Serotonergic neurons in the intestine of two teleosts, Carassius auratus and Oreochromis mossambicus, and the effect of serotonin on transepithelial ion-selectivity and muscle tension.
The application of an antiserum directed against rat serotonin demonstrated serotonin-immunoreactive cell bodies and varicose nerve fibres in the myenteric plexus of both goldfish and tilapia. In the circular muscle layer immunoreactive varicose nerve fibres and a few cell bodies could be detected. A fine network of varicose fibres was observed underlying the epithelial cells. Serotonin immunoreactivity was not observed along incoming mesenterial blood vessels, suggesting that the serotonergic neurons may be intrinsic to the intestine. Immunoreactive endocrine cells were shown in the intestinal epithelium of tilapia but not in goldfish. Serotonin caused a weak contraction of the intestinal wall of the goldfish which could be blocked by tetrodotoxin and by atropine, suggesting that serotonin has an indirect action on muscular contraction. In contrast, serotonin induced a relaxation of the intestinal wall of tilapia which could not be blocked by propranolol or by tetrodotoxin. This indicates that in this species serotonin may act directly on the muscle fibres. The ion-selectivity of the intestinal epithelium of both species was modulated by serotonin. Tetrodotoxin did not inhibit this effect, suggesting that serotonin acts directly on the epithelial cells. The presence of serotonergic fibres in the muscle layer and directly underneath the epithelium, along with the effect of serotonin on muscular tension and on the ion-selectivity of the epithelium, suggests that serotonin may play a role in the regulation of motility and the epithelial function of goldfish and tilapia intestine.
Kiliaan
A J
AJ
Department of Experimental Zoology, University of Amsterdam, The Netherlands.
Joosten
H W
HW
Bakker
R
R
Dekker
K
K
Groot
J A
JA
D000818:Animals; D003530:Cyprinidae / Q000378:metabolism*; D006054:Goldfish / Q000378:metabolism*; D007150:Immunohistochemistry; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000294:innervation*; D009129:Muscle Tonus / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism / Q000502:physiology*
D012701:Serotonin