An essential role for vesicular glutamate transporter 1 (VGLUT1) in postnatal development and control of quantal size

Nucleus tractus solitarius mediates hyperalgesia induced by chronic pancreatitis in rats

BACKGROUND

Central sensitization plays a pivotal role in the maintenance of chronic pain induced by chronic pancreatitis (CP). We hypothesized that the nucleus tractus solitarius (NTS), a primary central site that integrates pancreatic afferents apart from the thoracic spinal dorsal horn, plays a key role in the pathogenesis of visceral hypersensitivity in a rat model of CP.

AIM

To investigate the role of the NTS in the visceral hypersensitivity induced by chronic pancreatitis.

METHODS

CP was induced by the intraductal injection of trinitrobenzene sulfonic acid (TNBS) in rats. Pancreatic hyperalgesia was assessed by referred somatic pain via von Frey filament assay. Neural activation of the NTS was indicated by immunohistochemical staining for Fos. Basic synaptic transmission within the NTS was assessed by electrophysiological recordings. Expression of vesicular glutamate transporters (VGluTs), N-methyl-D-aspartate receptor subtype 2B (NR2B), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor subtype 1 (GluR1) was analyzed by immunoblotting. Membrane insertion of NR2B and GluR1 was evaluated by electron microscopy. The regulatory role of the NTS in visceral hypersensitivity was detected via pharmacological approach and chemogenetics in CP rats.

RESULTS

TNBS treatment significantly increased the number of Fos-expressing neurons within the caudal NTS. The excitatory synaptic transmission was substantially potentiated within the caudal NTS in CP rats (frequency: 5.87 ± 1.12 Hz in CP rats vs 2.55 ± 0.44 Hz in sham rats, P < 0.01; amplitude: 19.60 ± 1.39 pA in CP rats vs 14.71 ± 1.07 pA in sham rats; P < 0.01). CP rats showed upregulated expression of VGluT2, and increased phosphorylation and postsynaptic trafficking of NR2B and GluR1 within the caudal NTS. Blocking excitatory synaptic transmission via the AMPAR antagonist CNQX and the NMDAR antagonist AP-5 microinjection reversed visceral hypersensitivity in CP rats (abdominal withdraw threshold: 7.00 ± 1.02 g in CNQX group, 8.00 ± 0.81 g in AP-5 group and 1.10 ± 0.27 g in saline group, P < 0.001). Inhibiting the excitability of NTS neurons via chemogenetics also significantly attenuated pancreatic hyperalgesia (abdominal withdraw threshold: 13.67 ± 2.55 g in Gi group, 2.00 ± 1.37 g in Gq group, and 2.36 ± 0.67 g in mCherry group, P < 0.01).

CONCLUSION

Our findings suggest that enhanced excitatory transmission within the caudal NTS contributes to pancreatic pain and emphasize the NTS as a pivotal hub for the processing of pancreatic afferents, which provide novel insights into the central sensitization of painful CP.

A Mini-Review of the Role of Glutamate Transporter in Drug Addiction

Goals: The development of new treatment for drug abuse requires identification of targetable molecular mechanisms. The pathology of glutamate neurotransmission system in the brain reward circuit is related to the relapse of multiple drugs. Glutamate transporter regulates glutamate signaling by removing excess glutamate from the synapse. And the mechanisms between glutamate transporter and drug addiction are still unclear.

Methods: A systematic review of the literature searched in Pubmed and reporting drug addiction in relation to glutamate transporter. Studies were screened by title, abstract, and full text.

Results: This review is to highlight the effects of drug addiction on glutamate transporter and glutamate uptake, and targeting glutamate transporter as an addictive drug addiction treatment. We focus on the roles of glutamate transporter in different brain regions in drug addiction. More importantly, we suggest the functional roles of glutamate transporter may prove beneficial in the treatment of drug addiction.

Conclusion: Overall, understanding how glutamate transporter impacts central nervous system may provide a new insight for treatment of drug addiction.

Consequences of VGluT3 deficiency on learning and memory in mice

The aim of the present study was to test the hypothesis that vesicular glutamate transporter 3 (VGluT3) deficiency is associated with cognitive impairments. Male VGluT3 knockout (KO) and wild type (WT) mice were exposed to a behavioral test battery covering paradigms based on spontaneous exploratory behavior and reinforcement-based learning tests. Reversal learning was examined to test the cognitive flexibility. The VGluT3 KO mice clearly exhibited the ability to learn. The social recognition memory of KO mice was intact. The y-maze test revealed weaker working memory of VGluT3 KO mice. No significant learning impairments were noticed in operant conditioning or holeboard discrimination paradigm. In avoidance-based learning tests (Morris water maze and active avoidance), KO mice exhibited slightly slower learning process compared to WT mice, but not a complete learning impairment. In tests based on simple associations (operant conditioning, avoidance learning) an attenuation of cognitive flexibility was observed in KO mice. In conclusion, knocking out VGluT3 results in mild disturbances in working memory and learning flexibility. Apparently, this glutamate transporter is not a major player in learning and memory formation in general. Based on previous characteristics of VGluT3 KO mice we would have expected a stronger deficit. The observed hypolocomotion did not contribute to the mild cognitive disturbances herein reported, either.

Anterior insular cortex mediates hyperalgesia induced by chronic pancreatitis in rats

Central sensitization plays a pivotal role in the maintenance of chronic pain induced by chronic pancreatitis (CP), but cortical modulation of painful CP remains elusive. This study was designed to examine the role of anterior insular cortex (aIC) in the pathogenesis of hyperalgesia in a rat model of CP. CP was induced by intraductal administration of trinitrobenzene sulfonic acid (TNBS). Abdomen hyperalgesia and anxiety were assessed by von Frey filament and open field tests, respectively. Two weeks after surgery, the activation of aIC was indicated by FOS immunohistochemical staining and electrophysiological recordings. Expressions of VGluT1, NMDAR subunit NR2B and AMPAR subunit GluR1 were analyzed by immunoblottings. The regulatory roles of aIC in hyperalgesia and pain-related anxiety were detected via pharmacological approach and chemogenetics in CP rats. Our results showed that TNBS treatment resulted in long-term hyperalgesia and anxiety-like behavior in rats. CP rats exhibited increased FOS expression and potentiated excitatory synaptic transmission within aIC. CP rats also showed up-regulated expression of VGluT1, and increased membrane trafficking and phosphorylation of NR2B and GluR1 within aIC. Blocking excitatory synaptic transmission significantly attenuated abdomen mechanical hyperalgesia. Specifically inhibiting the excitability of insular pyramidal cells reduced both abdomen hyperalgesia and pain-related anxiety. In conclusion, our findings emphasize a key role for aIC in hyperalgesia and anxiety of painful CP, providing a novel insight into cortical modulation of painful CP and shedding light on aIC as a potential target for neuromodulation interventions in the treatment of CP.

Histone Deacetylase 4 Downregulation Elicits Post-Traumatic Psychiatric Disorders through Impairment of Neurogenesis

An enduring deficit in neurogenesis largely contributes to the development of severe post-traumatic psychiatric disorders such as anxiety, depression, and memory impairment following traumatic brain injury (TBI); however, the mechanism remains obscure. Here we have shown that an imbalance in the generation of γ-aminobutyric acid (GABA)ergic and glutamatergic neurons due to aberrant induction of vesicular glutamate transporter 1 (vGlut1)-positive glutamatergic cells is responsible for impaired neuronal differentiation in the hippocampus following TBI. To elucidate the molecular mechanism, we found that TBI activates a transcription factor, Pax3, by increasing its acetylation status, and subsequently induces Ngn2 transcription. This event, in turn, augments the vGlut1-expressing glutamatergic neurons and accumulation of excess glutamate in the hippocampus that can affect neuronal differentiation. In our study the acetylation of Pax3 was increased due to loss of its interaction with a deacetylase, histone deacetylase 4 (HDAC4), which was downregulated after TBI. TBI-induced activation of GSK3β was responsible for the degradation of HDAC4. We also showed that overexpression of HDAC4 before TBI reduces Pax3 acetylation by restoring an interaction between HDAC4 and Pax3 in the hippocampus. This event prevents the aberrant induction of vGlut1-positive glutamatergic neurons by decreasing the Ngn2 level and subsequently reinforces the balance between GABAergic and glutamatergic neurons following TBI. Further, we found that overexpression of HDAC4 in the hippocampus improves anxiety, depressive-like behavior, and memory functions following TBI.

