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Alzheimer's disease (AD) is one of the most common progressive neurodegenerative diseases associated with the degradation of memory and cognitive ability. Current pharmacotherapies show little therapeutic effect in AD treatment and still cannot prevent the pathological progression of AD. Deep brain stimulation (DBS) has shown to enhance memory in morbid obese, epilepsy and traumatic brain injury patients, and cognition in Parkinson's disease (PD) patients deteriorates during DBS off. Some relevant animal studies and clinical trials have been carried out to discuss the DBS treatment for AD. Reviewing the fornix trials, no unified conclusion has been reached about the clinical benefits of DBS in AD, and the dementia ratings scale has not been effectively improved in the long term. However, some patients have presented promising results, such as improved glucose metabolism, increased connectivity in cognition-related brain regions and even elevated cognitive function rating scale scores. The fornix plays an important regulatory role in memory, attention, and emotion through its complex fibre projection to cognition-related structures, making it a promising target for DBS for AD treatment. Moreover, the current stereotaxic technique and various evaluation methods have provided references for the operator to select accurate stimulation points. Related adverse events and relatively higher costs in DBS have been emphasized. In this article, we summarize and update the research progression on fornix DBS in AD and seek to provide a reliable reference for subsequent experimental studies on DBS treatment of AD., (© 2023 Stichting European Society for Clinical Investigation Journal Foundation. Published by John Wiley & Sons Ltd.)

Neurodevelopmental axonal pathfinding plays a central role in correct brain wiring and subsequent cognitive abilities. Within the growth cone, various intracellular effectors transduce axonal guidance signals by remodeling the cytoskeleton. Semaphorin-3E (Sema3E) is a guidance cue implicated in development of the fornix, a neuronal tract connecting the hippocampus to the hypothalamus. Microtubule-associated protein 6 (MAP6) has been shown to be involved in the Sema3E growth-promoting signaling pathway. In this study, we identified the collapsin response mediator protein 4 (CRMP4) as a MAP6 partner and a crucial effector in Sema3E growth-promoting activity. CRMP4-KO mice displayed abnormal fornix development reminiscent of that observed in Sema3E-KO mice. CRMP4 was shown to interact with the Sema3E tripartite receptor complex within detergent- resistant membrane (DRM) domains, and DRM domain integrity was required to transduce Sema3E signaling through the Akt/GSK3 pathway. Finally, we showed that the cytoskeleton-binding domain of CRMP4 is required for Sema3E's growth-promoting activity, suggesting that CRMP4 plays a role at the interface between Sema3E receptors, located in DRM domains, and the cytoskeleton network. As the fornix is affected in many psychiatric diseases, such as schizophrenia, our results provide new insights to better understand the neurodevelopmental components of these diseases., Competing Interests: BB, CR, AP, CB, CD, FA, ED, AK, MJ, AF, AA, SG, JD No competing interests declared, (© 2021, Boulan et al.)

Corticotropin releasing hormone (CRH) neurons located in the nucleus of hippocampal commissure (NHpC) have been proposed to be involved in the avian neuroendocrine regulation of stress and appeared to respond prior to CRH neurons in the hypothalamic paraventricular nucleus (PVN) when food deprivation stress was applied. Since the response of the NHpC was rapid and short-lived, was it regulated differentially from CRH neurons in the PVN? We, therefore, applied immobilization stress to test whether the NHpC response was stressor specific. Gene expression of CRH and stress-related genes in the NHpC, PVN, anterior pituitary (APit) as well as plasma corticosterone (CORT) were determined. Furthermore, brain derived neurotrophic factor (BDNF) and glucocorticoid receptor (GR) were examined regarding their possible roles in the regulation of CRH neurons. Data showed that rapid activation of CRH mRNA in the NHpC occurred and preceded a slower gene activation in the PVN, upregulation of proopiomelanocortin (POMC) transcripts in the APit and significant increases of CORT concentrations. Results suggested BDNF's role in negative feedback between CRH and CRHR1 in the NHpC and positive feedback between CRH and CRHR1 in the PVN. In the APit, V1bR activation appeared responsible for sustaining CORT release when stress persisted. Overall, data suggest that the NHpC functions as part of the HPA axis of birds and perhaps a comparable extra-hypothalamic structure occurs in other vertebrates.Lay SummaryThe nucleus of the hippocampal commissure, a structure outside of the hypothalamus, shows rapidly increased neural gene expression that appears to contribute to the early activation of the traditional hypothalamic-pituitary-adrenal (HPA) axis responsible for the production of stress hormones.

The 22q11.2 deletion syndrome (22q11DS) is associated with a wide spectrum of cognitive and psychiatric symptoms. Despite the considerable work performed over the past 20 years, the genetic etiology of the neurodevelopmental phenotype remains speculative. Here, we report de novo heterozygous truncating variants in the HIRA (Histone cell cycle regulation defective, S. Cerevisiae, homolog of, A) gene associated with a neurodevelopmental disorder in two unrelated patients. HIRA is located within the commonly deleted region of the 22q11DS and encodes a histone chaperone that regulates neural progenitor proliferation and neurogenesis, and that belongs to the WD40 Repeat (WDR) protein family involved in brain development and neuronal connectivity. To address the specific impact of HIRA haploinsufficiency in the neurodevelopmental phenotype of 22q11DS, we combined Hira knock-down strategies in developing mouse primary hippocampal neurons, and the direct study of brains from heterozygous Hira +/- mice. Our in vitro analyses revealed that Hira gene is mostly expressed during neuritogenesis and early dendritogenesis stages in mouse total brain and in developing primary hippocampal neurons. Moreover, shRNA knock-down experiments showed that a twofold decrease of endogenous Hira expression level resulted in an impaired dendritic growth and branching in primary developing hippocampal neuronal cultures. In parallel, in vivo analyses demonstrated that Hira +/- mice displayed subtle neuroanatomical defects including a reduced size of the hippocampus, the fornix and the corpus callosum. Our results suggest that HIRA haploinsufficiency would likely contribute to the complex pathophysiology of the neurodevelopmental phenotype of 22q11DS by impairing key processes in neurogenesis and by causing neuroanatomical defects during cerebral development.

Purposes: The recently developed myelin imaging method, inhomogeneous magnetization transfer (ihMT), is a surrogate measure of myelin content. The goal of the current study was to investigate alterations in myelin integrity in patients with recurrent major depressive disorder (rMDD)., Methods: Fifty-two patients with rMDD (36 female and 16 male) and 42 healthy controls (HC, 29 female and 13 male) were included. Two ihMT indices, quantitative ihMT (qihMT) and quantitative MT (qMT), were estimated from the ihMT data. A 50 white matter atlas was used to extract the regional quantitative values for each subject. The differences in qihMT and qMT values between the rMDD and HC groups were compared by a general linear model. Pearson correlation analyses were conducted to investigate associations between the significantly altered ihMT indices and clinical measures (Hamilton Depression Rating Scale scores and disease duration) in rMDD group., Results: The rMDD group showed significantly lower qihMT values in the fornix, left anterior limb of internal capsule, and left sagittal stratum, and lower qMT values in the fornix and left anterior limb of internal capsule than those of the HC group (p < 0.05, false discovery rate corrected). Both the qihMT and qMT values in the fornix of patients with rMDD were negatively correlated with disease duration (qihMT: r = -0.478, p < 0.001, Bonferroni corrected; qMT: r = -0.433, p = 0.001, Bonferroni corrected)., Conclusion: Our findings suggested that rMDD is associated with myelin impairment in the fornix, left anterior limb of internal capsule, and left sagittal stratum. In addition, this disruption of myelin integrity in the fornix could be cumulative as the disease progresses., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Recently we provided data showing that amygdala stimulation can ameliorate spatial memory impairments in rats with lesion in the fimbria-fornix (FF). The mechanisms for this improvement involve early gene expression and synthesis of BDNF, MAP-2, and GAP43 in the hippocampus and prefrontal cortex. Now we have studied which brain structures are activated by the amygdala using c-Fos as a marker of neural activation. First, we studied neuronal activation after tetanic stimulation to the amygdala in intact rats. We then carried out a second study in FF-lesioned rats in which the amygdala was stimulated 15 min after daily spatial memory training in the water maze. Our results showed that amygdala stimulation produces widespread brain activation, that includes cortical, thalamic, and brain stem structures. Activation was particularly intense in the dentate gyrus and the prefrontal cortex. Training in the water maze increased c-Fos positive nuclei in the dentate gyrus of the hippocampus and in medial prefrontal cortex. Amygdala stimulation to trained FF-lesioned rats induced an increase of neural activity in the dentate gyrus and medial prefrontal cortex relative to the FF-lesioned, but not stimulated group, like the c-Fos activity seen in trained control rats. Based on these and previous results we explain the mechanisms of amygdala reinforcement of neural plasticity and the partial recovery of spatial memory deficits., (© 2020 Wiley Periodicals, Inc.)

