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1 Neurobiology of Nutrition Laboratory, Pennington Biomedical Research Center, Louisiana State University, Baton Rouge, Louisiana 70808; and 2 Nerve-Gut Research Laboratory, Department of Gastroenterology, Hepatology and General Medicine, Royal Adelaide Hospital, Adelaide, SA 5000, Australia
Mechano- and
chemosensitive extrinsic primary afferents innervating the
gastrointestinal tract convey important information regarding the state
of ingested nutrients and specific motor patterns to the central
nervous system via splanchnic and vagal nerves. Little is known about
the organization of peripheral receptive sites of afferents and their
correspondence to morphologically identified terminal structures.
Mechano- and chemosensory characteristics and receptive fields of
single vagal fibers innervating the stomach as well as lumbar
splanchnic nerves innervating the distal colon were identified using an
in vitro perifusion system. Twenty-three (17%) of one-hundred
thirty-six vagal units identified were found to have multiple, punctate
receptive fields, up to 35 mm apart, and were distributed throughout
the stomach. Evidence was based on similarity of generated spike forms,
occlusion, and latency determinations. Most responded with brief bursts
of activity to 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 adapting 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, particularly from
the serosal side, and variously to chemical stimulation with
5-hydroxytryptamine and capsaicin. We conclude that a proportion of
gastrointestinal mechanosensors has multiple receptive fields and
suggest that they integrate mechanical and chemical information from an
entire organ, constituting the generalists in visceral sensation.
visceral afferents; electrophysiology; chemoreceptors; gastrointestinal innervation; vagus
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