Serotonin-induced contraction in isolated intestine from a teleost fish (Carassius auratus): characterization and interactions with melatonin (original) (raw)

2010, Neurogastroenterology & Motility

Background Serotonin (5-HT) plays a critical role in several gastrointestinal functions in vertebrates. In teleosts lacking enterochromaffin cells, intestinal 5-HT originates from serotonergic enteric neurons. In the present study, the foregut of a stomachless teleost, the goldfish (Carassius auratus), was used to evaluate the in vitro effect of 5-HT on fish intestinal motility. We also studied the role of melatonin (MEL), an indoleamine sharing the biosynthetic pathway with 5-HT, as regulator of serotonergic activity. Methods An organ bath system, with longitudinal strips from the goldfish intestinal bulb attached to an isometric transducer was used to record foregut smooth muscle contractions. Key Results Concentration-dependent curves of the contractile response exerted by 5-HT and its agonists, 5-methoxytryptamine (5-MT) and 5-carboxamidotryptamine (5-CT), suggest a receptor-mediated action, supported by the blockade by a general 5-HT antagonist, methysergide. The 5-HT-induced contraction was abolished in the presence of atropine, revealing the involvement of cholinergic transmission in gut actions of 5-HT. Furthermore, MEL inhibited the contractile effect of 5-HT and its agonists by up to 50%, which was counteracted by MEL antagonists. Conclusions & Inferences We can provisionally propose that at least two different 5-HT receptor subtypes are involved in fish intestinal motility, a 5-HT 4 -like (5-MTpreferring) and a 5-HT 7 -like (5-CT-and fluphenazinesensitive) receptor. In summary, our results indicate that 5-HT regulates the contractile activity of goldfish foregut through specific receptors located in cholinergic neurons, and that MEL can modulate these serotonergic actions through high-affinity membrane receptors.