IMMUNOCYTOCHEMICAL LOCALIZATION OF SYNAPTOPHYSIN (PROTEIN-P38) AND SYNAPSIN-I IN NERVE-TERMINALS OF RAT NEUROHYPOPHYSIS

Synaptophysin and synapsin I, the synaptic vesicle-associated proteins, were demonstrated immunocytochemically in nerve terminals of the neurohypophysis of rats. Although both are associated with microvesicles 50-60 nm in diameter, they are not localized on or around the large neurosecretory granules nor the clear vacuoles, 100-200 nm in diameter. These findings strongly suggest that the microvesicles in the nerve terminal of the neurohypophysis are, for the most part, not the structures involved in the retrieval of the limiting membranes of the released neurosecretory granules, but rather typical synaptic vesicles. The clear vacuoles, which are negative for synaptophysin and synapsin I, are considered to be related to the retrieval of the limiting membranes of the released neurosecretory granules.