The release of neuronal 5-HT from the intestine of a teleost fish, Platycephalus bassensis.

The superfused, isolated intestine of a teleost fish which lacks enterochromaffin cells spontaneously released 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), presumably from enteric neurons. The release of 5-HT, but not 5-HIAA, increased on transmural electrical stimulation. Addition of tetrodotoxin or omission of Ca2+ from the superfusate prevented the increase in 5-HT release on electrical stimulation. Fluoxetine added to the superfusate increased the amount of 5-HT released spontaneously but also prevented the increase in 5-HT release on stimulation. Pretreatment of fish with reserpine markedly reduced tissue levels of 5-HT and 5-HIAA and led to an almost complete loss of the spontaneous release of 5-HT and an elimination of the stimulated release of 5-HT.