Exposure to high ambient temperatures (HAT) is associated with increased mortality, weight loss, immunosuppression, and metabolic malfunction in birds, all of which are likely downstream effects of reduced food intake. While the mechanisms mediating the physiological responses to HAT are documented, the neural mechanisms mediating behavioral responses are poorly understood. The aim of the present study was thus to investigate the hypothalamic mechanisms mediating heat-induced anorexia in four-day old broiler chicks. In Experiment 1, chicks exposed to HAT reduced food intake for the duration of exposure compared to controls in a thermoneutral environment (TN). In Experiment 2, HAT chicks that were administered an intracerebroventricular (ICV) injection of neuropeptide Y (NPY) increased food intake for 60 min post-injection, while TN chicks that received NPY increased food intake for 180 min post-injection. In Experiment 3, chicks in both the TN and HAT groups that received ICV injections of corticotropin-releasing factor (CRF) reduced food intake for up to 180 min post-injection. In Experiment 4, chicks that were exposed to HAT and received an ICV injection of astressin ate the same as controls in the TN group. In Experiment 5, chicks exposed to HAT that received an ICV injection of α-melanocyte stimulating hormone reduced food intake at both a high and low dose, with the low dose not reducing food intake in TN chicks. In Experiment 6, there was increased c-Fos expression in the hypothalamic paraventricular nucleus (PVN), lateral hypothalamic area (LHA), and the nucleus of the hippocampal commissure (NHpC). In Experiment 7, exposure to HAT was associated with decreased CRF mRNA in the NHpC, increased CRF mRNA in the PVN, and decreased NPY mRNA in the arcuate nucleus (ARC). In sum, these results demonstrate that exposure to HAT causes a reduction in food intake that is likely mediated via downregulation of NPY via the CRF system., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Objectives: The authors investigated the topography of cholinergic vulnerability in patients with dementia with Lewy bodies (DLB) using positron emission tomography (PET) imaging with the vesicular acetylcholine transporter (VAChT) [ 18 F]-fluoroethoxybenzovesamicol ([ 18 F]-FEOBV) radioligand., Methods: Five elderly participants with DLB (mean age, 77.8 years [SD=4.2]) and 21 elderly healthy control subjects (mean age, 73.62 years [SD=8.37]) underwent clinical assessment and [ 18 F]-FEOBV PET., Results: Compared with the healthy control group, reduced VAChT binding in patients with DLB demonstrated nondiffuse regionally distinct and prominent reductions in bilateral opercula and anterior cingulate to mid-cingulate cortices, bilateral insula, right (more than left) lateral geniculate nuclei, pulvinar, right proximal optic radiation, bilateral anterior and superior thalami, and posterior hippocampal fimbria and fornices., Conclusions: The topography of cholinergic vulnerability in DLB comprises key neural hubs involved in tonic alertness (cingulo-opercular), saliency (insula), visual attention (visual thalamus), and spatial navigation (fimbria/fornix) networks. The distinct denervation pattern suggests an important cholinergic role in specific clinical disease-defining features, such as cognitive fluctuations, visuoperceptual abnormalities causing visual hallucinations, visuospatial changes, and loss of balance caused by DLB.

The Lateral Hypothalamus/Perifornical Area (LH/PFA) has been shown to be involved with the hypercapnic ventilatory response, in a state-dependent manner. We have demonstrated that purinergic signaling through ATP in the LH/PFA has an excitatory effect in ventilatory response to CO 2 in awake rats in the dark phase of the diurnal cycle, but it is unknown whether the ATP metabolite adenosine, acting in the LH/PFA, modulates the ventilatory responses to hypercapnia. Here, we studied the effects of the microdialysis of adenosine (A1/A2 adenosine receptors agonist; 17 mM) and an A1 receptor antagonist (DPCPX; 0.1 mM) into the LH/PFA of conscious rats on ventilation in room air and in 7% CO 2 during the light and the dark phases of the diurnal cycle. The microdialysis of adenosine and DPCPX caused no change in the CO 2 ventilatory responses of rats during wakefulness or NREM sleep in either the dark or light period. Our data suggest that adenosine in the LH/PFA does not contribute to the hypercapnic ventilatory response in conscious rats., Competing Interests: Declaration of Competing Interest The authors declare that they have no conflict of interest., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In Alzheimer's disease (AD), Tau and Aβ aggregates involve sequentially connected regions, sometimes distantly separated. These alterations were studied in the pillar of the fornix (PoF), an axonal tract, to analyse the role of axons in their propagation. The PoF axons mainly originate from the subicular neurons and project to the mamillary body. Forty-seven post-mortem cases at various Braak stages (Tau) and Thal phases (Aβ) were analysed by immunohistochemistry. The distribution of the lesions showed that the subiculum was affected before the mamillary body, but neither Tau aggregation nor Aβ deposition was consistently first. The subiculum and the mamillary body contained Gallyas positive neurofibrillary tangles, immunolabelled by AT8, TG3, PHF1, Alz50 and C3 Tau antibodies. In the PoF, only thin and fragmented threads were observed, exclusively in the cases with neurofibrillary tangles in the subiculum. The threads were made of Gallyas negative, AT8 and TG3 positive Tau. They were intra-axonal and devoid of paired helical filaments at electron microscopy. We tested PoF homogenates containing Tau AT8 positive axons in a Tau P301S biosensor HEK cell line and found a seeding activity. There was no Aβ immunoreactivity detected in the PoF. We could follow microcryodissected AT8 positive axons entering the mamillary body; contacts between Tau positive endings and Aβ positive diffuse or focal deposits were observed in CLARITY-cleared mamillary body. In conclusion, we show that non-fibrillary, hyperphosphorylated Tau is transported by the axons of the PoF from the subiculum to the mamillary body and has a seeding activity. Either Tau aggregation or Aβ accumulation may occur first in this system: this inconstant order is incompatible with a cause-and-effects relationship. However, both pathologies were correlated and intimately associated, indicating an interaction of the two processes, once initiated.

Background: Up to 80% of mesial temporal lobe epilepsy patients with hippocampal sclerosis (mTLE-HS) are resistant to pharmacological treatment, often necessitating surgical resection. Deep brain stimulation (DBS) has emerged as an alternative treatment for patients who do not qualify for resective brain surgery. Brain stimulation may also exert disease-modifying effects, and noncoding microRNAs have recently been proposed to shape the gene expression landscape in epilepsy., Objective: We compared the effect of DBS of 4 different hippocampal target regions on epileptogenesis and manifest epilepsy in a rat model of mTLE-HS. To explore mechanisms, we profiled the effect of the most effective DBS paradigm on hippocampal microRNA levels., Methods: MTLE-HS was induced by electrical stimulation of the perforant pathway (PP) in rats. This paradigm leads to spontaneous seizures within 4 weeks. We investigated DBS of 4 targets: PP, fimbria fornix (FF) formation, dentate gyrus (DG) and ventral hippocampal commissure (VHC). We applied both high- (130 Hz) and low-frequency (5 Hz or 1 Hz) stimulation. Functional microRNAs were identified in the hippocampus immediately after VHC-DBS and after a 97-day recording period by sequencing small RNAs bound to Argonaute-2, a component of the miRNA silencing complex., Results: Low frequency DBS of the VHC significantly delayed the occurrence of the first spontaneous recurrent seizure in the PPS model by ∼300%, from 19 to 56 days. No other stimulation regime altered the latency phase. Upregulation of 5 microRNAs during epileptogenesis was suppressed by VHC-stimulation., Conclusion: We conclude that DBS of the VHC delays epilepsy in the PPS model in rats and is associated with differential regulation of several miRNAs. Additional studies are required to determine whether VHC-regulated miRNAs serve causal roles in the anti-epileptogenic effects of this DBS model., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The fornix is the primary efferent white matter tract of the hippocampus and is implicated in episodic memory. In this study, we investigated whether baseline measures of altered fornix microstructure and elevated beta amyloid (Aβ) burden influence prospective cognitive decline. A secondary goal examined whether Aβ burden is negatively associated with fornix microstructure. 253 clinically normal older adults underwent diffusion-weighted imaging and Pittsburgh Compound B positron emission tomography at baseline. We applied a novel streamline tractography protocol to reconstruct a fornix bundle in native space. Cognition was measured annually in domains of episodic memory, executive function, and processing speed (median follow-up = 4.0 ± 1.4 years). After controlling for covariates, linear mixed-effects models demonstrated an interaction of fornix microstructure with Aβ burden on episodic memory, such that combined lower fornix microstructure and higher Aβ burden was associated with accelerated decline. By contrast, associations with executive function and processing speed were not significant. There was no cross-sectional association between Aβ burden and fornix microstructure. In conclusion, altered fornix microstructure may accelerate memory decline in preclinical Alzheimer's disease., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Recently, in addition to the paraventricular nucleus (PVN), the nucleus of the hippocampal commissure (NHpC) have been proposed to regulate stress in birds due to the discovery of corticotropin releasing hormone (CRH) neurons in the NHpC. Expression of CRH, CRHR1, CRHR2 and glucocorticoid receptors (GRs) were determined within the NHpC compared to the PVN. Additionally, two levels of the hypothalamo-pituitary-adrenal (HPA) axis: 1) anterior pituitary and 2) adrenal gland were examined following food deprivation (FD) stress including proopiomelanocortin (POMC) expression and plasma corticosterone (CORT), respectively. CRH expression in the NHpC increased rapidly, however it quickly returned to control levels, showing a negative feedback with CRHR1. In contrast, CRH expression in the PVN and its receptor CRHR1, steadily increased throughout the sampling period showing a positive feedback with CRH. Of interest, brain-derived neurotrophic factor (BDNF) mRNA was significantly elevated in the PVN, while no significant change in BDNF mRNA was observed in the NHpC. The rapid increase in BDNF expression that matched the pattern shown by CRHR1 in the PVN may play a role in the positive feedback of CRH and its receptor. GRs were downregulated in both the NHpC and PVN throughout the study. POMC hnRNA and mRNA were significantly elevated from 1 to 4 h of FD compared to controls. A significant increase in plasma CORT levels occurred at 2 h and persisted to the end of the experiment, suggesting that CRH neurons in the NHpC initiated, while PVN CRH neurons sustained the early response of the HPA axis to stress., (Copyright © 2019. Published by Elsevier B.V.)