Hippocampal neurons in direct contact with astrocytes exposed to amyloid β25-35 exhibit reduced excitatory synaptic transmission

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We exposed astrocytes to Aβ _25-35 and then co-cultured them with primary hippocampal neurons.

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The Aβ_25-35-exposed astrocytes lowered excitatory postsynaptic release and the size of the readily releasable synaptic pool.

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The number of excitatory synapses was reduced by direct contact between Aβ_25-35-exposed astrocytes and hippocampal neurons.

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The dendritic branching was decreased by direct contact between Aβ_25-35-exposed astrocytes and hippocampal neurons.

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The number of excitatory synapses and dendrite branches were conserved by putting distance from Aβ_25-35-exposed astrocytes.

Amyloid β protein (Aβ) is closely related to the progression of Alzheimer's disease because senile plaques consisting of Aβ cause synaptic depression and synaptic abnormalities. In the central nervous system, astrocytes are a major glial cell type that contribute to the modulation of synaptic transmission and synaptogenesis. In this study, we examined whether astrocytes exposed to Aβ fragment 25-35 (Aβ_25-35) affect synaptic transmission. We show that synaptic transmission by hippocampal neurons was inhibited by astrocytes exposed to Aβ_25-35. The Aβ_25-35-exposed astrocytes lowered excitatory postsynaptic release and the size of the readily releasable synaptic pool. The number of excitatory synapses was also reduced. However, the number of excitatory synapses was unchanged unless there was direct contact between Aβ_25-35-exposed astrocytes and hippocampal neurons. These data indicate that direct contact between Aβ_25-35-exposed astrocytes and neurons is critical for inhibiting synaptic transmission in the progression of Alzheimer’s disease.

Growth Differentiation Factor 11 treatment leads to neuronal and vascular improvements in the hippocampus of aged mice

Aging is the biggest risk factor for several neurodegenerative diseases. Parabiosis experiments have established that old mouse brains are improved by exposure to young mouse blood. Previously, our lab showed that delivery of Growth Differentiation Factor 11 (GDF11) to the bloodstream increases the number of neural stem cells and positively affects vasculature in the subventricular zone of old mice. Our new study demonstrates that GDF11 enhances hippocampal neurogenesis, improves vasculature and increases markers of neuronal activity and plasticity in the hippocampus and cortex of old mice. Our experiments also demonstrate that systemically delivered GDF11, rather than crossing the blood brain barrier, exerts at least some of its effects by acting on brain endothelial cells. Thus, by targeting the cerebral vasculature, GDF11 has a very different mechanism from that of previously studied circulating factors acting to improve central nervous system (CNS) function without entering the CNS.

Neurochemical fingerprinting of amygdalostriatal and intra-amygdaloid projections: a tracing-immunofluorescence study in the rat

Amygdalostriatal and intra-amygdaloid fiber connectivity was studied in rats via injections of one of the tracers Phaseolus vulgaris leucoagglutinin (PHA-L) or biotinylated dextran amine (BDA) into various amygdaloid nuclei. To determine the neurotransmitter identity of labeled fibers we combined tracer detection with immunofluorescence staining, using antibodies against vesicular transporters (VTs) associated with glutamatergic (VGluT1, VGluT2) or GABAergic (VGAT) neurotransmission. High-magnification confocal laser scanning images were screened for overlap: occurrence inside tracer labeled fibers or axon terminals of immunofluorescence signal associated with one of the VTs. Labeled amygdalostriatal fibers were seen when tracer had been injected into the magnocellular and parvicellular portions of the basal amygdaloid nucleus and the lateral amygdaloid nucleus (nuclei belonging to 'cortical type' amygdaloid nuclei). Intra-amygdaloidal projection fibers were mostly found after tracer injections in the central and medial amygdaloid nuclei ('striatal type' amygdaloid nuclei). Terminals of tracer-labeled amygdalostriatal fibers contained immunofluorescence signal associated mostly with VGluT1 and to a lesser degree with VGluT2 or VGAT. Intra-amygdaloid labeled fibers showed colocalization mostly of VGluT1, followed by VGAT. VGluT2 co-occurred in a minority of intra-amygdaloid tracer-containing fiber terminals. We conclude from our observations that both amygdalostriatal and intra-amygdaloid projections, arising from, respectively, 'cortical type' and 'striatal type' amygdaloid nuclei contain strong glutamatergic and modest GABAergic components. The glutamatergic fibers express either VGluT1 or VGluT2. The absence in large numbers of tracer labeled fibers of expression of one of the selected VTs leads us to suspect that amygdalostriatal projection fibers may contain hitherto neglected neurotransmitters in these connections, e.g., aspartate.

Repeated low level domoic acid exposure increases CA1 VGluT1 levels, but not bouton density, VGluT2 or VGAT levels in the hippocampus of adult mice

Domoic acid (DA) is a neurotoxin produced during harmful algal blooms that accumulates in marine organisms that serve as food resources for humans. While acute DA neurotoxicity can cause seizures and hippocampal lesions, less is known regarding how chronic, subacute DA exposure in adulthood impacts the hippocampus. With more frequent occurrences of harmful algal blooms, it is important to understand the potential impact of repeated, low-level DA exposure on human health. To model repeated, low-dose DA exposure, adult mice received a single low-dose (0.75 ± 0.05 μg/g) of DA or vehicle weekly for 22 consecutive weeks. Quantitative immunohistochemistry was performed to assess the effects of repeated, low-level DA exposure on hippocampal cells and synapses. Vesicular glutamate transporter 1 (VGluT1) immunoreactivity within excitatory boutons in CA1 of DA-exposed mice was increased. Levels of other vesicular transporter proteins (i.e., VGluT2 and the vesicular GABA transporter (VGAT)) within boutons, and corresponding bouton densities, were not significantly altered in CA1, CA3, or dentate gyrus. There were no significant changes in neuron density or glial fibrillary acidic protein (GFAP) immunoreactivity following chronic, low-dose exposure. This suggests that repeated low doses of DA, unlike high doses of DA, do not cause neuronal loss or astrocyte activation in hippocampus in adult mice. Instead, these findings demonstrate that repeated exposure to low levels of DA leads to subtle changes in VGluT1 expression within CA1 excitatory boutons, which may alter glutamatergic transmission in CA1 and disrupt behaviors dependent on spatial memory.

Nucleocytoplasmic export of HDAC5 and SIRT2 downregulation: two epigenetic mechanisms by which antidepressants enhance synaptic plasticity markers

RATIONALE

Antidepressant action has been linked to increased synaptic plasticity in which epigenetic mechanisms such as histone posttranslational acetylation could be involved. Interestingly, the histone deacetylases HDAC5 and SIRT2 are oppositely regulated by stress and antidepressants in mice prefrontal cortex (PFC). Besides, the neuroblastoma SH-SY5Y line is an in vitro neuronal model reliable to study drug effects with clear advantages over animals.

OBJECTIVES

We aimed to characterize in vitro the role of HDAC5 and SIRT2 in antidepressant regulation of neuroplasticity.

METHODS

SH-SY5Y cultures were incubated with imipramine, fluoxetine, and reboxetine (10 μM, 2 and 24 h) as well as the selective HDAC5 (MC3822, 5 μM, 24 h) or SIRT2 (33i, 5 μM, 24 h) inhibitors. The regulation of the brain-derived neurotrophic factor (BDNF), the vesicular glutamate transporter 1 (VGLUT1), the acetylated histones 3 (AcH3) and 4 (AcH4), HDAC5, and SIRT2 was studied. Comparatively, the long-term effects of these antidepressants (21 days, i.p.) in the mice (C57BL6, 8 weeks) PFC were studied.

RESULTS

Antidepressants increased both in vitro and in vivo expression of BDNF, VGLUT1, AcH3, and AcH4. Moreover, imipramine and reboxetine increased the phosphorylated form of HDAC5 (P-HDAC5), mediating its cytoplasmic export. Further, SIRT2 was downregulated by all antidepressants. Finally, specific inhibition of HDAC5 and SIRT2 increased neuroplasticity markers.

