Expression and function of 5-HT4 receptors in the mouse enteric nervous system.
The aim of the current study was to identify enteric 5-HT(4) splice variants, locate enteric 5-HT(4) receptors, determine the relationship, if any, of the 5-HT(4) receptor to 5-HT(1P) activity, and to ascertain the function of 5-HT(4) receptors in enteric neurophysiology. 5-HT(4a), 5-HT(4b), 5-HT(4e), and 5-HT(4f) isoforms were found in mouse brain and gut. The ratio of 5-HT(4) expression to that of the neural marker, synaptophysin, was higher in gut than in brain but was similar in small and large intestines. Submucosal 5-HT(4) expression was higher than myenteric. Although transcripts encoding 5-HT(4a) and 5-HT(4b) isoforms were more abundant, those encoding 5-HT(4e) and 5-HT(4f) were myenteric plexus specific. In situ hybridization revealed the presence of transcripts encoding 5-HT(4) receptors in subsets of enteric neurons, interstitial cells of Cajal, and smooth muscle cells. IgY antibodies to mouse 5-HT(4) receptors were raised, affinity purified, and characterized. Nerve fibers in the circular muscle and the neuropil in ganglia of both plexuses were highly 5-HT(4) immunoreactive, although only a small subset of neurons contained 5-HT(4) immunoreactivity. No 5-HT(4)-immunoreactive nerves were detected in the mucosa. 5-HT and 5-HT(1P) agonists evoked a G protein-mediated long-lasting inward current that was neither mimicked by 5-HT(4) agonists nor blocked by 5-HT(4) antagonists. In contrast, the 5-HT(4) agonists renzapride and tegaserod increased the amplitudes of nicotinic evoked excitatory postsynaptic currents. Enteric neuronal 5-HT(4) receptors thus are presynaptic and probably exert their prokinetic effects by strengthening excitatory neurotransmission.
Liu
Mintsai
M
Dept. of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA. ml27@columbia.edu
Geddis
Matthew S
MS
Wen
Ying
Y
Setlik
Wanda
W
Gershon
Michael D
MD
D017398:Alternative Splicing; D000818:Animals; D017615:Enteric Nervous System / Q000502:physiology* / Q000648:ultrastructure; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005260:Female; D008297:Male; D051379:Mice; D009474:Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000096:biosynthesis*; D044422:Receptors, Serotonin, 5-HT4 / Q000096:biosynthesis / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016708:Synaptophysin / Q000096:biosynthesis
D020033:Protein Isoforms; D016708:Synaptophysin; D044422:Receptors, Serotonin, 5-HT4