Excitation of spinal and vagal afferent neurons can induce the release of neuropeptides such as Substance P and CGRP, which control blood flow and immune cell function,113 while possibly possessing antimicrobial properties.114 Both peptides are also implicated in visceral and peripheral pain.115 Increased levels of Substance P have been seen in the colon after antibiotic treatment21 and in colitis models.116 As previously mentioned, vagal neurons release CGRP in response to TLR4 activation,69 but more work is needed to determine the physiological consequences of this signaling. This evidence concerns the gene TAC1 and colitis.