CONCLUSIONS

This study supports the validity of the SH-SY5Y model for studying epigenetic changes linked to synaptic plasticity induced by antidepressants as well as the effect of selective HDAC inhibitors. Particularly, nucleocytoplasmic export of HDAC5 and SIRT2 downregulation mediated by antidepressants could enhance synaptic plasticity markers leading to antidepressant action.

Vesicular glutamate transporter isoforms: The essential players in the somatosensory systems

In nervous system, glutamate transmission is crucial for centripetal conveyance and cortical perception of sensory signals of different modalities, which necessitates vesicular glutamate transporters 1-3 (VGLUT 1-3), the three homologous membrane-bound protein isoforms, to load glutamate into the presysnaptic vesicles. These VGLUTs, especially VGLUT1 and VGLUT2, selectively label and define functionally distinct neuronal subpopulations at each relay level of the neural hierarchies comprising spinal and trigeminal sensory systems. In this review, by scrutinizing each structure of the organism's fundamental hierarchies including dorsal root/trigeminal ganglia, spinal dorsal horn/trigeminal sensory nuclear complex, somatosensory thalamic nuclei and primary somatosensory cortex, we summarize and characterize in detail within each relay the neuronal clusters expressing distinct VGLUT protein/transcript isoforms, with respect to their regional distribution features (complementary distribution in some structures), axonal terminations/peripheral innervations and physiological functions. Equally important, the distribution pattern and characteristics of VGLUT1/VGLUT2 axon terminals within these structures are also epitomized. Finally, the correlation of a particular VGLUT isoform and its physiological role, disclosed thus far largely via studying the peripheral receptors, is generalized by referring to reports on global and conditioned VGLUT-knockout mice. Also, researches on VGLUTs relating to future direction are tentatively proposed, such as unveiling the elusive differences between distinct VGLUTs in mechanism and/or pharmacokinetics at ionic/molecular level, and developing VGLUT-based pain killers.

Zinc signaling and epilepsy

Evidence from both preclinical and clinical studies suggest the importance of zinc homeostasis in seizures/epilepsy. Undoubtedly, zinc, via modulation of a variety of targets, is necessary for maintaining the balance between neuronal excitation and inhibition, while an imbalance between excitation and inhibition underlies seizures. However, the relationship between zinc signaling and seizures/epilepsy is complex as both extracellular and intracellular zinc may produce either protective or detrimental effects. This review provides an overview of preclinical/behavioral, functional and molecular studies, as well as clinical data on the involvement of zinc in the pathophysiology and treatment of seizures/epilepsy. Furthermore, the potential of targeting elements associated with zinc signaling or homeostasis and zinc levels as a therapeutic strategy for epilepsy is discussed.

MLL1 is essential for retinal neurogenesis and horizontal inner neuron integrity

Development of retinal structure and function is controlled by cell type-specific transcription factors and widely expressed co-regulators. The latter includes the mixed-lineage leukemia (MLL) family of histone methyltransferases that catalyze histone H3 lysine 4 di- and tri-methylation associated with gene activation. One such member, MLL1, is widely expressed in the central nervous system including the retina. However, its role in retinal development is unknown. To address this question, we knocked out Mll1 in mouse retinal progenitors, and discovered that MLL1 plays multiple roles in retinal development by regulating progenitor cell proliferation, cell type composition and neuron-glia balance, maintenance of horizontal neurons, and formation of functional synapses between neuronal layers required for visual signal transmission and processing. Altogether, our results suggest that MLL1 is indispensable for retinal neurogenesis and function development, providing a new paradigm for cell type-specific roles of known histone modifying enzymes during CNS tissue development.

Distribution of vesicular glutamate transporters in the brain of the turtle (Pseudemys scripta elegans)

The distribution of glutamatergic neurons has been extensively studied in mammalian and avian brains, but its distribution in a reptilian brain remains unknown. In the present study, the distribution of subpopulations of glutamatergic neurons in the turtle brain was examined by in situ hybridization using probes for vesicular glutamate transporter (VGLUT) 1-3. Strong VGLUT1 expression was observed in the telencephalic pallium; the mitral cells of the olfactory bulb, the medial, dorsomedial, dorsal, and lateral parts of the cerebral cortex, pallial thickening, and dorsal ventricular ridge; and also, in granule cells of the cerebellar cortex. Moderate to weak expression was found in the lateral and medial amygdaloid nuclei, the periventricular cellular layer of the optic tectum, and in some brainstem nuclei. VGLUT2 was weakly expressed in the telencephalon but was intensely expressed in the dorsal thalamic nuclei, magnocellular part of the isthmic nucleus, brainstem nuclei, and the rostral cervical segment of the spinal cord. The cerebellar cortex was devoid of VGLUT2 expression. The central amygdaloid nucleus did not express VGLUT1 or VGLUT2. VGLUT3 was localized in the parvocellular part of the isthmic nucleus, superior and inferior raphe nuclei, and cochlear nucleus. Our results indicate that the distribution of VGLUTs in the turtle brain is similar to that in the mammalian brain rather than that in the avian brain.

Image-Based Profiling of Synaptic Connectivity in Primary Neuronal Cell Culture

Neurological disorders display a broad spectrum of clinical manifestations. Yet, at the cellular level, virtually all these diseases converge into a common phenotype of dysregulated synaptic connectivity. In dementia, synapse dysfunction precedes neurodegeneration and cognitive impairment by several years, making the synapse a crucial entry point for the development of diagnostic and therapeutic strategies. Whereas high-resolution imaging and biochemical fractionations yield detailed insight into the molecular composition of the synapse, standardized assays are required to quickly gauge synaptic connectivity across large populations of cells under a variety of experimental conditions. Such screening capabilities have now become widely accessible with the advent of high-throughput, high-content microscopy. In this review, we discuss how microscopy-based approaches can be used to extract quantitative information about synaptic connectivity in primary neurons with deep coverage. We elaborate on microscopic readouts that may serve as a proxy for morphofunctional connectivity and we critically analyze their merits and limitations. Finally, we allude to the potential of alternative culture paradigms and integrative approaches to enable comprehensive profiling of synaptic connectivity.

Cerebral oxidative metabolism mapping in four genetic mouse models of anxiety and mood disorders

The psychopathology of depression is highly complex and the outcome of studies on animal models is divergent. In order to find brain regions that could be metabolically distinctively active across a variety of mouse depression models and to compare the interconnectivity of brain regions of wild-type and such genetically modified mice, histochemical mapping of oxidative metabolism was performed by the measurement of cytochrome oxidase activity. We included mice with the heterozygous knockout of the vesicular glutamate transporter (VGLUT₁^-/+), full knockout of the cannabinoid 1 receptor (CB1^-/-), an anti-sense knockdown of the glucocorticoid receptor (GRi) and overexpression of the human 5-hydroxytryptamine transporter (h5-HTT). Altogether 76 mouse brains were studied to measure oxidative metabolism in one hundred brain regions, and the obtained dataset was submitted to a variety of machine learning algorithms and multidimensional scaling. Overall, the top brain regions having the largest contribution to classification into depression model were the lateroanterior hypothalamic nucleus, the anterior part of the basomedial amygdaloid nucleus, claustrum, the suprachiasmatic nucleus, the ventromedial hypothalamic nucleus, and the anterior hypothalamic area. In terms of the patterns of inter-regional relationship between wild-type and genetically modified mice there was little overall difference, while the most deviating brain regions were cortical amygdala and ventrolateral and ventral posteromedial thalamic nuclei. The GRi mice that most clearly differed from their controls exhibited deviation of connectivity for a number of brain regions, such as ventrolateral thalamic nucleus, the intermediate part of the lateral septal nucleus, the anteriodorsal part of the medial amygdaloid nucleus, the medial division of the central amygdaloid nucleus, ventral pallidum, nucleus of the vertical limb of the diagonal band, anteroventral parts of the thalamic nucleus and parts of the bed nucleus of the stria terminalis. Conclusively, the GRi mouse model was characterized by changes in the functional connectivity of the extended amygdala and stress response circuits.

