IN-SITU HYBRIDIZATION AND REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION STUDIES ON THE EXPRESSION OF THE GABA(C) RECEPTOR RHO-1-SUBUINT AND RHO-2-SUBUNIT GENES IN AVIAN AND RAT-BRAIN

The pharmacological properties of homo-oligomeric channels formed by t he GABA type A receptor-like p1 and p2 polypeptides are very reminisce nt of those of the GABA type C receptors that have been extensively ch aracterized in the retina. Similar receptors have been reported to occ ur in certain brain regions of a variety of vertebrate species. We hav e used in situ hybridization to investigate the expression patterns of the pi-and p2-polypeptide genes in the brain of the 1-day-old chick ( Gallus domesticus) and the adult rat (Rattus norvegicus). Our results show that in the chick both the p1-and p2-subunit transcripts are pres ent in the cerebellum, the optic tectum, the epithalamus and the nucle us pretectalis. However, the two messenger RNAs are often found in dif ferent populations of cells. Thus, only the pl-subunit gene is express ed in the deep cerebellar nuclei, the dorsal thalamus, the ectostriatu m and the tractus vestibulomesencephalicus, while only the p2-subunit gene is transcribed in the nucleus habenularis lateralis and the nucle us isthmo-opticus. In contrast, neither of the p-polypeptide messenger RNAs can be detected by in situ hybridization in the rat central nerv ous system, Reverse transcription-polymerase chain reaction amplificat ion has been used to confirm the expression of the two p-subunit genes in the chicken brain. Surprisingly, this highly sensitive technique a lso revealed transcription of these genes in the rat brain. We conclud e that the p1-and p2-subunit genes are expressed at a much higher leve l in the avian brain than in the rat brain and that, at least in birds , subtypes of the GABA(C) receptor exist.