Edinburgh Napier University

  cDNAs have been cloned that encode the chicken (Gallus domesticus) γ-aminobutyric acidA receptor γ1 subunit, the mature sequence of which shares 90, 79, and 69% identity with those of the rat γ1, γ2., and γ3 subunits, respectively. In situ hybridization reveals that there are pronounced differences in the regional and cellular localizations of the corresponding γ-aminobutyric acidAreceptor γ-subunit mRNA compared with that of the γ2-subunit mRNA in 1 -day-old chick brain. The absence of the γ1-subunit transcript in certain chick brain nuclei of visual and auditory pathways, in which γ 2-subunit mRNA is present, points to differences in the functional roles of receptors containing one or other of these polypeptides. Certain cells in other brain regions appear to contain both γ1 - and γ2-subunit mRNAs, suggesting that they either have two γ-aminobutyric acidA receptor subtypes or possess receptors incorporating two different γ subunits. We have also found contrasts in the distribution patterns, in homologous brain regions, of the chicken γ1-subunit mRNA and the rat γ1-subunit mRNA. These data may reflect different functional roles of the chicken and rat γ1subunits.