FACILITATION OF FEMALE RAT LORDOSIS BEHAVIOR BY HYPOTHALAMIC INFUSIONOF 5-HT2A 2C RECEPTOR AGONISTS/

Ovariectomized rats were hormonally primed with 0.5 mu g estradiol ben zoate and 500 mu g progesterone to produce two groups of rats differin g in their lordosis behavior. Females with a lordosis to mount (L/M) r atio < 0.5 were used to test the hypothesis that 5-HT2A/2C receptor ag onists could facilitate lordosis behavior. Females with L/M ratios gre ater than or equal to 0.5 were used to evaluate the potential suppress ive effect of 5-HT2A/2C receptor compounds. Lordosis behavior was exam ined following bilateral infusion of drugs into the ventromedial nucle us of the hypothalamus (VMN). Drugs examined were the 5-HT2A/2C recept or agonist, +/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane pane HC l (DOI), the 5-HT2A/2C receptor antagonist, l)-1-piperdinyl]ethyl]-2,4 (1H,3H)-quinazolinedione tartrate (ketanserin tartrate), and the non-s elective 5-HT receptor agents, 2-(1-piperazinyl)quinoline dimaleate (q uipazine) and N-(3-trifluoromethylphenyl)piperazine HCl (TFMPP). Drugs with agonist action at 5-HT2A/2C receptors increased lordosis behavio r in rats with low sexual receptivity. The 5-HT2A/2C receptor antagoni st, ketanserin, inhibited lordosis behavior in sexually receptive rats . DOI attenuated the lordosis-inhibiting effect of ketanserin, but ket anserin was less effective in preventing DOI from increasing lordosis behavior. These results strengthen prior inferences that activation of 5-HT2A/2C receptors can facilitate lordosis behavior and that the VMN is one site at which such facilitation can occur. (C) 1998 Elsevier S cience B.V.