Identification of γ1 subunit of GABAA receptor in rat testis

The isoform type of gamma subunits of GABA(A) receptor is a molecular determinant of its pharmacological characteristics. At present, the existence of GABA(A) receptor in mammalian sperm is still a controversy. By using degenerate primers designed according to highly conserved region in all three gamma (gamma(1), gamma(2) and gamma(3)) subunits cloned in rat brain, we performed reverse transcription polymerase chain reaction (RT-PCR) to examine the expression pattern of gamma subunits of GABA(A) receptor in rat testis. Only one 370 bp fragment was obtained from RT-PCR in rat testis and sequencing results showed that it represented gamma(1) subunit, but not gamma(2) or gamma(3) subunit. Using the cloned fragment as probe, a 3.8 kb transcript which in size as same as gamma(1) subunit in rat brain was detected in rat testis mRNA by performing Northern blot assay. Furthermore, results of in situ hybridization assay confirmed that gamma(1) subunit was expressed in round spermatids and spermatozoa, maybe also in secondary spermatocyte. These evidences proved that gamma(1) subunit of GABA(A) receptor is exclusively expressed in rat testis and this feature may be the structural basis of the specific function of GABA(A) receptors in sperm acrosome reaction.