Fluorescent histochemistry of the teleost gut: evidence for the presence of serotonergic neurones.

The guts of the teleosts Myoxocephalus scorpius, Pleuronectes platessa and Clupea harengus were examined using fluorescent histochemistry and the innervation compared to that in mammals and other lower vertebrates. In Myoxocephalus and Pleuronectes both greeen and yellow fast fading fluorescent nerves were found in the intestine. To test whether the yellow nerves might be serotonergic, an attempt was made to extract 5-HT from the intestine of these fish in a region where enterochromaffin cells were absent. Chromatography of extracts showed the presence of 5-HT, and, in Myoxocephalus, dopamine.