 and α7 nicotinic ACh receptor (nAChR) subtypes as well as selective antagonists for M1 and M3 muscarinic ACh receptors (mAChR). The ACh‐induced inhibition was attenuated by selective M2 and M4 mAChR receptor antagonists. Furthermore, we found ACh increased the frequency of excitatory postsynaptic currents (EPSCs) on a majority of aPVT neurons but decreased EPSC frequency on a larger number of pPVT neurons. In addition, ACh caused an acute increase followed by a lasting reduction in inhibitory postsynaptic currents (IPSCs) on PVT neurons of both subregions. Together, these data suggest that multiple AChR subtypes coordinate a differential modulation of ACh on aPVT and pPVT neurons. [ABSTRACT FROM AUTHOR]

Spinal cerebrospinal fluid-contacting neurons (CSF-cNs) form an evolutionary conserved bipolar cell population localized around the central canal of all vertebrates. CSF-cNs were shown to express molecular markers of neuronal immaturity into adulthood; however, the impact of their incomplete maturation on the chloride (Cl-) homeostasis as well as GABAergic signaling remains unknown. Using adult mice from both sexes, in situ hybridization revealed that a proportion of spinal CSF-cNs (18.3%) express the Na+-K+-Cl- cotransporter 1 (NKCC1) allowing intracellular Cl- accumulation. However, we did not find expression of the K+-Cl- cotransporter 2 (KCC2) responsible for Cl- efflux in any CSF-cNs. The lack of KCC2 expression results in low Cl- extrusion capacity in CSF-cNs under high Cl- load in whole-cell patch clamp. Using cell-attached patch clamp allowing recordings with intact intracellular Cl- concentration, we found that the activation of ionotropic GABAA receptors (GABAA-Rs) induced both depolarizing and hyperpolarizing responses in CSF-cNs. Moreover, depolarizing GABA responses can drive action potentials as well as intracellular calcium elevations by activating voltage-gated calcium channels. Blocking NKCC1 with bumetanide inhibited the GABAinduced calcium transients in CSF-cNs. Finally, we show that metabotropic GABAB receptors have no hyperpolarizing action on spinal CSF-cNs as their activation with baclofen did not mediate outward K+ currents, presumably due to the lack of expression of G-protein-coupled inwardly rectifying potassium (GIRK) channels. Together, these findings outline subpopulations of spinal CSF-cNs expressing inhibitory or excitatory GABAA-R signaling. Excitatory GABA may promote the maturation and integration of young CSF-cNs into the existing spinal circuit. [ABSTRACT FROM AUTHOR]

Proinflammatory cytokines are implicated in promoting neurodegeneration in multiple sclerosis (MS) by affecting excitatory and inhibitory transmission at central synapses. Conversely, the synaptic effects of anti-inflammatory molecules remain underexplored, despite their potential neuroprotective properties and their presence in the cerebrospinal fluid (CSF) of patients. In a study involving 184 newly diagnosed relapsing–remitting (RR)-MS patients, we investigated whether CSF levels of the anti-inflammatory interleukin (IL)-10 were linked to disease severity and neurodegeneration measures. Additionally, we examined IL-10 impact on synaptic transmission in striatal medium spiny neurons and its role in counteracting inflammatory synaptopathy induced by IL-1β in female C57BL/6 mice with experimental autoimmune encephalomyelitis (EAE). Our findings revealed a significant positive correlation between IL-10 CSF levels and changes in EDSS (Expanded Disability Status Scale) scores one year after MS diagnosis. Moreover, IL-10 levels in the CSF were positively correlated with volumes of specific subcortical brain structures, such as the nucleus caudate. In both MS patients’ CSF and EAE mice striatum, IL-10 and IL-1β expressions were upregulated, suggesting possible antagonistic effects of these cytokines. Notably, IL-10 exhibited the ability to decrease glutamate transmission, increase GABA transmission in the striatum, and reverse IL-1β-induced abnormal synaptic transmission in EAE. In conclusion, our data suggest that IL-10 exerts direct neuroprotective effects in MS patients by modulating both excitatory and inhibitory transmission and attenuating IL-1β-induced inflammatory synaptopathy. These findings underscore the potential therapeutic significance of IL-10 in mitigating neurodegeneration in MS.

Background: Anxiolytic properties of Korean Red Ginseng (KRG) have been previously reported. However, the exact mechanism(s) of action remains to be elucidated. The present study investigated the effect of KRG on immobilization-induced anxiety-like behaviors in mice and explored the involvement of the serotonin and GABA systems and BDNF in the anxiolytic action. Methods: Mice were orally administered with KRG (200 mg/kg/day) for 4 weeks and immobilized once daily for 2 h. p-Chlorophenylalanine (p-CPA) was intraperitoneally injected on day 22-28, and flumazenil or bicuculline was injected on day 25-28. After behavioral evaluations, brains were dissected for biochemical analyses. Results: KRG improved immobilization-induced anxiety-like behaviors in mice, as assessed by the elevated plus maze (EPM) and marble burying tests (MBT). The anxiolytic effect of KRG was comparable to that of fluoxetine, a reference drug clinically used for anxiety disorders. A serotonin synthesis inhibitor, p-CPA, blocked the effect of KRG in the EPM and MBT, indicating the requirement of serotonin synthesis for anxiolytic action. In addition, the anxiolytic effect of KRG was inhibited by bicuculline (a GABAA antagonist) in MBT, implying the involvement of GABA transmission. Western blotting analyses revealed that KRG upregulated the expression of tryptophan hydroxylase and GABAA receptor in the brain, which was blocked by p-CPA. Enhanced BDNF expression by KRG in the hippocampus was also indicated to mediate the anxiolytic action of KRG in immobilized mice. Conclusion: KRG exhibited the anxiolytic effect in immobilized mice by multiple mechanisms of action, involving enhanced serotonin and GABA transmissions and BDNF expression.

