Striosomes Mediate Value-Based Learning Vulnerable in Age and a Huntington's Disease Model.

Learning valence-based responses to favorable and unfavorable options requires judgments of the relative value of the options, a process necessary for species survival. We found, using engineered mice, that circuit connectivity and function of the striosome compartment of the striatum are critical for this type of learning. Calcium imaging during valence-based learning exhibited a selective correlation between learning and striosomal but not matrix signals. This striosomal activity encoded discrimination learning and was correlated with task engagement, which, in turn, could be regulated by chemogenetic excitation and inhibition. Striosomal function during discrimination learning was disturbed with aging and severely so in a mouse model of Huntington's disease. Anatomical and functional connectivity of parvalbumin-positive, putative fast-spiking interneurons (FSIs) to striatal projection neurons was enhanced in striosomes compared with matrix in mice that learned. Computational modeling of these findings suggests that FSIs can modulate the striosomal signal-to-noise ratio, crucial for discrimination and learning.

Scaling of smaller pyramidal neuron size and lower energy production in schizophrenia.

BACKGROUND: Dorsolateral prefrontal cortex (DLPFC) dysfunction in schizophrenia appears to reflect alterations in layer 3 pyramidal neurons (L3PNs), including smaller cell bodies and lower expression of mitochondrial energy production genes. However, prior somal size studies used biased strategies for identifying L3PNs, and somal size and levels of energy production markers have not been assessed in individual L3PNs. STUDY DESIGN: We combined fluorescent in situ hybridization (FISH) of vesicular glutamate transporter 1 (VGLUT1) mRNA and immunohistochemical-labeling of NeuN to determine if the cytoplasmic distribution of VGLUT1 mRNA permits the unbiased identification and somal size quantification of L3PNs. Dual-label FISH for VGLUT1 mRNA and cytochrome C oxidase subunit 4I1 (COX4I1) mRNA, a marker of energy production, was used to assess somal size and COX4I1 transcript levels in individual DLPFC L3PNs from schizophrenia (12 males; 2 females) and unaffected comparison (13 males; 1 female) subjects. STUDY RESULTS: Measures of L3PN somal size with NeuN immunohistochemistry or VGLUT1 mRNA provided nearly identical results (ICC = 0.96, p < 0.0001). Mean somal size of VGLUT1-identified L3PNs was 8.7% smaller (p = 0.004) and mean COX4I1 mRNA levels per L3PN were 16.7% lower (p = 0.01) in schizophrenia. These measures were correlated across individual L3PNs in both subject groups (rrm = 0.81-0.86). CONCLUSIONS: This preliminary study presents a novel method for combining unbiased neuronal identification with quantitative assessments of somal size and mRNA levels. We replicated findings of smaller somal size and lower COX4I1 mRNA levels in DLPFC L3PNs in schizophrenia. The normal scaling of COX4I1 mRNA levels with somal size in schizophrenia suggests that lower markers of energy production are secondary to L3PN morphological alterations in the illness.

Uncoupling endosomal CLC chloride/proton exchange causes severe neurodegeneration.

CLC chloride/proton exchangers may support acidification of endolysosomes and raise their luminal Cl- concentration. Disruption of endosomal ClC-3 causes severe neurodegeneration. To assess the importance of ClC-3 Cl- /H+ exchange, we now generate Clcn3unc/unc mice in which ClC-3 is converted into a Cl- channel. Unlike Clcn3-/- mice, Clcn3unc/unc mice appear normal owing to compensation by ClC-4 with which ClC-3 forms heteromers. ClC-4 protein levels are strongly reduced in Clcn3-/- , but not in Clcn3unc/unc mice because ClC-3unc binds and stabilizes ClC-4 like wild-type ClC-3. Although mice lacking ClC-4 appear healthy, its absence in Clcn3unc/unc /Clcn4-/- mice entails even stronger neurodegeneration than observed in Clcn3-/- mice. A fraction of ClC-3 is found on synaptic vesicles, but miniature postsynaptic currents and synaptic vesicle acidification are not affected in Clcn3unc/unc or Clcn3-/- mice before neurodegeneration sets in. Both, Cl- /H+ -exchange activity and the stabilizing effect on ClC-4, are central to the biological function of ClC-3.

