Muscarinic cholinoceptors mediate neurally evoked pigment aggregation in glass catfish melanophores

Sympathetic innervation to the melanophores of a siluroidParasilurus has been the sole instance of such innervation among lower vertebrates, in which the peripheral transmission to the effector cells is peculiarly cholinergic (Fujii andMiyashita, 1976). In an effort to find a similar case, we studied the nature of transmission to melanophores of a glass catfishKryptopterus. Electrical nervous stimulation brought about melanosome aggregation in the melanophores. While catecholamines were found ineffective, acetylcholine and its analogues were potently active in aggregating pigment. Atropine or scopolamine interferred with the action of both nervous stimulation and acetylcholine. Physostigmine, on the other hand, augmented the cholinergic effects. The conclusion was that the transmission was cholinergic, being mediated by cholinoceptors of muscarinic type, as in the case ofParasilurus.