Inhibition of planarian regeneration by melatonin

Abstract

Melatonin, which is a substance produced by the pineal body in vertebrates, inhibited regeneration in the planarian Dugesia japonica japonica Ichikawa et Kawakatsu. When decapitated planarians were maintained in a 1 mmol dm^-3 solution of melatonin, formation of the head was retarded; formation of the eyes, however, was not disturbed. Similarly in animals from which the tail was cut, regeneration of the tail was retarded if the animals were kept in melatonin solution of 1 mmol dm^-3. The effect was reversible once the melatonin was removed. Retardation of regeneration did not occur with similar application of three melatonin derivatives, serotonin hydrochloride, N-acetylserotonin, and 6- hydroxymelatonin. Melatonin endogenous to the planarian could be demonstrated by means of radioimmunoassay and was more abundant in the head region than other regions of the body. Melatonin, thus, appears to playa role in regulating regeneration in planarians and conceivably provides positional information in that process.