Edinburgh Napier University

  Two variants of the GABAA receptor γ2 subunit are known to exist, which differ by the presence (γ2L) or absence (γ2S) of eight amino acids in the presumed intracellular loop between the third and fourth membrane-spanning domains. These variants have been shown to be generated by alternative splicing of the γ2-subunit primary gene transcript in mouse (Kofuji et at., J. Neurochem., 56, 713–715, 1991), and in bovine and human (Whiting et al., Proc. Natl. Acad. Sci. USA, 87, 9966–9970, 1990) brain. We describe here the cloning, from chick (Gallus domesticus) brain, of cDNAs that encode the γ2L and γ2S subunits, and report on the regional and cellular localization of the corresponding mRNAs as revealed by in situ hybridization histochemistry with transcript-specific oligonucleotide probes. While the two transcripts are found to be colocalized throughout the chick neuroaxis, certain nuclei (for example, the nucleus isthmi, pars magnocellularis, the nucleus isthmi, pars parvocellularis, the nucleus solitarius and the paleostriatum primitivum) are found to contain predominantly either the γ2S- or the γ2L-subunit mRNA. We conclude that receptors that contain either the γ2S or the γ2L subunit occur, and that these probably have functionally different roles in the modulation of neurotransmission in the central nervous system. In addition, our data indicate that certain cells may produce both transcripts. Consequently, these will have either a single receptor subtype that contains both a γ2S and a γ2L subunit, or two receptor subtypes, one of which contains a γ2S subunit and the other a γ2L subunit.