Aging leads to gray and white matter decline but their causation remains unclear. We explored two classes of models of age and dementia risk related brain changes. The first class of models emphasises the importance of gray matter: age and risk-related processes cause neurodegeneration and this causes damage in associated white matter tracts. The second class of models reverses the direction of causation: aging and risk factors cause white matter damage and this leads to gray matter damage. We compared these models with linear mediation analysis and quantitative MRI indices (from diffusion, quantitative magnetization transfer and relaxometry imaging) of tissue properties in two limbic structures implicated in age-related memory decline: the hippocampus and the fornix in 166 asymptomatic individuals (aged 38-71 years). Aging was associated with apparent glia but not neurite density damage in the fornix and the hippocampus. Mediation analysis supported white matter damage causing gray matter decline; controlling for fornix glia damage, the correlations between age and hippocampal damage disappear, but not vice versa. Fornix and hippocampal differences were both associated with reductions in episodic memory performance. These results suggest that fornix white matter glia damage may cause hippocampal gray matter damage during age-dependent limbic decline.

Aging-related tau astrogliopathy (ARTAG) is defined by the presence of two types of tau-bearing astrocytes: thorn-shaped astrocytes (TSAs) and granular/fuzzy astrocytes in the brain of old-aged individuals. The present study is focused on TSAs in rare forms of ARTAG with no neuronal tau pathology or restricted to entorhinal and transentorhinal cortices, to avoid bias from associated tauopathies. TSAs show 4Rtau phosphorylation at several specific sites and abnormal tau conformation, but they lack ubiquitin and they are not immunostained with tau-C3 antibodies which recognize truncated tau at Asp421. Astrocytes in ARTAG have atrophic processes, reduced glial fibrillary acidic protein (GFAP) and increased superoxide dismutase 2 (SOD2) immunoreactivity. Gel electrophoresis and western blotting of sarkosyl-insoluble fractions reveal a pattern of phospho-tau in ARTAG characterized by two bands of 68 and 64 kDa, and several middle bands between 35 and 50 kDa which differ from what is seen in AD. Phosphoproteomics of dissected vulnerable regions identifies an increase of phosphorylation marks in a large number of proteins in ARTAG compared with controls. GFAP, aquaporin 4, several serine-threonine kinases, microtubule associated proteins and other neuronal proteins are among the differentially phosphorylated proteins in ARTAG thus suggesting a hyper-phosphorylation background that affects several molecules, including many kinases and proteins from several cell compartments and various cell types. Finally, present results show for the first time that tau seeding is produced in neurons of the hippocampal complex, astrocytes, oligodendroglia and along fibers of the corpus callosum, fimbria and fornix following inoculation into the hippocampus of wild type mice of sarkosyl-insoluble fractions enriched in hyper-phosphorylated tau from selected ARTAG cases. These findings show astrocytes as crucial players of tau seeding in tauopathies., (© 2018 International Society of Neuropathology.)

The fornix and parahippocampal cingulum are 2 major limbic tracts in the core memory network of the hippocampus. Although these fiber tracts are known to degrade with Alzheimer's disease (AD), little is known about their vulnerability in the asymptomatic phase of AD. In this longitudinal study of cognitively normal adults, we assessed amyloid-beta (Aβ) plaques using positron emission tomography and white matter microstructure using diffusion tensor imaging. We found that an increase of neocortical Aβ burden over time was associated with an increase of radial diffusivity in the fornix but not in the parahippocampal cingulum. The effect of increasing neocortical Aβ burden on the fornix remained significant after controlling for baseline measures, head motion, global brain atrophy, regional Aβ burden in the hippocampus, or microstructural changes in the global white matter. In addition, microstructural changes in the fornix were not associated with decline of episodic memory or other cognitive abilities. Our findings suggest that microstructural changes in the fornix may be an early sign in the asymptomatic phase of AD., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Clinical trials are currently underway to assess the efficacy of forniceal deep brain stimulation (DBS) for improvement of memory in Alzheimer's patients, and forniceal DBS has been shown to improve learning and memory in a mouse model of Rett syndrome (RTT), an intellectual disability disorder caused by loss-of-function mutations in MECP2 . The mechanism of DBS benefits has been elusive, however, so we assessed changes in gene expression, splice isoforms, DNA methylation, and proteome following acute forniceal DBS in wild-type mice and mice lacking Mecp2 . We found that DBS upregulates genes involved in synaptic function, cell survival, and neurogenesis and normalized expression of ~25% of the genes altered in Mecp2 -null mice. Moreover, DBS induced expression of 17-24% of the genes downregulated in other intellectual disability mouse models and in post-mortem human brain tissue from patients with Major Depressive Disorder, suggesting forniceal DBS could benefit individuals with a variety of neuropsychiatric disorders., Competing Interests: AP, HY, AR, YW, MG, SH, HJ, JT, ZL No competing interests declared, HZ Senior editor, eLife, (© 2018, Pohodich et al.)

Background: A beneficial memory effect of acute fornix deep brain stimulation (DBS) has been reported in clinical studies. The aim of this study was to investigate the acute changes in glucose metabolism induced by fornix DBS., Methods: First, the Morris water maze test and novel object recognition memory test were used to confirm declined memory in aged mice (C57BL/6, 20-22 months old). Then, four groups of mice were used as follows: aged mice with stimulation (n = 12), aged mice with sham-stimulation (n = 8), adult mice (3-4 months old) with stimulation (n = 12), and adult mice with sham-stimulation (n = 8). Ipsilateral hippocampal glucose metabolism and glutamate levels were measured in vivo by microdialysis before, during, and after fornix DBS treatment. Histological staining was used to verify the localization of electrodes and mice with inaccurate placement were excluded from subsequent analyses. The effects of fornix DBS on extracellular glucose, lactate, pyruvate, and glutamate levels over time were analyzed by repeated-measures analysis of variance followed by Fisher's least significant difference post hoc test., Results: The aged mice had a higher basal lactate/pyruvate ratio (LPR) and lactate/glucose ratio (LGR) than the adult mice (LPR: 0.34 ± 0.04 vs. 0.13 ± 0.02, t = 4.626, P < 0.0001; LGR: 6.06 ± 0.59 vs. 4.14 ± 0.36, t = 2.823, P < 0.01). Fornix DBS decreased the ipsilateral hippocampal pyruvate and lactate levels (P < 0.05), but the glucose levels were not obviously changed in aged mice. Similarly, the LGR and LPR also decreased in aged mice after fornix DBS treatment (P < 0.05). Glucose metabolism in adult mice was not significantly influenced by fornix DBS. In addition, fornix DBS significantly decreased the ipsilateral hippocampal extracellular levels of glutamate in aged mice (P < 0.05), while significant alterations were not found in the adult mice., Conclusions: The present study provides experimental evidence that fornix DBS could significantly improve hippocampal glucose metabolism in aged mice by promoting cellular aerobic respiration activity., Competing Interests: There are no conflicts of interest.

