Activation of A-type γ-amino butyric acid receptors excites gonadotrophin-releasing hormone neurones isolated from adult rats

Gonadotrophin-releasing hormone (GnRH) neurones represent the final output neurones in the neuroendocrine control of reproduction, and gamma-amino butyric acid (GABA) is one of the major players in the regulation of GnRH neurones. GABA inhibits a large proportion of brain neurones in adult animals by acting on A-type GABA receptors (GABA(A)Rs). Two contradictory reports on the action of GABA in the GnRH neurones of adult mice have been published. DeFazio et al. (Mol Endocrinol 2002; 16: 2872) demonstrated that activation of GABA(A)Rs excites the GnRH neurones of adult mice, whereas Han et al. (Endocrinology 2002; 143: 1459) showed that the response to GABA on GnRH neurones switches from depolarisation to hyperpolarisation around puberty in female mice. Therefore, we examined the reversal potential of GABA(A)R currents by means of perforated patch-clamp recording with gramicidin in overnight-cultured GnRH neurones isolated from adult GnRH-enhanced green fluorescent protein transgenic rats. The reversal potential was -26 +/- 1.4 mV (mean +/- SEM, n = 42) in GnRH neurones, whereas it was -57 +/- 2.7 mV (n = 34) in unidentified neurones, and GABA depolarised the GnRH neurones in current-clamp condition. The GABA(A)R currents in rat GnRH neurones were augmented by neurosteroids, allopregnanolone and 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one, at submicromolar concentrations. In addition, the expression patterns of GABA(A)R subunit mRNAs were determined by multi-cell reverse transcription-polymerase chain reaction, which revealed that the alpha 2, beta 3, gamma 1 and gamma 2 subunits were dominant and the alpha 6 and gamma 3 subunits were negative in rat GnRH neurones. These results indicate that GABA(A)Rs in the soma of rat GnRH neurones are comprised mainly of alpha 2, beta 3 and gamma 1 or gamma 2 subunits and that they are sensitive to neurosteroids; moreover, they suggest that activation of these receptors depolarises GnRH neurones. Thus, GABA and neurosteroids influence the electrical activity of GnRH neurones.