The action of reserpine on teleost melanophores

Reserpine caused darkening of both pencil fish and angelfish, this effect lasted for at least 10 and 25 days respectively.The aggregation of pigment granules within the melanophores evoked by stimulation of the nerves supplying the melanophores was inhibited by reserpine in both species. Reserpine caused a lowering of the catecholamine content of pencil fish skin. The time course both these effects paralleled the time course of darkening. The response of the melanophores of the angelfish to adrenaline, noradrenaline, dopamine, and melatonin was not affected by treatment with reserpine for 3 days. However, reserpine treatment for 14 days induced a marked sensitivity to noradrenaline. Reserpine partially abolished the response to tyramine in both pencil fish and angelfish. Small doses of noradrenaline and adrenaline given to reserpine-treated angelfish partially restored the response of the melanophores to nerve stimulation. No action of ACTH, MSH, nor direct effect of reserpine could be demonstrated on melanophores of either species. It was concluded that reserpine acts on the melanophores of pencil fish and angelfish in an indirect way by depletion of catecholamines from the sympathetic nerves supplying the melanophores.