Differential expression of gamma-aminobutyric acid receptors in immortalized luteinizing hormone-releasing hormone neurons

gamma-Aminobutyric acid (GABA) has been shown both to stimulate and inhibit LH secretion in vivo. GABA apparently exerts these effects at the hypothalamic level by regulating the release of LHRH. In this study, we have investigated the effect of GABAergic agents on LHRH secretion from an immortalized hypothalamic neuronal cell line (GT1-7). LHRH secretion was stimulated in a dose-dependent manner with increasing concentrations of GABA. This effect was mimicked by the GABAA receptor agonist, muscimol, and was blocked by the selective antagonist, bicuculline. The stimulatory effect of muscimol on LHRH secretion was synergistic with low concentrations of [K+]. By comparison, neither activation of the GABAB receptors with baclofen nor blockade with phaclofen influenced basal LHRH secretion. Baclofen, however, did depress [K+]-induced LHRH release. Binding studies confirmed the presence of GABAA and GABAB receptors on GT1-7 cells. In addition, Northern blots with probes to the GABAA receptor alpha 1, beta 3, and gamma 2L subunits revealed that only the beta 3 messenger RNA (mRNA) was expressed in the GT1-7 cells. These data provide the first demonstration that immortalized LHRH neurons are directly responsive to GABAergic agents. To the extent that these immortalized neurons may resemble those in vivo, our results suggest that GABAergic agents may play a dual role in reproductive physiology by exerting both stimulatory and inhibitory control over LHRH release.