<prompt> Melatonin is secreted from which cells of pineal glandGlial cellsPinealocytesOncocytesZymogen cells  <response>: The pineal gland is a Neuroendocrine Transducer as it forms and secretes a hormone called Melatonin in response to sympathetic nerve activity. It consists of parenchymal cells Pinealocytes, glial cells neuroglia, secretory cells and numerous post-ganglionic sympathetic nerve fibres from cells in the superior cervical ganglion. It contains high amounts of 5 HT serotonin, Nor-epinephrine and melatonin. Melatonin is synthesized from 5 HT and norepinephrine by the parenchymal cells pinealocytes.Ref: Textbook of physiology, Dir. Prof. AK Jain, 5th edition. 