Mental Illnesses-Associated Fxr1 and Its Negative Regulator Gsk3β Are Modulators of Anxiety and Glutamatergic Neurotransmission

Genetic variants of the fragile X mental retardation syndrome-related protein 1 (FXR1) have been associated to mood regulation, schizophrenia, and bipolar disorders. Nonetheless, genetic association does not indicate a functional link of a given gene to neuronal activity and associated behaviors. In addition, interaction between multiple genes is often needed to sculpt complex traits such as behavior. Thus, modulation of neuronal functions by a given gene product, such as Fxr1, has to be thoroughly studied in the context of its interactions with other gene products. Glycogen synthase kinase-3 beta (GSK3β) is a shared target of several psychoactive drugs. In addition, interaction between functional polymorphisms of GSK3b and FXR1 has been implicated in mood regulation in healthy subjects and bipolar patients. However, the mechanistic underpinnings of this interaction remain unknown. We used somatic CRISPR/Cas9 mediated knockout and overexpression to investigate the impact of Fxr1 and its regulator Gsk3β on neuronal functions directly in the adult mouse brain. Suppression of Gsk3β or increase of Fxr1 expression in medial prefrontal cortex neurons leads to anxiolytic-like responses associated with a decrease in AMPA mediated excitatory postsynaptic currents. Furthermore, Fxr1 and Gsk3β modulate glutamatergic neurotransmission via regulation of AMPA receptor subunits GluA1 and GluA2 as well as vesicular glutamate transporter VGlut1. These results underscore a potential mechanism underlying the action of Fxr1 on neuronal activity and behaviors. Association between the Gsk3β-Fxr1 pathway and glutamatergic signaling also suggests how it may contribute to emotional regulation in response to mood stabilizers, or in illnesses like mood disorders and schizophrenia.

Age-dependent changes in vesicular glutamate transporter 1 and 2 expression in the gerbil hippocampus

Glutamate is a major excitatory neurotransmitter that is stored in vesicles located in the presynaptic terminal. Glutamate is transported into vesicles via the vesicular glutamate transporter (VGLUT). In the present study, the age‑associated changes of the major VGLUTs, VGLUT1 and VGLUT2, in the hippocampus were investigated, based on immunohistochemistry and western blot analysis at postnatal month 1 (PM1; adolescent), PM6, PM12 (adult group), PM18 and PM24 (the aged groups). VGLUT1 immunoreactivity was primarily detected in the mossy fibers, Schaffer collaterals and stratum lacunosum‑moleculare. By contrast, VGLUT2 immunoreactivity was observed in the granule cell layer and the outer molecular layer of the dentate gyrus, stratum pyramidale, Schaffer collaterals and stratum lacunosum‑moleculare in the hippocampal CA1‑3 regions. VGLUT1 immunoreactivity and protein levels remained constant across all age groups. However, VGLUT2 immunoreactivity and protein levels decreased in the PM3 group when compared with the PM1 group. VGLUT2 immunoreactivity and protein levels were not altered in the PM12 group; however, they increased in the PM18 group. In addition, in the PM18 group, highly immunoreactive VGLUT2 cells were also identified in the stratum radiatum and oriens of the hippocampal CA1 region. In the PM24 group, VGLUT2 immunoreactivity and protein levels were significantly decreased and were the lowest levels observed amongst the different groups. These results suggested that VGLUT1 may be less susceptible to the aging process; however, the increase of VGLUT2 in the non‑pyramidal cells in the PM18 group, and the consequent decrease in VGLUT2, may be closely linked to age‑associated memory impairment in the hippocampus.

Moderate decline in select synaptic markers in the prefrontal cortex (BA9) of patients with Alzheimer's disease at various cognitive stages

Synaptic loss, plaques and neurofibrillary tangles are viewed as hallmarks of Alzheimer's disease (AD). This study investigated synaptic markers in neocortical Brodmann area 9 (BA9) samples from 171 subjects with and without AD at different levels of cognitive impairment. The expression levels of vesicular glutamate transporters (VGLUT1&2), glutamate uptake site (EAAT2), post-synaptic density protein of 95 kD (PSD95), vesicular GABA/glycine transporter (VIAAT), somatostatin (som), synaptophysin and choline acetyl transferase (ChAT) were evaluated. VGLUT2 and EAAT2 were unaffected by dementia. The VGLUT1, PSD95, VIAAT, som, ChAT and synaptophysin expression levels significantly decreased as dementia progressed. The maximal decrease varied between 12% (synaptophysin) and 42% (som). VGLUT1 was more strongly correlated with dementia than all of the other markers (polyserial correlation = -0.41). Principal component analysis using these markers was unable to differentiate the CDR groups from one another. Therefore, the status of the major synaptic markers in BA9 does not seem to be linked to the cognitive status of AD patients. The findings of this study suggest that the loss of synaptic markers in BA9 is a late event that is only weakly related to AD dementia.

Contribution of Vesicular Glutamate Transporters to Stress Response and Related Psychopathologies: Studies in VGluT3 Knockout Mice

Maintenance of the homeostasis in a constantly changing environment is a fundamental process of life. Disturbances of the homeostatic balance is defined as stress response and is induced by wide variety of challenges called stressors. Being the main excitatory neurotransmitter of the central nervous system glutamate is important in the adaptation process of stress regulating both the catecholaminergic system and the hypothalamic-pituitary-adrenocortical axis. Data are accumulating about the role of different glutamatergic receptors at all levels of these axes, but little is known about the contribution of different vesicular glutamate transporters (VGluT1-3) characterizing the glutamatergic neurons. Here we summarize basic knowledge about VGluTs, their role in physiological regulation of stress adaptation, as well as their contribution to stress-related psychopathology. Most of our knowledge comes from the VGluT3 knockout mice, as VGluT1 and 2 knockouts are not viable. VGluT3 was discovered later than, and is not as widespread as the VGluT1 and 2. It may co-localize with other transmitters, and participate in retrograde signaling; as such its role might be unique. Previous reports using VGluT3 knockout mice showed enhanced anxiety and innate fear compared to wild type. Moreover, these knockout animals had enhanced resting corticotropin-releasing hormone mRNA levels in the hypothalamus and disturbed glucocorticoid stress responses. In conclusion, VGluT3 participates in stress adaptation regulation. The neuroendocrine changes observed in VGluT3 knockout mice may contribute to their anxious, fearful phenotype.

VGLUT1 functions as a glutamate/proton exchanger with chloride channel activity in hippocampal glutamatergic synapses

Glutamate is the major excitatory transmitter in the vertebrate nervous system. To maintain synaptic efficacy, recycling synaptic vesicles (SV) are refilled with glutamate by vesicular glutamate transporters (VGLUTs). The dynamics and mechanism of glutamate uptake in intact neurons are still largely unknown. Here, we show by live-cell imaging with pH- and chloride-sensitive fluorescent probes in cultured hippocampal neurons of wild-type and VGLUT1-deficient mice that in SVs VGLUT functions as a glutamate/proton exchanger associated with a channel-like chloride conductance. After endocytosis most internalized Cl⁻ is substituted by glutamate in an electrically, and presumably osmotically, neutral manner, and this process is driven by both the Cl⁻ gradient itself and the proton motive force provided by the vacuolar H⁺-ATPase. Our results shed light on the transport mechanism of VGLUT under physiological conditions and provide a framework for how modulation of glutamate transport via Cl⁻ and pH can change synaptic strength.

During neurotransmission synaptic vesicles are filled with glutamate by vesicular glutamate transporters (VGLUTs). Here, authors image intact neurons and show that in synaptic vesicles VGLUT functions as a glutamate/proton exchanger associated with a channel-like chloride conductance.