The medial shell region of the nucleus accumbens (msNAc) is a key center for the regulation of goal-directed behavior and is likely to be dysfunctional in neuropsychiatric disorders such as addiction, depression and schizophrenia. Nitric oxide (NO)-producing interneurons in the msNAc are potently modulated by dopamine (DA) and may play an important role in synaptic integration in msNAc networks. In this study, neuronal NO synthase (nNOS) activity was measured in anesthetized rats using amperometric microsensors implanted into the msNAc or via histochemical techniques. In amperometric studies, NO oxidation current was recorded prior to and during electrical stimulation of the ipsilateral fimbria. Fimbria stimulation elicited a frequency and intensity-dependent increase in msNAc NO efflux which was attenuated by systemic administration of the nNOS inhibitor N G -propyl-l-arginine. Parallel studies using NADPH-diaphorase histochemistry to assay nNOS activity produced highly complementary outcomes. Moreover, systemic administration of either a DA D1 receptor agonist or a DA D2 receptor antagonist potentiated nNOS activity in the msNAc elicited by fimbria stimulation. These observations demonstrate for the first time that NO synthesis in nNOS expressing interneurons in the msNAc is facilitated by robust activation of hippocampal afferents in a manner that is differentially modulated by DA D1 and D2 receptor activation., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Whereas early Alzheimer disease (AD) neuropathology and mild cognitive impairment are relatively common in aging, accurate prediction of patients that will progress to dementia requires new biomarkers. Recently, substantial work has focused on phospho-tau/MAPT (p-MAPT) neuropathology since its regional propagation correlates with the degree of cognitive impairment in AD. Recent diffusion tensor imaging studies in AD suggest that increased diffusion in the fornix secondary to p-MAPT-related axonal injury could serve as a predictive biomarker of the risk of disease progression. However, our knowledge of p-MAPT neuropathology in the fornix is limited. To address this gap in knowledge, we examined p-MAPT neuropathology in the fornix and basal forebrain nuclei via AT8 immunohistochemistry in 39 brain autopsies spanning the spectrum of AD neuropathologic changes. We found that the fornix and its precommissural efferent target nuclei (septum and nucleus accumbens) demonstrated neuronal and thread-like p-MAPT neuropathology only in National Institute on Aging/Alzheimer Association (NIA/AA) stages B2 and B3 of neurofibrillary degeneration, consistent with involvement after (and propagation from) the hippocampal formation. Interestingly, although tau astrogliopathy was frequently observed in the mammillary bodies in stage B2, neuronal tauopathy was not observed in the postcommissural targets (mammillary bodies and anterior thalamic nucleus) until stage B3. Tauopathy in the nucleus basalis of Meynert was strongly correlated with p-MAPT-positive axons in the fornix, suggesting that projections to the hippocampus also likely contribute to fornix tauopathy. Our cross-sectional autopsy findings indicate that the fornix is involved by p-MAPT neuropathology secondary to hippocampal involvement by AD neuropathology. Furthermore, our findings are compatible with the goal of in vivo detection of p-MAPT-related axonal pathology in the fornix in AD as a possible biomarker of p-MAPT progression from the hippocampal formation and underscore a need for additional clinical-radiologic-pathologic correlation studies.

Background: Deep brain stimulation (DBS) is used to modulate the activity of dysfunctional brain circuits. The safety and efficacy of DBS in dementia is unknown., Objective: To assess DBS of memory circuits as a treatment for patients with mild Alzheimer's disease (AD)., Methods: We evaluated active "on" versus sham "off" bilateral DBS directed at the fornix-a major fiber bundle in the brain's memory circuit-in a randomized, double-blind trial (ClinicalTrials.gov NCT01608061) in 42 patients with mild AD. We measured cognitive function and cerebral glucose metabolism up to 12 months post-implantation., Results: Surgery and electrical stimulation were safe and well tolerated. There were no significant differences in the primary cognitive outcomes (ADAS-Cog 13, CDR-SB) in the "on" versus "off" stimulation group at 12 months for the whole cohort. Patients receiving stimulation showed increased metabolism at 6 months but this was not significant at 12 months. On post-hoc analysis, there was a significant interaction between age and treatment outcome: in contrast to patients <65 years old (n = 12) whose results trended toward being worse with DBS ON versus OFF, in patients≥65 (n = 30) DBS-f ON treatment was associated with a trend toward both benefit on clinical outcomes and a greater increase in cerebral glucose metabolism., Conclusion: DBS for AD was safe and associated with increased cerebral glucose metabolism. There were no differences in cognitive outcomes for participants as a whole, but participants aged≥65 years may have derived benefit while there was possible worsening in patients below age 65 years with stimulation.

Previous research has shown that dorsal hippocampus plays an important role in spatial memory process. Music exposure can enhance brain-derived neurotrophic factor (BDNF) expression level in dorsal hippocampus (DH) and thus enhance spatial cognition ability. But whether music experience may affect different subregions of DH in the same degree remains unclear. Here, we studied the effects of exposure to Mozart K.448 on learning behavior in developing rats using the classical Morris water maze task. The results showed that early music exposure could enhance significantly learning performance of the rats in the water maze test. Meanwhile, the BDNF/TrkB level of dorsal hippocampus CA3 (dCA3) and dentate gyrus (dDG) was significantly enhanced in rats exposed to Mozart music as compared to those without music exposure. In contrast, the BDNF/TrkB level of dorsal hippocampus CA1 (dCA1) was not affected. The results suggest that the spatial memory improvement by music exposure in rats may be associated with the enhanced BDNF/TrkB level of dCA3 and dDG., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Background: The forniceal area is currently being evaluated as a target for deep brain stimulation (DBS) to improve cognitive function in patients with Alzheimer's disease. The molecular changes at downstream targets within the stimulated circuit are unknown., Objective: To analyze the modulation of hippocampal protein expression following 1 h of fornix DBS in the rat., Methods: Animals underwent bilateral forniceal DBS for 1 h and sacrificed at different time-points after the initiation of the stimulation (1 h, 2.5 h, 5 h, 25 h). Bilateral hippocampi were isolated for western blot analyses., Results: Forniceal DBS led to a dramatic elevation of cFos post-stimulation, suggesting that forniceal DBS activates the hippocampus. There was also a significant increase in candidate proteins including several trophic factors, such as brain derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) but not glial cell-derived neurotrophic factor (GDNF). There was in addition, increased expression of the synaptic markers growth associated protein 43 (GAP-43), synaptophysin and α-synuclein. No changes were observed at the studied time-points in Alzheimer's-related proteins including amyloid precursor protein (APP), tau, phosphorylated tau (ptau), or selected chaperone proteins (HSP40, HSP70 and CHIP)., Conclusions: Forniceal DBS triggers hippocampal activity and rapidly modulate the expression of neurotrophic factors and markers of synaptic plasticity known to play key roles in memory processing. The clinical effects of DBS of the fornix may, in part, be mediated by producing changes in the expression of these proteins., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Aberrant white matter structures in fronto-temporal regions have previously been identified in patients with schizophrenia. However, scant research has focused on white matter integrity in patients presenting with a first episode of psychosis (FEP) with persistent negative symptoms (PNS). This study aimed to explore microstructure in the neurocircuitry proposed to be involved in PNS, by using a region-of-interest approach. Secondly, the relationship between individual negative symptoms and white matter were explored. Fractional anisotropy (FA) was measured in the fornix and three other tracts bilaterally including the uncinate fasciculus, superior longitudinal fasciculus and the cingulum bundle. Twelve patients with PNS were compared to a non-PNS group (52) and a healthy control group (51). Results showed that the PNS group had significantly lower FA values in the fornix when compared to healthy controls and that the non-PNS group had significantly lower FA values in the right uncinate fasciculus compared to healthy controls. Significant correlations were observed between SANS global score for anhedonia-asociality and lower FA values in the right cingulum bundle. Our results suggest that fronto-temporal white matter might be more closely related to PNS and that this relationship may possibly be mediated by greater anhedonia in PNS patients., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Microglia are resident immunocompetent cells having important roles in innate immunity in the brains. In the present study, we found that a single lipopolysaccharide (LPS) administration significantly increased microglial proliferation in the fornix and dentate gyrus (DG) but not the cerebral cortex and corpus callosum of adult mice. LPS-induced microglial proliferation was especially robust at the white matter of the fornix. The density of microglia increased in the fornix and DG for roughly one week and returned to basal levels at least 20days after a single LPS administration. Consecutive LPS administration did not induce such dramatic increase of microglial proliferation in the fornix. The inhibition of vascular endothelial growth factor signaling by AZD2171 largely suppressed LPS-induced increase of microglial proliferation in the fornix. In conclusion, the present study indicates that the hippocampal neuronal system has a higher proliferative microglial capability against LPS-induced inflammatory administration compared with other brain regions., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Structural microtubule associated proteins (MAPs) stabilize microtubules, a property that was thought to be essential for development, maintenance and function of neuronal circuits. However, deletion of the structural MAPs in mice does not lead to major neurodevelopment defects. Here we demonstrate a role for MAP6 in brain wiring that is independent of microtubule binding. We find that MAP6 deletion disrupts brain connectivity and is associated with a lack of post-commissural fornix fibres. MAP6 contributes to fornix development by regulating axonal elongation induced by Semaphorin 3E. We show that MAP6 acts downstream of receptor activation through a mechanism that requires a proline-rich domain distinct from its microtubule-stabilizing domains. We also show that MAP6 directly binds to SH3 domain proteins known to be involved in neurite extension and semaphorin function. We conclude that MAP6 is critical to interface guidance molecules with intracellular signalling effectors during the development of cerebral axon tracts.

