Our results from the current funding period provide evidence for reorganization of sacral reflex circuits after removal of descending inputs by spinal cord transection (SC Tx). This reorganization seems to be different in different efferent neuronal pools. That is, in the sacral parasympathetic nucleus (SPN) the total number of synapses declines, suggesting denervation (although replacement and reorganization of remaining afferents may also take place). In Onuf's nucleus (ON), the data suggest removal and almost complete replacement of synapses. Additional data supporting the role of synaptic reorganization in reflex alterations comes from our studies of hormonal regulation of synapse number on sacral motoneurons (MNs). The goals for the next granting period are to identify the afferent synapses lost and replaced after SC Tx. Immunocytochemistry will be used to identify populations of synaptic terminals containing CGRP, VIP, GABA, enkephalin (ENK), tyrosine hydroxylase (TH), and serotonin (5-HT). These classes of synaptic inputs will be examined on identified preganglionic neurons (PGNs), motoneurons (MNs), in ON, and segmental interneurons projecting to these PGNs and MNs, and will be compared in normal and spinalized cats. The PGNs controlling bladder and bowel function and the MNs in ON controlling the sphincter muscles will be retrogradely labelled using HRP. Interneurons will be labelled using trans-synaptic retrograde transport of tracers. Analyses will be carried out at both light and EM levels. Recovery of bladder and bowel function will also be monitored. The goal is to gain more specific information concerning the rules and features of the synaptic reorganizations we have observed, and eventually, to plan strategies for pharmacologic interventions to improve micturition, defecation, and sexual reflexes in the chronic spinal state. Studies in this project are most closely related to project 4 which is studying plasticity and regeneration of connections in developing spinal cord; the current studies are examining the retention of the ability to reorganize synaptic connections in the adult mammalian spinal cord. This project is broadly related to the theme of the PPG in that it examines anatomical substrates for reflex system functional alterations following spinal cord injury, which represent substantial problems for recovery in human SCI patients.
