MOTONEURON DEVELOPMENT AFTER DEAFFERENTATION .1. DORSAL RHIZOTOMY DOES NOT ALTER GROWTH IN THE SPINAL NUCLEUS OF THE BULBOCAVERNOSUS (SNB)

The spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral n ucleus (DLN) are sexually dimorphic motor nuclei in the rat lumbar spi nal cord. During postnatal development, SNB and DLN motoneurons grow s ubstantially in measures of soma size, dendritic length, and radial de ndritic extent. SNB motoneurons exhibit a biphasic pattern of dendriti c growth, where there is an initial period of exuberant growth followe d by a period of retraction to mature lengths by 7 weeks. In this expe riment, we examined whether primary afferent input to the SNB nucleus was necessary for the normal postnatal growth of SNB motoneurons. We p artially deafferented the SNB via unilateral dorsal rhizotomy of lumbo sacral dorsal roots in male rats at 1 week of age. Using cholera toxin horseradish peroxidase (BHRP) to visualize SNB motoneurons, we examin ed SNB motoneuron morphology at 4 and 7 weeks of age. SNB motoneurons in rhizotomized males developed normally; measures of dendritic length in rhizotomized males were typically exuberant at 4 weeks of age, and declined significantly to mature lengths by 7 weeks of age. In additi on, dorsal rhizotomy did not alter the development of SNB motoneuron s oma size or radial dendritic extent. These results are discussed in re ference to sensorimotor connections in the SNB, the extent of the deaf ferentation, and dendrodendritic interactions.