Facilitatory effects of WAY-100635, a 5-HT _1A receptor antagonist, on lordosis in female rats

Effects of the serotonin (5-HT) receptor 1A antagonist, WAY-100635, on lordosis in female rats were examined. Ovariectomized rats were implanted with a silicon tube containing estradiol and behavioral tests were performed. Next, 5, 10 or 20 mg/kg bw WAY-100635 or saline was injected subcutaneously in female rats with a lordosis quotient (LQ) from 10 to 30 and the behavioral test was performed again. As a result, the mean LQs in 10 or 20 mg WAY-100635-treated groups were higher than in the saline-treated group (P < 0.01 and P < 0.05, 10 or 20 mg groups versus saline, respectively). In the experiment on the time-course of change in LQ after injection with 10 mg WAY-100635, the mean LQ was increased (P < 0.01, versus saline) 15 min after the injection and high levels persisted for 1 h. This finding shows that WAY-100635 has the potency to enhance lordosis behavior acutely in female rats with a low estrous state. In order to investigate relationships between the 5-HT _1A receptor and the GABA _B receptor in regulating lordosis, 10 mg baclofen, a GABA _B receptor agonist, was injected and this was followed 1 h later by the injection of 10 mg/kg WAY-100635. Mean LQ decreased after the injection of baclofen (P < 0.0001, versus placebo-treated control), but the decrease in LQs was not reversed by injection with WAY-100635.