Neuronal Nuclei (NeuN) protein is a neuron-specific, DNA-binding nuclear protein in vertebrates. NeuN is observed in most neuronal cell types throughout the nervous system, including cerebellum, cerebral cortex, hippocampus, thalamus, and spinal cord, as well as the dorsal root ganglia, sympathetic chain ganglia, and enteric ganglia of the peripheral nervous system. Only few cell types are not reactive with this antibody include Purkinje, photoreceptor, and mitral cells. NeuN immunoreactivity is first observed in neurons when they become post-mitotic, and are initiating cellular and morphological differentiation. No staining is observed in proliferation zones. NeuN has been used as an immunohistochemical marker for excitotoxic lesions of the brain, as well as for the diagnosis of a wide range of human tissue specimens from the central and peripheral nervous system.