Effects of the GABA-A receptor agonist and antagonist on the in vitro release of hypothalamic catecholamines: Apparent parallelism between these effects and the LHRH secretion in adult male rats

GABA (gamma-aminobutyric acid) has a well-known inhibitory effect on the lu teinizing hormone-releasing hormone (LHRH) secretion. In order to evaluate the contribution of the catecholaminergic neurotransmitters on the inhibito ry effect produced by GABA on the LHRH release, we measured in adult male r ats the in vitro hypothalamic output of LHRH. epinephrine (E), norepinephri ne (NE) and dopamine (DA); after the administration of, either muscimol 1 m u M (GABA-A agonist), and\or 1 mu M bicuculline (GABA-A antagonist). The fo llowing results were obtained: muscimol inhibited LHRH secretion, and this effect was accompanied by a decrease of NE, E and DA output. The opposite e ffects were observed after the addition of bicuculline, i.e, stimulation of LHRH, NE, E and DA release In conclusion, our results show that, in the ad ult male rats, GABA has an inhibitory effect on the in vitro release of LHR H. acting on the GABA-A receptor. This effect on LHRH secretion might be ex erted directly, or indirectly, by altering the release of either NE,E, and\ or DA.