SEQUENCE AND NOVEL DISTRIBUTION OF THE CHICKEN HOMOLOG OF THE MAMMALIAN GAMMA-AMINOBUTYRIC ACID(A) RECEPTOR-GAMMA-1 SUBUNIT

cDNAs have been cloned that encode the chicken (Gallus domesticus) gam ma-aminobutyric acid(A) receptor gamma1 subunit, the mature sequence o f which shares 90, 79, and 69% identity with those of the rat gamma1, gamma2, and gamma3 subunits, respectively. In situ hybridization revea ls that there are pronounced differences in the regional and cellular localizations of the corresponding gamma-aminobutyric acid, receptor g amma-subunit mRNA compared with that of the gamma2-subunit mRNA in 1-d ay-old chick brain. The absence of the gamma1-subunit transcript in ce rtain chick brain nuclei of visual and auditory pathways, in which gam ma2-subunit mRNA is present, points to differences in the functional r oles of receptors containing one or other of these polypeptides. Certa in cells in other brain regions appear to contain both gamma1- and gam ma2-subunit mRNAs, suggesting that they either have two gamma-aminobut yric acid(A) receptor subtypes or possess receptors incorporating two different gamma subunits. We have also found contrasts in the distribu tion patterns, in homologous brain regions, of the chicken gamma1-subu nit mRNA and the rat gamma1-subunit mRNA. These data may reflect diffe rent functional roles of the chicken and rat gamma1 subunits.