Pannexin-1 (Panx1) hemichannel is a non-selective transmembrane channel that may play important roles in intercellular signaling by allowing the permeation of ions and metabolites, such as ATP. Although recent evidence shows that the Panx1 hemichannel is involved in controlling excitatory synaptic transmission, the role of Panx1 in inhibitory transmission remains unknown. Here, we studied the contribution of Panx1 to the GABAergic synaptic efficacy onto CA1 pyramidal neurons (PyNs) by using patch–clamp recordings and pharmacological approaches in wild-type and Panx1 knock-out (Panx1-KO) mice. We reported that blockage of the Panx1 hemichannel with the mimetic peptide 10Panx1 increases the synaptic level of endocannabinoids (eCB) and the activation of cannabinoid receptors type 1 (CB1Rs), which results in a decrease in hippocampal GABAergic efficacy, shifting excitation/inhibition (E/I) balance toward excitation and facilitating the induction of long-term potentiation. Our finding provides important insight unveiling that Panx1 can strongly influence the overall neuronal excitability and play a key role in shaping synaptic changes affecting the amplitude and direction of plasticity, as well as learning and memory processes. [ABSTRACT FROM AUTHOR]

Pannexin-1 (Panx1) hemichannel is a non-selective transmembrane channel that may play important roles in intercellular signaling by allowing the permeation of ions and metabolites, such as ATP. Although recent evidence shows that the Panx1 hemichannel is involved in controlling excitatory synaptic transmission, the role of Panx1 in inhibitory transmission remains unknown. Here, we studied the contribution of Panx1 to the GABAergic synaptic efficacy onto CA1 pyramidal neurons (PyNs) by using patch–clamp recordings and pharmacological approaches in wild-type and Panx1 knock-out (Panx1-KO) mice. We reported that blockage of the Panx1 hemichannel with the mimetic peptide 10Panx1 increases the synaptic level of endocannabinoids (eCB) and the activation of cannabinoid receptors type 1 (CB1Rs), which results in a decrease in hippocampal GABAergic efficacy, shifting excitation/inhibition (E/I) balance toward excitation and facilitating the induction of long-term potentiation. Our finding provides important insight unveiling that Panx1 can strongly influence the overall neuronal excitability and play a key role in shaping synaptic changes affecting the amplitude and direction of plasticity, as well as learning and memory processes.

The K+-Cl- cotransporter KCC2, encoded by the Slc12a5 gene, is a neuron-specific chloride extruder that tunes the strength and polarity of GABAA receptor-mediated transmission. In addition to its canonical ion transport function, KCC2 also regulates spinogenesis and excitatory synaptic function through interaction with a variety of molecular partners. KCC2 is enriched in the vicinity of both glutamatergic and GABAergic synapses, the activity of which in turn regulates its membrane stability and function. KCC2 interaction with the submembrane actin cytoskeleton via 4.1N is known to control its anchoring near glutamatergic synapses on dendritic spines. However, the molecular determinants of KCC2 clustering near GABAergic synapses remain unknown. Here, we used proteomics to identify novel KCC2 interacting proteins in the adult rat neocortex. We identified both known and novel candidate KCC2 partners, including some involved in neuronal development and synaptic transmission. These include gephyrin, the main scaffolding molecule at GABAergic synapses. Gephyrin interaction with endogenous KCC2 was confirmed by immunoprecipitation from rat neocortical extracts. We showed that gephyrin stabilizes plasmalemmal KCC2 and promotes its clustering in hippocampal neurons, mostly but not exclusively near GABAergic synapses, thereby controlling KCC2-mediated chloride extrusion. This study identifies gephyrin as a novel KCC2 anchoring molecule that regulates its membrane expression and function in cortical neurons. [ABSTRACT FROM AUTHOR]

Seizures and brain injury lead to water and Cl− accumulation in neurons. The increase in intraneuronal Cl− concentration ([Cl−]i) depolarizes the GABAA reversal potential (EGABA) and worsens seizure activity. Neocortical neuronal membranes have a low water permeability due to the lack of aquaporins necessary to move free water. Instead, neurons use cotransport of ions including Cl− to move water. Thus, increasing the extracellular osmolarity during seizures should result in an outward movement of water and salt, reducing [Cl−]i and improving GABAA receptor-mediated inhibition. We tested the effects of hyperosmotic therapy with a clinically relevant dose of mannitol (20 mM) on epileptiform activity, spontaneous multiunit activity, spontaneous inhibitory post-synaptic currents (sIPSCs), [Cl−]i, and neuronal volume in layer IV/V of the developing neocortex of C57BL/6 and Clomeleon mice. Using electrophysiological techniques and multiphoton imaging in acute brain slices (post-natal day 7–12) and organotypic neocortical slice cultures (post-natal day 14), we observed that mannitol: 1) decreased epileptiform activity, 2) decreased neuronal volume and [Cl−]i through CCCs, 3) decreased spontaneous multi-unit activity frequency but not amplitude, and 4) restored the anticonvulsant efficacy of the GABAA receptor modulator diazepam. Increasing extracellular osmolarity by 20 mOsm with hypertonic saline did not decrease epileptiform activity. We conclude that an increase in extracellular osmolarity by mannitol mediates the efflux of [Cl−]i and water through CCCs, which results in a decrease in epileptiform activity and enhances benzodiazepine actions in the developing neocortex in vitro. Novel treatments aimed to decrease neuronal volume may concomitantly decrease [Cl−]i and improve seizure control.

