HTR4 and irritable bowel syndrome: However, since this receptor does not seem to affect colonic transit time, IBS treatments targeting 5-HT receptors have classically focused on 5-HT3 (facilitates enteric to central nervous system signalling and promotes gut motility), 5-HT4 (augments peristalsis and intestinal secretion), 5-HT1B (initiates peristalsis) receptors [73] and even 5-HT1AR—for which decreased activity has been linked to exacerbated symptoms of depression [90], a known co-morbidity in IBS.