GABAρ subunits confer a bicuculline-insensitive component to GFAP ⁺ cells of cerebellum

Abstract

GABA-A receptors mediating synaptic or extrasynaptic transmission are molecularly and functionally distinct, and glial cells are known to express a plethora of GABA-A subunits. Here we demonstrate that GFAP + cells of the granular layer of cerebellum express GABAρ subunits during early postnatal development, thereby conferring peculiar pharmacologic characteristics to GABA responses. Electron microscopy revealed the presence of GABAρ in the plasma membrane of GFAP + cells. In contrast, expression in the adult was restricted to Purkinje neurons and a subset of ependymal cells. Electrophysiological studies in vitro revealed that astrocytes express functional receptors with an EC 50 of 52.2 ± 11.8 μM for GABA. The evoked currents were inhibited by bicuculline (100 μM) and TPMPA (IC 50 , 5.9 ± 0.6 μM), indicating the presence of a GABAρ component. Coimmunoprecipitation demonstrated protein-protein interactions between GABAρ1 and GABAα1, and double immunofluorescence showed that these subunits colocalize in the plasma membrane. Three populations of GABA-A receptors in astrocytes were identified: classic GABA-A, bicuculline-insensitive GABAρ, and GABA-A-GABAρ hybrids. Clusters of GABA-A receptors were distributed in the perinuclear space and along the processes of GFAP + cells. Time-lapse microscopy showed GABAρ2-GFP accumulation in clusters located in the soma and along the processes. The clusters were relatively immobile, with mean displacement of 9.4 ± 0.9 μm and a net distance traveled of 1-2 μm, owing mainly to directional movement or simple diffusion. Modulation of GABAρ dynamics may be a novel mechanism of extrasynaptic transmission regulating GABAergic control of GFAP + cells during early postnatal development.astrocytes | cerebellum | GABA-A receptor | GABAρ receptor | protein trafficking

GABAA receptors are selectively expressed in NG2 glia of the cerebellar white matter

“…The lack of muscimol response in astrocytes was surprising considering that functional expression of GABAARs was demonstrated in Bergmann glia at P5-P7 and GABAAmediated signaling at P20-P30 was drastically reduced or undetectable (Müller et al, 1994), suggesting that while GABAA signaling is important through early postnatal development of the cerebellum, there is an apparently different regulation for WM. In support of this hypothesis, functional expression of GABAARs was also reported in ependymal glial cells from the cerebellum located at the roof of the fourth ventricle (Reyes-Haro et al, 2013a), while immunofluorescence studies revealed the expression of the GABAAρ1 subunit in astrocytes from the granular layer of the cerebellar lobule X (Pétriz, et al, 2014). Astrocytes from WM give rise to interneurons of the molecular layer during the postnatal development of the cerebellum (Silbereis et al, 2009).…”

“…Classically, the astrocyte-like precursor cells are responsive to GABA in multiple brain regions, such as the hippocampus (Seri et al, 2001, Ge et al, 2006 and sub-ventricular zones (Bolteus andBordey, 2004, Liu et al, 2005). Functional expression of GABAARs has been demonstrated in diverse glial cells from the cerebellum, for example in Bergmann's glia (Müller et at., 1994), in ependymal cells from the periventricular zone (Reyes-Haro et al, 2013) and in primary cultures of cerebellar astrocytes (Pétriz et al, 2014). Moreover, the functional expression of GABAARs in NG2 glial cells from cerebellar WM was also reported (Zonouzi et al, 2015).…”

Gene‐based interaction analysis shows GABAergic genes interacting with parenting in adolescent depressive symptoms

“…Parental support interacted with two GABA‐related genes (gamma‐aminobutyric acid): GABRR1 and GABRR2 (both genes coding for subunits of the GABA A ‐rho receptor, formerly known as GABA C ‐receptor (Enz, ; D. Zhang, Pan, Awobuluyi, & Lipton, )). It is well‐known that both GABA A and GABA A ‐rho receptors are ionotropic receptors, but the exact mechanism of different subunits involved in the GABA A ‐rho receptor function in the central nervous system remains unclear (Olsen & Sieghart, ; Pétriz, Reyes‐Haro, González‐González, Miledi, & Martínez‐Torres, ; Yoon & Lee, ).…”

GABA‐ρ receptors: distinctive functions and molecular pharmacology

“…However, GABA‐ρ receptors express as homomeric ion channels, and some studies suggest pseudoheteromeric channels consisting of different ρ subunits (Connolly et al, ). There is some limited in vitro evidence to support co‐assembly of ρ subunits with other GABA A subunits, particularly with α1 and γ2 (Milligan et al, ; Pétriz et al, ), and also with glycine receptor α1 and α2 subunits (Pan et al, ).…”

“…The presence of GABA ρ1 and ρ2 subunits, either homomerically or combined with other GABA A (α1 and γ2) subunits, has also been identified in cultured cerebellar astrocytes. It is proposed that these GABA‐ρ subunits may contribute to the regulation of glial development in the cerebellum (Pétriz et al, ). Although GABA‐ρ receptors are mainly expressed in the CNS, they are also found in the peripheral nervous system, for example, in the gastrointestinal tract (Jansen et al, ), and sperm cells (Li et al, ).…”