Icariin rescues developmental BPA exposure induced spatial memory deficits in rats.

Bisphenol A (BPA) has been implicated in cognitive impairment. Icariin is the main active ingredient extracted from Epimedium Herb with protective function of nervous system. However, the potential therapeutic effects of Icariin on spatial memory deficits induced by developmental BPA exposure in Sprague-Dawley rats have not been investigated. This study investigated the therapeutic effect of Icariin (10 mg/kg/day, from postnatal day (PND) 21 to PND 60 by gavage) on spatial memory deficits in rat induced by developmental BPA exposure (1 mg/kg/day, from embryonic to PND 60), demonstrating that Icariin can markedly improve spatial memory in BPA-exposed rat. Furthermore, intra-gastric administration of Icariin could attenuate abnormal hippocampal cell dispersion and loss, improved the dendritic spine density and Nissl bodies. Moreover, Icariin reversed BPA induced reduction of frequency of miniature excitatory postsynaptic currents(mEPSC) and decrease of Vesicular glutamate transporter 1(VGlut1). Collectively, Icariin could effectively rescue BPA-induced spatial memory impairment in male rats by preventing cell loss and reduction of dendritic spines in the hippocampus. In addition, we also found that VGlut1 is a critical target in the repair of BPA-induced spatial memory by Icariin. Thus, Icariin may be a promising therapeutic agent to attenuate BPA-induced spatial memory deficits.

Environmental enrichment alleviates hyperalgesia by modulating central sensitization in a nitroglycerin-induced chronic migraine model of mice.

BACKGROUND: Chronic migraine (CM) is a debilitating neurofunctional disorder primarily affecting females, characterized by central sensitization. Central sensitization refers to the enhanced response to sensory stimulation, which involves changes in neuronal excitability, synaptic plasticity, and neurotransmitter release. Environmental enrichment (EE) can increase the movement, exploration, socialization and other behaviors of mice. EE has shown promising effects in various neurological disorders, but its impact on CM and the underlying mechanism remains poorly understood. Therefore, the purpose of this study was to determine whether EE has the potential to serve as a cost-effective intervention strategy for CM. METHODS: A mouse CM model was successfully established by repeated administration of nitroglycerin (NTG). We selected adult female mice around 8 weeks old, exposed them to EE for 2 months, and then induced the CM model. Nociceptive threshold tests were measured using Von Frey filaments and a hot plate. The expression of c-Fos, calcitonin gene-related peptide (CGRP) and inflammatory response were measured using WB and immunofluorescence to evaluate central sensitization. RNA sequencing was used to find differentially expressed genes and signaling pathways. Finally, the expression of the target differential gene was investigated. RESULTS: Repeated administration of NTG can induce hyperalgesia in female mice and increase the expression of c-Fos and CGRP in the trigeminal nucleus caudalis (TNC). Early exposure of mice to EE reduced NTG-induced hyperalgesia in CM mice. WB and immunofluorescence revealed that EE inhibited the overexpression of c-Fos and CGRP in the TNC of CM mice and alleviated the inflammatory response of microglia activation. RNA sequencing analysis identified that several central sensitization-related signaling pathways were altered by EE. VGluT1, a key gene involved in behavior, internal stimulus response, and ion channel activity, was found to be downregulated in mice exposed to EE. CONCLUSION: EE can significantly ameliorate hyperalgesia in the NTG-induced CM model. The mechanisms may be to modulate central sensitization by reducing the expression of CGRP, attenuating the inflammatory response, and downregulating the expression of VGluT1, etc., suggesting that EE can serve as an effective preventive strategy for CM.

Overexpression of NaV1.6 in the rostral ventrolateral medulla in rats mediates stress-induced hypertension via glutamate regulation.

