The GABA A receptor complex in the chicken brain: immunocytochemical distribution of α1- and γ2-subunits and autoradiographic distribution of BZ1 and BZ2 binding sites

Abstract

Two antibodies, raised against the rat GABA A receptor α1- and γ2-subunits, were used for an immunocytochemical study of the distribution of these proteins in the chicken brain. The immunoreactive bands obtained by Western blotting and the similar labelling distribution found in the rat and chicken brain support the suitability of these antibodies for the labelling of GABA A receptors in birds. We found abundant α1 and γ2 immunoreactivity throughout the chicken brain, mainly in the paleostriata and lobus paraolfactorius, dorsal thalamus and some nuclei of the brainstem. The α1-subunit was more abundant in the telencephalon, thalamus and cerebellum, while the presence of the γ2-subunit was stronger in the optic tectum and brainstem. We also report the autoradiographic distribution of the BZ1 and BZ2 benzodiazepine receptor subtypes in the chicken brain using [ 3H]flunitrazepam. Benzodiazepine binding was unevenly distributed throughout the chicken brain, and the anatomical distribution of the BZ1 and BZ2 subtypes was similar to that described in mammals. The highest binding values were found in the olfactory bulb, paleostriatum primitivum, optic tectum, nucleus mesencephalicus lateralis pars dorsalis and nucleus isthmi pars parvocellularis, the BZ2 subtype being predominant in the paleostriatum primitivum and optic tectum. A general agreement in the distribution of BZ1 and α1 immunoreactivity was observed in structures such as the olfactory bulb, paleostriata, lobus parolfactorius and dorsal thalamus, although some discrepancies were observed in areas such as the optic tectum or nucleus isthmi pars parvocellularis, with high BZ1 binding and low or no α1 immunolabelling.