Identification of γ₁ subunit of GABA_A receptor in rat testis

The isoform type of γ 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 γ (γ₁, γ₂ and γ₃) subunits cloned in rat brain, we performed reverse transcription polymerase chain reaction (RT-PCR) to examine the expression pattern of γ 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 γ₁ subunit, but not γ₂ or γ₃ subunit. Using the cloned fragment as probe, a 3.8 kb transcript which in size as same as γ₁ subunit in rat brain was detected in rat testis mRNA by performing Northern blot assay. Furthermore, results of in situ hybridization assay confirmed that γ₁ subunit was expressed in round spermatids and spermatozoa, maybe also in secondary spermatocyte. These evidences proved that γ₁ 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.