Stromal derived factor-1α (SDF-1α), a critical chemokine that promotes cell homing to target tissues, was presumed to be involved in the traumatic brain injury cortex. In this study, we determined the expression of SDF-1α in the hippocampus after transection of the fimbria fornix (FF). Realtime PCR and ELISA showed that mRNA transcription and SDF-1α proteins increased significantly after FF transection. In vitro, the expression of SDF-1α in radial glial cells (RGCs) incubated with deafferented hippocampus extracts was observed to be greater than in those incubated with normal hippocampus extracts. The co-culture of neural progenitor cells (NPCs) and RGCs indicated that the extracts of deafferented hippocampus induced more NPCs migrating toward RGCs than the normal extracts. Suppression or overexpression of SDF-1α in RGCs markedly either decreased or increased, respectively, the migration of NPCs. These results suggest that after FF transection, SDF-1α in the deafferented hippocampus was upregulated and might play an important role in RGC induction of NPC migration; therefore, SDF-1α is a target for additional research for determining new therapy for brain injuries., (© 2015 International Federation for Cell Biology.)

Background: Deep Brain Stimulation (DBS) is thought to improve the symptoms of selected neurological disorders by modulating activity within dysfunctional brain circuits. To date, there is no evidence that DBS counteracts progressive neurodegeneration in any particular disorder., Objective/hypothesis: We hypothesized that DBS applied to the fornix in patients with Alzheimer's Disease (AD) could have an effect on brain structure., Methods: In six AD patients receiving fornix DBS, we used structural MRI to assess one-year change in hippocampal, fornix, and mammillary body volume. We also used deformation-based morphometry to identify whole-brain structural changes. We correlated volumetric changes to hippocampal glucose metabolism. We also compared volumetric changes to those in an age-, sex-, and severity-matched group of AD patients (n = 25) not receiving DBS., Results: We observed bilateral hippocampal volume increases in the two patients with the best clinical response to fornix DBS. In one patient, hippocampal volume was preserved three years after diagnosis. Overall, mean hippocampal atrophy was significantly slower in the DBS group compared to the matched AD group, and no matched AD patients demonstrated bilateral hippocampal enlargement. Across DBS patients, hippocampal volume change correlated strongly with hippocampal metabolism and with volume change in the fornix and mammillary bodies, suggesting a circuit-wide effect of stimulation. Deformation-based morphometry in DBS patients revealed local volume expansions in several regions typically atrophied in AD., Conclusion: We present the first in-human evidence that, in addition to modulating neural circuit activity, DBS may influence the natural course of brain atrophy in a neurodegenerative disease., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Previous reports suggested an important role for serotonin (5-hydroxytryptamine [5-HT]) in enhancing the counterregulatory response (CRR) to hypoglycemia. To elucidate the sites of action mediating this effect, we initially found that insulin-induced hypoglycemia stimulates 5-HT release in widespread forebrain regions, including the perifornical hypothalamus (PFH; 30%), ventromedial hypothalamus (34%), paraventricular hypothalamus (34%), paraventricular thalamic nucleus (64%), and cerebral cortex (63%). Of these, we focused on the PFH because of its known modulation of diverse neurohumoral and behavioral responses. In awake, behaving rats, bilateral PFH glucoprivation with 5-thioglucose stimulated adrenal medullary epinephrine (Epi) release (3,153%) and feeding (400%), while clamping PFH glucose at postprandial brain levels blunted the Epi response to hypoglycemia by 30%. The PFH contained both glucose-excited (GE) and glucose-inhibited (GI) neurons; GE neurons were primarily excited, while GI neurons were equally excited or inhibited by 5-HT at hypoglycemic glucose levels in vitro. Also, 5-HT stimulated lactate production by cultured hypothalamic astrocytes. Depleting PFH 5-HT blunted the Epi (but not feeding) response to focal PFH (69%) and systemic glucoprivation (39%), while increasing PFH 5-HT levels amplified the Epi response to hypoglycemia by 32%. Finally, the orexin 1 receptor antagonist SB334867A attenuated both the Epi (65%) and feeding (47%) responses to focal PFH glucoprivation. Thus we have identified the PFH as a glucoregulatory region where both 5-HT and orexin modulate the CRR and feeding responses to glucoprivation., (© 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Objective: White matter diffusivity measures of the fornix change with aging, which likely relates to changes in memory and cognition in older adults. Subregional variations in forniceal diffusivity may exist, given its heterogeneous anatomy and connectivity; however, these have not been closely examined in vivo. We examined diffusivity parameters (fractional anisotropy, FA; radial diffusivity, RD; axial diffusivity, AD) in forniceal subregions of healthy subjects and correlated them with age and hippocampal volume., Methods: Diffusion-weighted imaging and streamline tractography of the fornix were performed on 20 healthy, right-handed females (23-66 years). Six anatomical subregions were defined: midline (body, column, precommissural fornix) or lateral (fimbria, crura, postcommissural fornix). Regression analysis was performed comparing diffusivities against age. Hippocampal and ventricular volumes were also compared., Results: Diffusivity values revealed statistical changes with age in both midline and lateralized subregions. The fornix body and left crus showed age-related alterations in all metrics (FA, RD, AD), whereas only right crus FA was altered. There was no significant change in hippocampal volumes, suggesting that forniceal changes may precede hippocampal age-related changes., Conclusions: Age-related changes in fornix diffusivity measures appear subregion dependent and asymmetrical. Specific subregion diffusivity measures may be a more sensitive aging marker than hippocampal volume change.

Learning active or reactive responses to fear involves different brain circuitry. This study examined how the nuclus accumbens (NAc), dorsal hippocampus (DH) and medial prefrontal cortex (mPFC) may interact in memory processing for these two kinds of responses. Male Wistar rats with cannulae implanted in these areas were trained on a contextual fear conditioning or inhibitory avoidance task that respectively engaged a reactive or active response to fear in the test. Immediately after training, a memory modulating factor released by stress, norepinephrine (NE), was infused into one region and 4% lidocaine into another to examine if an upstream activation effect could be blocked by the downstream suppression. Retention tested 1 day later showed that in both tasks posttraining infusion of NE at different doses into either the DH or mPFC enhanced retention but the enhancement was blocked by concurrent infusion of lidocaine into the other region, suggesting reliance of the effect on functional integrity of both regions. Further, posttraining intra-NAc lidocaine infusion attenuated memory enhancement of NE infused to the DH or mPFC in the inhibitory avoidance task but did not do so in contextual fear conditioning. These results suggest that NE regulation of memory formation for the reactive and active responses to fear may rely on distinct interactions among the DH, mPFC and NAc., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Background: The importance of developing unique, neural circuitry-based treatments for the cognitive and neuropsychiatric symptoms of Alzheimer disease (AD) was the impetus for a phase I study of deep brain stimulation (DBS) in patients with AD that targeted the fornix., Objective: To test the hypotheses that DBS would increase cerebral glucose metabolism in cortical and hippocampal circuits and that increased metabolism would be correlated with better clinical outcomes., Design: Open-label trial., Setting: Academic medical center., Patients: A total of 5 patients with mild, probable AD (1 woman and 4 men, with a mean [SD] age of 62.6 [4.2] years)., Intervention: Deep brain stimulation of the fornix., Main Outcome Measures: All patients underwent clinical follow-up and high-resolution positron emission tomography studies of cerebral glucose metabolism after 1 year of DBS., Results: Functional connectivity analyses revealed that 1 year of DBS increased cerebral glucose metabolism in 2 orthogonal networks: a frontal-temporal-parietal-striatal-thalamic network and a frontal-temporal-parietal-occipital-hippocampal network. In similar cortical regions, higher baseline metabolism prior to DBS and increased metabolism after 1 year of DBS were correlated with better outcomes in global cognition, memory, and quality of life., Conclusions: Increased connectivity after 1 year of DBS is observed, which is in contrast to the decreased connectivity observed over the course of AD. The persistent cortical metabolic increases after 1 year of DBS were associated with better clinical outcomes in this patient sample and are greater in magnitude and more extensive in the effects on cortical circuitry compared with the effects reported for pharmacotherapy over 1 year in AD.

