Differential expression of GABA_A/benzodiazepine receptor β₁, β₂, and β₃ subunit mRNAs in the developing mouse cerebellum

Abstract

Gamma aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian cerebellum. Cerebellar granule, Purkinje, and deep nuclear neurons are known to receive GABAergic afferents. Since GABA exerts its inhibitory effects via GABA receptors, it is of interest to determine the temporal relationship between the formation of GABAergic synapses and the expression of genes coding for the GABA receptor. In a previous study, we have examined the developmental expression of binding sites for [3H]muscimol, which binds with high affinity to the beta subunits of the GABAA/benzodiazepine (GABAA/BZ) receptor. In the present study, [35S]cRNA probes were used to examine the appearance and distribution of GABAA/BZ beta 1, beta 2, and beta 3 subunit mRNAs in the developing C57BL/6 mouse cerebellum by in situ hybridization. In the adult cerebellum, the distribution of the three subunit mRNAs was clearly different, despite considerable overlap, and their temporal expression differed throughout postnatal development. The beta 1 hybridization signal appeared within the cerebellar cortex during the second postnatal week as a discrete band at the interface of the molecular and granule cell layers. Grains were distributed diffusely over small densely staining cells surrounding the Purkinje cells; relatively few grains were visible over Purkinje cell bodies themselves. This distribution may reflect an association with Bergmann glia or basket cells. The beta 2 and beta 3 hybridization signals were present considerably earlier than that of the beta 1 mRNA. The beta 2 signal was present at birth in the molecular/Purkinje cell layer; as development progressed, the signal became increasingly intense over both granule and Purkinje cells. At birth, the beta 3 subunit mRNA was present in the external germinal and molecular layers, later becoming largely localized within the granule cell layer. Dense beta 2 and beta 3 cRNA probe labeling was present over the adult granule cell layer. Moderate levels of beta 2 signal were seen over Purkinje cell bodies; considerably less labeling was observed with the beta 3 probe. The adult distribution of beta 2 and beta 3 cRNA probes showed good spatial correspondence with the known GABAA receptor beta subunit markers, [3H]-muscimol and the mAb 62-3G1 antibody, each being present within the granule cell layer. Our results indicate that the temporal expression of GABAA/BZ receptor beta subunit messages within a given cell type may be independently regulated, and that acquisition of the beta 2 and beta 3 mRNAs occurs before these cells become integrated into mature synaptic circuits.

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

“…The developmental pattern of GABAρ subunit localization partially agrees with earlier reports suggesting expression of GABAρ1 and GABAρ2 at low levels in rat Purkinje and Golgi neurons during early postnatal development (30,31). Previous studies have unequivocally demonstrated the presence of other GABA-A subunits (α x β x γ x ) in immature neurons of the cerebellum, and the expression of this receptor is a fundamental element in proper formation of the synaptic circuitry (32)(33)(34). Glial cells are also part of the tripartite synapse, and GABA-A subunits have been identified in Bergmann glia (α 2 γ 1 δ) and EGCs (α 1 ρ 1 ) (9, 10, 35), where they might play a key role as extrasynaptic sensors of GABAergic tone, similar to what occurs in astrocyte-like GFAP + progenitors (36).…”

Novel receptor protein tyrosine phosphatase (RPTP?) and acidic fibroblast growth factor (FGF-1) transcripts delineate a rostrocaudal boundary in the granule cell layer of the murine cerebellar cortex

“…at 260 nm Ϸ 33 µg/ml). The purified oligonucleotides were 3Ј end labeled with [ 35 S] ␣-dATP (Amersham) as described previously (Zdilar et al, 1992). Specific activity of the oligonucleotide probes was approximately 0.8-1.2 ϫ 10 9 dpm/µg.…”

Prenatal Exposure to the Pesticide Dieldrin or the GABA_A Receptor Antagonist Bicuculline Differentially Alters Expression of GABA_A Receptor Subunit mRNAs in Fetal Rat Brainstem

“…GABA A receptors develop in approximate spatiotemporal synchrony with GABAergic pathways in the embryonic rat brain [Cobas et al, 1991;Schlumpf et al, 1989;. Transient patterns of GABA A receptor subunit expression have been found in developing rat and primate brain [Gambarana et al, 1991;MacLennan et al, 1991;Frostholm et al, 1992;Laurie et al, 1992a;Poulter et al, 1992;Zdilar et al, 1992;Ma et al, 1993;Fritschy et al, 1994;Chang et al, 1995;Ma and Barker, 1995;Hornung and Fritschy, 1996]. Coordinate development of GABAergic pathways and GABA A receptors has led to speculation that GABA may regulate (modulate) expression of its own receptors [Schousboe and Redburn, 1995].…”