B-50 (GAP-43) IN ONUF NUCLEUS OF THE ADULT CAT

The nucleus of Onuf in the sacral spinal cord contains motoneurons tha t innervate the pelvic floor muscles and possess somatic and autonomic characteristics. We show in this study that in the intact adult cat, the immunocytochemical labelling of the nervous tissue-specific growth -associated protein, B-50 (GAP-43), which persists in Onuf's nucleus, differs markedly from that in the remaining 'purely somatic' motor nuc lei of the sacral spinal cord. At the light microscopic level, an inte nse B-50 (GAP-43) immunoreactivity (B-50-IR) in the neuropil of Onuf's nucleus contrasts with a faint staining in the other spinal motor nuc lei. Ultrastructurally, B-50-IR is found in Onuf s nucleus within some unmyelinated small diameter nerve fibres and numerous axon terminals on dendritic and somatic surfaces. Conversely, in all other motor nucl ei only a few of these structures are stained. No other cellular profi les show B-50-IR in the tissue examined. According to the proposed fun ctions of B-50 (GAP-43), its persistence in mature spinal axon termina ls may indicate a latent capability of functional and structural remod eling, as well as an involvement in long-term enhancement in synaptic transmission. If so, these properties would be considerably more prono unced in Onuf's nucleus as compared to purely somatic motor nuclei.