Melatonin is secreted by
Retinohypothalamic fibers synapse in the suprachiasmatic nuclei (SCN), and there are connections from the SCN to sympathetic preganglionic neurons in the spinal cord that project to the superior cervical ganglion. Postganglionic neurons project from this ganglion to the pineal gland that secretes melatonin. The cyclic activity of SCN sets up a circadian rhythm for melatonin release. This rhythm is entrained to light/dark cycles by neurons in the retina.(Ref: Ganong's Review of Medical Physiology Twenty-Third Edition)
Hypothalamus
Adrenal coex
Pineal gland
Melanocytes
Nervous system