Synaptophysin is a synaptic vesicle glycoprotein used in synaptic transmission of neurons. Synaptophysin is a calcium-binding and integral membrane glycoprotein present in presynaptic vesicles in almost all neurons. Synaptophysin has four transmembrane domains and it forms a complex with dynamin at high calcium concentrations suggesting an involvement in synaptic vesicle endocytosis. It is also involved in the regulation of short-term and long-term synaptic plasticity. Synaptophysin is currently the most widely used marker for nerve terminals and for differentiating neuroendocrine tumors. Mutations in the gene can result in mental retardation, X-linked 96. Anti-Synaptophysin stains the gastrointestinal mucosa and lung neuroendocrine cells of the human adrenal medulla, carotid body, pancreas, pituitary, skin, and thyroid. Synaptophysin also stains neuroendocrine neoplasms. Use of Anti-Synaptophysin produces diffuse, finely granular, cytoplasmic staining. The presence of synaptophysin does not correlate with neuron-specific enolase or other neuroendocrine markers.