Immunogold characteristics of VGLUT3‐positive GABAergic nerve terminals suggest corelease of glutamate

Abstract

There is compelling evidence that glutamate can act as a cotransmitter in the mammalian brain. Interestingly, the third vesicular glutamate transporter (VGLUT3) is primarily found in neurons that were anticipated to be nonglutamatergic. Whereas the function of VGLUT3 in acetylcholinergic and serotoninergic neurons has been elucidated, the role of VGLUT3 in neurons releasing gamma-aminobutyric acid (GABA) is not settled. We have previously shown that VGLUT3 is found together with the vesicular GABA transporter (VIAAT) on synaptic vesicle membranes in the hippocampus. Now we provide novel electron microscopic data from the rat hippocampus suggesting that glutamate is enriched in inhibitory nerve terminals containing VGLUT3 compared to those lacking VGLUT3. The opposite was found for GABA; VGLUT3-positive inhibitory terminals contained lower density of GABA labeling compared to VGLUT3-negative inhibitory terminals. In addition, semiquantitative confocal immunofluorescence showed that N-methyl-D-aspartate (NMDA)-receptor labeling was present more frequently in VGLUT3-positive/VIAAT-positive synapses versus in VGLUT3-negative/VIAAT-positive synapses. Electron microscopic immunogold data further suggest that NMDA receptors are enriched in VGLUT3 containing inhibitory terminals. Our data reveal new chemical characteristics of a subset of GABAergic interneurons in the hippocampus. The analyses suggest that glutamate is coreleased with GABA from hippocampal basket cell-synapses to act on NMDA receptors.

Vesicular Glutamate Release from Feeder-FreehiPSC-Derived Neurons

“…Expression of the genes for subunits of voltage-dependent Ca 2+ channels is consistent with the presence of the Ca 2+ channels allowing depolarization-evoked Ca 2+ entry and coupling to activation of vesicle fusion. Notably, the expression of V-Glut3 (present also in non-glutamatergic neurons; [96][97][98][99]) may indicate the ability of this protocol to differentiate hiPSCs into neurons co-releasing glutamate and other neurotransmitters such as acetylcholine, GABA, or serotonin; this may be subject to future research. The new methodological approach to achieve feeder-free neuronal differentiation from hiPSCs, avoiding inter-species contamination, may therefore represent a step-ahead not only in experimental neuroscience but also in neurotoxicology and neurodevelopmental toxicology as a platform for mechanistic assessment of excitotoxicity/neurotoxicity or for drug discovery [82][83][84][85].…”

Glutamate Cotransmission in Cholinergic, GABAergic and Monoamine Systems: Contrasts and Commonalities

“…A subset of GABAergic terminals co-labeled with VGLUT3 has also been reported in the intermediolateral cell column of the spinal cord (Stornetta et al, 2005). In the terminals of hippocampal GABA neurons, ultrastructural and biochemical evidence for the presence of VGLUT3 on vesicles containing VIAAT has been provided (Stensrud et al, 2013, 2015). Indeed, VGLUT3 seems to be expressed by VIAAT-positive SVs and furthermore these SVs are able to accumulate [ 3 H]glutamate (Fasano et al, 2017).…”

Genes Involved in the Development and Physiology of Both the Peripheral and Central Auditory Systems

“…VGLUT3 mutations lead to an autosomal dominant form of progressive deafness (DFNA25) (Ruel et al 2008) and Vglut3 inactivation in mice causes profound deafness (Seal et al 2008). Vglut3 is found in several discrete populations across the brain (Herzog et al 2004) and its encoding gene is expressed in several types of inhibitory neurons that co-release glutamate (Stensrud et al 2015). In the auditory system, it is expressed by inhibitory glycinergic MNTB neurons, which receive glutamatergic inputs from CN spherical bushy cells of the contralateral ear and project to LSO principal neurons.…”