The γ subunit of the γ-aminobutyric acid type A receptor (GABA(A)-R) is essential for bestowing both normal single channel conductance and sensitivity to benzodiazepines on native GABA(A)-Rs. The long splice variant of the γ2 subunit (γ2L) has been postulated to be essential in mediating the modulatory actions of ethanol at the GABA(A)-R. In order to evaluate this hypothesis, gene targeting was used to delete the 24bp exon which distinguishes γ2L from the short splice variant (γ2S). Mice homozygous for this exon deletion (γ2L(-/-)) are viable and indistinguishable from wild-type (γ2L(+/+)) mice. No γ2L mRNA was detected in these mice, nor could γ2L-containing GABA(A)-R protein be detected by specific antibodies. Radioligand binding studies showed the total amount of γ2 subunit protein to be not significantly changed, suggesting that γ2S replaces γ2L in the brains of the knockout animals. Electrophysiological recordings from dorsal root ganglion neurons revealed a normal complement of functional receptors. There was no difference in the potentiation of GABA currents by ethanol (20-200 mM) observed in neurons from γ2L(+/+) or γ2L (-/-) mice. Several behavioral effects of ethanol, such as sleep time, anxiolysis, acute functional tolerance, chronic withdrawal hyperexcitability and hyperlocomotor activity were also unaffected by genotype. It is concluded that γ2L is not required for ethanol's modulatory action at the GABA(A)-R or whole animal behavioral effects.
- Gene knockout
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience