Octopamine in Lumbricus terrestris: presence, synthesis and effect of octopamine on the spontaneous rhythmic contractions of the ventral nerve cord.

A radiochemical-enzymatic assay was utilized to measure endogenous levels of octopamine in the nerve cord and blood of the earthworm. The results show the presence of octopamine in the ventral nerve cord and blood at concentrations of 2.79 +/- 0.5 (means +/- S.D.) ng/mg wet tissue weight and 9.5 +/- 1.6 x 10(-8) M (means +/- S.D.) respectively. The ability of the ventral nerve cord to synthesize octopamine was investigated by incubating the tissue in vitro in radiolabeled percursors. The results show the synthesis of [3H]octopamine from both precursor [3H]tyrosine and [3H]tyramine. In vitro incubation of the isolated ventral nerve cord in physiological concentrations of octopamine revealed modulation of the spontaneous rhythmic contractions of the nerve cord. The data provide direct support for a modulatory role of octopamine in L. terrestris.