Brain homeostasis is the dynamic equilibrium whereby physiological parameters are kept actively within a specific range. The homeostatic range is not fixed and may change throughout the individual's lifespan, or may be transiently modified in the presence of severe perturbations. The endocannabinoid system has emerged as a safeguard of homeostasis, e.g., it modulates neurotransmission and protects neurons from prolonged or excessively strong activation. We used genetically engineered mouse lines that lack the cannabinoid type-1 receptor (CB1) either in dorsal telencephalic glutamatergic or in forebrain GABAergic neurons to create new allostatic states, resulting from alterations in the excitatory/inhibitory (E/I) balance. Previous studies with these two mouse lines have shown dichotomic results in the context of behavior, neuronal morphology, and electrophysiology. Thus, we aimed at analyzing the transcriptomic profile of the hippocampal CA region from these mice in the basal condition and after a mild behavioral stimulation (open field). Our results provide insights into the gene networks that compensate chronic E/I imbalances. Among these, there are differentially expressed genes involved in neuronal and synaptic functions, synaptic plasticity, and the regulation of behavior. Interestingly, some of these genes, e.g., Rab3b, Crhbp, and Kcnn2, and related pathways showed a dichotomic expression, i.e., they are up-regulated in one mutant line and down-regulated in the other one. Subsequent interrogation on the source of the alterations at transcript level were applied using exon-intron split analysis. However, no strong directions toward transcriptional or post-transcriptional regulation comparing both mouse lines were observed. Altogether, the dichotomic gene expression observed and their involved signaling pathways are of interest because they may act as “switches” to modulate the directionality of neural homeostasis, which then is relevant for pathologies, such as stress-related disorders and epilepsy.

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mature brain but has the paradoxical property of depolarizing neurons during early development. Depolarization provided by GABAA transmission during this early phase regulates neural stem cell proliferation, neural migration, neurite outgrowth, synapse formation, and circuit refinement, making GABA a key factor in neural circuit development. Importantly, depending on the context, depolarizing GABAA transmission can either drive neural activity or inhibit it through shunting inhibition. The varying roles of depolarizing GABAA transmission during development, and its ability to both drive and inhibit neural activity, makes it a difficult developmental cue to study. This is particularly true in the later stages of development when the majority of synapses form and GABAA transmission switches from depolarizing to hyperpolarizing. Here, we addressed the importance of depolarizing but inhibitory (or shunting) GABAA transmission in glutamatergic synapse formation in hippocampal CA1 pyramidal neurons. We first showed that the developmental depolarizing-to-hyperpolarizing switch in GABAA transmission is recapitulated in organotypic hippocampal slice cultures. Based on the expression profile of K+−Cl− co-transporter 2 (KCC2) and changes in the GABA reversal potential, we pinpointed the timing of the switch from depolarizing to hyperpolarizing GABAA transmission in CA1 neurons. We found that blocking depolarizing but shunting GABAA transmission increased excitatory synapse number and strength, indicating that depolarizing GABAA transmission can restrain glutamatergic synapse formation. The increase in glutamatergic synapses was activity-dependent but independent of BDNF signaling. Importantly, the elevated number of synapses was stable for more than a week after GABAA inhibitors were washed out. Together these findings point to the ability of immature GABAergic transmission to restrain glutamatergic synapse formation and suggest an unexpected role for depolarizing GABAA transmission in shaping excitatory connectivity during neural circuit development.

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the mature brain but has the paradoxical property of depolarizing neurons during early development. Depolarization provided by GABAA transmission during this early phase regulates neural stem cell proliferation, neural migration, neurite outgrowth, synapse formation, and circuit refinement, making GABA a key factor in neural circuit development. Importantly, depending on the context, depolarizing GABAA transmission can either drive neural activity or inhibit it through shunting inhibition. The varying roles of depolarizing GABAA transmission during development, and its ability to both drive and inhibit neural activity, makes it a difficult developmental cue to study. This is particularly true in the later stages of development when the majority of synapses form and GABAA transmission switches from depolarizing to hyperpolarizing. Here, we addressed the importance of depolarizing but inhibitory (or shunting) GABAA transmission in glutamatergic synapse formation in hippocampal CA1 pyramidal neurons. We first showed that the developmental depolarizing-to-hyperpolarizing switch in GABAA transmission is recapitulated in organotypic hippocampal slice cultures. Based on the expression profile of K+−Cl− co-transporter 2 (KCC2) and changes in the GABA reversal potential, we pinpointed the timing of the switch from depolarizing to hyperpolarizing GABAA transmission in CA1 neurons. We found that blocking depolarizing but shunting GABAA transmission increased excitatory synapse number and strength, indicating that depolarizing GABAA transmission can restrain glutamatergic synapse formation. The increase in glutamatergic synapses was activity-dependent but independent of BDNF signaling. Importantly, the elevated number of synapses was stable for more than a week after GABAA inhibitors were washed out. Together these findings point to the ability of immature GABAergic transmission to restrain glutamatergic synapse formation and suggest an unexpected role for depolarizing GABAA transmission in shaping excitatory connectivity during neural circuit development. [ABSTRACT FROM AUTHOR]