Vesicular glutamate transporter 1 (VGLUT1)-mediated glutamate release and membrane GluA1 activation is involved in the rapid antidepressant-like effects of scopolamine in mice

Emerging data have identified certain drugs such as scopolamine as rapidly acting antidepressants for major depressive disorder (MDD) that increase glutamate release and induce neurotrophic factors through α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activation in rodent models. However, little research has addressed the direct mechanisms of scopolamine on AMPAR activation or vesicular glutamate transporter 1 (VGLUT1)-mediated glutamate release in the prefrontal cortex (PFC) of mice. Herein, using a chronic unpredictable stress (CUS) paradigm, acute treatment with scopolamine rapidly reversed stress-induced depression-like behaviors in mice. Our results showed that CUS-induced depression-like behaviors, accompanied by a decrease in membrane AMPAR subunit 1 (GluA1), phosphorylated GluA1 Ser845 (pGluA1 Ser845), brain-derived neurotrophic factor (BDNF) and VGF (non-acronymic) and an increase in bicaudal C homolog 1 gene (BICC1) in the PFC of mice, and these biochemical and behavioral abnormalities were ameliorated by acute scopolamine treatments. However, pharmacological block of AMPAR by NBQX infusion into the PFC significantly abolished these effects of scopolamine. In addition, knock down of VGLUT1 by lentiviral-mediated RNA interference in the PFC of mice was sufficient to induce depression-like phenotype, to decrease extracellular glutamate accumulation and to cause similar molecular changes with CUS in mice. Remarkably, VGLUT1 knockdown alleviated the rapid antidepressant-like actions of scopolamine and the effects of scopolamine on membrane GluA1-mediated BDNF, VGF and BICC1 changes. Altogether, our findings suggest that VGLUT1-mediated glutamate release and membrane GluA1 activation may play a critical role in the rapid-acting antidepressant-like effects of scopolamine in mice.

Reduced responses to glutamate receptor agonists follow loss of astrocytes and astroglial glutamate markers in the nucleus tractus solitarii

Saporin (SAP) or SAP conjugates injected into the nucleus tractus solitarii (NTS) of rats kill astrocytes. When injected in its unconjugated form, SAP produces no demonstrable loss of or damage to local neurons. However bilateral injections of SAP significantly attenuate responses to activation of baroreceptor reflexes that are mediated by transmission of signals through glutamate receptors in the NTS We tested the hypothesis that SAP would reduce cardiovascular responses to activation of NTS glutamate receptors despite its recognized ability to spare local neurons while killing local astrocytes. In animals treated with SAP and SAP conjugates or, as a control, with the toxin 6-hydroxydopamine (6-OHDA), we sought to determine if dose-related changes of arterial pressure (AP) or heart rate (HR) in response to injection into NTS of N-methyl-d-aspartate (NMDA) or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) were attenuated. Also we quantified changes in immunoreactivity (IR) for EAAT2, EAAC1, and VGluT2 in NTS after SAP and SAP conjugates. Our earlier studies showed that IR for NMDA and AMPA receptors was not changed after injection of SAP We found that EAAT2 and EAAC1, both found in astrocytes, were reduced by SAP or its conjugates but not by 6-OHDA In contrast, VGluT2-IR was increased by SAP or conjugates but not by 6-OHDA AP and HR responses to NMDA and AMPA were attenuated after SAP and SAP conjugate injection but not after 6-OHDA Results of this study are consistent with others that have shown interactions between astroglia and neurons in synaptic transmission mediated by glutamate receptor activation in the NTS.

Age-related changes in cerebellar and hypothalamic function accompany non-microglial immune gene expression, altered synapse organization, and excitatory amino acid neurotransmission deficits

We describe age-related molecular and neuronal changes that disrupt mobility or energy balance based on brain region and genetic background. Compared to young mice, aged C57BL/6 mice exhibit marked locomotor (but not energy balance) impairments. In contrast, aged BALB mice exhibit marked energy balance (but not locomotor) impairments. Age-related changes in cerebellar or hypothalamic gene expression accompany these phenotypes. Aging evokes upregulation of immune pattern recognition receptors and cell adhesion molecules. However, these changes do not localize to microglia, the major CNS immunocyte. Consistent with a neuronal role, there is a marked age-related increase in excitatory synapses over the cerebellum and hypothalamus. Functional imaging of these regions is consistent with age-related synaptic impairments. These studies suggest that aging reactivates a developmental program employed during embryogenesis where immune molecules guide synapse formation and pruning. Renewed activity in this program may disrupt excitatory neurotransmission, causing significant behavioral deficits.

Conditional Loss of Hoxa5 Function Early after Birth Impacts on Expression of Genes with Synaptic Function

Hoxa5 is a member of the Hox gene family that plays critical roles in successive steps of the central nervous system formation during embryonic and fetal development. In the mouse, Hoxa5 was recently shown to be expressed in the medulla oblongata and the pons from fetal stages to adulthood. In these territories, Hoxa5 transcripts are enriched in many precerebellar neurons and several nuclei involved in autonomic functions, while the HOXA5 protein is detected mainly in glutamatergic and GABAergic neurons. However, whether HOXA5 is functionally required in these neurons after birth remains unknown. As a first approach to tackle this question, we aimed at determining the molecular programs downstream of the HOXA5 transcription factor in the context of the postnatal brainstem. A comparative transcriptomic analysis was performed in combination with gene expression localization, using a conditional postnatal Hoxa5 loss-of-function mouse model. After inactivation of Hoxa5 at postnatal days (P)1–P4, we established the transcriptome of the brainstem from P21 Hoxa5 conditional mutants using RNA-Seq analysis. One major finding was the downregulation of several genes associated with synaptic function in Hoxa5 mutant specimens including different actors involved in glutamatergic synapse, calcium signaling pathway, and GABAergic synapse. Data were confirmed and extended by reverse transcription quantitative polymerase chain reaction analysis, and the expression of several HOXA5 candidate targets was shown to co-localize with Hoxa5 transcripts in precerebellar nuclei. Together, these new results revealed that HOXA5, through the regulation of key actors of the glutamatergic/GABAergic synapses and calcium signaling, might be involved in synaptogenesis, synaptic transmission, and synaptic plasticity of the cortico-ponto-cerebellar circuitry in the postnatal brainstem.

Optogenetic Tools for Subcellular Applications in Neuroscience

The ability to study cellular physiology using photosensitive, genetically encoded molecules has profoundly transformed neuroscience. The modern optogenetic toolbox includes fluorescent sensors to visualize signaling events in living cells and optogenetic actuators enabling manipulation of numerous cellular activities. Most optogenetic tools are not targeted to specific subcellular compartments but are localized with limited discrimination throughout the cell. Therefore, optogenetic activation often does not reflect context-dependent effects of highly localized intracellular signaling events. Subcellular targeting is required to achieve more specific optogenetic readouts and photomanipulation. Here we first provide a detailed overview of the available optogenetic tools with a focus on optogenetic actuators. Second, we review established strategies for targeting these tools to specific subcellular compartments. Finally, we discuss useful tools and targeting strategies that are currently missing from the optogenetics repertoire and provide suggestions for novel subcellular optogenetic applications.

Astrocytes with previous chronic exposure to amyloid β-peptide fragment 1-40 suppress excitatory synaptic transmission

Synaptic dysfunction and neuronal death are responsible for cognitive and behavioral deficits in Alzheimer's disease (AD). It is well known that such neurological abnormalities are preceded by long-term exposure of amyloid β-peptide (Aβ) and/or hyperphosphorylated tau prior. In addition to the neurological deficit, astrocytes as a major glial cell type in the brain, significantly participate in the neuropathogenic mechanisms underlying synaptic modulation. Although astrocytes play a significant key role in modulating synaptic transmission, little is known on whether astrocyte dysfunction caused by such long-term Aβ exposure affects synapse formation and function. Here, we show that synapse formation and synaptic transmission are attenuated in hippocampal-naïve neurons co-cultured with astrocytes that have previously experienced chronic Aβ_1-40 exposure. In this abnormal astrocytic condition, hippocampal neurons exhibit decrements of evoked excitatory post-synaptic currents (EPSCs) and miniature EPSC frequency. Furthermore, size of readily releasable synaptic pools and number of excitatory synapses were also significantly decreased. Contrary to these negative effects, release probability at individual synapses was significantly increased in the same astrocytic condition. Taken together, our data indicate that lower synaptic transmission caused by astrocytes previously, and chronically, exposed to Aβ1-40 is attributable to a small number of synapses with higher release probability.

