IMMUNOCYTOCHEMISTRY OF B-50 (GAP-43) IN THE SPINAL-CORD AND IN DORSAL-ROOT GANGLIA OF THE ADULT CAT

The distribution of the neural-specific growth associated protein B-50 (GAP-43), which persists in the mature spinal cord and dorsal root ga nglia, has been studied by light and electron microscopic immunohistoc hemistry in the cat. Throughout the spinal cord, B-50 immunoreactivity was seen confined to the neuropil, whereas neuronal cell bodies were unreactive. The most conspicuous immunostaining was observed in the do rsal horn, where it gradually decreased from superficial laminae (I-II ) toward more ventral laminae (III-V), and in the central portion of t he intermediate gray (mainly lamina X). In these regions, the labellin g was localized within unmyelinated, small diameter nerve fibres and a xon terminals. In the rest of the intermediate zone (laminae VI-VIII), B-50 immunoreactivity was virtually absent. The intermediolateral nuc leus in the thoracic and cranial lumbar cord showed a circumscribed in tense B-50 immunoreactivity brought about by the labelling of many axo n terminals on preganglionic sympathetic neurons. In motor nuclei of t he ventral horn (lamina IX), low levels of B-50 immunoreactivity were present in a few axon terminals on dendritic and somal profiles of mot oneurons. In dorsal root ganglia, B-50 immunoreactivity was mainly loc alized in the cell bodies of small and medium-sized sensory neurons. T he selective distribution of persisting B-50 immunoreactivity in the m ature cat throughout sensory, motor, and autonomic areas of the spinal cord and in dorsal root ganglia suggests that B-50-positive systems r etain in adult life the capacity for structural and functional plastic ity.