Methysergide inhibits and facilitates lordosis behavior in the female rat in a time-dependent manner.

Reports in the literature have indicated a facilitatory effect of the serotonin antagonist methysergide on lordosis behavior, suggesting an inhibitory role for serotonergic activity. In the present series of experiments, methysergide (7 mg/kg) was found to inhibit lordosis behavior 30 min after intraperitoneal administration to females, treated chronically with estradiol benzoate, or acutely with estradiol benzoate and progesterone. However, methysergide was found to facilitate lordosis behavior 200 and 300 min after administration to female rats treated acutely with estradiol benzoate. These data suggest a time-dependent inhibitory effect of methysergide, and are consistent with the hypothesis that the activity of serotonin type 2 receptors facilitates lordosis behavior in the female rat.