HYPOTHALAMIC INFUSION OF THE 5-HT2 1C AGONIST, DOI, PREVENTS THE INHIBITORY ACTIONS OF THE 5-HT1A AGONIST, 8-OH-DPAT, ON LORDOSIS BEHAVIOR/

Sexually receptive, intact, proestrous rats were infused bilaterally i nto the ventromedial nucleus of the hypothalamus (VMN) with 200 ng of the 5-H-1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) , with 2000 ng of the 5-HT1A, agonist, (+/-)-(2,5-dimethoxy-4-iodophen yl)-2-amino HCl (DOI), or with both 8-OH-DPAT and DOI. Alone, VMN infu sions of 8-OH-DPAT, but not DOI, inhibited lordosis behavior. When 200 0 ng DOI was infused simultaneously with 8-OH-DPAT, the inhibitory eff ects of 8-OH-DPAT were completely abolished. These results suggest tha t neural sites responsible for the reported facilitatory effects of 5- HT2/1C agonists on lordosis behavior coexist in the VMN with those sit es in which 5-HT1A agonists are effective in reducing lordosis behavio r. In contrast to the protective action of the 5-HT2/1C receptor agoni st following VMN infusion, no protection was seen when both DOI and 8- OH-DPAT were administered intraperitoneally. Thus, the interaction of these two receptor subtypes in the control of lordosis behavior may be different in regions outside the VMN.