Identification of neurons that express 5-hydroxytryptamine4 receptors in intestine

Abstract

5-Hydroxytryptamine (5-HT) is an endogenous stimulant of intestinal propulsive reflexes. It exerts its effects partly through 5-HT4 receptors; 5-HT4 receptor agonists that are stimulants of intestinal transit are in clinical use. Both pharmacological and recent immunohistochemical studies indicate that 5-HT4 receptors are present on enteric neurons but the specific neurons that express the receptors have not been determined. In the present work, we describe the characterization of an anti-5-HT4 receptor antiserum that reveals immunoreactivity for enteric neurons and other cell types in the gastrointestinal tract. With this antiserum, 5-HT4 receptor immunoreactivity has been found in the muscularis mucosae of the rat oesophagus, a standard assay tissue for 5-HT4 receptors. It is also present in the muscularis mucosae of the guinea-pig and mouse oesophagus. In guinea-pig small intestine and rat and mouse colon, 5-HT4 receptor immunoreactivity occurs in subpopulations of enteric neurons, including prominent large neurons. Double-staining has shown that these large neurons in the guinea-pig small intestine are also immunoreactive for two markers of intrinsic primary afferent neurons, cytoplasmic NeuN and calbindin. Some muscle motor neurons in the myenteric ganglia are immunoreactive for this receptor, whereas it is rarely expressed by secretomotor neurons. Immunoreactivity also occurs in the interstitial cells of Cajal but is faint in the external muscle. Expression of the protein and mRNA has been confirmed in extracts containing enteric neurons. The observations suggest that one site of action of 5-HT4 receptor agonists is the intrinsic primary afferent neurons.

Serotonin and cholecystokinin mediate nutrient-induced segmentation in guinea pig small intestine

“…While 5-HT 3 receptors have been confirmed in the myenteric plexus, the role and location of 5-HT 4 receptors are subjects of debate in the literature (21,22,27,31,38). The presence of 5-HT 4 receptors has been confirmed on submucosal and myenteric ISNs projecting to the mucosa in guinea pig small intestine (33) and may be involved in the regulation of motility (32). Li et al (25) observed decreased motility in tryptophan hydroxylase (TPH) type 2 (TPH2) knockout mice, which lack the neuronal isoform of TPH2, the rate-limiting enzyme in 5-HT biosynthesis; however, TPH1 knockout mice lacking the nonneuronal isoform expressed in EC cells did not show altered motility.…”

Synaptic Transmission at Functionally Identified Synapses in the Enteric Nervous System: Roles for Both Ionotropic and Metabotropic Receptors

“…They exhibit slow EPSPs in response to trains of stimuli [10] and express immunoreactivity for NK 1 [73], 5-HT 4 [100], GluR1 [69] and CRF1 receptors [71] (Table 1). Some excitatory input comes from myenteric AH/Dogiel type II neurons [42], which express tachykinins [16], suggesting that the slow EPSPs are mediated via NK 1 receptors.…”

Exogenous Serotonin Regulates Proliferation of Interstitial Cells of Cajal in Mouse Jejunum Through 5-HT2B Receptors

“…11 Of the 7 classes of 5-HT receptors, 5-HT 1 , 5-HT 2 , 5-HT 3 , 5-HT 4 , and 5-HT 7 receptors are known to be expressed in the gastrointestinal tract and to affect gastrointestinal motor function. [12][13][14][15][16][17][18][19][20] The role of 5-HT in regulating gastrointestinal motility by mediating the transduction of luminal signals across the mucosa and by participating in enteric neurotransmission is well established. 21,22 There is however significant evidence, mostly from outside the gastrointestinal tract but also in studies on enteric nervous system development, that shows that 5-HT can also regulate cell survival and proliferation.…”