DISTRIBUTION OF GAP-43 IN RELATION TO CGRP AND SYNAPTIC VESICLE MARKERS IN RAT SKELETAL-MUSCLES DURING DEVELOPMENT

GAP 43 in nerve terminal structures of rat skeletal muscles, was inves tigated during postnatal development using immunofluorescence and conf ocal laser scanning microscopy. Comparison with synaptophysin, synapsi n, SV2, CGRP, SP and NF was done in double immunoincubation studies. G AP 43-like immunoreactivity (LI) was demonstrated in preterminal axons and motor endplates in all age groups (from E18 to adult), although t he intensity of immunofluorescence was considerably higher in the youn ger rats. The outgrowing nerve sprouts in E18 muscles were strongly GA P 43-positive. The intensity decreased with increasing age, but even i n adult animals GAP 43-LI was present in some p38- or SV2-positive end plates. GAP 43-LI was also present in muscle spindles and preterminal nerve branches, and likewise decreased with age. Perivascular nerve te rminals (around arteries mainly) were, however, strong in GAP 43-LI du ring both development and adulthood. GAP 43-LI was strong, and present in both small and large granules. SP-LI was observed in a few thin, p resumably sensory, axons around vessels, which also contained a few GA P 43-positive large granules. Most of the strongly GAP 43-positive ter minals around vessels were probably autonomic postganglionic terminals . The results suggest that GAP 43, in addition to development and rege neration, may play a significant role also in normal adult rats, espec ially in perivascular nerve terminals, possibly connected with a high potential for plasticity in this kind of nerve terminals.