Light-Pituitary Reflex and the Adrenergic-Cholinergic Sympathetic Nerve in a Teleost

Abstract

Working on the snake fish (Ophiocephalus argus, Cantor), we found that its melanophores are under two types of control, one through the pituitary which is regulated by light and darkness, and the other through the sympathetic nerve which is partly adrenergic and partly cholinergic.

The Pituitary Control. After removal of the sympathetic chains at the level between the pectoral fin and cloaca, the fish developed, on a white background under the continuous illumination from a lamp of 100 W, a black color over the anterior denervated region. Subsequent enucleation of the eyes intensified this color into coal-black, whereas a previous hypophysectomy would prevent such an appearance. These results indicate clearly that the black color is due to the expansion of the melanophores produced by the pituitary principle whose continuous discharge is increased by darkness, 1 and whose effect is accentuated in the absence of the sympathetic influence. Similar results were obtained from frogs (Rana nigromaculata).

The Sympathetic Control. Adrenergic fibers. When the denervated area had become sufficiently sensitized, usually 3 days after the abdominal sympathectomy, stimulation of the myelencephalic sympathetic center would turn the black denervated area pale. From 10 days onward, the same phenomenon would occur spontaneously under continuous light illumination. This pallor is apparently due to diffusion into the denervated area of adrenaline-like substance liberated at the nerve-endings of the neighboring normal region in response to electrical or light stimulation. We may recall that Parker 3 has advanced similar explanation for the fading of the dark caudal band in Fundulus.