FIGURE 2.

Role of CGRP-expressing intrinsic primary afferent neurons (IPANs) in the peristaltic motor activity of the intestine through activation of ascending excitatory and descending inhibitory pathways in the enteric nerve plexus. CGRP-expressing IPANs are stimulated by mechanical or chemical stimulation of the mucosa and intestinal wall. Ascending contraction of the circular muscle above the stimulus is mediated by interneurons and excitatory cholinergic motor neurons, while descending relaxation of the circular muscle below the stimulus is brought about by interneurons and inhibitory motor neurons (expressing nitric oxide synthase and various relaxant mediators). The different types of neuron are depicted by different color codes as explained in the graph. The model shown in the graph takes particular account of the findings reported by Grider et al. (1998) and Smolilo et al. (2020). CM, circular muscle; 5-HT, 5-hydroxytryptamine; LM, longitudinal muscle; MP, myenteric plexus; SMP, submucosal plexus.