BACKGROUND: The rostral ventrolateral medulla (RVLM) plays a key role in mediating the development of stress-induced hypertension (SIH). Furthermore, enhanced glutamate transport within glutamatergic neurons in the RVLM mediates pressor responses. Data from our previous studies suggest that the voltage-gated sodium channel NaV1.6 is overexpressed in neurons in the RVLM in SIH model rats and participates in the resulting elevation of blood pressure. However, previous studies have not investigated the relationship between NaV1.6 expression and glutamatergic neurons. METHODS: Here, we constructed an SIH rat model by knocking down NaV1.6 via microinjection of clustered regularly interspaced short palindromic repeats (CRISPR) guide RNA into the RVLM. Glutamate-related markers were quantified by Western blotting and immunofluorescence, and blood pressure was measured in the rats. RESULTS: Our findings showed that vesicular glutamate transporter 1 (VGluT1) protein expression in the RVLM was higher in SIH rats than in Control rats, and GAD67 protein expression in SIH rats was lower than that in Control rats. Therefore, the number of VGluT1-positive neurons increased, while the number of GAD67-labeled neurons decreased after stress. After knocking down NaV1.6 expression in the RVLM, VGluT1 expression and the number of VGluT1-positive neurons decreased relative to those in SIH rats, while GAD67 protein expression and the number of GAD67-labeled neurons increased relative to those in SIH rats. CONCLUSIONS: These results indicate that overexpression of NaV1.6 in the RVLM may mediate the transport and transformation of glutamate in neurons, and NaV1.6 may participate in SIH.

Dynamic Foot Stimulations During Short-Term Hindlimb Unloading Prevent Dysregulation of the Neurotransmission in the Hippocampus of Rats.

Spaceflight and simulated microgravity both affect learning and memory, which are mostly controlled by the hippocampus. However, data about molecular alterations in the hippocampus in real or simulated microgravity conditions are limited. Adult Wistar rats were recruited in the experiments. Here we analyzed whether short-term simulated microgravity caused by 3-day hindlimb unloading (HU) will affect the glutamatergic and GABAergic systems of the hippocampus and how dynamic foot stimulation (DFS) to the plantar surface applied during HU can contribute in the regulation of hippocampus functioning. The results demonstrated a decreased expression of vesicular glutamate transporters 1 and 2 (VGLUT1/2) in the hippocampus after 3 days of HU, while glutamate decarboxylase 67 (GAD67) expression was not affected. HU also significantly induced Akt signaling and transcriptional factor CREB that are supposed to activate the neuroprotective mechanisms. On the other hand, DFS led to normalization of VGLUT1/2 expression and activity of Akt and CREB. Analysis of exocytosis proteins revealed the inhibition of SNAP-25, VAMP-2, and syntaxin 1 expression in DFS group proposing attenuation of excitatory neurotransmission. Thus, we revealed that short-term HU causes dysregulation of glutamatergic system of the hippocampus, but, at the same time, stimulates neuroprotective Akt-dependent mechanism. In addition, most importantly, we demonstrated positive effect of DFS on the hippocampus functioning that probably depends on the regulation of neurotransmitter exocytosis.

Spinal Motor Circuit Synaptic Plasticity after Peripheral Nerve Injury Depends on Microglia Activation and a CCR2 Mechanism.

Peripheral nerve injury results in persistent motor deficits, even after the nerve regenerates and muscles are reinnervated. This lack of functional recovery is partly explained by brain and spinal cord circuit alterations triggered by the injury, but the mechanisms are generally unknown. One example of this plasticity is the die-back in the spinal cord ventral horn of the projections of proprioceptive axons mediating the stretch reflex (Ia afferents). Consequently, Ia information about muscle length and dynamics is lost from ventral spinal circuits, degrading motor performance after nerve regeneration. Simultaneously, there is activation of microglia around the central projections of peripherally injured Ia afferents, suggesting a possible causal relationship between neuroinflammation and Ia axon removal. Therefore, we used mice (both sexes) that allow visualization of microglia (CX3CR1-GFP) and infiltrating peripheral myeloid cells (CCR2-RFP) and related changes in these cells to Ia synaptic losses (identified by VGLUT1 content) on retrogradely labeled motoneurons. Microgliosis around axotomized motoneurons starts and peaks within 2 weeks after nerve transection. Thereafter, this region becomes infiltrated by CCR2 cells, and VGLUT1 synapses are lost in parallel. Immunohistochemistry, flow cytometry, and genetic lineage tracing showed that infiltrating CCR2 cells include T cells, dendritic cells, and monocytes, the latter differentiating into tissue macrophages. VGLUT1 synapses were rescued after attenuating the ventral microglial reaction by removal of colony stimulating factor 1 from motoneurons or in CCR2 global KOs. Thus, both activation of ventral microglia and a CCR2-dependent mechanism are necessary for removal of VGLUT1 synapses and alterations in Ia-circuit function following nerve injuries.SIGNIFICANCE STATEMENT Synaptic plasticity and reorganization of essential motor circuits after a peripheral nerve injury can result in permanent motor deficits due to the removal of sensory Ia afferent synapses from the spinal cord ventral horn. Our data link this major circuit change with the neuroinflammatory reaction that occurs inside the spinal cord following injury to peripheral nerves. We describe that both activation of microglia and recruitment into the spinal cord of blood-derived myeloid cells are necessary for motor circuit synaptic plasticity. This study sheds new light into mechanisms that trigger major network plasticity in CNS regions removed from injury sites and that might prevent full recovery of function, even after successful regeneration.

