Paradoxical network excitation by glutamate release from VGluT3+ GABAergic interneurons

In violation of Dale’s principle several neuronal subtypes utilize more than one classical neurotransmitter. Molecular identification of vesicular glutamate transporter three and cholecystokinin expressing cortical interneurons (CCK+VGluT3+INTs) has prompted speculation of GABA/glutamate corelease from these cells for almost two decades despite a lack of direct evidence. We unequivocally demonstrate CCK+VGluT3+INT-mediated GABA/glutamate cotransmission onto principal cells in adult mice using paired recording and optogenetic approaches. Although under normal conditions, GABAergic inhibition dominates CCK+VGluT3+INT signaling, glutamatergic signaling becomes predominant when glutamate decarboxylase (GAD) function is compromised. CCK+VGluT3+INTs exhibit surprising anatomical diversity comprising subsets of all known dendrite targeting CCK+ interneurons in addition to the expected basket cells, and their extensive circuit innervation profoundly dampens circuit excitability under normal conditions. However, in contexts where the glutamatergic phenotype of CCK+VGluT3+INTs is amplified, they promote paradoxical network hyperexcitability which may be relevant to disorders involving GAD dysfunction such as schizophrenia or vitamin B6 deficiency.

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Excitotoxic Mechanisms of Ischemic Injury in Myelinated White Matter

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/sj.jcbfm.9600455 ◽

2007 ◽

Vol 27 (9) ◽

pp. 1540-1552 ◽

Cited By ~ 84

Author(s):

Selva Baltan Tekkök ◽

ZuCheng Ye ◽

Bruce R Ransom

Keyword(s):

White Matter ◽

High Performance ◽

Glutamate Release ◽

Glutamate Transporter ◽

Ischemic Injury ◽

Glucose Deprivation ◽

Kainate Receptors ◽

Adult Mice ◽

Direct Exposure ◽

Glutamate Receptor Agonist

Axonal injury and dysfunction in white matter (WM) are caused by many neurologic diseases including ischemia. We characterized ischemic injury and the role of glutamate-mediated excitotoxicity in a purely myelinated WM tract, the mouse optic nerve (MON). For the first time, excitotoxic WM injury was directly correlated with glutamate release. Oxygen and glucose deprivation (OGD) caused duration-dependent loss of axon function in optic nerves from young adult mice. Protection of axon function required blockade of both α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and kainate receptors, or removal of extracellular Ca2+. Blockade of N-methyl-D-aspartate receptors did not preserve axon function. Curiously, even extended periods of direct exposure to glutamate or kainate or AMPA failed to induce axon dysfunction. Brief periods of OGD, however, caused glutamate receptor agonist exposure to become toxic, suggesting that ionic disruption enabled excitotoxic injury. Glutamate release, directly measured using quantitative high-performance liquid chromatography, occurred late during a 60-mins period of OGD and was due to reversal of the glutamate transporter. Brief periods of OGD (i.e., 15 mins) did not cause glutamate release and produced minimal injury. These results suggested that toxic glutamate accumulation during OGD followed the initial ionic changes mediating early loss of excitability. The onset of glutamate release was an important threshold event for irreversible ischemic injury. Regional differences appear to exist in the specific glutamate receptors that mediate WM ischemic injury. Therapy for ischemic WM injury must be designed accordingly.

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Disruption of GABA or glutamate release from POMC neurons in the adult mouse does not affect metabolic end points

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00180.2020 ◽

2020 ◽

Vol 319 (5) ◽

pp. R592-R601

Author(s):

Andrew R. Rau ◽

Connie M. King ◽

Shane T. Hentges

Keyword(s):

Amino Acid ◽

Transmitter Release ◽

Adult Mouse ◽

Glutamate Release ◽

Glutamate Transporter ◽

Vesicular Glutamate Transporter ◽

Metabolic Phenotypes ◽

Adult Mice ◽

Physiological Processes

Proopiomelanocortin (POMC) neurons contribute to the regulation of many physiological processes; the majority of which have been attributed to the release of peptides produced from the POMC prohormone such as α-MSH, which plays key roles in food intake and metabolism. However, it is now clear that POMC neurons also release amino acid transmitters that likely contribute to the overall function of POMC cells. Recent work indicates that constitutive deletion of these transmitters can affect metabolic phenotypes, but also that the expression of GABAergic or glutamatergic markers changes throughout development. The goal of the present study was to determine whether the release of glutamate or GABA from POMC neurons in the adult mouse contributes notably to energy balance regulation. Disturbed release of glutamate or GABA specifically from POMC neurons in adult mice was achieved using a tamoxifen-inducible Cre construct ( Pomc-CreERT2) expressed in mice also carrying floxed versions of Slc17a6 (vGlut2) or Gad1 and Gad2, encoding the vesicular glutamate transporter type 2 and GAD67 and GAD65 proteins, respectively. All mice in the experiments received tamoxifen injections, but control mice lacked the tamoxifen-inducible Cre sequence. Body weight was unchanged in Gad1- and Gad2- or vGlut2-deleted female and male mice. Additionally, no significant differences in glucose tolerance or refeeding after an overnight fast were observed. These data collectively suggest that the release of GABA or glutamate from POMC neurons in adult mice does not significantly contribute to the metabolic parameters tested here. In light of prior work, the data also suggest that amino acid transmitter release from POMC cells may contribute to separate functions in the adult versus the developing mouse.

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Faculty Opinions recommendation of Increased expression of the Drosophila vesicular glutamate transporter leads to excess glutamate release and a compensatory decrease in quantal content.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1022585.258639 ◽

2004 ◽

Author(s):

Nils Brose

Keyword(s):

Glutamate Release ◽

Glutamate Transporter ◽

Quantal Content ◽

Vesicular Glutamate Transporter

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Vitamin B6 deficiency disrupts serotonin signaling in pancreatic islets and induces gestational diabetes in mice

Communications Biology ◽

10.1038/s42003-021-01900-0 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Ashley M. Fields ◽

Kevin Welle ◽

Elaine S. Ho ◽

Clementina Mesaros ◽

Martha Susiarjo

Keyword(s):

Cell Proliferation ◽

Insulin Secretion ◽

Pancreatic Islets ◽

Glucose Intolerance ◽

Vitamin B6 ◽

Serotonin Receptor ◽

Dependent Manner ◽

Β Cell ◽

Vitamin B6 Deficiency ◽

Maternal Glucose

AbstractIn pancreatic islets, catabolism of tryptophan into serotonin and serotonin receptor 2B (HTR2B) activation is crucial for β-cell proliferation and maternal glucose regulation during pregnancy. Factors that reduce serotonin synthesis and perturb HTR2B signaling are associated with decreased β-cell number, impaired insulin secretion, and gestational glucose intolerance in mice. Albeit the tryptophan-serotonin pathway is dependent on vitamin B6 bioavailability, how vitamin B6 deficiency impacts β-cell proliferation during pregnancy has not been investigated. In this study, we created a vitamin B6 deficient mouse model and investigated how gestational deficiency influences maternal glucose tolerance. Our studies show that gestational vitamin B6 deficiency decreases serotonin levels in maternal pancreatic islets and reduces β-cell proliferation in an HTR2B-dependent manner. These changes were associated with glucose intolerance and insulin resistance, however insulin secretion remained intact. Our findings suggest that vitamin B6 deficiency-induced gestational glucose intolerance involves additional mechanisms that are complex and insulin independent.

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