Vagal and spinal mechanosensors in the rat stomach and colon have multiplereceptive fields

Mechano- and chemosensitive extrinsic primary afferents innervating the gas trointestinal tract convey important information regarding the state of ing ested nutrients and specific motor patterns to the central nervous system v ia splanchnic and vagal nerves. Little is known about the organization of p eripheral receptive sites of afferents and their correspondence to morpholo gically identified terminal structures. Mechano- and chemosensory character istics and receptive fields of single vagal fibers innervating the stomach as well as lumbar splanchnic nerves innervating the distal colon were ident ified using an in vitro perifusion system. Twenty-three (17%) of one-hundre d thirty-six vagal units identified were found to have multiple, punctate r eceptive fields, up to 35 mm apart, and were distributed throughout the sto mach. Evidence was based on similarity of generated spike forms, occlusion, and latency determinations. Most responded with brief bursts of activity t o mucosal stroking with von Frey hairs (10-200 mg) but not to stretch, and 32% responded to capsaicin (10(-5) M). They were classified as rapidly adap ting mucosal receptors. Four (8%) of fifty-three single units recorded from the lumbar splanchnic nerve had more than one, punctate receptive field in the distal colon, up to 40 mm apart. They responded to blunt probing, part icularly from the serosal side, and variously to chemical stimulation with 5-hydroxytryptamine and capsaicin. We conclude that a proportion of gastroi ntestinal mechanosensors has multiple receptive fields and suggest that the y integrate mechanical and chemical information from an entire organ, const ituting the generalists in visceral sensation.