Inhibitory effects of the 5-HT 1A agonists, 5-hydroxy- and 5-methoxy-(3-(di-n-propylamino)chroman), on female lordosis behavior

Abstract

Sexually receptive, intact, proestrous rats were infused bilaterally into the ventromedial nucleus of the hypothalamus with one of several serotonin (5-HT) agonists and with the endogenous ligand, 5-HT. Serotonin (2000 ng) and the 5-HT 1A agonists, 8-hydroxy-2-(di- n-propylamino)tetralin [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 min of the infusion. The rank order of the effectiveness of these compounds was 8-OH-DPAT > 5-OH-DPAC ⩾ 5-MEO-DPAC > 5-HT. The nonselective 5-HT agonist, 1-( m-trifluoromethylphenyl) piperazine [TFMPP (2000 ng)], did not reduce lordosis behavior. In addition to their reduction of lordosis behavior, the 5-HT 1A agonists elicited resistive behavior toward the male's attempts to mount. There were minimal effects of the 5-HT 1A agonists on either quality of the lordosis reflex or on proceptivity. However, rats pretreated with TFMPP and infused with 8-OH-DPAT 1 hr later, did show a transient suppression of lordosis quality. These results provide further evidence that the ventromedial nucleus of the hypothalamus contains 5-HT 1A sites, the activation of which reduces lordosis behavior in regularly cycling, proestrous rats.