We have recently shown in rats that adolescent cocaine exposure induces prolonged modifications on synapses in medial prefrontal cortex (mPFC), which might contribute to long-term behavioral outcomes in adulthood. In this study, we further investigated the molecular mechanisms underlying adolescent cocaine exposure-related psychiatric problems in adulthood, especially focusing on the alterations of GABAergic transmission in prelimbic cortex (PrL), 1 subregion of mPFC. Consistent with a previous study, adolescent cocaine-exposed mice exhibited enhanced anxiety-like behaviors in their adulthood. In the same mice models, depression-like behaviors increased as well, but the conditioned place preference formed normally. In parallel, activities of pyramidal neurons at layer V of PrL were reduced after adolescent cocaine exposure, accompanied by an increase in the percentage of symmetric synapses in PrL of adult mice. Additionally, miniature inhibitory postsynaptic currents rather than miniature excitatory postsynaptic currents were increased on these pyramidal neurons, and increased levels of GABA were found in adult PrL. The molecules in the GABAergic system in adult PrL were also changed by adolescent cocaine use, as indicated by increased glutamate decarboxylase 67 kDa, GABAA-a1, and decreased GABA transporter 1. In the same mice, some regulators to GABAergic transmission such as neuregulin 1/ErbB4 signals were heightened as well. Collectively, these findings revealed that adolescent cocaine exposure results in permanent enhancement of GABAergic transmission on pyramidal neurons in PrL, which subsequently attenuate the activities of these neurons and ultimately contributes to the development of psychiatric disorders in later life.--Shi, P., Nie, J., Liu, H., Li, Y., Lu, X., Shen, X., Ge, F., Yuan, T.-F., Guan, X. Adolescent cocaine exposure enhances the GABAergic transmission in the prelimbic cortex of adult mice. [ABSTRACT FROM AUTHOR]

Abstract Seizures and brain injury lead to water and Cl− accumulation in neurons. The increase in intraneuronal Cl− concentration ([Cl−] i) depolarizes the GABA A reversal potential (E GABA) and worsens seizure activity. Neocortical neuronal membranes have a low water permeability due to the lack of aquaporins necessary to move free water. Instead, neurons use cotransport of ions including Cl− to move water. Thus, increasing the extracellular osmolarity during seizures should result in an outward movement of water and salt, reducing [Cl−] i and improving GABA A receptor-mediated inhibition. We tested the effects of hyperosmotic therapy with a clinically relevant dose of mannitol (20 mM) on epileptiform activity, spontaneous multiunit activity, spontaneous inhibitory post-synaptic currents (sIPSCs), [Cl−] i , and neuronal volume in layer IV/V of the developing neocortex of C57BL/6 and Clomeleon mice. Using electrophysiological techniques and multiphoton imaging in acute brain slices (post-natal day 7–12) and organotypic neocortical slice cultures (post-natal day 14), we observed that mannitol: 1) decreased epileptiform activity, 2) decreased neuronal volume and [Cl−] i through CCCs, 3) decreased spontaneous multi-unit activity frequency but not amplitude, and 4) restored the anticonvulsant efficacy of the GABA A receptor modulator diazepam. Increasing extracellular osmolarity by 20 mOsm with hypertonic saline did not decrease epileptiform activity. We conclude that an increase in extracellular osmolarity by mannitol mediates the efflux of [Cl−] i and water through CCCs, which results in a decrease in epileptiform activity and enhances benzodiazepine actions in the developing neocortex in vitro. Novel treatments aimed to decrease neuronal volume may concomitantly decrease [Cl−] i and improve seizure control. Graphical abstract Unlabelled Image Highlights • Mannitol reduces neuronal volume and [Cl−] i in neurons with high initial [Cl−] i. • Chloride co-transporters primarily mediate the linked movement of water and Cl− out of neurons. • Mannitol decreases neocortical seizure activity during early brain development. • Mannitol potentiates the anticonvulsive effect of diazepam in the young neocortex. [ABSTRACT FROM AUTHOR]

Corticostriatal circuits are generally characterized by the release of glutamate neurotransmitter from cortical terminals within the striatum. It is well known that cortical excitatory input to the dorsal striatum regulates addictive drug-related behaviors. We previously reported that anterior insular cortex (AIC) synaptic inputs to the dorsolateral striatum (DLS) control binge alcohol drinking in mice. These AIC-DLS glutamate synapses are also the sole sites of corticostriatal mu opioid receptor-mediated excitatory long-term depression (MOR-LTD) in the DLS. Recent work demonstrates that some regions of cortex send long-range, direct inhibitory inputs into the dorsal striatum. Nothing is known about the existence and regulation of AIC-DLS inhibitory synaptic transmission. Here, using a combination of patch clamp electrophysiology and optogenetics, we characterized a novel AIC-DLS corticostriatal inhibitory circuit and its regulation by MOR-mediated inhibitory LTD (MOR-iLTD). First, we found that the activation of presynaptic MORs produces MOR-iLTD in the DLS and dorsomedial striatum. Then, we showed that medium spiny neurons within the DLS receive direct inhibitory synaptic input from the cortex, specifically from the motor cortex and AIC. Using transgenic mice that express cre-recombinase within parvalbumin-expressing inhibitory neurons, we determined that this specific cortical neuron subtype sends direct GABAergic projections to the DLS. Moreover, these AIC-DLS inhibitory synaptic input subtypes express MOR-iLTD. These data suggest a novel GABAergic corticostriatal circuit that could be involved in the regulation of drug and alcohol consumption-related behaviors. • MOR activation induces long-term depression of inhibitory synaptic transmission in the DLS. • Medium spiny neurons in the DLS receive direct inhibitory synaptic input from motor cortex and AIC. • GABAergic AIC synaptic inputs to the DLS originate from AIC-resident parvalbumin-expressing neurons. • MOR-mediated inhibitory LTD in the DLS occurs presynaptically at inhibitory inputs from AIC parvalbumin-positive neurons. [ABSTRACT FROM AUTHOR]

