Factors Influencing the State of Dispersion of the Dermal Melanophores in Rainbow Trout

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Abstract
The purpose of the investigation was to ascertain the optimum conditions for max. reactivity of these cells both in the live trout and in isolated skin strips and to determine the nature of their responses to various environmental and other stimuli. The rates of concn. and dispersion of the trout melanophores are among the most rapid recorded for teleost fishes. The normal state appears to be the dispersed phase. The melanophores in the live trout respond to certain influences, viz. changes in background illumination,O2 lack, and surface pressure which have no effect on these pigment cells in isolated skin strips. Light and asphyxia exert their action by way of the nervous system. The pressure effect is probably produced by K liberated from underlying muscle. Other factors, e.g., temp., pH, and numerous chemical and pharmacological compounds, produce similar changes in situ and detached melanophores. Reproducible quantitative studies were carried out more satisfactorily with skin strips. Optimum conditions for maintaining the reactivity of such isolated melanophores were a balanced soln. consisting of NaCl 0.8% and KC1 0.1%, temperature of 10[degree] and pH 5-0 to 9.0. To investigate the role of the autonomic system in the trout''s response to changes in intensity of background illumination, the effects of sympatho- and parasympathomimetic compounds were studied. The former, including epinephrine, ephedrine and neosynephrine, produced concentration of the melanophores; the latter, including acetylcholine, physostigmine and pilocarpine, caused dispersion. Acetylcholine produced re-dispersion of melanophores concentrated by epinephrine. Histamine showed only a slight concentrating effect while antihistaminics produced marked dispersion. Extracts of mammalian posterior pituitary gland injd. subcut. were found to produce local dispersion of light-concentrated melanophores. This effect could not be demonstrated in vitro. Extracts of mammalian thyroid caused marked concn. of the trout''s melanophores both in vivo and in vitro.