Ciliary beat frequency (CBF) was measured in slice preparations of the Fallopian tube fimbria, using videomicroscopy with a high-speed (500 Hz) camera in guinea pigs that were treated with β-oestradiol benzoate (βE2B) and medroxy progesterone (mPRG). In non-ovulating guinea pigs at 4 weeks of age, the CBF of the fimbria was high (17.8 Hz). In sexually mature guinea pigs (12-16 weeks of age) with constant ovulation, the CBF varied from 12 Hz to 16 Hz. The in vivo administration of both ICI-182,780 (a blocker of βE2 receptors) and mifepristone (a blocker of PRG receptors) induced high CBF (17.4 Hz). The administration of βE2B at a low (3.2 mg/kg/day) or high (32 mg/kg/day) dose decreased the CBF to 14.5 Hz or 11 Hz, respectively. ICI-182,780 abolished the βE2B-induced changes in CBF and decreased CBF to 12 Hz. The administration of mPRG (6.4 mg/kg/day) decreased CBF to 12.5 Hz. Mifepristone abolished this mPRG-induced decrease in CBF and maintained the CBF at 15 Hz. However, administering both βE2B and mPRG increased CBF to 17.5 Hz, suggesting that βE2B inhibits mPRG actions and vice versa. To confirm the interactions between βE2B and mPRG, we administered both βE2B and mPRG to guinea pigs that were pretreated for 1.5 days with either mPRG (6.4 mg/kg/day) or βE2B (3.2 mg/kg/day). Prior treatment with βE2B or mPRG prevented the increase in CBF that was otherwise by βE2B plus mPRG, and maintained the CBF at 14.5 Hz or 13 Hz, respectively. The administration of βE2B plus mPRG still induced the expression of PRG receptors, indicating that the highest CBF is not the result of no expression of the receptors. In the beating cilia of the fimbria, the signals that are activated by the βE2 and PRG receptors are proposed to antagonize each other in regulating the frequency.

To elucidate compositional changes of the limbic system with aging, the authors investigated age-related changes of elements in the hippocampus, dentate gyrus, and fornix and the relationships among elements by direct chemical analysis. After ordinary dissections at Nara Medical University were finished, the hippocampi, dentate gyri, and fornices were resected from identical cerebra of the subjects which consisted of 23 men and 23 women, ranging in age from 70 to 101 years. After ashing with nitric acid and perchloric acid, element contents were determined by inductively coupled plasma-atomic emission spectrometry. The average contents of P, Zn, and Na were significantly less in both the hippocampi and dentate gyri compared with the fornices. It was found that the Ca and Mg contents increased significantly in the hippocampus with aging; the P content increased significantly in the dentate gyrus with aging, whereas the Na content decreased in the dentate gyrus with aging; and the Mg content increased significantly in the fornix with aging. Regarding the relationships among elements, a significant direct correlation between Ca and Fe contents and an extremely significant inverse correlation between P and Zn contents were found in both the hippocampi and dentate gyri. In addition, a significant direct correlation between P and Mg contents was found in both the hippocampi and fornices. Pearson's correlation was used to examine whether there were elements with significant correlation among the hippocampus, dentate gyrus, fornix, and mammillary body. Significant correlations were found in five elements of Ca, P, Mg, Zn, and Fe except for S and Na among the hippocampus, dentate gyrus, and mammillary body with one exception. Regarding the fornix, significant correlations were found in two elements of P and Fe between the fornix and hippocampus, dentate gyrus, or mammillary body.

The peptide melanin-concentrating hormone (MCH), produced mainly by cells in the lateral hypothalamus (LH), perifornical area (PF) and zona incerta (ZI), is suggested to have a role in the consumption of rewarding substances, such as ethanol, sucrose and palatable food. However, there is limited information on the specific brain sites where MCH acts to stimulate intake of these rewarding substances and on the feedback effects that their consumption has on the expression of endogenous MCH. The current study investigated MCH in relation to ethanol consumption, in Sprague-Dawley rats. In Experiment 1, chronic consumption of ethanol (from 0.70 to 2.7 g/kg/day) dose-dependently reduced MCH gene expression in the LH. In Experiments 2-4, the opposite effect was observed with acute oral ethanol, which stimulated MCH expression specifically in the LH but not the ZI. In Experiment 5, the effect of MCH injection in brain-cannulated rats on ethanol consumption was examined. Compared to saline, MCH injected in the paraventricular nucleus (PVN) and nucleus accumbens (NAc) selectively stimulated ethanol consumption without affecting food or water intake. In contrast, it reduced ethanol intake when administered into the LH, while having no effect in the ZI. These results demonstrate that voluntary, chronic consumption of ethanol leads to local negative feedback control of MCH expression in the LH. However, with a brief exposure, ethanol stimulates MCH-expressing neurons in this region, which through projections to the feeding-related PVN and reward-related NAc can promote further drinking behavior., (Copyright © 2010 Elsevier Inc. All rights reserved.)

While diffusion tensor imaging (DTI) has been extensively used to infer micro-structural characteristics of cerebral white matter in human conditions, correlations between human in vivo DTI and histology have not been performed. Temporal lobe epilepsy (TLE) patients with mesial temporal sclerosis (MTS) have abnormal DTI parameters of the fimbria-fornix (relative to TLE patients without MTS) which are presumed to represent differences in axonal/myelin integrity. Medically intractable TLE patients who undergo temporal lobe resection including the fimbria-fornix provide a unique opportunity to study the anatomical correlates of water diffusion abnormalities in freshly excised tissue. Eleven patients with medically intractable TLE were recruited (six with and five without MTS) for presurgical DTI followed by surgical excision of a small specimen of the fimbria-fornix which was processed for electron microscopy. Blinded quantitative analysis of the microphotographs included axonal diameter, density and area, cumulative axon membrane circumference, and myelin thickness and area. As predicted by DTI the fimbria-fornix of TLE patients with MTS had increased extra-axonal fraction, and reduced cumulative axonal membrane circumference and myelin area. Consistent with the animal literature, water diffusion anisotropy over the crus of the fimbria-fornix was strongly correlated with axonal membranes (cumulative membrane circumference) within the surgical specimen (approximately 15% of what was analyzed with DTI). The demonstration of a correlation between histology and human in vivo DTI, in combination with the observation that in vivo DTI accurately predicted white matter abnormalities in a human disease condition, provides strong validation of the application of DTI as a noninvasive marker of white matter pathology.

Food is acquired (obtained by foraging) and frequently stored (hoarded) across animal taxa, including humans, but the physiological mechanisms underlying these behaviors are virtually unknown. We found that peptides that stimulate food intake in rats stimulate food foraging and/or hoarding more than intake in Siberian hamsters. Neuropeptide Y (NPY) is a potent orexigenic peptide that increases food foraging and hoarding (appetitive behavior) and food intake (consummatory behavior). Given that NPY injections into the hypothalamic paraventricular nucleus (PVH) or perifornical area (PFA) increase food intake by rats, it is possible that these injections may stimulate food foraging or hoarding by Siberian hamsters. We also tested whether antagonism of the NPY Y1 receptor (Y1-R), the agonism of which stimulates hoarding, would inhibit post-food-deprivation increases in foraging and hoarding. We injected one of three doses of NPY or vehicle into the PVH or PFA of animals housed in a simulated foraging-hoarding housing system and measured these behaviors at 1, 2, 4, and 24 h. A subset of animals was subsequently food deprived and then given PVH or PFA Y1-R antagonist microinjections before they were refed. NPY PVH microinjections decreased foraging but increased hoarding and food intake, whereas NPY PFA microinjections increased all three behaviors, but the greatest increase was in hoarding. Y1-R antagonist inhibited post-food-deprivation increases in hoarding when injected into the PVH and PFA and inhibited foraging when injected into the PFA. These results support the view that NPY is involved in appetitive and consummatory ingestive behaviors, but each may be controlled by different brain areas and/or NPY receptor subtypes.

