8-OH-DPAT in the midbrain central gray inhibits lordosis behavior

Sexually receptive female rats were infused intracranially with 500-2,000 ng 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) into the midbrain central gray (MCG), in the vicinity of the dorsal raphe nucleus (DRN), or directly into the DRN. When cannulae were located within the DRN, there was little evidence of change in lordosis behavior but a decrease in locomotor activity was commonly observed. In contrast, when cannulae were located anterior, ventromedial, or lateral to the DRN inhibition of lordosis behavior was rapid and robust. Both the lordosis-to-mount ratio (L/M) and the quality of the lordosis reflex were reduced following the infusion. The MCG receives lordosis-facilitating input from the ventromedial nucleus of the hypothalamus and from ascending sensory pathways and contributes information to descending motor systems involved in the lordosis response. Thus, the MCG is a critical link in the completion of the estrogen-dependent lordosis reflex. The present results suggest that 5-hydroxytryptamine1A receptors in the MCG prevent the completion of this reflex.