The proposed project will study the influence of hormones upon reproductive behavior and the morphology of neurons which mediate that behavior, by focusing upon a simple neuromuscular system in adult male rats. Motoneurons in the spinal nucleus of the bulbocavernosus (SNB) innervate the striated perineal muscle bulbocavernosus (BC). The BC is active during copulation and aids in the formation and removal of cervical plugs which are crucial for reproductive success in this species. The BC is also active during penile flips that can be mediated by the isolated spinal cord. Androgen manipulations in adulthood alter both the reflexes and several neuroanatomical measures of the SNB, including soma size, nuclear size and dendritic extent. Experiments will be conducted to determine which cellular population(s) interact with androgen in order to alter neural morphology. These experiments include local application of androgen and the manipulation of systemic androgen levels after isolation of various components of the SNB system. Only after the primary site of androgen action is ascertained can further experiments be performed to understand the cellular mechanisms behind these changes in neural structure and behavior. The project will also investigate the ways in which various afferent inputs to the SNB alter its structure and function. These experiments will include pharmacological manipulation of oxytocin receptors, anatomical determination of brain afferents to the SNB motoneurons, and varying copulatory experience. These studies should provide further understanding of reproductive behaviors and the means by which hormones can alter behavior. Furthermore, by studying the mechanisms of neural plasticity, one can gain a greater understanding of learning and memory processes.