PAK1 inhibitors are known to markedly improve social and cognitive function in several animal models of brain disorders, including autism, but the underlying mechanisms remain elusive. We show here that disruption of PAK1 in mice suppresses inhibitory neurotransmission through an increase in tonic, but not phasic, secretion of endocannabinoids (eCB). Consistently, we found elevated levels of anandamide (AEA), but not 2-arachidonoylglycerol (2-AG) following PAK1 disruption. This increased tonic AEA signaling is mediated by reduced cyclooxygenase-2 (COX-2), and COX-2 inhibitors recapitulate the effect of PAK1 deletion on GABAergic transmission in a CB1 receptor-dependent manner. These results establish a novel signaling process whereby PAK1 upregulates COX-2, reduces AEA and restricts tonic eCB-mediated processes. Because PAK1 and eCB are both critically involved in many other organ systems in addition to the brain, our findings may provide a unified mechanism by which PAK1 regulates these systems and their dysfunctions including cancers, inflammations and allergies.

ABSTRACT Addictive drugs modulate synaptic transmission in the meso-corticolimbic system by hijacking normal adaptive forms of experience-dependent synaptic plasticity. Psychostimulants such as METH have been shown to affect hippocampal synaptic plasticity, albeit with a less understood synaptic mechanism. METH is one of the most addictive drugs that elicit long-term alterations in the synaptic plasticity in brain areas involved in reinforcement learning and reward processing. Dopamine transporter (DAT) is one of the main targets of METH. As a substrate for DAT, METH decreases dopamine uptake and increases dopamine efflux via the transporter in the target brain regions such as nucleus accumbens (NAc) and hippocampus. Due to cross talk between NAc and hippocampus, stimulation of NAc has been shown to alter hippocampal plasticity. In this study, we tested the hypothesis that manipulation of glutamatergic and GABA-ergic systems in the shell-NAc modulates METH-induced enhancement of long term potentiation (LTP) in the hippocampus. Rats treated with METH (four injections of 5 mg/kg) exhibited enhanced LTP as compared to saline-treated animals. Intra-NAc infusion of muscimol (GABA receptor agonist) decreased METH-induced enhancement of dentate gyrus (DG)-LTP, while infusion of AP5 (NMDA receptor antagonist) prevented METH-induced enhancement of LTP. These data support the interpretation that reducing NAc activity can ameliorate METH-induced hippocampal LTP through a hippocampus-NAc-VTA circuit loop. Synapse 70:325-335, 2016. © 2016 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a gaseous molecule acting as a messenger in both the peripheral and the central nervous systems. NO affects synaptic activity by modulating neurotransmitter release and/or receptor function. We previously observed that NO-active compounds modify the bioelectric activity of basal ganglia (BG) units. In this study, we applied microiontophoresis to extracellular in vivo recordings to investigate the effect of NO-active compounds on GABA-evoked responses in the globus pallidus (GP) of anesthetized rats. The changes induced by NO-active drugs on the GABA-induced inhibition were used as indicators of NO modulation. The response to GABA release was tested on recorded GP neurons before and during the administration of S-nitroso-glutathione (SNOG, a NO donor) and/or Nω-nitro- l-arginine methyl ester ( l-NAME), an inhibitor of nitric oxide synthase (NOS); furthermore, SNOG and l-NAME were tested at different ejection currents in order to highlight the possibility of a current-dependent effect in the nitrergic modulation of GABA transmission. In general, during SNOG ejection the magnitude of GABA-evoked responses was reduced, whereas the administration of l-NAME produced the opposite effect. The results suggest that NO-active drugs modulate the response of GP neurons to GABA transmission; the effects induced by SNOG and l-NAME were strictly related to the ejection currents. Then, the modulation of GABAergic transmission by NO could represent a mechanism to finely regulate the GP neurons activity with important consequences on the overall BG function. [ABSTRACT FROM AUTHOR]

Ghrelin, a natural ligand of the growth hormone secretagogue receptor (GHS-R), is synthesized in the stomach but may also be expressed in lesser quantity in the hypothalamus where the GHS-R is located on growth hormone-releasing hormone (GHRH) neurons. Obestatin, a peptide derived from the same precursor as ghrelin, is able to antagonize the ghrelin-induced increase of growth hormone (GH) secretion in vivo but not from pituitary explants in vitro. Thus, the blockade of ghrelin-induced GH release by obestatin could be mediated at the hypothalamic level by the neuronal network that controls pituitary GH secretion. Ghrelin increased GHRH and decreased somatostatin (somatotropin-releasing inhibitory factor) release from hypothalamic explants, whereas obestatin only reduced the ghrelin-induced increase of GHRH release, thus indicating that the effect of ghrelin and obestatin is targeted to GHRH neurons. Patch-clamp recordings on mouse GHRH-enhanced green fluorescent protein neurons indicated that ghrelin and obestatin had no significant effects on glutamatergic synaptic transmission. Ghrelin decreased GABAergic synaptic transmission in 44% of the recorded neurons, an effect blocked in the presence of the GHS-R antagonist BIM28163, and stimulated the firing rate of 78% of GHRH neurons. Obestatin blocked the effects of ghrelin by acting on a receptor different from the GHS-R. These data suggest that: (i) ghrelin increases GHRH neuron excitability by increasing their action potential firing rate and decreasing the strength of GABA inhibitory inputs, thereby leading to an enhanced GHRH release; and (ii) obestatin counteracts ghrelin actions. Such interactions on GHRH neurons probably participate in the control of GH secretion. [ABSTRACT FROM AUTHOR]

