EFFECTS OF ADRENERGIC DRUGS ON MELANOPHORES OF MINNOW PHOXINUS PHOXINUS (L)

1. 1. The chromatic activity and potency of some adrenergic drugs (sympathomimetic amines, α- and β-adrenergic blocking agents and hypotensive agents) were investigated in intact and operated minnows using the Derived Ostwald Index as a simple method for measuring melanophore responses. 2. 2. The actions of the drugs, and the changes in sensitivity of sympathomimetic amines after operations, suggest that chromatic fibres entering the autonomic chain of the fish are preganglionic and possibly cholinergic. 3. 3. Postganglionic fibres from sympathetic ganglia are adrenergic, pass straight to the skin in the mixed spinal nerves and innervate the melan directly. 4. 4. The fibres release catecholamine transmitter from an adrenergic store in or near the axon terminals which stimulates pigment aggregation by combination with an adrenergic receptor which has α-properties. © 1969.