Inactivation of the medial preoptic area/anterior hypothalamus by lidocaine reduces male sexual behavior and sexual incentive motivation in male rats

Abstract

Permanent bilateral lesions of the medial preoptic area anterior hypothalamus (MPOA/AH) produce a drastic inhibition of male sexual behavior in all species studied to date. The present experiment was designed to evaluate if temporal inactivation of the MPOA/AH by infusions of lidocaine also inhibits sexual behavior in male rats. This would allow us to rule out the possibility that the behavioral effects observed after damage of the MPOA/AH could be associated with plastic changes induced by the lesion in other brain regions. We also evaluated sexual incentive motivation in males after the infusion of lidocaine in a test in which copulation is not possible but where males maintain approach behavior to the estrous females despite repeated testing. The percentage of animals displaying mounts, intromissions and ejaculation was significantly reduced while mount and intromission latency were prolonged after infusion of lidocaine. No changes were observed in sexual behavior after infusion of lidocaine in animals with cannulae outside the MPOA/AH suggesting that the inhibitory effects are specific to this brain region. Sexual incentive motivation was also affected by administration of lidocaine. Males consistently showed a clear preference for the sexually receptive female except when infused with lidocaine. After the infusion of the compound a significant reduction in the time spent in the incentive zone of the stimulus female was observed. These results support the hypothesis that neurons of the MPOA/AH are involved in the control of male sexual motivation.