VIP and irritable bowel syndrome: In a chronic and acute stress (CAS)-induced IBS rat model adopted by Li et al. (2016) in their study, accelerated transit of small intestine was accompanied by an increase in the secretory motor neurons in the submucosal plexus, along with an increase in the secretion of excitatory neurotransmitters of enteric nervous system, such as acetylcholine and vasoactive intestinal peptide (VIP) [66].