Differential Contributions of Glutamatergic Hippocampal→Retrosplenial Cortical Projections to the Formation and Persistence of Context Memories.

Learning to associate stressful events with specific environmental contexts depends on excitatory transmission in the hippocampus, but how this information is transmitted to the neocortex for lasting memory storage is unclear. We identified dorsal hippocampal (DH) projections to the retrosplenial cortex (RSC), which arise mainly from the subiculum and contain either the vesicular glutamate transporter 1 (vGlut1) or vGlut2. Both vGlut1+ and vGlut2+ axons strongly excite and disynaptically inhibit RSC pyramidal neurons in superficial layers, but vGlut2+ axons trigger greater inhibition that spreads to deep layers, indicating that these pathways engage RSC circuits via partially redundant, partially differentiated cellular mechanisms. Using contextual fear conditioning in mice to model contextual associative memories, together with chemogenetic axonal silencing, we found that vGlut1+ projections are principally involved in processing recent context memories whereas vGlut2+ projections contribute to their long-lasting storage. Thus, within the DH→RSC pathway, engagement of vGlut1+ and vGlut2+ circuits differentially contribute to the formation and persistence of fear-inducing context memories.

Adenosine A2A Receptor Agonist PSB-0777 Modulates Synaptic Proteins and AMPA Receptor Expression in a Dose- and Time-Dependent Manner in Rat Primary Cortical Neurons.

Regulating synaptic formation and transmission is critical for the physiology and pathology of psychiatric disorders. The adenosine A2A receptor subtype has attracted widespread attention as a key regulator of neuropsychiatric activity, neuroprotection and injury. In this study, we systematically investigated the regulatory effects of a novel A2A receptor agonist, PSB-0777, on the expression of synaptic proteins and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid glutamate receptors (AMPA receptors) at the cellular level in a time- and dose-dependent manner. After 30 min of high-dose PSB-0777 stimulation, the expression of Synapsin-1 (Syn-1), postsynaptic density protein 95 (PSD95), and AMPA receptors and the number of synapses were rapidly and significantly increased in rat primary cortical neurons compared with the control. Sustained elevation was found in the low and medium-dose groups after 24 h and 3 d of treatment. In contrast, after stimulation with PSB-0777 for 3 consecutive days, the expression of Syn-1 was decreased, and PSD95, AMPA receptors and the number of synapses were no longer increased in the high-dose group. Our study focuses on the detailed and systematic regulation of synaptic proteins and AMPA receptors by an A2A receptor agonist, PSB-0777, which may result in both beneficial and detrimental effects on neurotransmission and neuroprotection and may contribute to the pathophysiology of psychiatric disorders related to A2A receptors. These experimental data may contribute to understanding of the mechanisms for neuroprotective and therapeutic effect of A2A receptor agonists.

Selective neuronal vulnerability is involved in cerebellar lesions of Guinea pigs infected with bovine spongiform encephalopathy (BSE) prions: Immunohistochemical and electron microscopic investigations.

