γ‐Aminobutyric acid‐ρ expression in ependymal glial cells of the mouse cerebellum

Abstract

The ependymal glial cells (EGCs) from the periventricular zone of the cerebellum were studied to determine their distribution and the functional properties of their γ-aminobutyric acid type A (GABA(A) ) receptors. EGCs were identified by the presence of ciliated structures on their ventricular surface and their expression of glial fibrillary acidic protein (GFAP). Interestingly, diverse cell types, including neurons, astrocytes, and other types of glia, were identified in the subventricular zone by their current profiles. Electron microscopy showed ciliated cells and myelinated axons in this zone, but we found no collateral connections to suggest the presence of functional synapses. GABA-mediated currents were recorded from EGCs in cerebellar slices from postnatal days 13 to 35 (PN13-PN35). These currents were blocked by TPMPA (a highly specific GABA(A) ρ subunit antagonist) and bicuculline (a selective antagonist for classic GABA(A) receptors). Pentobarbital failed to modulate GABA(A)-mediated currents despite the expression of GABAα1 and GABAγ2 subunits. In situ hybridization, RT-PCR, and immunofluorescence studies confirmed GABAρ1 expression in EGCs of the cerebellum. We conclude that cerebellar EGCs express GABAρ1, which is functionally involved in GABA(A) receptor-mediated responses that are unique among glial cells of the brain.

Identification of novel cellular clusters define a specialized area in the cerebellar periventricular zone

“…It has been shown previously that the subventricular zone of the cerebellum exhibits a diversity of cells that display different electrophysiological characteristics1. Whole-cell patch-clamp revealed that electric responses obtained from the subventricular zone of the cerebellum, which corresponds to lobes I and X, include neurons, astrocytes, oligodendrocytes and stem-cell like cells1.…”

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

“…These cells generate GABA currents on exogenous administration of GABA owing to the presence of an array of GABA-A subunits that include GABAρ. GABA responses are partially blocked by TPMPA or bicuculline and totally abolished by a combination of the two compounds (10). Here we present evidence that during postnatal development of the cerebellum, GABAρ subunits are widely expressed in EGCs and even in GFAP + cells of the GL and subventricular zone.…”

“…Expression of GABAα1 is crucial for proper GABAergic neurotransmission in the cerebellum (24), and this subunit is known to be present mainly in the adult neurons with scattered expression in GFAP + cells (10). At P5 and P10, immunolabeling for GABAα1 was present mainly in non-GFAP + cells, although Bergmann glial processes in the close vicinity of Purkinje cells exhibited limited immunolabeling at P5 (Fig.…”

“…In cerebellar astrocytes, the array of GABA-A subunits is heterogeneous, and modulation by benzodiazepines is different from that by neurons (8). Indeed, GABA responses of Bergmann cells and ependymal glial cells (EGCs) are insensitive to benzodiazepines or pentobarbital, owing to the assembly of receptors that include GABAδ or GABAρ subunits (9,10).…”

“…The role of GABAρ in neuronal tonic (extrasynaptic) and phasic (synaptic) transmission has been demonstrated in the Purkinje neurons of the cerebellum (20); however, GABAρ subunits are also expressed in a large fraction of EGCs, specialized, ciliated GFAP + cells that permit the flow of cerebrospinal fluid circulating in the fourth ventricle (10,21). GABAionic currents in these cells are insensitive to pentobarbital and partially blocked by the GABA-A antagonist bicucculline as well as by (1,2,5,6-Tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA), the first synthesized GABAρ antagonist (22).…”