INHIBITORY EFFECTS OF THE 5-HT(1A) AGONISTS, 5-HYDROXY-(3(DI-N-PROPYLAMINO)CHROMAN) AND 5-METHOXY-(3-(DI-N-PROPYLAMINO)CHROMAN), ON FEMALE LORDOSIS BEHAVIOR

Sexually receptive, intact, proestrous rats were infused bilaterally i nto the ventromedial nucleus of the hypothalamus with one of several s erotonin (5-HT) agonists and with the endogenous ligand, 5-HT. Seroton in (2000 ng) and the 5-HT1A agonists, 8-hydroxy-2-(di-n-propylamino)te tralin [8-OH-DPAT (200 ng)], 5-methoxy-3-(di-n-propylamino)chroman [5- MEO-DPAC (200-2000 ng)] and 5-hydroxy-3-(N-di-n-propylamino)chroman [5 -OH-DPAC (200-2000 ng)] inhibited female lordosis behavior within 10 m in of the infusion. The rank order of the effectiveness of these compo unds was 8-OH-DPAT > 5-OH-DPAC greater-than-or-equal-to 5-MEO-DPAC > 5 -HT. The nonselective 5-HT agonist, 1-(m-trifluoromethylphenyl) pipera zine [TFMPP (2000 ng)], did not reduce lordosis behavior. In addition to their reduction of lordosis behavior, the 5-HT1A agonists elicited resistive behavior toward the male's attempts to mount. There were min imal effects of the 5-HT1A agonists on either quality of the lordosis reflex or on proceptivity. However, rats pretreated with TFMPP and inf used with 8-OH-DPAT 1 hr later, did show a transient suppression of lo rdosis quality. These results provide further evidence that the ventro medial nucleus of the hypothalamus contains 5-HT1A sites, the activati on of which reduces lordosis behavior in regularly cycling, proestrous rats.