While activation of alpha7 nicotinic receptors protects neurons from a variety of apoptotic insults in vitro, little is known about this neuroprotective action in vivo, especially under amyloidogenic conditions that mimic Alzheimer's disease. We therefore investigated the effects of 4OH-GTS-21, a selective partial agonist for these receptors, on septohippocampal cholinergic and GABAergic neuron survival following fimbria fornix (FFX) lesions in three strains of mice: C57BL/6J wild type mice; human presenilin-1 mutant M146L (PS1) transgenic mice; and mice expressing both mutant PS1 and Swedish mutant K670N/M671L amyloid precursor protein (APP). Initial studies to demonstrated that 4OH-GTS-21 is likely brain permeant based on its ability to improve passive avoidance and Morris water task behaviors in nucleus basalis-lesioned rats. In FFX-lesioned mice, twice per day i.p. injections of 1 mg/kg of 4OH-GTS-21 for 2 weeks promoted the survival and prevented the atrophy of septal cholinergic neurons. Septal parvalbumin-staining GABAergic neurons were not protected by this treatment, although they also express alpha7 nicotinic receptors, suggesting an indirect, nerve growth factor (NGF)-mediated mechanism. No protection of cholinergic neurons was observed in similarly treated PS1 or APP/PS1 transgenic mice. 4OH-GTS-21 treatment actually reduced cholinergic neuronal size in APP/PS1 mice. Hippocampal amyloid deposition was not affected by FFX lesions or treatment with this alpha7 nicotinic receptor agonist in APP/PS1 mice under these conditions. These results indicate that brain alpha7 nicotinic receptors are potential targets for protecting at-risk brain neurons in Alzheimer's disease, perhaps via their effects on NGF receptors; however, this protection may be sensitive under some conditions to environmental factors such as inhibitory amyloid-peptides.

The fate of neural stem/progenitor cells (NSCs/NPCs) in vivo lies on the local microenvironment. Whether the denervated hippocampus provides a stimulative role on the survival and differentiation of the anterior subventricular zone (SVZa) progenitors was investigated in the present study. In vivo the SVZa progenitors were transplanted into the denervated hippocampus and the contralateral side, and were found migrating along the subgranular layer. More implanted cells were found survived and differentiated into the Neurofilament 200 (NF-200) or beta-Tubulin-III positive neurons in the denervated than in the normal hippocampus at all points studied. In vitro the extracts from the denervated and normal hippocampus were used to induce differentiation of the SVZa progenitors. More progenitors incubated with the denervated hippocampal extract differentiated significantly into the MAP-2 or AChE positive neurons than those incubated with the normal hippocampal extract (P<0.05). We concluded that the deafferented hippocampus provided proper microenvironment for the survival and neuronal differentiation of neural progenitors.

We demonstrated previously that when hippocampal-dependent learning and plasticity are compromised by fornix lesions, behaviorally induced expression of the immediate early gene, Arc, is correspondingly low. The medial septum and the vertical diagonal band are major sources of subcortical afferents that innervate the hippocampus via the fornix. Here we assessed the specific contribution of cholinergic afferents from these regions to the impairments in spatial learning and behavioral induction of Arc transcription produced by fornix lesions. The immunotoxin, 192 IgG-saporin, was used to produce selective lesions of cholinergic cell bodies in the medial septum and vertical diagonal band. Rats were then trained on both cued and spatial delayed match-to-place tasks in a radial arm water maze. Animals with 192 IgG-saporin lesions learned both cue and place discrimination tasks in the water maze normally, and showed only a mild and transient impairment when switching from the cued to the spatial version of the task. Following behavioral testing, rats explored two novel environments sequentially in a setting known to induce Arc expression in hippocampal pyramidal neurons. In marked contrast to the effects of complete fornix transection, quantitative in situ autoradiography revealed no differences in Arc mRNA expression between sham and lesion animals in CA1, CA3 or stratum radiatum. The conclusion from these data is that cholinergic deafferentation alone cannot account for the spatial learning deficits or impaired behavioral induction of Arc transcription produced by fornix lesions.

The rodent dentate gyrus (DG) is formed in the embryo when progenitor cells migrate from the dentate neuroepithelium to establish a germinal zone in the hilus and a secondary germinal matrix, near the fimbria, called the hippocampal subventricular zone (HSVZ). The developmental plasticity of progenitors within the HSVZ is not well understood. To delineate the migratory routes and fates of progenitors within this zone, we injected a replication-incompetent retrovirus, encoding the enhanced green fluorescent protein (EGFP), into the HSVZ of postnatal day 5 (P5) mice. Between P6 and P45, retrovirally-infected EGFP(+) of progenitors migrated into the DG, established a reservoir of progenitor cells, and differentiated into neurons and glia. By P6-7, EGFP(+) cells were observed migrating into the DG. Subsets of these EGFP(+) cells expressed Sox2 and Musashi-1, characteristic of neural stem cells. By P10, EGFP(+) cells assumed positions within the DG and expressed immature neuronal markers. By P20, many EGFP(+) cells expressed the homeobox prospero-like protein Prox1, an early and specific granule cell marker in the CNS, and extended mossy fiber projections into the CA3. A subset of non-neuronal EGFP(+) cells in the dentate gyrus acquired the morphology of astrocytes. Another subset included EGFP(+)/RIP(+) oligodendrocytes that migrated into the fimbria, corpus callosum, and cerebral cortex. Retroviral injections on P15 labeled very few cells, suggesting depletion of HSVZ progenitors by this age. These findings suggest that the early postnatal HSVZ progenitors are multipotent and migratory, and contribute to both dentate gyrus neurogenesis as well as forebrain gliogenesis.

Sexual dimorphism of neurons and astrocytes has been demonstrated in different centers of the brain, but sexual dimorphism of oligodendrocytes and myelin has not been examined. We show, using immunocytochemistry and in situ hybridization, that the density of oligodendrocytes in corpus callosum, fornix, and spinal cord is 20-40% greater in males compared with females. These differences are present in young and aged rodents and are independent of strain and species. Proteolipid protein and carbonic anhydrase-II transcripts, measured by real-time PCR, are approximately two to three times greater in males. Myelin basic protein and 2', 3'-cyclic nucleotide 3'-phosphodiesterase, measured by Western blots, are 20-160% greater in males compared with females. Surprisingly, both generation of new glia and apoptosis of glia, including oligodendrocytes, are approximately two times greater in female corpus callosum. These results indicate that the lifespan of oligodendrocytes is shorter in females than in males. Castration of males produces a female phenotype characterized by fewer oligodendrocytes and increased generation of new glia. These findings indicate that exogenous androgens differentially affect the lifespan of male and female oligodendrocytes, and they can override the endogenous production of neurosteroids. The data imply that turnover of myelin is greater in females than in males. Mu-calpain, a protease upregulated in degeneration of myelin, is dramatically increased at both transcriptional and translational levels in females compared with males. These morphological, molecular, and biochemical data show surprisingly large differences in turnover of oligodendrocytes and myelin between sexes. We discuss the potential significance of these differences to multiple sclerosis, a sexually dimorphic disease, whose progression is altered by exogenous hormones.

Prompted by the theoretical prediction that damage to the hippocampal system should abolish exploratory behavior, the present study examined exploratory movements in control monkeys (CON) and monkeys with transection of the fornix (FNX), a major input/output pathway of the hippocampus. CON and FNX monkeys were introduced to a novel octagonal chamber for six daily sessions, each lasting 20 min. Both groups visited, punctuated by stops, the majority of the floor space of the environment in each of the sessions. The exploratory movements of CON and FNX groups were not significantly different on most of the measures taken over six consecutive days. These measures included cumulative distance traveled, number and duration of stops, traveling patterns, and proportion of time spent in each of 12 designated zones of floor space. The high degree of similarity in behavior between CON and FNX groups suggests that an intact hippocampal system is not necessary for the display of normal exploratory movement per se. On the other hand, the CON and FNX groups did behave differently on two measures. First, the CON group exhibited a decrement in distance traversed over consecutive epochs within the first test session, whereas FNX animals did not. Second, on those days in which the chamber was made visually asymmetrical, the CON animals tended to show a predilection for spending proportionally more time within one particular quadrant of the chamber. These observations are consistent with the idea that interrupting normal hippocampal system function by means of fornix transection is detrimental to learning about the spatial layout of environments. We therefore suggest that while monkeys with fornix transection still display intact locomotor and exploratory behavior patterns, their new learning of visuospatial context is impaired., (Copyright 2006 Wiley-Liss, Inc.)

