ULTRASTRUCTURAL-LOCALIZATION OF B-50 GROWTH-ASSOCIATED PROTEIN-43 TO ANTEROGRADELY TRANSPORTED SYNAPTOPHYSIN-POSITIVE AND CALCITONIN-GENE-RELATED PEPTIDE-NEGATIVE VESICLES IN THE REGENERATING RAT SCIATIC-NERVE/

The growth-associated protein-43/B-50 (B-50/GAP-43) is conveyed from t he neuronal soma into the axon by fast axonal transport and moved to t he nerve terminal. To visualize and determine the type of vesicles by which B-50/GAP-43 is anterogradely transported in the regenerating rat sciatic nerve, we have investigated Lowicryl HM20 embedded nerve piec es dissected from the proximal side of a collection ligature. Ultrastr ucturally, numerous vesicular profiles of various sizes, tubules and m itochondria were seen to accumulate proximal to the collection ligatur e. Both, in unmyelinated and myelinated axons, B-50/GAP-43 immunoreact ivity was associated with vesicular profiles which had a diameter of 5 0 nm. A fraction of the B-50/GAP-43 label co-localized with the small vesicle marker synaptophysin. Go-localization of B-50/GAP-43 was not d etected with the large dense-core vesicle marker calcitonin gene-relat ed peptide. These results indicate that, in rat sciatic nerve axons, B -50/GAP-43 is anterogradely transported in small 50 nm vesicles of the constitutive pathway. These transport vesicles were distinguished in two types. We suggest that one type carrying, both, B-50 GAP-43 and sy naptophysin has as destination the nerve terminal, whereas the second type, which only contains B-50/GAP-43 and no synaptophysin, may be pri marily targeted to the axolemma for local membrane fusion.