色素胞運動におけるシグナル変換機構

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We found that peripheral darkened area generated by nerve cutting paled during the night. The phenomenon was due to the increased secretion from the pineal of melatonin. Electron microscope observations revealed that motile iridophores of the blue-green stripe of neon tetras show their motility through a mechanism resembling the "Venetian blind", and that dynein-tubulin system is mainly concerned with the cellular motility. By penetrating the chromatophores, choline actively dispersed melanosomes. Common pencilfish displays a longitudinal dark stripe, while it shows a few spots at night. We found that the area outside the stripe but within the spots darkened at night, and concluded that the melanosome dispersion there may also be due to melatonin, but novel receptors that mediate pigment dispersion are involved. The receptors concerned may be designated as beta-melatonin receptors. Atropine was shown to penetrate the melanophores to induce pigment. Morphological color changes due to prolonged background adaptation were found to be deeply related to the presence of chromatic nerves. Outside the order Siluriformes, muscarinic cholinoceptors were first found to present in the melanophores of two ciprinid species. Red abdominal skin of tetra fish exhibits circadian color changes, becoming pale during the night. Increased levels of melatonin may cause aggregation of pigment in erythrophores. Endothelin-1 strongly aggregated melanosomes in many species of fish. Prolactins from tilapia produced dispersion of pigment in xanthophores of tilapia. It may therfore suggested that it acts as yellowing hormon.