Adrenergic nerves and the alpha₂‐adrenoceptor system regulating melanosome aggregation within fish melanophores

Abstract

Nervous control of melanosome aggregation of melanophores of Labrus ossifagus was studied by electrical field stimulation of isolated scales. Field stimulation elicited a rapid melanosome aggregation which was reversible upon interruption of the stimuli. The response was blocked by guanethidine indicating that adrenergic nerves were stimulated. The melanophore receptors which mediate the nerve-controlled pigment aggregation were characterized to be of the alpha 2-adrenoceptor subtype, since they were inhibited by yohimbine but not by prazosin. Stimulation of the alpha 2-adrenoceptors by noradrenaline was associated with a significant reduction of the cyclic AMP content of the melanophores. It is suggested that adrenergic nerves control melanosome aggregation via alpha 2-adrenoceptors and that these receptors are coupled to the adenylate cyclase-cyclic AMP system of the melanophores.