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Strain-specific genetics, anatomy and function of enteric neural serotonergic pathways in inbred mice

By Kathleen B Neal, Laura J Parry and Joel C Bornstein


Serotonin (5-HT) powerfully affects small intestinal motility and 5-HT-immunoreactive (IR) neurones are highly conserved between species. 5-HT synthesis in central neurones and gastrointestinal mucosa depends on tissue-specific isoforms of the enzyme tryptophan hydroxylase (TPH). RT-PCR identified strain-specific expression of a polymorphism (1473C/G) of the tph2 gene in longitudinal muscle–myenteric plexus preparations of C57Bl/6 and Balb/c mice. The former expressed the high-activity C allele, the latter the low-activity G allele. Confocal microscopy was used to examine close contacts between 5-HT-IR varicosities and myenteric neurones immunoreactive for neuronal nitric oxide synthase (NOS) or calretinin in these two strains. Significantly more close contacts were identified to NOS- (P < 0.05) and calretinin-IR (P < 0.01) neurones in C57Bl/6 jejunum (NOS 1.6 ± 0.3, n= 52; calretinin 5.2 ± 0.4, n= 54), than Balb/c jejunum (NOS 0.9 ± 0.2, n= 78; calretinin 3.5 ± 0.3, n= 98). Propagating contractile complexes (PCCs) were identified in the isolated jejunum by constructing spatiotemporal maps from video recordings of cannulated segments in vitro. These clusters of contractions usually arose towards the anal end and propagated orally. Regular PCCs were initiated at intraluminal pressures of 6 cmH2O, and abolished by tetrodotoxin (1 μm). Jejunal PCCs from C57Bl/6 mice were suppressed by a combination of granisetron (1 μm, 5-HT3 antagonist) and SB207266 (10 nm, 5-HT4 antagonist), but PCCs from Balb/c mice were unaffected. There were, however, no strain-specific differences in sensitivity of longitudinal muscle contractions to exogenous 5-HT or blockade of 5-HT3 and 5-HT4 receptors. These data associate a genetic difference with significant structural and functional consequences for enteric neural serotonergic pathways in the jejunum

Topics: Neuroscience
Publisher: Blackwell Science Inc
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Provided by: PubMed Central
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