Neuroanatomical analysis of peptidergic input in the spinal nucleus of bulbocavernosus.

The spinal nucleus of bulbocavernosus (SNB) is located in the anterior horn of the lower lumbar and upper sacral segments of the spinal cord and plays a significant role in the regulation of external sphincters and other muscles of the urogenital tract and rectum. The present study examined characteristic features of peptidergic input to this nucleus in rat using a double immunostaining method at both light and electron microscopic levels, focused on an analysis of relationship between cholinergic motoneurons and neuropeptide Y (NPY) axon terminals in the SNB. At the light microscopic level, NPY immunoreactive terminals were frequently distributed in the SNB and some were in the vicinity of the cholinergic cells. At the electron microscopic level, some of NPY immunoreactive terminals were seen to form synaptic contacts with cholinergic neurons on their somata and dendrites in the SNB. These findings suggest that NPY terminals are involved in the functioning of cholinergic SNB motoneurons via the synapse.