SOME NEUROHUMORAL EVIDENCE FOR DOUBLE INNERVATION OF XANTHOPHORES IN KILLIFISH (FUNDULUS)

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Abstract
In a majority of over 50 Fundulus majalis tested, the part of a previously faded primary denervated caudal band flanked by two new secondary bands showed pigment dispersal in its xanthophores, as if affected by the stronger dispersal in those of the adjacent secondary bands. The effect appeared whether or not the radial blood vessels were cut by the incision that produced the primary band. Intact control bands, flanked identically, generally gave no sign of a like effect. A few experiments on F. heteroclitus revealed comparable responses by its xanthophores. These observations derived from the xanthophores were paralleled by some from the melanophores in F. majalis. Characteristically, slow changes in the xanthophores in response to bottom color proceeded axipetally in primary bands, and they took place in secondary bands by an analogous invasion from the edge adjoining an innervated sector rather than from the edge of the primary band. Quick pigment concentration apparently excited by handling, holding on the microscope stage, etc., appears in denervated bands as soon as in intact sectors. These results, certain exceptions, and other available evidence together prompt the conclusion that the xanthophores of Fundulus are probably controlled by nervous and humoral mechanisms involving the following components in addition to a dispersing pituitary secretion and some concentrating hormone (adrenaline?): A. Double autonomic innervation, which includes (1) dispersing fibers, (2) concentrating fibers. B. Chemical mediation, the nerves secreting, respectively, (1) a dispersing neurohumor, (2) a concentrating neurohumor. C. Cellular transmission of these neurohumors to neighboring xanthophores.