Physiology of somatosensory and estrogenic control over the lordosis reflex.

The simplest mechanism for lordosis behavior, as allowed by the present data, is as follows. Estrogen acts on the ventromedial nucleus of hypothalamus (VMN) to induce a tonic facilitatory output, which is relayed by neurons in mesencephalic central gray and then the medullary reticulospinal tract to the spinal cord. To trigger the lordosis reflex, sensory inputs from cutaneous touch-pressure receptors located in rump-perineal skin are required. Neural pathways exist for transmitting these inputs to motor neurons in the spinal cord and to certain supraspinal locations, but our electrophysiological studies indicate that the most likely place where these sensory inputs interact with estrogen-influenced neural activity to elicit the reflex is the spinal cord itself.