The cerebellar lesions of bovine spongiform encephalopathy (BSE)-infected guinea pigs were characterized as severe atrophy of the cerebellar cortex associated with the loss of granule cells, decrease in the width of the molecular layer, and intense protease-resistant prion protein (PrPSc ) accumulations that are similar to cerebellar lesions in kuru and the VV2 type of sporadic Creutzfeldt-Jakob disease. The aim of this study is to assess the relationships between the distribution and localization of PrPSc and synapses expressing neurotransmitter transporters in order to reveal the pathogenesis of the disease. We used cell-type-specific immunohistochemical makers recognizing glutamatergic and γ-aminobutylic acid (GABA)ergic terminals to identify terminals impaired with PrPSc accumulations. The distribution of PrPSc accumulations and immunoreactivity of synaptic vesicles were studied throughout the neuroanatomical pathways in cerebellar lesions. Time course study demonstrated that PrPSc accumulation showed a tendency to spread from granular layer to molecular layer. The immunoreactivity of vesicular glutamate transporter 1 (VGluT1) was localized in axon terminals of cerebellar granule cells, and decreased in association with the severity of PrPSc accumulations and loss of granule cells. Immunoreactivities of vesicular glutamate transporter 2 (VGluT2) and vesicular GABA transporter (VGAT) that exist in axon terminals of inferior olivary neurons and GABAergic synapses of Purkinje cells, respectively, were preserved well in these lesions. In brainstem, VGluT1 immunoreactivity decreased selectively in pontine nuclei that are a component of the pontocerebellar pathway, although other neurotransmitter immunoreactivities were preserved well. Our findings suggest that the selective loss of VGluT1-immunoreactive synapses subsequent to PrPSc accumulations can contribute to the pathogenesis of cerebellar lesions of BSE-infected guinea pigs.

Role of specific presynaptic calcium channel subtypes in isoflurane inhibition of synaptic vesicle exocytosis in rat hippocampal neurones.

BACKGROUND: P/Q- and N-type voltage-gated calcium channels (VGCC) are the principal subtypes mediating synaptic vesicle (SV) exocytosis. Both the degree of isoflurane inhibition of SV exocytosis and VGCC subtype expression vary between brain regions and neurotransmitter phenotype. We hypothesised that differences in VGCC subtype expression contribute to synapse-selective presynaptic effects of isoflurane. METHODS: We used quantitative live-cell imaging to measure exocytosis in cultured rat hippocampal neurones after transfection of the fluorescent biosensor vGlut1-pHluorin. Selective inhibitors of P/Q- and N-type VGCCs were used to isolate subtype-specific effects of isoflurane. RESULTS: Inhibition of N-type channels by 1 µM ω-conotoxin GVIA reduced SV exocytosis to 81±5% of control (n=10). Residual exocytosis mediated by P/Q-type channels was further inhibited by isoflurane to 42±4% of control (n=10). The P/Q-type channel inhibitor ω-agatoxin IVA at 0.4 µM inhibited SV exocytosis to 29±3% of control (n=10). Residual exocytosis mediated by N-type channels was further inhibited by isoflurane to 17±3% of control (n=10). Analysis of isoflurane effects at the level of individual boutons revealed no difference in sensitivity to isoflurane between P/Q- or N-type channel-mediated SV exocytosis (P=0.35). There was no correlation between the effect of agatoxin (P=0.91) or conotoxin (P=0.15) and the effect of isoflurane on exocytosis. CONCLUSIONS: Sensitivity of SV exocytosis to isoflurane in rat hippocampal neurones is independent of the specific VGCC subtype coupled to exocytosis. The differential sensitivity of VGCC subtypes to isoflurane does not explain the observed neurotransmitter-selective effects of isoflurane in hippocampus.

Age-related loss of VGLUT1 excitatory, but not VGAT inhibitory, immunoreactive terminals on motor neurons in spinal cords of old sarcopenic male mice.

