Comparison of extrinsic efferent innervation of guinea pig distal colon and rectum

Abstract

The extrinsic efferent innervation of the distal colon and rectum of the guinea pig was compared, by using retrograde tracing combined with immunohistochemistry. Application of the carbocyanine tracer DiI to the rectum filled significantly greater numbers of extrinsic neurons than similar injections into the distal colon. Approximately three-fourths of all filled neurons from either location were either sympathetic or parasympathetic; the rest were spinal sensory neurons. Nerve cell bodies in sympathetic prevertebral ganglia labelled from the two regions were similar in number. Both regions were innervated by sympathetic neurons in paravertebral ganglia; however, the rectum received much more input from this source than the colon. The rectum received significantly more input from pelvic ganglia than the colon. The rectum also received direct innervation from two groups of neurons in the spinal cord. Neurons located in the spinal parasympathetic nucleus in segment S2 and S3 were labelled by DiI injected into the rectal wall. Similar numbers of neurons, located in intermediolateral cell column and dorsal commissural nucleus of lumbar segments, also projected directly to rectum, but not colon. The great majority (>80%) of retrogradely labelled nerve cell bodies in sympathetic ganglia were immunoreactive for tyrosine hydroxylase. In pelvic ganglia, retrogradely labelled neurons contained choline acetyltransferase and/or nitric oxide synthase or tyrosine hydroxylase. Although the rectum and colon in this species are continuous and macroscopically indistinguishable, they have significantly different patterns of extrinsic efferent innervation, presumably reflecting their different functions.

Effect of the artificial sweetener, sucralose, on gastric emptying and incretin hormone release in healthy subjects

“…Direct exposure of carbohydrate to the mucosa of the small intestine appears to be an essential requirement for GLP-1 and GIP secretion (10), and the magnitude of the former is dependent on the rate of delivery of glucose into the small intestine (35). Elements of the sweet taste receptor present in the tongue have recently been identified in both rodent (34,44) and human (43) small intestine. The T1R2ϩ3 heterodimer should, by analogy to the tongue, respond to various sweet-tasting molecules as diverse as sucrose, saccharin, acesulfame K, and sucralose (32,47).…”

“…T1R2ϩT1R3 couples to a G protein, gustducin, and, in turn, to the transient receptor potential ion channel TRPM5 (39). It has recently been established that the ␣-subunit of gustducin, ␣-gustducin, is expressed in the mucosa of the murine gastrointestinal tract (34,44). Expression of ␣-gustducin is evident throughout the mouse small intestine and, among several cell types, appears to colocalize with GLP-1-secreting L cells.…”

Extrinsic primary afferent signalling in the gut

“…130 This estimation was based on recordings made from either pelvic nerves or splanchnic nerves while electrically stimulating axons peripherally. These numbers might be an overestimate, as paravertebral sympathetic efferent axons 131 might have been activated in these pathways by the same electrical stimuli.…”

Autonomic Nerve Regulation of Colonic Peristalsis in Guinea Pigs

“…12 Parasympathetic innervation of the guinea pig distal colon comes from sacral S2-S4 roots as pelvic nerves (PN) and coalesces in anterior and posterior pelvic ganglia to distribute to the rectum as rectal nerves. 13 The anterior pelvic ganglia are located bilaterally adherent to the lateral aspect of the proximal part of the seminal vesicles, in the angle between ductus deference and the seminal vesicle. 14 The posterior ganglion contributes to a much smaller extent to efferent innervation compared to the anterior ganglion.…”

“…14 The posterior ganglion contributes to a much smaller extent to efferent innervation compared to the anterior ganglion. 13,15 The anterior pelvic ganglia send and receive projections from the inferior mesenteric ganglion (IMG) via hypogastric nerves, thus making it a mixed parasympathetic/sympathetic structure, as it is in the rat. 15 The majority of anterior ganglion projections travel to the rectum and not the distal colon.…”