NERVE GROWTH-FACTOR INDUCED MODIFICATION OF PRESYNAPTIC ELEMENTS IN ADULT VISUAL-CORTEX IN-VIVO

Nerve growth factor (NGF) has been shown to play important roles in ne uronal survival, growth and differentiation. Recently, we have found t hat intracortical infusion of NGF into adult cat visual cortex can rec reate ocular dominance plasticity, suggesting that NGF is also involve d in activity-dependent modification of synaptic connectivity in the a dult brain. To further explore the mechanisms of NGF-induced plasticit y in adult visual cortex, we studied two presynaptic markers: GAP-43 a nd synaptophysin. Immunocytochemical staining showed that NGF-treatmen t of adult visual cortex selectively increased the level of the phosph orylated form of GAP-43, while the total level of GAP-43 was not chang ed. These results demonstrate that NGF-treatment stimulates phosphoryl ation processes of GAP-43 in vivo. In addition, NGF-treatment of adult visual cortex increased the level of synaptophysin immunoreactivity. Since the phosphorylated form of GAP-43 is known to be enriched in the membrane skeleton of growth cones and of developing synapses, and the phosphorylation of GAP-43 has been linked with events that underlie s ynaptic plasticity, and since synaptophysin is a major component of pr esynaptic vesicles, our results suggest that NGF-treatment of adult vi sual cortex modulates presynaptic terminals, possibly by inducing axon al sprouting and formation of new synapses, and that these changes may play a role in the NGF-induced functional plasticity.