The pigmentary effector system. VI. The dual character of endocrine co-ordination in amphibian colour change

Abstract

The Pigmentary Effector System. VI. The Dual Character ofEndocrine Co-ordination in Amphibian Colour Change. In foregoing contributions to this series an attempt has been made to analyse the process of co-ordination in a characteristic mode of behaviour encountered in Amphibia and Reptiles. It is now clearly established that the pituitary gland is an essential agency in determining Amphibian colour change. Accept ing this conclusion, it is still possible to entertain the hypothesis that the secretion of the pituitary gland is merely a condition of the response of the melanophores to nervous impulses in efferent fibres supplying the skin. The present investigation is an attempt to subject this possibility to more rigorous examination. The direct innervation of Amphibian melanophores has not been established by histological examination, and the time relations of pig mentary effector activity in Amphibia do not suggest the intervention of a peripheral nervous mechanism. As shown in the last communication of this series, the melanophores of Reptiles are directly innervated. Experiments on on May 11, 2018 http://rspb.royalsocietypublishing.org/ Downloaded from Pigmentary Effector System. 11 stimulation and section of peripheral nerve trunks have led investigators on Amphibian colour change to ambiguous results, which have been extensively criticised elsewhere. The chief source of misunderstanding arises from the fact that peripheral nerves in general contain vasomotor components. In work on the chameleon it has been possible to demonstrate segmental effects of nervous origin, by employing as a stimulus to generalised pallor an agency for which the receptor surface is localised. For further analysis of co-ordination in Amphibian colour change it now becomes necessary to undertake a more precise definition of the receptive field. A visual response naturally suggests itself as the most convenient type for this purpose. In the European frog (Rana temporaria) various factors, including humidity and temperature, significantly co-operate with illumination to determine pigmentary effector activity. The South African clawed toad is an aquatic Anuran whose chromatic responses are almost entirely determined by photic stimuli. This circumstance has made it possible to explore the problem of co-ordination more thoroughly than in previous researches recorded in this series of communications.In Xenopus as in other Anura there are three types of pigmentary effector organs. These are (a) the epidermal melanophores, (b) the dermal melano phores, and (c) the xantholeucophores. The dermal melanophores are the most important agents in the visible reaction. Their condition can easily be followed by microscopic examination of the web. In what ensues attention is directed to the dermal melanophores, unless otherwise stated.Those who have studied pigmentary effector activity in the English common frog are agreed that humidity and temperature are eminently significant external agencies. In consequence the influence of light assumes a sub ordi...

Nitric oxide synthase and background adaptation in Xenopus laevis

“…The toads were kept under constant illumination on either a black or a white background for at least 3 weeks (22°C) and fed beef heart and trout pellets (Trouvit, Trouw, Putten, The Netherlands) once a week. Melanophore indices were estimated according to the protocol of Hogben and Slome (1931).…”

Characterization of pigment aggregating α2‐adrenoceptors of fish melanophores by use of different agonists after partial irreversible receptor inactivation

“…The effects of different drugs on the aggregating response of the melanophores were studied through a light microscope (Leitz SM Lux) using a magnification of x 100. The effects were evaluated according to the melanophore index (Hogben & Slome, 1931;Andersson et al, 1984;Karlsson et al, 1987). All drugs used in the experiments were dissolved in the saline buffer solution.…”

Morphology of the pars intermedia and the melanophore-stimulating cells in Xenopus laevis in relation to background adaptation

“…All animals were eared and held on a grey background before the ex periments started. Consequently, they showed a meanophore index (MI) of 3 or less, according to the protocol of Hogben and Slome (1931). A MI of 1 indi cates full aggregation of melanin in dermal melanophores, a MI of 5 indicates full dispersion.…”