CNS synapses are stabilized trans-synaptically by laminins and laminin-interacting proteins

The retina expresses several laminins in the outer plexiform layer (OPL), where they may provide an extracellular scaffold for synapse stabilization. Mice with a targeted deletion of the laminin β2 gene (Lamb2) exhibit retinal disruptions: photoreceptor synapses in the OPL are disorganized and the retinal physiological response is attenuated. We hypothesize that laminins are required for proper trans-synaptic alignment. To test this, we compared the distribution, expression, association and modification of several pre- and post-synaptic elements in wild-type and Lamb2-null retinae. A potential laminin receptor, integrin α3, is at the presynaptic side of the wild-type OPL. Another potential laminin receptor, dystroglycan, is at the post-synaptic side of the wild-type OPL. Integrin α3 and dystroglycan can be co-immunoprecipitated with the laminin β2 chain, demonstrating that they may bind laminins. In the absence of the laminin β2 chain, the expression of many pre-synaptic components (bassoon, kinesin, among others) is relatively undisturbed although their spatial organization and anchoring to the membrane is disrupted. In contrast, in the Lamb2-null, β-dystroglycan (β-DG) expression is altered, co-localization of β-DG with dystrophin and the glutamate receptor mGluR6 is disrupted, and the post-synaptic bipolar cell components mGluR6 and GPR179 become dissociated, suggesting that laminins mediate scaffolding of post-synaptic components. In addition, although pikachurin remains associated with β-DG, pikachurin is no longer closely associated with mGluR6 or α-DG in the Lamb2-null. These data suggest that laminins act as links among pre- and post-synaptic laminin receptors and α-DG and pikachurin in the synaptic space to maintain proper trans-synaptic alignment.

The hyperexcitability of dentate granule neurons in organotypic hippocampal slice cultures is due to reorganization of synaptic inputs in vitro

Organotypic hippocampal slice cultures (OHSCs) provide the experimental flexibility of cell culture while leaving much of the natural neuronal connectivity intact. Previously, it was shown that the functional and morphological features of CA1 pyramidal neurons in OHSCs resemble, to a surprising extent, those of CA1 neurons in the acute brain slice preparation. However, the extent to which the characteristics of other principle hippocampal neurons change or are preserved in cultured slices remains to be determined. In the present study, I initially sought to understand whether and how the synaptic inputs and morphology of cultured dentate granule neurons (GCs) differ from GCs that have developed in vivo. To this end, I compared GCs in OHSCs and GCs in acute slices at two equivalent developmental time points (P14 vs. DIV7 and P21 vs. DIV21). The findings suggest that there is considerable reorganization of synaptic input to the organotypic GCs, such that these cells are more susceptible to hyperexcitation than GCs in acute slices after 3 weeks. It appears that this hyperexcitability emerges through an increase in the proportion of mature synapses at proximal dendritic sites and is accompanied by an increase in inhibitory neuron activity. These alterations appear to arise in a coordinated manner such that the substantial increase in excitatory synaptic drive received by the DIV21 GCs in OHSCs remains local and is not translated into excessive output possibly leading to damage or major morphological alterations of downstream pyramidal neurons.

Vesicular Glutamate Transporter 1 Knockdown in Infralimbic Prefrontal Cortex Augments Neuroendocrine Responses to Chronic Stress in Male Rats

Chronic stress-associated pathologies frequently associate with alterations in the structure and activity of the medial prefrontal cortex (mPFC). However, the influence of infralimbic cortex (IL) projection neurons on hypothalamic-pituitary-adrenal (HPA) axis activity is unknown, as is the involvement of these cells in chronic stress-induced endocrine alterations. In the current study, a lentiviral-packaged vector coding for a small interfering RNA (siRNA) targeting vesicular glutamate transporter (vGluT) 1 messenger RNA (mRNA) was microinjected into the IL of male rats. vGluT1 is responsible for presynaptic vesicular glutamate packaging in cortical neurons, and knockdown reduces the amount of glutamate available for synaptic release. After injection, rats were either exposed to chronic variable stress (CVS) or remained in the home cage as unstressed controls. Fifteen days after the initiation of CVS, all animals were exposed to a novel acute stressor (30-minute restraint) with blood collection for the analysis of adrenocorticotropic hormone (ACTH) and corticosterone. Additionally, brains were collected for in situ hybridization of corticotrophin-releasing hormone mRNA. In previously unstressed rats, vGluT1 siRNA significantly enhanced ACTH and corticosterone secretion. Compared with CVS animals receiving the green fluorescent protein control vector, the vGluT1 siRNA further increased basal and stress-induced corticosterone release. Further analysis revealed enhanced adrenal responsiveness in CVS rats treated with vGluT1 siRNA. Collectively, our results suggest that IL glutamate output inhibits HPA responses to acute stress and restrains corticosterone secretion during chronic stress, possibly at the level of the adrenal. Together, these findings pinpoint a neurochemical mechanism linking mPFC dysfunction with aberrant neuroendocrine responses to chronic stress.

Unveiling of miRNA Expression Patterns in Purkinje Cells During Development

MicroRNAs (miRNAs) are short noncoding RNAs of 19-25 nucleotides in length that regulate gene expression at the post-transcriptional level. Dysregulation of miRNAs is associated with many disorders and neurodegenerative diseases affecting numerous different pathways and processes, of which many have not yet been completely explored. Recent studies even indicate a crucial role of miRNAs during brain development, with differential expression patterns of several miRNAs seen in both developing and mature cells. A miRNA profiling in brain tissue and the fundamental understanding of their effects might optimize the therapeutical treatment of various neurological disorders. In this study, we performed miRNA array analysis of enriched cerebellar Purkinje cell (PC) samples from both young and mature rat cerebella. We used laser microdissection (LMD) to enrich PC for a highly specific miRNA profiling. Altogether, we present the expression profile of at least 27 miRNAs expressed in rat cerebellar PC and disclose a different expression pattern of at least three of these miRNAs during development. These miRNAs are potential candidates for the regulation and control of cerebellar PC development, including neuritic and dendritic outgrowth as well as spine formation.

Enhanced Cognition and Hypoglutamatergic Signaling in a Growth Hormone Receptor Knockout Mouse Model of Successful Aging

Growth hormone receptor knockout (GHR-KO) mice are long lived with improved health span, making this an excellent model system for understanding biochemical mechanisms important to cognitive reserve. The purpose of the present study was to elucidate differences in cognition and glutamatergic dynamics between aged (20- to 24-month-old) GHR-KO and littermate controls. Glutamate plays a critical role in hippocampal learning and memory and is implicated in several neurodegenerative disorders, including Alzheimer's disease. Spatial learning and memory were assessed using the Morris water maze (MWM), whereas independent dentate gyrus (DG), CA3, and CA1 basal glutamate, release, and uptake measurements were conducted in isoflurane anesthetized mice utilizing an enzyme-based microelectrode array (MEA) coupled with constant potential amperometry. These MEAs have high temporal and low spatial resolution while causing minimal damage to the surrounding parenchyma. Littermate controls performed worse on the memory portion of the MWM behavioral task and had elevated DG, CA3, and CA1 basal glutamate and stimulus-evoked release compared with age-matched GHR-KO mice. CA3 basal glutamate negatively correlated with MWM performance. These results support glutamatergic regulation in learning and memory and may have implications for therapeutic targets to delay the onset of, or reduce cognitive decline, in Alzheimer's disease.

