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

Abstract
Nervous control of melanosome aggregation of melanophores of L. 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 alpha2-adrenoceptor subtype, since they were inhibited by yohimbine but not by prazosin. Stimulation of the alpha2-adrenoceptors by noradrenaline [norepinephrine] was associated with a significant reduction of the cAMP content of the melanophores. Adrenergic nerves apparently control melanosome aggregation via alpha2-adrenoceptors and these receptors are coupled to the adenylate cyclase-cAMP system of the melanophores.

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