Antiepileptic drugs (AEDs) such as phenobarbital, phenytoin, and valproic acid, when given in therapeutic doses to neonatal rats, cause pronounced neuronal apoptotic cell death. This effect is especially pronounced in the striatum and cortex during the second postnatal week, a period corresponding to the “brain growth spurt” (third trimester of gestation and early infancy) in humans. Of particular concern is the fact that phenobarbital is the most frequently used therapy for neonatal epilepsy. If AED-induced neuronal cell death leads to long-term functional impairment, then it becomes crucial to find therapies that avoid this neurotoxicity in the sensitive period. Herein we examine short- and long-term functional effects following exposure of neonatal rat pups to phenobarbital; the functions tested include striatal γ-aminobutyric acid (GABA)ergic synaptic responses and reflex development in pups, and fear conditioning, emotionality, and sensory-motor gating in adults. In all cases, phenobarbital exposure during the second postnatal week was sufficient to cause significant impairment. In contrast, adult animals exposed as pups to lamotrigine (given in a dose that does not cause apoptotic neuronal death) were not impaired on the tasks we examined. Our data suggest that treatments devoid of proapoptotic actions may be promising therapies for avoiding adverse outcomes after neonatal exposure. In addition, our findings identify early exposure to certain AEDs as an important potential risk factor contributing to psychiatric and neurologic abnormalities later in life. [ABSTRACT FROM AUTHOR]

Several G protein-associated receptors and synaptic proteins function within lipid rafts, which are subdomains of the plasma membranes that contain high concentrations of cholesterol. In this study we addressed the possible role of lipid rafts in the control of endocannabinoid system in striatal slices. Disruption of lipid rafts following cholesterol depletion with methyl-β-cyclodestrin (MCD) failed to affect synthesis and degradation of anandamide, while it caused a marked increase in the synthesis and concentration of 2-arachidonoylglycerol (2-AG), as well as in the binding activity of cannabinoid CB1 receptors. Surprisingly, endogenous 2-AG-mediated control of GABA transmission was not potentiated by MCD treatment and, in contrast, neither basal nor 3,5-Dihydroxyphenylglycine-stimulated 2-AG altered GABA synapses in cholesterol-depleted slices. Synaptic response to the cannabinoid CB1 receptor agonist HU210 was however intact in MCD-treated slices, indicating that reduced sensitivity of cannabinoid CB1 receptors does not explain why endogenous 2-AG is ineffective in inhibiting striatal GABA transmission after cholesterol depletion. Confocal microscopy analysis suggested that disruption of raft integrity by MCD might uncouple metabotropic glutamate 5-CB1 receptor interaction by altering the correct localization of both receptors in striatal neuron elements. In conclusion, our data indicate that disruption of raft integrity causes a complex alteration of the endocannabinoid signalling in the striatum. [ABSTRACT FROM AUTHOR]

In the central amygdala (CeA), ethanol acts via corticotrophin-releasing factor (CRF) type 1 receptors to enhance GABA release. Amygdala CRF mediates anxiety associated with stress and drug dependence, and it regulates ethanol intake. Because mutant mice that lack PKCϵ exhibit reduced anxiety-like behavior and alcohol consumption, we investigated whether PKCϵ lies downstream of CRF[sub1] receptors in the CeA. Compared with PKCϵ[sup+/+ CeA neurons, PKCϵ[sup-/-] neurons showed increased GABAergic tone due to enhanced GABA release. CRF and ethanol stimulated GABA release in the PKCϵ[sup+/+] CeA, but not in the PKCϵ[sup-/-] CeA. A PKCϵ-specific inhibitor blocked both CRF- and ethanol-induced GABA release in the PKCϵ[sup+/+] CeA, confirming findings in the PKCϵ[sup-/-] CeA. These results identify a PKCϵ signaling pathway in the CeA that is activated by CRF[sub1] receptor stimulation, mediates GABA release at nerve terminals, and regulates anxiety and alcohol consumption. [ABSTRACT FROM AUTHOR]

Background: A neonatal ventral hippocampal lesion (NVHL) induces behavioral and physiological anomalies mimicking pathophysiological changes of schizophrenia. Because prefrontal cortical (PFC) pyramidal neurons recorded from adult NVHL rats exhibit abnormal responses to activation of the mesocortical dopaminergic (DA) system, we explored whether these changes are due to an altered DA modulation of pyramidal neurons. Methods: Whole-cell recordings were used to examine the effects of DA and glutamate agonists on cell excitability in brain slices obtained from pre- (postnatal day [PD] 28–35) and post-pubertal (PD > 61) sham and NVHL animals. Results: N-methyl d-aspartate (NMDA), α-amino-3-hydroxy-5-methylisoxazole propionate (AMPA), and the D1 agonist SKF38393 increased excitability of deep layer pyramidal neurons in a concentration-dependent manner. The opposite effect was observed with the D2 agonist quinpirole. The effects of NMDA (but not AMPA) and SKF38393 on cell excitability were significantly higher in slices from NVHL animals, whereas quinpirole decrease of cell excitability was reduced. These differences were not observed in slices from pre-pubertal rats, suggesting that PFC DA and glutamatergic systems become altered after puberty in NVHL rats. Conclusions: A disruption of PFC dopamine–glutamate interactions might emerge after puberty in brains with an early postnatal deficit in hippocampal inputs, and this disruption could contribute to the manifestation of schizophrenia-like symptoms. [Copyright &y& Elsevier]