SIRT2 inhibition reverses anhedonia in the VGLUT1+/- depression model

Some histone deacetylase (HDACs) enzymes have been proposed as epigenetic targets involved in the pathophysiology of depression and antidepressant-like action. Among them, we have recently identified SIRT2, a class III NAD⁺-dependent HDAC, as being oppositely regulated by stress and antidepressants. Moreover, SIRT2 inhibition has shown antianhedonic-like action in the chronic mild stress model of depression. Here we have extended the study using an alternative model of depression based in a genetic manipulation of glutamate function. Specifically, mice heterozygous for the vesicular glutamate transporter 1 (VGLUT1+/-) were used. Firstly, mRNA expression of the different members of the HDAC superfamily in the prefrontal cortex (PFC) of VGLUT1+/- mice and WT littermates were studied by RT-PCR. Secondly, the effect of repeated treatment with the selective SIRT2 inhibitor 33i and the antidepressant imipramine on anhedonic behaviour of VGLUT1+/- mice was studied by weekly monitoring of sucrose intake. Further, the interaction of 33i towards specific monoaminergic targets such as serotonin or noradrenaline transporters as well as the monoaminooxidase enzyme was studied. The mRNA occurance of the different members of HDAC superfamily was not altered in the PFC of VGLUT1+/- mice. While repeated imipramine showed an anti-anhedonic action in both VGLUT1+/- and WT, the selective SIRT2 inhibitor 33i fully reversed anhedonia of VGLUT1+/-. Further, 33i showed no interaction with the above mentioned monoaminergic molecular targets. These results confirm that SIRT2 inhibition is able to reverse anhedonia in different animal models and highlight the need to further investigate the role of SIRT2 inhibitors as new antidepressant agents.

The AMPA receptor positive allosteric modulator S 47445 rescues in vivo CA3-CA1 long-term potentiation and structural synaptic changes in old mice

Positive allosteric modulators of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are small molecules that decrease deactivation of AMPARs via an allosteric site. These molecules keep the receptor in an active state. Interestingly, this type of modulator has been proposed for treating cognitive decline in ageing, dementias, and Alzheimer's disease (AD). S 47445 (8-cyclopropyl-3-[2-(3-fluorophenyl)ethyl]-7,8-dihydro-3H-[1,3]oxazino[6,5-g][1,2,3]benzotriazine-4,9-dione) is a novel AMPAR positive allosteric modulator (AMPA-PAM). Here, the mechanisms by which S 47445 could improve synaptic strength and connectivity were studied and compared between young and old mice. A single oral administration of S 47445 at 10 mg/kg significantly increased long-term potentiation (LTP) in CA3-CA1 hippocampal synapses in alert young mice in comparison to control mice. Moreover, chronic treatment with S 47445 at 10 mg/kg in old alert animals significantly counteracted the deficit of LTP due to age. Accordingly, chronic treatment with S 47445 at 10 mg/kg seems to preserve synaptic cytoarchitecture in old mice as compared with young control mice. It was shown that the significant decreases in number and size of pre-synaptic buttons stained for VGlut1, and post-synaptic dendritic spines stained for spinophilin, observed in old mice were significantly prevented after chronic treatment with 10 mg/kg of S 47445. Altogether, by its different effects on LTP, VGlut1-positive particles, and spinophilin, S 47445 is able to modulate both the structure and function of hippocampal excitatory synapses known to be involved in learning and memory processes. These results open a new window for the treatment of specific age-dependent cognitive decline and dementias such as AD.

Multi-level characterization of balanced inhibitory-excitatory cortical neuron network derived from human pluripotent stem cells

Generation of neuronal cultures from induced pluripotent stem cells (hiPSCs) serve the studies of human brain disorders. However we lack neuronal networks with balanced excitatory-inhibitory activities, which are suitable for single cell analysis. We generated low-density networks of hPSC-derived GABAergic and glutamatergic cortical neurons. We used two different co-culture models with astrocytes. We show that these cultures have balanced excitatory-inhibitory synaptic identities using confocal microscopy, electrophysiological recordings, calcium imaging and mRNA analysis. These simple and robust protocols offer the opportunity for single-cell to multi-level analysis of patient hiPSC-derived cortical excitatory-inhibitory networks; thereby creating advanced tools to study disease mechanisms underlying neurodevelopmental disorders.

Vesicular glutamate transporters play a role in neuronal differentiation of cultured SVZ-derived neural precursor cells

The role of glutamate in the regulation of neurogenesis is well-established, but the role of vesicular glutamate transporters (VGLUTs) and excitatory amino acid transporters (EAATs) in controlling adult neurogenesis is unknown. Here we investigated the implication of VGLUTs in the differentiation of subventricular zone (SVZ)-derived neural precursor cells (NPCs). Our results show that NPCs express VGLUT1-3 and EAAT1-3 both at the mRNA and protein level. Their expression increases during differentiation closely associated with the expression of marker genes. In expression analyses we show that VGLUT1 and VGLUT2 are preferentially expressed by cultured SVZ-derived doublecortin+ neuroblasts, while VGLUT3 is found on GFAP+ glial cells. In cultured NPCs, inhibition of VGLUT by Evans Blue increased the mRNA level of neuronal markers doublecortin, B3T and MAP2, elevated the number of NPCs expressing doublecortin protein and promoted the number of cells with morphological appearance of branched neurons, suggesting that VGLUT function prevents neuronal differentiation of NPCs. This survival- and differentiation-promoting effect of Evans blue was corroborated by increased AKT phosphorylation and reduced MAPK phosphorylation. Thus, under physiological conditions, VGLUT1-3 inhibition, and thus decreased glutamate exocytosis, may promote neuronal differentiation of NPCs.

Sub-chronic variable stress induces sex-specific effects on glutamatergic synapses in the nucleus accumbens

Men and women manifest different symptoms of depression and under current diagnostic criteria, depression is twice as prevalent in woman. However, little is known of the mechanisms contributing to these important sex differences. Sub-chronic variable stress (SCVS), a rodent model of depression, induces depression-like behaviors in female mice only, modeling clinical evidence of higher susceptibility to mood disorders in women. Accumulating evidence indicates that altered neuroplasticity of excitatory synapses in the nucleus accumbens (NAc) is a key pathophysiological feature of susceptibility to social stress in males. Here we investigated the effects of SCVS on pre- and post-synaptic protein levels and morphology of glutamatergic synapses of medium spiny neurons (MSNs) in the NAc of female and male mice. Animals underwent six-day exposure to alternating stressors including shock, tail suspension and restraint. MSNs from the NAc were filled with a Lucifer yellow dye and spine density and type were examined using NeuronStudio. In a separate group of animals, immunofluorescence staining was performed for vesicular glutamate transporter 1 (VGLUT1) and vesicular glutamate transporter 2 (VGLUT2), in order to label cortical and subcortical glutamatergic terminals. Immunostaining for post-synaptic density 95 (PSD95) was employed to evaluate post-synaptic density. Females demonstrated circuit-specific pre-synaptic alterations in VGLUT1 and VGLUT2 containing synapses that may contribute to stress susceptibility in the absence of post-synaptic alterations in PSD95 puncta, spine density or type. These data indicate that susceptibility to stress in females is associated with changes in the frequency of distinct glutamatergic inputs to the NAc.

Characterization of a Human Point Mutation of VGLUT3 (p.A211V) in the Rodent Brain Suggests a Nonuniform Distribution of the Transporter in Synaptic Vesicles

The atypical vesicular glutamate transporter type 3 (VGLUT3) is expressed by subpopulations of neurons using acetylcholine, GABA, or serotonin as neurotransmitters. In addition, VGLUT3 is expressed in the inner hair cells of the auditory system. A mutation (p.A211V) in the gene that encodes VGLUT3 is responsible for progressive deafness in two unrelated families. In this study, we investigated the consequences of the p.A211V mutation in cell cultures and in the CNS of a mutant mouse. The mutation substantially decreased VGLUT3 expression (-70%). We measured VGLUT3-p.A211V activity by vesicular uptake in BON cells, electrophysiological recording of isolated neurons, and its ability to stimulate serotonergic accumulation in cortical synaptic vesicles. Despite a marked loss of expression, the activity of the mutated isoform was only minimally altered. Furthermore, mutant mice displayed none of the behavioral alterations that have previously been reported in VGLUT3 knock-out mice. Finally, we used stimulated emission depletion microscopy to analyze how the mutation altered VGLUT3 distribution within the terminals of mice expressing the mutated isoform. The mutation appeared to reduce the expression of the VGLUT3 transporter by simultaneously decreasing the number of VGLUT3-positive synaptic vesicles and the amount of VGLUT3 per synapses. These observations suggested that VGLUT3 global activity is not linearly correlated with VGLUT3 expression. Furthermore, our data unraveled a nonuniform distribution of VGLUT3 in synaptic vesicles. Identifying the mechanisms responsible for this complex vesicular sorting will be critical to understand VGLUT's involvement in normal and pathological conditions.SIGNIFICANCE STATEMENT VGLUT3 is an atypical member of the vesicular glutamate transporter family. A point mutation of VGLUT3 (VGLUT3-p.A211V) responsible for a progressive loss of hearing has been identified in humans. We observed that this mutation dramatically reduces VGLUT3 expression in terminals (∼70%) without altering its function. Furthermore, using stimulated emission depletion microscopy, we found that reducing the expression levels of VGLUT3 diminished the number of VGLUT3-positive vesicles at synapses. These unexpected findings challenge the vision of a uniform distribution of synaptic vesicles at synapses. Therefore, the overall activity of VGLUT3 is not proportional to the level of VGLUT3 expression. These data will be key in interpreting the role of VGLUTs in human pathologies.