Age-related changes in ventral lumbar spinal cord (L3-L5) were compared in young [3 month, (M)] and old (27 M) C57BL/6J male mice. The aged mice had previously been shown to exhibit sarcopenia and changes to peripheral nerve morphology. The putative connectivity of ß-III tubulin positive α-motor neurons was compared in immunostained transverse sections using excitatory and inhibitory terminal markers vesicular glutamate transporter-1 (VGLUT1) and vesicular GABA transporter (VGAT). Glial fibrillary acidic protein (GFAP) and ionized calcium binding adaptor molecule 1 (Iba1) immunostaining was used to monitor changes in astrocyte and microglial phenotype respectively. For a given motor neuron, the neuronal perimeter was outlined and terminals immunoreactive for VGLUT1 or VGAT in close apposition to the soma were identified. By 27 M, the percentage coverage and total number of VGLUT1 immunoreactive terminals immediately adjacent to the soma of α-motor neurons was significantly decreased compared with young mice. However, percentage coverage of immunoreactive VGAT inhibitory terminals did not change significantly with age. The gray matter of 27 M spinal cords showed increased astrocytic and microglial activity. The loss of VGLUT1 terminals on α-motor neurons, terminals known to be derived from proprioceptive muscle afferents, may further impair sensorimotor control of hind limb skeletal muscle function in old mice.

Differential expression of synaptic vesicle protein 2A after status epilepticus and during epilepsy in a lithium-pilocarpine model.

Synaptic vesicle protein 2A (SV2A) has become an attractive target of investigation because of its role in the pathophysiology of epilepsy; SV2A is expressed ubiquitously throughout the brain in all nerve terminals independently of their neurotransmitter content and plays an important but poorly defined role in neurotransmission. Previous studies have shown that modifications in the SV2A protein expression could be a direct consequence of disease severity. Furthermore, these SV2A modifications may depend on specific changes in the nerve tissue following the induction of epilepsy and might be present in both excitatory and inhibitory terminals. Thus, we evaluated SV2A protein expression throughout the hippocampi of lithium-pilocarpine rats after status epilepticus (SE) and during early and late epilepsy. In addition, we determined the γ-aminobutyric acid (GABA)ergic or glutamatergic nature associated with SV2A modifications. Wistar rats were treated with lithium-pilocarpine to induce SE and subsequently were shown to present spontaneous recurrent seizures (SRS). Later, we conducted an exhaustive semi-quantitative analysis of SV2A optical density (OD) throughout the hippocampus by immunohistochemistry. Levels of the SV2A protein were substantially increased in layers formed by principal neurons after SE, mainly because of GABAergic activity. No changes were observed in the early stage of epilepsy. In the late stage of epilepsy, there were minor changes in SV2A OD compared with the robust modifications of SE; however, SV2A protein expression generally showed an increment reaching significant differences in two dendritic layers and hilus, without clear modifications of GABAergic or glutamatergic systems. Our results suggest that the SV2A variations may depend on several factors, such as neuronal activity, and might appear in both excitatory and inhibitory systems depending on the epilepsy stage.

Conductive Hearing Loss Has Long-Lasting Structural and Molecular Effects on Presynaptic and Postsynaptic Structures of Auditory Nerve Synapses in the Cochlear Nucleus.

UNLABELLED: Sound deprivation by conductive hearing loss increases hearing thresholds, but little is known about the response of the auditory brainstem during and after conductive hearing loss. Here, we show in young adult rats that 10 d of monaural conductive hearing loss (i.e., earplugging) leads to hearing deficits that persist after sound levels are restored. Hearing thresholds in response to clicks and frequencies higher than 8 kHz remain increased after a 10 d recovery period. Neural output from the cochlear nucleus measured at 10 dB above threshold is reduced and followed by an overcompensation at the level of the lateral lemniscus. We assessed whether structural and molecular substrates at auditory nerve (endbulb of Held) synapses in the cochlear nucleus could explain these long-lasting changes in hearing processing. During earplugging, vGluT1 expression in the presynaptic terminal decreased and synaptic vesicles were smaller. Together, there was an increase in postsynaptic density (PSD) thickness and an upregulation of GluA3 AMPA receptor subunits on bushy cells. After earplug removal and a 10 d recovery period, the density of synaptic vesicles increased, vesicles were also larger, and the PSD of endbulb synapses was larger and thicker. The upregulation of the GluA3 AMPAR subunit observed during earplugging was maintained after the recovery period. This suggests that GluA3 plays a role in plasticity in the cochlear nucleus. Our study demonstrates that sound deprivation has long-lasting alterations on structural and molecular presynaptic and postsynaptic components at the level of the first auditory nerve synapse in the auditory brainstem. SIGNIFICANCE STATEMENT: Despite being the second most prevalent form of hearing loss, conductive hearing loss and its effects on central synapses have received relatively little attention. Here, we show that 10 d of monaural conductive hearing loss leads to an increase in hearing thresholds, to an increased central gain upstream of the cochlear nucleus at the level of the lateral lemniscus, and to long-lasting presynaptic and postsynaptic structural and molecular effects at the endbulb of the Held synapse. Knowledge of the structural and molecular changes associated with decreased sensory experience, along with their potential reversibility, is important for the treatment of hearing deficits, such as hyperacusis and chronic otitis media with effusion, which is prevalent in young children with language acquisition or educational disabilities.

