Evidence for GABA involvement in stress-induced inhibition of male amphibian sexual behavior.

The behavioral effects of GABA analogs were investigated to determine whether GABAergic neurotransmission is involved in the stress-induced inhibition of masculine sexual behaviors in rough-skinned newts (Taricha granulosa). Injections of bicuculline, a GABA antagonist, stimulated male sexual behaviors in a dose-dependent fashion, and the minimum effective dose was 40-fold less when administered centrally rather than systemically, suggesting a central nervous system site of action. Injections of muscimol, a GABA agonist, suppressed reproductive behaviors in male newts, and this inhibition lasted at least 5 hr and was proportional to the dose of muscimol administered. The inhibitory effects of muscimol on newt sexual behaviors could be reversed by a single 100-microgram ip injection of arginine vasotocin. The inhibitory effects of confinement stress or corticosterone (CS) injections on newt sexual behaviors were blocked by pretreatment of newts with mercaptopropionic acid, a blocker of GABA synthesis. As well, bicuculline prevented the inhibition of sexual behavior induced by CS injection. These results support the conclusion that, in a male amphibian, the GABAergic system is involved in the inhibitory mechanisms regulating sexual behaviors and that CS mediates the stress-induced inhibition of sexual behaviors through the GABAergic system.