CALB1 and irritable bowel syndrome: To our knowledge, this study is the first to demonstrate reduced densities of enteric cholinergic and intrinsic primary afferent NFs labeled with specific markers hpChAT [34, 35] and Calb [32] in the colonic mucosa of IBS, which appeared to be more prominent in IBS‐C than IBS‐D, using a novel 3D imaging technique.