Octopamine-containing neurons in the alimentary tract of the earthworm (Eisenia fetida).

Octopamine-containing nerve cells have been demonstrated in the enteric plexus of the earthworm (Eisenia fetida), applying immunocytochemistry and HPLC assay. A few octopamine-immunoreactive neurons occurred in the fore- and hindgut, whereas their number in the midgut was considerably greater. Octopamine levels detected by HPLC correlated with the distribution of octopamine-containing nerve cells. A regulatory role for these intrinsic octopaminergic neurons is suggested in the enteric plexus in the earthworm alimentary tract. This is the first report on the occurrence of octopamine-containing nerve cells in the peripheral nervous system of an invertebrate.