NeuN, encoded by FOX3, is a neuron-specific nuclear protein. Anti-NeuN stains exclusively neuronal cells in the central and peripheral nervous systems, especially postmitotic and differentiating neurons, as well as terminally differentiated neurons. Anti-NeuN has been used widely as a reliable tool to detect most postmitotic neuronal cell types. The immunohistochemical staining is primarily localized in the nucleus of the neurons with lighter staining in the cytoplasm.