5-HT3 RECEPTORS IN THE VENTROMEDIAL NUCLEUS OF THE HYPOTHALAMUS AND FEMALE SEXUAL-BEHAVIOR

Within the ventromedial nucleus of the hypothalamus (VMN), serotonin e xerts a dual role in the control of female rat lordosis behavior. Most emphasis has been placed on 5-HT1A and 5-HT2 receptors, which inhibit and facilitate the behavior, respectively. In the current experiment, a potential role for VMN 5-HT3 receptors in the control of lordosis b ehavior was examined. Ovariectomized rats, hormonally primed with 25 m u g estradiol benzoate and 500 mu g progesterone, received bilateral V MN infusions with 100 ng, 250 ng or 500 ng of the 5-HT3 receptor antag onist, tropisetron. In these rats, there was a dose-dependent decline in both the lordosis to mount (L/M) ratio and in the quality of the lo rdosis reflex with 500 ng tropisetron producing the most consistent ch ange in lordosis behavior. Relative to hormone-primed, ovariectomized rats, lordosis behavior of proestrous females was less affected by VMN infusions with the 5-HT3 receptor antagonist. The 5-HT3 receptor agon ist, m-chlorophenylbiguanide (mCPBG), attenuated the effect of tropise tron; of the three mCPBG doses (500 ng, 1000 ng, 1500 ng) examined, 10 00 ng was the most effective, perhaps because, alone, 1500 ng mCPBG sl ightly reduced lordosis behavior. These observations emphasize the pot ential role for VMN 5-HT3 receptors in the control of lordosis behavio r. (C) 1997 Elsevier Science B.V.