Autoradiographic detection of indolamine and catecholamine neurons in the nervous system of Owenia fusiformis (Polychaeta, Annelida).

Light- and electron-microscopic autoradiographic studies were carried out on Owenia to detect selectively catecholaminergic and indolaminergic neurons at two appropriate body levels according to the regenerative properties of this annelid, i.e. in the 1st and the 4th abdominal segments. Autoradiographically, intense 3H-5-hydroxytryptamine accumulation is seen in the 1st abdominal segment, and a less intense autoradiographic reaction in the 4th segment. Roughly, a similar difference in the distribution of the label is seen at both levels following 3H-noradrenaline administration. These observations, confirmed by a quantitative uptake analysis, suggest the presence of catecholaminergic and indolaminergic neurons in Owenia.