PHENOTYPIC AND GENOTYPIC ANALYSIS OF RATS WITH CEREBELLAR GABA(A) RECEPTORS COMPOSED FROM MUTANT AND WILD-TYPE ALPHA-6 SUBUNITS

The alcohol-sensitive (ANT) rat line, developed for high behavioral se nsitivity to ethanol, also exhibits enhanced sensitivity to benzodiaze pines, such as diazepam, The rat line carries a point mutation in the cerebellum-specific gamma-aminobutyric acid type A (GABA(A)) receptor subunit alpha 6, making their diazepam-insensitive (DIS) receptors sen sitive to diazepam. We now report that phenotypes of individual ANT an d alcohol-insensitive rats, classified on diazepam sensitivity of cere bellar [H-3]Ro 15-4513 binding, correlated well with homozygous wildty pe, homozygous mutant, and heterozygous genotypes, although some heter ozygotes were biased toward the parental phenotypes. GABA down-modulat ed DIS [H-3]Ro 15-4513 binding in mutant homozygotes but tended to up- modulate it in heterozygotes and wild-type homozygotes, Slopes for GAB A inhibition of cerebellar t-butyl-bicyclophosphoro [S-35]thionate bin ding were larger in mutant than in wild-type homozygotes, with heteroz ygotes being intermediate. Diazepam displacement of [H-3] Ro 15-4513 b inding in heterozygotes revealed three components, with their affiniti es indistinguishable from those in combined wild-type and mutant homoz ygotes. This lack of interaction in DIS binding between wild-type and mutant alpha 6 subunits was substantiated by experiments on recombinan t receptors. The data suggest that the alpha 6 subunit-containing GABA (A) receptors in the heterozygotes are formed from individual mutant a nd wild-type subunits with their relative expression differing from an imal to animal.