Functional integration among 5-hydroxytryptamine receptor families in the control of female rat sexual behavior

Abstract Serotonin (5-HT) receptor interaction in the control of female rat lordosis behavior was examined. Ovariectomized rats, with bilateral implants in the ventromedial nucleus of the hypothalamus (VMN), were hormonally primed with 25 μg estradiol benzoate and 500 μg progesterone. Rats were infused with the 5-HT 3 receptor antagonist, 3-tropanyl-indole-3 carbonylate (tropisetron; 500 ng), or were coinfused with the 5-HT 3 receptor antagonist and the 5-HT 2A/2C receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI; 500, 1500, or 2000 ng). Additional ovariectomized, hormone-primed rats received bilateral VMN infusions with the 5-HT 1A receptor agonist, 8-hydroxy-2-(di- n -propylamino) tetralin (8-OH-DPAT; 200 ng), or were coinfused with the 5-HT 1A receptor agonist and the 5-HT 3 receptor agonist, m -chlorophenyl-biguanide (mCPBG; 250, 500, or 1000 ng). Lordosis behavior was observed prior to VMN infusion, during the infusion and for 30 consecutive minutes thereafter. Tropisetron reduced the lordosis to mount (L/M) ratio in every animal investigated but the decline was attenuated by coinfusion with DOI. Similarly, the L/M ratio declined following infusion with 8-OH-DPAT and the decline was dose-dependently reduced by coinfusion with mCPBG. Only the 5-HT 3 receptor agonist altered the quality of the lordosis reflex. These studies provide evidence that the effects of 5-HT on female rat lordosis behavior involve the integrated activity of at least 3 different 5-HT receptor families.