Optic nerve, superior colliculus, visual thalamus, and primary visual cortex of the northern elephant seal (Mirounga angustirostris) and California sea lion (Zalophus californianus)

The northern elephant seal (Mirounga angustirostris) and California sea lion (Zalophus californianus) are members of a diverse clade of carnivorous mammals known as pinnipeds. Pinnipeds are notable for their large, ape-sized brains, yet little is known about their central nervous system. Both the northern elephant seal and California sea lion spend most of their lives at sea, but each also spends time on land to breed and give birth. These unique coastal niches may be reflected in specific evolutionary adaptations to their sensory systems. Here, we report on components of the visual pathway in these two species. We found evidence for two classes of myelinated fibers within the pinniped optic nerve, those with thick myelin sheaths (elephant seal: 9%, sea lion: 7%) and thin myelin sheaths (elephant seal: 91%, sea lion: 93%). In order to investigate the architecture of the lateral geniculate nucleus, superior colliculus, and primary visual cortex, we processed brain sections from seal and sea lion pups for Nissl substance, cytochrome oxidase, and vesicular glutamate transporters. As in other carnivores, the dorsal lateral geniculate nucleus consisted of three main layers, A, A1, and C, while each superior colliculus similarly consisted of seven distinct layers. The sea lion visual cortex is located at the posterior side of cortex between the upper and lower banks of the postlateral sulcus, while the elephant seal visual cortex extends far more anteriorly along the dorsal surface and medial wall. These results are relevant to comparative studies related to the evolution of large brains.

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.

Proprioceptive mechanisms in occlusion-stimulated masseter hypercontraction

Neurons in the trigeminal mesencephalic nucleus (Vme) have an axon that branches peripherally to innervate the orofacial region and projects centrally to the trigeminal motor nucleus (Vmo). They function as the primary neurons conveying proprioceptive messages. The present study aimed to demonstrate the presence of a periodontal-Vme-Vmo circuit and to provide evidence for its involvement in an experimental unilateral anterior crossbite (UAC) model, which can induce osteoarthritis in the temporomandibular joint. Cholera toxin B subunit (CTb) was injected into the inferior alveolar nerve of rats to help identify the central axon terminals of Vme neurons in the Vmo. The levels of vesicular glutamate transporter 1 (VGLUT1) expressed in the periodontal region, Vme, Vmo, and masseter, and the level of acetylcholinesterase (AChE) expressed in the masseter, were assessed in UAC rats and controls. In CTb-treated rats, many CTb-labeled cell bodies and endings were identified in the Vme and in the Vmo, respectively. In UAC rats, VGLUT1 was expressed at a statistically significantly higher level in the periodontal ligament, Vme, Vmo, and masseter than it was in control rats. The level of AChE protein was 1.97 times higher in UAC rat masseter compared with control rat masseter. These findings reveal a trigeminal mechanism underlying masseter hyperactivity induced by an altered occlusion.

Morphological Plasticity of Emerging Purkinje Cells in Response to Exogenous VEGF

Vascular endothelial growth factor (VEGF) is well known as the growth factor with wide-ranging functions even in the central nervous system (CNS). Presently, most attention is given to the investigation of its role in neuronal protection, growth and maturation processes, whereby most effects are mediated through VEGF receptor 2 (VEGFR-2). The purpose of our current study is to provide new insights into the impact of VEGF on immature and mature Purkinje cells (PCs) in accordance with maturity and related receptor expression. Therefore, to expand our knowledge of VEGF effects in PCs development and associated VEGFR-2 expression, we used cultivated organotypic cerebellar slice cultures in immunohistochemical or microinjection studies, followed by confocal laser scanning microscopy (CLSM) and morphometric analysis. Additionally, we incorporated in our study the method of laser microdissection, followed by quantitative polymerase chain reaction (qPCR). For the first time we could show the age-dependent VEGF sensitivity of PCs with the largest promoting effects being on dendritic length and cell soma size in neonatal and juvenile stages. Once mature, PCs were no longer susceptible to VEGF stimulation. Analysis of VEGFR-2 expression revealed its presence in PCs throughout development, which underlined its mediating functions in neuronal cells.

Using the shared genetics of dystonia and ataxia to unravel their pathogenesis

In this review we explore the similarities between spinocerebellar ataxias and dystonias, and suggest potentially shared molecular pathways using a gene co-expression network approach. The spinocerebellar ataxias are a group of neurodegenerative disorders characterized by coordination problems caused mainly by atrophy of the cerebellum. The dystonias are another group of neurological movement disorders linked to basal ganglia dysfunction, although evidence is now pointing to cerebellar involvement as well. Our gene co-expression network approach identified 99 shared genes and showed the involvement of two major pathways: synaptic transmission and neurodevelopment. These pathways overlapped in the two disorders, with a large role for GABAergic signaling in both. The overlapping pathways may provide novel targets for disease therapies. We need to prioritize variants obtained by whole exome sequencing in the genes associated with these pathways in the search for new pathogenic variants, which can than be used to help in the genetic counseling of patients and their families.

Genetic findings in sport-related concussions: potential for individualized medicine?

Concussion is a traumatic transient disturbance of the brain. In sport, the initial time and severity of concussion is known giving an opportunity for subsequent analysis. Variability in susceptibility and recovery between individual athletes depends, among other parameters, on genetic factors. The genes-encoding polypeptides that determine incidence, severity and prognosis for concussion are the primary candidates for genetic analysis. Genetic polymorphisms in the genes contributing to plasticity and repair (APOE), synaptic connectivity (GRIN2A), calcium influx (CACNA1E), uptake and deposit of glutamate (SLC17A7) are potential biomarkers of concussion incidence and recovery rate. With catalogued genetic variants, prospective genotyping of athletes at the beginning of their career will allow medical professionals to improve concussion management and return-to-play decisions.

Mutation of the HERC 1 Ubiquitin Ligase Impairs Associative Learning in the Lateral Amygdala

Tambaleante (tbl/tbl) is a mutant mouse that carries a spontaneous Gly483Glu substitution in the HERC1 (HECT domain and RCC1 domain) E3 ubiquitin ligase protein (HERC1). The tbl/tbl mutant suffers an ataxic syndrome given the almost complete loss of cerebellar Purkinje cells during adult life. More recent analyses have identified alterations at neuromuscular junctions in these mice, as well as in other neurons of the central nervous system, such as motor neurons in the spinal cord, or pyramidal neurons in the hippocampal CA3 region and the neocortex. Accordingly, the effect of the tbl/tbl mutation apparently extends to other regions of the nervous system far from the cerebellum. As HERC1 mutations in humans have been correlated with intellectual impairment, we studied the effect of the tbl/tbl mutation on learning. Using a behavioral test, ex vivo electrophysiological recordings, immunohistochemistry, and Golgi method, we analyzed the associative learning in the lateral amygdala of the tbl/tbl mouse. The tbl/tbl mice perform worse than wild-type animals in the passive avoidance test, and histologically, the tbl/tbl mice have more immature forms of dendritic spines. In addition, LTP cannot be detected in these animals and their STP is dampened, as is their glutamatergic input to the lateral amygdala. Together, these data suggest that HERC1 is probably involved in regulating synaptic function in the amygdala. Indeed, these results indicate that the tbl/tbl mutation is a good model to analyze the effect of alterations to the ubiquitin-proteasome pathway on the synaptic mechanisms involved in learning and its defects.