The neurohormonal interface that mediates sexual behavior in the female laboratory rat, Rattus norvegicus

The lordosis reflex is a widely used model for studying how hormones can interact with the nervous system to control behavior. Previous studies have demonstrated that the basic pathway controlling the motor aspect of this behavioral response originates with estrogen-sensitive neurons within the ventromedial nucleus of the hypothalamus. Neurons within this structure project to the midbrain periaqueductal gray, which contains neurons that project to the medullary reticular formation. The medullary reticular formation contains neurons that, in turn, project to motoneurons in the lumbar spinal cord that control the lordosis-producing lumbar epaxial muscles. The serial, hierarchical organization of these brain structures has been deduced from the combination of numerous techniques, but transneuronal connectivity had not been demonstrated. Using modern tracing techniques, coupled with immunohistochemical identification of lordosis-relevant transmitter and receptor systems, the studies described within this dissertation examine the transneuronal organization of the putative lordosis-producing network. The data collected across several experiments address three questions. First, are the putative lordosis-relevant neural populations serially connected? Second, what are the anatomical substrates of the effects of estrogen and oxytocin on the lordosis-relevant neuraxis? Third, are the previously demonstrated results confounded by the tracing through the sympathetic nervous system? In addressing these questions, the present data provide support for the previously implied hierarchical organization of the pathway and bring to bear new questions relevant to the micro-organization of the neurons within the ventromedial nucleus of the hypothalamus