EXPRESSION OF SYNAPTOPHYSIN IN SPROUTING NEURONS AFTER ENTORHINAL LESION IN THE RAT

Expression of the synaptic vesicle protein synaptophysin was studied i n lesion-induced sprouting neurons of the contralateral entorhinal cor tex and in the contralateral dentate gyrus using immunocytochemistry a t the light-and electron-microscopic level. Perikaryal immunoreactivit y for synaptophysin was found between a and 10 days postlesion. Light microscopy revealed that synaptophysin immunostaining was present in a lmost all neurons of layers II and III of the contralateral medial ent orhinal cortex. These neurons give rise to the sprouting, crossed temp orodentate pathway. In addition, some hilar neurons of the contralater al dentate gyrus, which are the parent cells of sprouting commissural fibers, were immunostained for synaptophysin. Transient immunostaining for synaptophysin was observed within cell bodies and dendrites, Addi tionally, the cell bodies were outlined by immunoreactive puncta, iden tified by electron microscopy as nerve terminals. Our results revealed that sprouting neurons express the major synaptic vesicle protein syn aptophysin during reactive synaptogenesis in a pattern that reflects b iosynthesis and sorting of this protein as seen in developing neurons during synapse formation.