Neurotransmitter content heterogeneity within an interneuron class shapes inhibitory transmission at a central synapse

Abstract

Neurotransmitter content is deemed the most basic defining criterion for neuronal classes, contrasting with the intercellular heterogeneity of many other molecular and functional features. Here we show, in the adult mouse brain, that neurotransmitter content variegation within a neuronal class is a component of its functional heterogeneity. Golgi cells (GoCs), the well-defined class of cerebellar interneurons inhibiting granule cells (GrCs), contain cytosolic glycine, accumulated by the neuronal transporter GlyT2, and GABA in various proportions. By performing acute manipulations of cytosolic GABA and glycine supply, we find that competition of glycine with GABA reduces the charge of IPSC evoked in GrCs and, more specifically, the amplitude of a slow component of the IPSC decay. We then pair GrCs recordings with optogenetic stimulations of single GoCs, which preserve the intracellular transmitter mixed content. We show that the strength and decay kinetics of GrCs IPSCs, which are entirely mediated by GABAA receptors, are negatively correlated to the presynaptic expression of GlyT2 by GoCs. We isolate a slow spillover component of GrCs inhibition that is also affected by the expression of GlyT2, leading to a 56% decrease in relative charge. Our results support the hypothesis that presynaptic loading of glycine negatively impacts the GABAergic transmission in mixed interneurons, most likely through a competition for vesicular filling. We discuss how the heterogeneity of neurotransmitter supply within mixed interneurons like the GoC class may provide a presynaptic mechanism to tune the gain of microcircuits such as the granular layer, thereby expanding the realm of their possible dynamic behaviors.

Variations on the theme: focus on cerebellum and emotional processing

“…There is no evidence in literature that different GoC subtypes are present in positive and negative stripes, though two clusters have been identified based on the transcriptomic profile ( Kozareva et al, 2021 ). Moreover, a recent study highlighted the functional heterogeneity of GoCs depending on the expression of the human glycine neuronal transporter type 2 (GlyT2), affecting the inhibitory control over GrCs ( Dumontier et al, 2023 ). Additionally, GoCs receive inhibition from nucleo-cortical projections in several lobules ( Ankri et al, 2015 ), decreasing GoC inhibition over GrCs.…”

Coincidence detection between apical and basal dendrites drives STDP in cerebellar Golgi cells

“…Whole-cell patch-clamp recordings were performed on GFP-positive GoCs in acute cerebellar slices obtained from GlyT2-eGFP mice (P16-P21). Fluorescent GoCs, which represent 86% of the entire GoC population, were visually identified 39,51,52 . It should be noted that other glycinergic interneurons of the GL also exhibit GFP-positivity, specifically Lugaro cells and globular cells 37,51 .…”

Revisiting the development of cerebellar inhibitory interneurons in the light of single-cell genetic analyses

“…Specifically, the two Golgi cell clusters identified by Kozareva et al ( 2021 ) align with Golgi cells expressing or devoid of the mGluR2 receptor as defined by Simat et al ( 2007 ). While Golgi neurons are traditionally viewed as an electrophysiologically quite homogeneous group of cells (e.g., Geurts et al 2003 ; Prestori et al 2019 ), the recent observation that they may release, in a regulated manner, GABA and glycine at variable ratios (Dumontier et al 2023 ), added a novel, dynamically tunable degree of variability of these cells. Gene expression data (Kozareva et al 2021 ) further broaden the perspective granted by Simat et al ( 2007 ) and Dumontier et al ( 2023 ) and reveal additional heterogeneity of these cells.…”

“…While Golgi neurons are traditionally viewed as an electrophysiologically quite homogeneous group of cells (e.g., Geurts et al 2003 ; Prestori et al 2019 ), the recent observation that they may release, in a regulated manner, GABA and glycine at variable ratios (Dumontier et al 2023 ), added a novel, dynamically tunable degree of variability of these cells. Gene expression data (Kozareva et al 2021 ) further broaden the perspective granted by Simat et al ( 2007 ) and Dumontier et al ( 2023 ) and reveal additional heterogeneity of these cells. Thus, several of the genes expressed in a differential, if graded fashion more or less along the axis defined by the two Golgi cell clusters mentioned above have been associated with (synaptic) cell adhesion, axonal development, extracellular matrix structure, and/or code for ion channels (e.g., Cntn3, Cntn4, Cntn5, Cntn6, Kirrel3, Efna5, Epha4, Ebf3, Vwc2, Kcnd2).…”