Identification of γ1 subunit of GABAA receptor in rat testis

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Abstract
The isoform type of g subunits of GABAA receptor is a molecular determinant of its pharmacological characteristics. At present, the existence of GABAA 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 g subunits of GABAA receptor in rat testis. Only one 370 bp fragment was obtained from RT-PCR in rat testis and sequencing results showed that it represented g1 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 GABAA receptor is exclusively expressed in rat testis and this feature may be the structural basis of the specific function of GABAA receptors in sperm acrosome reaction.