Loss of striatal 90-kDa ribosomal S6 kinase (Rsk) is a key factor for motor, synaptic and transcription dysfunction in Huntington's disease.

Huntington's disease (HD) is characterized by motor dysfunction due to the expression of mutant huntingtin that promotes degeneration of striatal GABAergic medium-sized spiny neurons. Here we explore the role of the 90-kDa ribosomal S6 kinase (Rsk) in the physiopathology of HD. First, we show a reduction of Rsk1 and 2 protein levels in the striatum of two HD mouse models, R6/1 and Hdh(Q7/Q111) knock-in mice, at ages when they suffer from motor disturbances. Interestingly, the analysis of post-mortem samples from HD patients revealed a significant reduction of both Rsk forms in the putamen and caudate, but not in the cortex. Rsk1 and 2 levels were also reduced in the striatum of BDNF heterozygous mice, and upon BDNF neutralization in striatal cultures, suggesting that striatal loss of BDNF could be involved in the decrease of Rsk levels. Finally, we injected recombinant adeno-associated-virus (AAV5)-Rsk in the striatum of R6/1 mice at the onset of motor symptoms. Four weeks later, we found higher Rsk levels in the striatum accompanied by improvements in motor coordination, enhanced expression of synaptic markers and increased expression of genes related to synaptic plasticity, such as cfos and egr1. Altogether, we identified Rsk as a key factor in striatal alterations associated with motor deficits in HD.

Lipoic acid improves neuronal insulin signalling and rescues cognitive function regulating VGlut1 expression in high-fat-fed rats: Implications for Alzheimer's disease.

The concept of central insulin resistance and dysfunctional insulin signalling in sporadic Alzheimer's disease (AD) is now widely accepted and diabetes is recognized as one of the main risk factors for developing AD. Moreover, some lines of evidence indicated that VGlut1 is impaired in frontal regions of AD patients and this impairment is correlated with the progression of cognitive decline in AD. The present work hypothesizes that ketosis associated to insulin resistance could interfere with the normal activity of VGlut1 and its role in the release of glutamate in the hippocampus, which might ultimately lead to cognitive deficits. High fat diet (HFD) rats showed memory impairments and both peripheral (as shown by increased fasting plasma insulin levels and HOMA index) and hippocampal (as shown by decreased activation of insulin receptor, IRS-1 and pAkt) insulin pathway alterations, accompanied by increased ketone bodies production. All these effects were counteracted by α-lipoic acid (LA) administration. VGlut1 levels were significantly decreased in the hippocampus of HFD rats, and this decrease was reversed by LA. Altogether, the present results suggest that HFD induced alterations in central insulin signalling could switch metabolism to produce ketone bodies, which in turn, in the hippocampus, might lead to a decreased expression of VGlut1, and therefore to a decreased release of glutamate and hence, to the glutamatergic deficit described in AD. The ability of LA treatment to prevent the alterations in insulin signalling in this model of HFD might represent a possible new therapeutic target for the treatment of AD.

Function and expression of a splicing variant of vesicular glutamate transporter 1.

