The inhibitory effects on sexual behavior and ambulatory activity of the mixed GABAA/GABAB agonist progabide are differentially blocked by GABA receptor antagonists.

Progabide inhibited male rat sexual behavior at a dose of 200 mg/kg. This dose had only modest effects on ambulatory activity and no effect at all on motor coordination as evaluated by a rotarod test. The GABAA antagonist bicuculline, at a dose of 1 mg/kg, blocked the effects of progabide on sex behavior. In contrast, the GABAB antagonist CGP 35348, at doses of 50 and 100 mg/kg, was ineffective. These doses have previously been shown to block the actions of baclofen on sexual behavior. It was concluded that the GABAA but not the GABAB receptor is important for the inhibitory effects of progabide on that behavior. The actions of progabide on ambulatory activity were not blocked by bicuculline or CGP 35348 at any of the doses used (up to 2 and 200 mg/kg, respectively). Even the combination of both antagonists was ineffective. This suggests that the motor effects of progabide are mediated by either a non-GABAergic receptor or by a subtype of the GABAA or the GABAB receptor that is not sensitive to the antagonists. Present results show that the effects of progabide on motor functions depend on mechanisms different from those involved in its effects on sexual behavior. They further suggest that the GABAA receptor may be important for drug actions on male sexual behavior.