The adrenal medulla is a second major center of dopamine formation. Chromaffin granules in cells of the adrenal medulla carry dopamine hydroxylase , an ascorbate dependent monooxygenase which produces norepinephrine. Some brain tissues also produce norepinephrine. Epinephrine is released into blood from chromaffin granules in response to an acetylcholine signal from nerve fibers of the sympathetic nervous system. The different receptor classes are distinguished by their different responses to drugs.
Agonists produce a response, while antagonists block response to natural epinephrine.
In the pineal gland, serotonin is further modified by acetylation and O-methylation to give melatonin . Serotonin is a neurotransmitter, particularly of neurons in the hypothalamus and brainstem, innervating the spinal cord, and stimulant of smooth muscle contraction and vasoconstrictor. It is also store and released by mast cells. Lysergic acid is an antagonist of serotonin receptors. Prozac acts by enhancing the availability of serotonin.