Vesicular glutamate transporter (VGLUT) is an active transporter responsible for vesicular storage of glutamate in synaptic vesicles and plays an essential role in glutamatergic neurotransmission. VGLUT consists of three isoforms, VGLUT1, VGLUT2, and VGLUT3. The VGLUT1 variant, VGLUT1v, with an additional 75-base pair sequence derived from a second intron between exons 2 and 3, which corresponds to 25 amino acid residues in the 1st loop of VGLUT1, is the only splicing variant among VGLUTs, although whether VGLUT1v protein is actually translated at the protein level remains unknown. In the present study, VGLUT1v was expressed in insect cells, solubilized, purified to near homogeneity, and its transport activity was examined. Proteoliposomes containing purified VGLUT1v were shown to accumulate glutamate upon imposition of an inside-positive membrane potential (Δψ). The Δψ-driven glutamate uptake activity requires Cl- and its pharmacological profile and kinetics are comparable to those of other VGLUTs. The retinal membrane contained two VGLUT1 moieties with apparent molecular masses of 65 and 57kDa. VGLUT1v-specific antibodies against an inserted 25-amino acid residue sequence identified a 65-kDa immunoreactive polypeptide. Immunohistochemical analysis indicated that VGLUT1v immunoreactivity is present in photoreceptor cells and is associated with synaptic vesicles. VGLUT1v immunoreactivity is also present in pinealocytes, but not in other areas, including the brain. These results indicated that VGLUT1v exists in a functional state in rat photosensitive cells and is involved in glutamatergic chemical transmission.

Co-expression of VGLUT1 and VGAT sustains glutamate and GABA co-release and is regulated by activity in cortical neurons.

In adult neocortex, VGLUT1 (also known as SLC17A7), the main glutamate vesicular transporter, and VGAT (also known as SLC32A1), the γ-aminobutyric acid (GABA) vesicular transporter, are co-expressed in a subset of axon terminals forming both symmetric and asymmetric synapses, where they are sorted into the same vesicles. However, the functional consequence of this colocalization in cortical neurons has not been clarified. Here, we tested the hypothesis that cortical axon terminals co-expressing VGLUT1 and VGAT can evoke simultaneously monosynaptic glutamate and GABA responses, and investigated whether the amount of terminals co-expressing VGLUT1 and VGAT is affected by perturbations of excitation-inhibition balance. In rat primary cortical neurons, we found that a proportion of synaptic and autaptic responses were indeed sensitive to consecutive application of selective glutamate and GABAA receptor blockers. These 'mixed' synapses exhibited paired-pulse depression. Notably, reducing the activity of the neuronal network by treatment with glutamate receptor antagonists decreased the amount of 'mixed' synapses, whereas reducing spontaneous inhibition by treatment with bicuculline increased them. These synapses might contribute to homeostatic regulation of excitation-inhibition balance.

Developmental Trajectories of Auditory Cortex Synaptic Structures and Gap-Prepulse Inhibition of Acoustic Startle Between Early Adolescence and Young Adulthood in Mice.

Cortical excitatory and inhibitory synapses are disrupted in schizophrenia, the symptoms of which often emerge during adolescence, when cortical excitatory synapses undergo pruning. In auditory cortex, a brain region implicated in schizophrenia, little is known about the development of excitatory and inhibitory synapses between early adolescence and young adulthood, and how these changes impact auditory cortex function. We used immunohistochemistry and quantitative fluorescence microscopy to quantify dendritic spines and GAD65-expressing inhibitory boutons in auditory cortex of early adolescent, late adolescent, and young adult mice. Numbers of spines decreased between early adolescence and young adulthood, during which time responses increased in an auditory cortex-dependent sensory task, silent gap-prepulse inhibition of the acoustic startle reflex (gap-PPI). Within-bouton GAD65 protein and GAD65-expressing bouton numbers decreased between late adolescence and young adulthood, a delay in onset relative to spine and gap-PPI changes. In mice lacking the spine protein kalirin, there were no significant changes in spine number, within-bouton GAD65 protein, or gap-PPI between adolescence and young adulthood. These results illustrate developmental changes in auditory cortex spines, inhibitory boutons, and auditory cortex function between adolescence and young adulthood, and provide insights into how disrupted adolescent neurodevelopment could contribute to auditory cortex synapse pathology and auditory impairments.