ESTROGEN-PROGESTERONE AND 8-OH-DPAT ATTENUATE THE LORDOSIS-INHIBITINGEFFECTS OF THE 5-HT1A AGONIST IN THE VMN

Ovariectomized rats were treated for 2 consecutive weeks with 25 mu g estradiol benzoate followed 48 h later with 500 mu g progesterone. Bil ateral infusions of 200 ng 8-hydroxy-2-(di-n-propylamino)tetralin (8-O H-DPAT) into the ventromedial nucleus of the hypothalamus (VMN) inhibi ted female sexual behavior on the first but not the second week of hor mone priming. Such attenuation on the second week of priming did not a ppear to result from an enhanced receptivity of the female rats since there were no differences in the L/M ratios prior to drug infusion; no r was the attenuation a consequence of infusion-induced VMN damage sin ce neither saline nor 8-OH-DPAT preinfusions prevented the later inhib itory effects of 8-OH-DPAT on lordosis behavior. However, preinfusion with 8-OH-DPAT may have reduced the duration of the inhibition. Hormon e priming (without any VMN infusion) also partially attenuated the eff ect of 8-OH-DPAT. Both hormone priming and treatment with 8-OH-DPAT we re required to eliminate the effects of the second 8-OH-DPAT treatment . Thus, the present results suggest that gonadal hormones, alone, slig htly attenuate the effects of agonist activation of 5-HT1A receptors i nvolved in the inhibition of lordosis behavior; that agonist activatio n of 5-HT1A receptors also produces a slight attenuation; but that bot h treatments together have a robust protective action against the inhi bitory effect of a 5-HT1A agonist on female lordosis behavior.