THE EFFECT OF CAFFEINE ON THE MELANOPHORES OF FUNDULUS

¹ Marine Biological Laboratory, Woods Hole, Massachusetts

The melanophores of larvae and adults of Fundulus are modified or specialized smooth muscle cells innervated by the sympathetic nerves. There seems to be no evidence of a parasympathetic innervation. For this reason the intact melanophore proved to be suitable material for a study of the differential effect of caffeine on the nerves and smooth muscle.

Caffeine in concentrations varying from m/100 to m/1000 in sea water produced an expansion of previously contracted melanophores. There is no evidence that caffeine produces a contraction of expanded cells. Melanophores which had been freed from the nervous system by cutting the nerves did not respond to caffeine. Melanophores expanded in caffeine solution slowly recovering when the fish were removed to normal sea water.

From the results of the experiments presented it seems evident that caffeine has a marked depressing effect on the sympathetic nervous system supplying the melanophore but no effect upon the modified smooth muscle cells.