Which neurotransmitter is most closely associated with vomiting? A.  Noradrenaline B.  Calcitonin gene-related peptide (CGRP) C.  Acetylcholine (Ach) D.  Substance P E.  Vasoactive intestinal peptide The answer is D. Substance P (SP)-neurokinin-1 (NK1) receptor pathways are involved in the pathophysiology of emesis and depression. It is a potent vaso-dilator mediated by endothelial release of NO. [...]