Dopamine D2 receptor (D2DR)-mediated transmission in the striatum is remarkably flexible, and changes in its efficacy have been heavily implicated in a variety of physiological and pathological conditions. Although receptor-associated proteins are clearly involved in specific forms of synaptic plasticity, the molecular mechanisms regulating the sensitivity of D2 receptors in this brain area are essentially obscure. We have studied the physiological responses of the D2DR stimulations in mice lacking the brain cytoplasmicRNABC1, a small noncoding dendritically localized RNA that is supposed to play a role in mRNA translation. We show that the efficiency of D2-mediated transmission regulating striatal GABA synapses is under the control of BC1 RNA, through a negative influence onD2 receptor protein level affecting the functional pool of receptors. Ablation of the BC1 gene did not result in widespread dysregulation of synaptic transmission, because the sensitivity of cannabinoid CB1 receptors was intact in the striatum of BC1 knock-out (KO) mice despite D2 and CB1 receptors mediated similar electrophysiological actions. Interestingly, the fragileXmental retardation protein FMRP, one of the multiple BC1 partners, is not involved in the BC1 effects on the D2-mediated transmission. Because D2DR mRNA is apparently equally translated in the BC1-KO and wild-type mice, whereas the protein level is higher in BC1-KO mice, we suggest that BC1 RNA controls D2DR indirectly, probably regulating translation of molecules involved in D2DR turnover and/or stability. [ABSTRACT FROM AUTHOR]

Abstract: In GAD65-knockout mice, lack of GAD65 expression was confirmed. The expression level of vesicular GABA transporter (VGAT) was upregulated, and no change in the synaptic vesicles (SV)-associated GAD67 was found. GAD65(−/−) SV transported cytosolic GABA much more efficiently than that of the wild type, further supporting our model that there is a structural and functional coupling between GABA synthesis and packaging into SV. Both full-length and truncated forms of GAD65 could bind to GABAergic SV, indicating the N-terminus is not required for the anchoring of GAD65 to SV. Although both GAD65(−/−) SV reconstituted with either GAD65 or GAD67 could synthesize GABA from [3H] glutamate and transport this newly synthesized GABA into SV, the combined evidence suggests that GAD65 plays a major role in GABA transmission in normal physiological condition. However, GAD67 could serve this role under some pathological conditions. [Copyright &y& Elsevier]

Purpose: Stiripentol (STP) is currently an efficient drug for add-on therapy in infantile epilepsies because it improves the efficacy of antiepileptic drugs (AEDs) through its potent inhibition of liver cytochromes P450. In addition, STP directly reduces seizures in several animal models of epilepsy, suggesting that it might also have anticonvulsive effects of its own. However, its underlying mechanisms of action are unknown. Methods: We examined the interactions of STP with γ-aminobutyric acid (GABA) transmission by using patch-clamp methods in CA3 pyramidal neurons in the neonatal rat. Results: STP markedly increased miniature inhibitory postsynaptic current (mIPSC) decay-time constant in a concentration-dependent manner. The prolongation of mIPSC duration does not result from an interaction with GABA transporters because it persisted in the presence of GAT-1 inhibitors (SKF-89976A and NO-711). An interaction with benzodiazepine or neurosteroid binding sites also was excluded because STP-mediated increase of decay time was still observed when these sites were initially saturated (by clobazam, zolpidem, or pregnanolone) or blocked (by flumazenil or dehydroepiandrosterone sulfate), respectively. In contrast, saturating barbiturate sites with pentobarbital clearly occluded this effect of STP, suggesting that STP and barbiturates interact at the same locus. This was directly confirmed by using outside-out patches, because STP increased the duration and not the frequency of opening of GABAA channels. Conclusions: At clinically relevant concentrations, STP enhances central GABA transmission through a barbiturate-like effect, suggesting that STP should possess an antiepileptic effect by itself. [ABSTRACT FROM AUTHOR]

Abstract: The interactions between adenosine A2A receptors and dopamine D2 receptors on the modulation of depolarization-evoked [3H]-γ-amino-butyric-acid release (GABA) were examined in slices of the globus pallidus of the rat. The stimulation of release caused by activation of A2A receptors was blocked when dopaminergic influences were eliminated with three independent methods: a) antagonism of D2 receptors with sulpiride; b) alkylation of these receptors with N-ethoxycarbonyl-2-ethoxy-1, 2-dihydroquinoline (EEDQ); c) depletion of dopamine with reserpine. In turn, activation of A2A receptors modified the response to stimulation of D2 receptors: the EC50 for quinpirole increased nearly one thousand times when A2A receptors were stimulated. Antagonism of A2A receptors in the absence of added agonists inhibited [3H] GABA release indicating receptor occupancy by endogenous adenosine. The dopamine dependence and the large effects of activating A2A receptors on the potency of dopaminergic agonists clarify some of the therapeutic properties of A2A antagonists in parkinsonian animals and patients. [Copyright &y& Elsevier]

We explored the role of dopamine D4 receptors on [3H]GABA release in the subthalamic nucleus. [3H]GABA release was evoked by high K+ in slices of the nucleus. The selective dopamine D4 receptor agonist PD168,077 (N-[[4-(2-cyanophenyl)-1-piperazynil]methyl]-3-methyl-benzamide) inhibited GABA release with greater potency (EC50=3.2 nM) than quinpirole (EC50=200 nM). SKF 21297 (6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide), a dopamine D1-like receptor agonist, had no effect. L-745,870 (3-{[4-(4-chlorophenyl)piperazin-1-yl]methyl}-1-1H-pyrollo[2,3-b] pyridine), a selective dopamine D4 receptor antagonist, reverted the quinpirole inhibition with greater potency (IC50=8.7 nM) than that of the dopamine D2/D3 receptor antagonist sulpiride and raclopride (IC50=4804 and 788 nM, respectively). Both methylphenidate and methamphetamine, dopamine reuptake blockers, inhibited by 30% high K+-evoked GABA release; the inhibition was blocked by L-745,870. These results show that dopamine D4 receptors modulate GABA release in the subthalamic nucleus. The results would explain how agents that increase interstitial dopamine like methylphenidate and amphethamine might control locomotor hyperactivity seen in disorders of dopamine D4 receptors. [Copyright &y& Elsevier]