Abnormal accumulation of alpha-synuclein is regarded as a key pathological step in a wide range of neurodegenerative processes, not only in Parkinson's disease (PD) and dementia with Lewy bodies (DLB) but also in multiple-system atrophy (MSA). Nevertheless, the mechanism of alpha-synuclein accumulation remains unclear. Leupeptin, a protease inhibitor, has been known to cause various neuropathological changes in vivo resembling those of aging or neurodegenerative processes in the human brain, including the accumulation of neuronal processes and neuronal cytoskeletal abnormalities leading to neurofibrillary tangle (NFT)-like formations. In the present study, we administered leupeptin into the rat ventricle and found that alpha-synuclein-positive structures appeared widely in the neuronal tissue, mainly in neuronal processes of the fimbria and alveus. Immunoelectron microscopic study revealed that alpha-synuclein immunoreactivity was located in the swollen axons of the fimbria and alveus, especially in the dilated presynaptic terminals. In addition colocalization of alpha-synuclein with ubiquitin was rarely observed in confocal laser-scan image. This is the first report of experimentally induced in vivo accumulation of alpha-synuclein in non-transgenic rodent brain injected with a well-characterized protease inhibitor by an infusion pump. The present finding suggests that the local accumulation of alpha-synuclein might be induced by the impaired metabolism of alpha-synuclein, which are likely related to lysosomal or ubiquitin-independent proteasomal systems.

Hippocampal theta rhythm (HPCtheta) may be important for various phenomena, including attention and acquisition of sensory information. Two types of HPCtheta (types I and II) exist based on pharmacological, behavioral, and electrophysiological characteristics. Both types occur during locomotion, whereas only type II (atropine-sensitive) is present under urethane anesthesia. The circuit of HPCtheta synchronization includes the medial septum-diagonal band of Broca (MSDB), with cholinergic and gamma-aminobutyric acid (GABA)ergic neurons comprising the two main projections from MSDB to HPC. The primary aim of the present study was to assess the effects of GABAergic MSDB lesions on urethane- and locomotion-related HPCtheta, and compare these effects to those of cholinergic MSDB lesions. Saline, kainic acid (KA), or 192 IgG-saporin (SAP) was injected into MSDB before recording. KA preferentially destroys GABAergic MSDB neurons, whereas SAP selectively eliminates cholinergic MSDB neurons. A fixed recording electrode was placed in the dentate mid-molecular layer, and stimulating electrodes were placed in the posterior hypothalamus (PH), and medial perforant path (PP). Under urethane anesthesia, HPCtheta was induced by tail pinch, PH stimulation, and systemic physostigmine; none of the rats with KA or SAP showed HPCtheta in any of these conditions. During locomotion, HPCtheta was attenuated, but not eliminated, in rats with KA or SAP lesions. Intraseptal KA in combination with either intraseptal SAP or PP lesions reduced locomotion-related HPCtheta beyond that observed with each lesion alone, virtually eliminating HPCtheta. In contrast, intraseptal SAP combined with PP lesions did not reduce HPCtheta beyond the effect of each lesion alone. We conclude that both GABAergic and cholinergic MSDB neurons are necessary for HPCtheta under urethane, and that each of these septohippocampal projections contributes to HPCtheta during locomotion., (Copyright (c) 2005 Wiley-Liss, Inc.)

An essential characteristic of the CNS function is the formation of reciprocal connections between brain areas. Although the mechanisms controlling the establishment of neuronal connections are being determined, very little is known about the development of reciprocal connections, which often course along identical pathways. Here, we show that Netrin-1, expressed along the fimbria, chemoattracts both septohippocampal and hippocamposeptal fibers. Moreover, we show that both Semaphorins 3A and 3F expressed in regions nearby the septum prevent the growth of septal axons into these regions. Blocking experiments with recombinant ecto-Neuropilins indicate that both Semaphorins 3A and 3F act cooperatively in the repulsion of septal axons. Furthermore, netrin-1-deficient mice develop a reduced septohippocampal projection. We conclude that the coordinated actions of Netrin-1 and Semaphorins 3A and 3F cooperate in the development of septohippocampal and hippocamposeptal connections, indicating that the same molecular cues serve the construction of reciprocal connections in both directions of growth.

In contrast to the regeneration-competent peripheral nervous system (PNS), lesions of nerve tracts within the central nervous system (CNS) lead to chronically impaired neuronal connections. We have analysed changes in gene expression patterns occurring as a consequence of postcommissural fornix transection at a time when spontaneous axonal growth has ceased at the lesion site. This was done in order to describe both extrinsic and intrinsic determinants of regeneration failure. Using a genomic approach we have identified a number of so far undetected factors such as bamacan and semaphorin 6B, which relate to chronic axonal growth arrest and therefore are promising candidates for lesion-induced axonal growth inhibitors. In addition, we observed that within the subiculum, where the fornix axons originate, neuronal Oct-6 was induced and NG2 was down-regulated, indicating that axotomized neurons as well as glial cells react at the level of gene expression to remote axotomy.

This study examined the distribution of vesicular glutamate transporter 2 (VGLUT2)-immunoreactive neuronal structures in the ipsilateral and contralateral hippocampi of unilateral fimbria/fornix transected, unilateral entorhinal cortex ablated, and intact female and male rats. In the hippocampi of intact animals, the highest density of VGLUT2-positive boutons was observed in the supragranular layer of the dentate gyrus, followed by the CA2 pyramidal and oriens layers, and the stratum lacunosum-moleculare of the CA1 field. This staining pattern was identical both in males and in females. Electron microscopic examination revealed that the immunolabeling was confined to axon terminals forming exclusively asymmetric synaptic contacts. The quantitative analysis of the synaptic targets of VGLUT2-positive terminals showed that in the dentate gyrus, 59% of the synaptic targets were dendritic spines, followed by dendritic shafts (22%) and granule cell somata (19%). In the pyramidal layer of the CA2 field, VGLUT2-immunoreactive boutons contacted mostly dendritic shafts (85%), only some of which (15%) synapsed with spines. The synaptic targets of VGLUT2-positive varicosities were dendritic spines (71%) and shafts (29%) in the stratum lacunosum-moleculare of the CA1 field. The fimbria/fornix transection caused a significant reduction in the density of VGLUT2-positive boutons only in the CA2 field, while entorhinal cortex ablation elicited no change in fiber density in any of the areas analyzed. Furthermore, our latest experiments on colchicine-treated animals revealed a large population of VGLUT2-positive neurons in the hippocampus that may be a possible intrinsic source of hippocampal VGLUT2 boutons. Our results suggest that the most likely sources of VGLUT2-positive boutons in the dentate supragranular layer, the CA2 area, as well as in the stratum lacunosum-moleculare of the CA1 field, might be the mossy cells, the supramammillary area, and the nucleus reuniens thalami, respectively., (Copyright 2004 Wiley-Liss, Inc.)

Glutamatergic signal transduction occurs in CNS white matter, but quantitative data on glutamate uptake and metabolism are lacking. We report that the level of the astrocytic glutamate transporter GLT in rat fimbria and corpus callosum was approximately 35% of that in parietal cortex; uptake of [3H]glutamate was 24 and 43%, respectively, of the cortical value. In fimbria and corpus callosum levels of synaptic proteins, synapsin I and synaptophysin were 15-20% of those in cortex; the activities of glutamine synthetase and phosphate-activated glutaminase, enzymes involved in metabolism of transmitter glutamate, were 11-25% of cortical values, and activities of aspartate and alanine aminotransferases were 50-70% of cortical values. The glutamate level in fimbria and corpus callosum was 5-6 nmol/mg tissue, half the cortical value. These data suggest a certain capacity for glutamatergic neurotransmission. In optic and trigeminal nerves, [3H]glutamate uptake was < 10% of the cortical uptake. Formation of [14C]glutamate from [U-14C]glucose in fimbria and corpus callosum of awake rats was 30% of cortical values, in optic nerve it was 13%, illustrating extensive glutamate metabolism in white matter in vivo. Glutamate transporters in brain white matter may be important both physiologically and during energy failure when reversal of glutamate uptake may contribute to excitotoxicity.