A pinealocyte is one of the cell of the pineal body. A pinealocyte has long cytoplasmic processes which end in bulbous expansions, resembling the axons of neurons. Pinealocytes are the main cells which make up the pineal gland. These cells secrete melatonin. Pinealocytes have an organelle called the synaptic ribbon, which is a specific marker for pinealocytes. Some of the enzymes of the pinealocytes include 5-HT N-acetyl transferase and 5-hydroxyindole-O-methyltransferase which are used to convert serotonin to melatonin.
Pinealocytes secrete melatonin into capillaries via the long processes. Secretion of melatonin is stimulated by sympathetic innervation from superior cervical ganglion. They also have shorter cytoplasmic processes that connect to adjacent pinealocytes via desmosomes and gap junctions. Pinealocytes have large irregularly shaped nuclei with prominent nucleoli.