We have isolated a cDNA, from the chicken, that encodes a fourth type of γ subunit of the vertebrate brain GABAA receptor. The mature polypeptide (which we name γ4) displays 67%, 69% and 70% identity, respectively, to the rat γ1, γ2 and γ3 subunits. In the developing chicken brain, the γ4-subunit mRNA is first detected at embryonic day 13; the transcript level then increases progressively during embryogenesis. In situ hybridization reveals that the γ4-subunit mRNA is abundant in several brain regions, including the ectostriatum, nucleus rotundus and hyperstriatum ventrale, which are involved in visual processing and learning.
