Distinct patterns of expression and regulation of GABA_A receptors containing the δ subunit in cerebellar granule and hippocampal neurons

Abstract

Neuronal plasticity is achieved by regulation of the expression of genes for neurotransmitter receptors such as the type A receptor (GABA A R) for c-aminobutyric acid. We now show that two different rat neuronal populations in culture manifest distinct patterns of GABA A R plasticity in response to identical stimuli. Whereas prolonged exposure to ethanol had no effect on expression of the d subunit of GABA A Rs at the mRNA or protein level in cerebellar granule neurons, it increased the abundance of d subunit mRNA and protein in hippocampal neurons. Subsequent ethanol withdrawal transiently downregulated d subunit expression in cerebellar granule neurons and gradually normalized that in hippocampal neurons. These effects of ethanol exposure and withdrawal were accompanied by corresponding functional changes in GABA A Rs. GA-BA A Rs containing the d subunit were also distributed differentially in the cerebellar and hippocampal neurons. Type A receptors for c-aminobutyric acid (GABA A Rs) in mammalian neurons differ in subunit composition and function as well as manifest differential sensitivity to the natural agonist (GABA) and to various drugs and endogenous modulators (Sieghart 1995;Barnard et al. 1998;Hevers and Luddens 1998;Sieghart and Sperk 2002). The expression of distinct GABA A R subunit genes is developmentally regulated (Laurie et al. 1992a). Furthermore, whereas specific neuronal populations as well as glial cells in certain brain regions express only select GABA A R subunits (Wisden et al. 1989;Bovolin et al. 1992;Laurie et al. 1992b), other brain areas express most of the identified receptor subunits (Laurie et al. 1992a,b;Wisden et al. 1992;Pirker et al. 2000). The molecular mechanisms responsible for regulation of both the expression of the genes for the various GABA A R subunits and the assembly of specific subunit combinations to form functional receptors remain unclear (Moss and Smart 2001; Bollan et al. 2003a,b).The pattern of GABA A R gene expression is affected by environmental stimuli, physiological processes, and drugs that modulate GABA A R-mediated neurotransmission (Fenelon and Herbison 1996;Holt et al. 1996;Concas et al. 1998;Smith et al. 1998;Follesa et al. 2001;Cagetti et al. 2003;Follesa et al. 2003;Sanna et al. 2003). However, whether such induced changes in gene expression for a given GABA A R subunit are identical among different neuronal populations that express that subunit in a specific brain area is not known.Recent evidence that transient activation of synaptic GABA A Rs is responsible for conventional phasic inhibition, whereas continuous activation of extrasynaptic GABA A Rs generates a form of tonic inhibition (Brickley et al. 1996;Mody 2001;Hamann et al. 2002;Nusser and Mody 2002; Received February 14, 2005; revised

Regulation of GABAAReceptor Subunit Expression by Pharmacological Agents

“…In cultured rat hippocampal neurons, CE strongly up-regulated ␦ mRNA and polypeptide expression (Follesa et al, 2005). The ␦ mRNA and polypeptide levels elevated by CE in hippocampal neurons returned to control levels by 12 h (Follesa et al, 2005). The results suggest brain region-specific down-regulation of ␦ subunit.…”

“…In cultured rat CGCs, CE had no effect on ␦ mRNA and polypeptide expression, whereas wdr-CE slightly down-regulated both ␦ mRNA and polypeptide (Follesa et al, 2005;Biggio et al, 2007). In cultured rat hippocampal neurons, CE strongly up-regulated ␦ mRNA and polypeptide expression (Follesa et al, 2005). The ␦ mRNA and polypeptide levels elevated by CE in hippocampal neurons returned to control levels by 12 h (Follesa et al, 2005).…”

“…After wdr-CE (Marutha Ravindran et al, 2007b) or wdr-CIE (Petrie et al, 2001), the expression of cerebellar and hippocampal ␦ mRNA and polypeptide did not differ from the expression in control animals, whereas a down-regulation of hippocampal ␦ polypeptide after wdr-CIE was detected . In cultured rat CGCs, CE had no effect on ␦ mRNA and polypeptide expression, whereas wdr-CE slightly down-regulated both ␦ mRNA and polypeptide (Follesa et al, 2005;Biggio et al, 2007). In cultured rat hippocampal neurons, CE strongly up-regulated ␦ mRNA and polypeptide expression (Follesa et al, 2005).…”

Neurosteroids, GABAA receptors, and ethanol dependence

“…The number of arrows indicates: one, from 20 to 30%; two, from 30 to 50%; three, more than 50%. Data for α 3 and α 5 subunit mRNAs in cerebellar granule cells are original; all other data are published (Follesa et al , 2004(Follesa et al , 2005Sanna et al 2003) ethanol withdrawal also induced up-regulation of α 4 subunit expression (Table 1). Chronic treatment of rats with ethanol was found to increase GABA A R α 4 subunit gene expression in both the cerebral cortex and hippocampus Devaud et al 1995Devaud et al , 1997Mahmoudi et al 1997;Matthews et al 1998).…”

Changes in Expression and Function of Extrasynaptic GABAAReceptors in the Rat Hippocampus during Pregnancy and after Delivery

“…Immunoblot analysis of a crude membrane fraction of the rat hippocampus with these antibodies yielded a single immunoreactive band at a position corresponding to a molecular size of ϳ54 kDa (Follesa et al, 2005). The specificity of the antibody preparation was also confirmed by immunocytochemical analysis (Follesa et al, 2005;Serra et al, 2006). The antibodies to the ␣ 4 subunit were generated in response to a peptide corresponding to the N-terminal region of the rat protein.…”