Rat and gerbil pinealocytes contain the synaptosomal-associated protein 25 (SNAP-25)

It has recently been established that the neuroendocrine pinealocytes of mammals contain several synaptic membrane proteins that are involved in the regulation of vesicle trafficking in the nerve terminal. In the present study, we have conducted immunoblot and immunocytochemical analyses to demonstrate that another key component of the presynaptic plasmalemma, i.e., protein SNAP-25 (synaptosomal-associated protein 25 kDa), can be detected in pinealocytes. Immunostaining of serial semi-thin sections of plastic-embedded rat and gerbil pineals with monoclonal SNAP-25 antibodies showed that SNAP-25 was present in pinealocytes of both species. We proved its coexpression with other synaptic membrane proteins (synaptophysin, synaptotagmin I, synaptobrevin II, and syntaxin I) at the single cell level. Thus, pinealocytes obviously are endowed with the major proteins that are thought to regulate the targeting and exocytosis of secretory vesicles, in particular of synaptic-like microvesicles.