Melatonin is associated with all of the following except: March 2010

Ans. A: Vomiting Melatonin and the enzymes responsible for its synthesis from serotonin by N-acetylation and 0-methylation are present in pineal parenchymal cells, and the hormone is secreted by them into the blood and the cerebrospinal fluid. Melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during the daylight hours. This remarkable diurnal variation in secretion is brought about by norepinephrine secreted by the postganglionic sympathetic nerves (nervi conarii) that innervate the pineal. The norepinephrine acts -adrenergic receptors in the pineal to increase intracellular cAMP, and the cAMP in turn produces a marked increase in N-acetyltransferase activity. This results in increased melatonin synthesis and secretion. Effects of Melatonin: It plays a role in sleep mechanism It is supposed to decrease gonadotropic hormone secretion by anterior pituitary Vomiting centre is located in the brain stem. From here, motor impulses that cause the actual vomiting are transmitted from the vomiting center by the way of the 5th,7th,9th,10th and 12th cranial nerves to the upper GIT, through vagal and sympathetic nerves to the lower tract and through spinal nerves to the diaphragm and abdominal vessels.