INDUCTION OF PRESYNAPTIC REEXPRESSION OF AN ADHESION PROTEIN IN LAMINA-II AFTER DORSAL-ROOT DEAFFERENTATION IN ADULT-RAT SPINAL-CORD

Limbic system-associated membrane protein (LAMP), a 64-kDa membrane pr otein, is an axon guidance adhesion molecule expressed by neurons in l imbic system-related areas of the CNS, During development, LAMP is exp ressed on growing axons, growth canes, and their target neurons, but i n adults it is restricted to membranes of somata and dendrites. In the adult spinal cord, LAMP immunoreactivity is found only on neurons of lamina II, lamina X, and the intermediolateral cell column and its ult rastructural localization is entirely postsynaptic, We studied changes in the expression of LAMP in lamina II of adult rat spinal, cord afte r L1-S2 dorsal rhizotomy, a procedure that partially deafferents lamin a II neurons and induces axonal sprouting by spared systems in lamina II. At the light microscopic level, LAMP immunoreactivity in lamina II was decreased in density at 3, 10, and 60 days postoperatively, This decrease in immunoreactivity suggests that LAMP expression by lamina I I neurons may normally be regulated by specific afferent activity. Ult rastructurally, in control lamina PI and after deafferentation in both control and deafferented lamina II at 3 and 60 days postoperatively, LAMP expression was restricted to postsynaptic membranes. Ten days aft er deafferentation, however, when axons are actively sprouting, LAMP w as expressed on both axonal and postsynaptic membranes, The reexpressi on of LAMP on axonal profiles after deafferentation may identify axons that undergo sprouting in response to deafferentation. (C) 1998 Acade mic Press.