Compelling evidence indicates that endocannabinoids are implicated in drug addiction. In the present study, we have addressed the interaction between cocaine and endocannabinoid system by means of neurochemical and neurophysiological experiments in rat brain slices. Using gas chromatography-electron impact mass spectrometry, we have found that cocaine increased the levels of the endocannabinoid anandamide in the striatum, a brain area primarily involved in the compulsive drug-seeking and drug-taking behaviors typical of addiction. This effect was attenuated by pharmacological inhibition of D2-like receptors but not DI-like receptors, and it was mimicked by D2-like but not DI-like receptor stimulation. The cocaine-induced increase in anandamide concentrations was attributable to both stimulation of its synthesis and inhibition of its degradation, as suggested by the ability of cocaine and quinpirole, a D2-like receptor agonist, to enhance the activity of NAPE-phospholipase D and to inhibit fancy acid amide hydrolase. By means of electrophysiological recordings from single striatal neurons, we have then observed that the ability of cocaine to inhibit, via D2-like receptors, GABA transmission was partially prevented following blockade of cannabinoid receptors, suggesting that endocannabinoids may act as downstream effectors in the action of cocaine in the striatum. Understanding the molecular and physiological effects of drugs of abuse in the brain is essential for the development of effective strategies against addiction. [ABSTRACT FROM AUTHOR]

The neurophysiological interactions between the high pressure neurological syndrome (HPNS) and a new β carboline, abecarnil, were studied in the nonhuman primate Papio anubis. Abecarnil is a partial agonist at the benzodiazepine site on the GABA/benzodiazepine receptor. Six animals were exposed on two occasions to pressures of 91 ATA in an environment of helium and oxygen. One exposure was pretreated with a total dose of abecarnil 1.0 mg/kg, the other with an equivalent volume of vehicle. Treatment with abecarnil prevented the severe signs of HPNS occurring between 51 and 91 ATA. Onset pressures of the various signs were unaffected. Some signs, e.g. myoclonus, became more frequent when abecarnil was used. A residual protective effect of abecarnil was present 4 weeks after the dose was given, active at pressures less than 71 ATA. Changes with pressure in the EEG were recorded primarily from the frontal cortex, but were also present in the parietal and occipital areas of the left cortex. Amplitude and frequency spectra were calculated and changes with pressure in the four conventional wavebands, plus two others, analysed. The most striking change was the prevention by abecarnil of the pressure-induced 100% increase in alpha wave amplitude in the frontal region. It is concluded that modulation of GABA transmission is important in controlling the expression of HPNS. [ABSTRACT FROM AUTHOR]

Alcohol elicits a neuroimmune response in the brain contributing to the development and maintenance of alcohol use disorder (AUD). While pro-inflammatory mediators initiate and drive the neuroimmune response, anti-inflammatory mediators provide an important homeostatic mechanism to limit inflammation and prevent pathological damage. However, our understanding of the role of anti-inflammatory signaling on neuronal physiology in critical addiction-related brain regions and pathological alcohol-dependence induced behaviors is limited, precluding our ability to identify promising therapeutic targets. Here, we hypothesized that chronic alcohol exposure compromises anti-inflammatory signaling in the central amygdala, a brain region implicated in anxiety and addiction, consequently perpetuating a pro-inflammatory state driving aberrant neuronal activity underlying pathological behaviors. We found that alcohol dependence alters the global brain immune landscape increasing IL-10 producing microglia and T-regulatory cells but decreasing local amygdala IL-10 levels. Amygdala IL-10 overexpression decreases anxiety-like behaviors, suggesting its local role in regulating amygdala-mediated behaviors. Mechanistically, amygdala IL-10 signaling through PI3K and p38 MAPK modulates GABA transmission directly at presynaptic terminals and indirectly through alterations in spontaneous firing. Alcohol dependence-induces neuroadaptations in IL-10 signaling leading to an overall IL-10-induced decrease in GABA transmission, which normalizes dependence-induced elevated amygdala GABA transmission. Notably, amygdala IL-10 overexpression abolishes escalation of alcohol intake, a diagnostic criterion of AUD, in dependent mice. This highlights the importance of amygdala IL-10 signaling in modulating neuronal activity and underlying anxiety-like behavior and aberrant alcohol intake, providing a new framework for therapeutic intervention. [ABSTRACT FROM AUTHOR]

Summary Top-down attention is crucial for meaningful behaviors and impaired in various mental disorders. However, its underpinning regulatory mechanisms are poorly understood. We demonstrate that the hippocampal-prefrontal synchrony associates with levels of top-down attention. Both attention and synchrony are reduced in mutant mice of ErbB4, a receptor of neuregulin-1. We used chemical genetic and optogenetic approaches to inactivate ErbB4 kinase and ErbB4+ interneurons, respectively, both of which reduce gamma-aminobutyric acid (GABA) activity. Such inhibitions in the hippocampus impair both hippocampal-prefrontal synchrony and top-down attention, whereas those in the prefrontal cortex alter attention, but not synchrony. These observations identify a role of ErbB4-dependent GABA activity in the hippocampus in synchronizing the hippocampal-prefrontal pathway and demonstrate that acute, dynamic ErbB4 signaling is required to command top-down attention. Because both neuregulin-1 and ErbB4 are susceptibility genes of schizophrenia and major depression, our study contributes to a better understanding of these disorders. Video Abstract [ABSTRACT FROM AUTHOR]