Early experience shapes the neural and behavioral development of individuals. Maternal care is one such experience, regulating development and exerting a lifelong impact on the nervous system, behavior, and disease. Reducing maternal licking influences both the number of motoneurons in the spinal nucleus of the bulbocavernosus (SNB), which control penile reflexes, as well as the consequent reflexes themselves. The goals of this thesis were to determine whether maternal licking also shapes dendritic development of these motoneurons and to elucidate the mechanisms through which maternal licking exerts its effects. I determined that reduced licking produced decreases in SNB motoneuron dendritic length, especially in the rostral portion of the dendritic arbor. In a second experiment, I found that reduced licking-like tactile stimulation of the perineum produced decreases in SNB dendritic length as well as deficits in adult penile reflex behavior.

The regional specificity of the effects of maternal licking on the SNB suggested that specific afferent populations are altered by maternal licking, thus I next investigated whether sensory or supraspinal afferents were involved in mediating these effects. Sensory afferents from the licked perineal skin innervate the SNB dendritic field, thus it is possible that changes in local spinal cord activity mediate the effects of maternal licking on the SNB. Using anatomical and immunohistochemical techniques, I determined that sensory afferents are distributed in a caudally-biased manner relative to the SNB, and that licking-like tactile stimulation increased neural activity in the caudal portion of the SNB dendritic field. Oxytocin is also released following sensory stimulation, and oxytocin afferents from the hypothalamus innervate the SNB dendritic field and regulate copulatory behavior. Using enzyme immunoassay and immunohistochemistry, I determined that licking-like tactile stimulation increases oxytocin levels in the spinal cord as well as increasing the activity of parvocellular oxytocinergic neurons in the hypothalamus, some of which project to the lumbosacral spinal cord. Thus, changes in oxytocin signaling induced by maternal licking may interact with changes in primary sensory afferent signaling to shape the development of the SNB. Together, these experiments give insight into the mechanisms by which maternal care regulates neural and behavioral development.