Noradrenaline‐ and Melatonin‐Mediated Regulation of Pigment Aggregation in Fish Melanophores

Abstract

The effects of melatonin and noradrenaline (NA) on bi-directional melanosome transport were analysed in primary cultures of melanophores from the Atlantic cod. Both agents mediated rapid melanosome aggregation, and by using receptor antagonists, melatonin was found to bind to a melatonin receptor whereas NA binds to an alpha2-adrenoceptor. It has previously been stated that melatonin-mediated melanosome aggregation in Xenopus is coupled with tyrosine phosphorylation of a so far unidentified high molecular weight protein and we show that although acting through different receptors and through somewhat different downstream signalling events, tyrosine phosphorylation is of the utmost importance for melanosome aggregation mediated by both NA and melatonin in cod melanophores. Together with cyclic adenosine 3-phosphate-fluctuations, tyrosine phosphorylation functions as a switch signal for melanosome aggregation and dispersion in these cells.

A Critical Appraisal of Vitiligo Etiologic Theories. Is Melanocyte Loss a Melanocytorrhagy?

“…In frog skin, norepinephrine causes pigment aggregation with lightening and epinephrine has the same effect on cultured melanocytes from the embryonic newt (48). Recent studies in fish confirm these observations (83). In our experience, the addition of epinephrine or norepinephrine in established cultures of vitiligo or control melanocytes rapidly elicit a retraction and loss of dendrites over a period of 24 h (not shown).…”

Different strategies for color change

“…The extracellular stimuli that trigger bidirectional pigment translocations can be neuronal (fish) or hormonal (fish and amphibians). Noradrenaline stimulates very fast pigment aggregation in fish melanophores, and the circadian hormone melatonin has been shown to either induce aggregation per se [28], or to potentiate noradrenaline-induced aggregation in these cells [29]. Binding of noradrenaline to a2-adrenoreceptors induces inhibition of adenylate cyclase followed by a decrease in cAMP and inactivation of PKA.…”

Skin Biopsies as Tools to Measure Fish Coloration and Colour Change

“…Melanophores isolated by this procedure were used for immunocytochemistry, microinjections of anti-dynein antibodies, melanosome trackings and various other manipulations. Altogether, melanophore primary cultures have experimentally been a very powerful system for the present theory of the intracellular transport mechanisms in these cells -from the cytoskeleton to second messengers and receptors (Nilsson et al, 1996;Nilsson andWallin 1997, 1998;Aspengren et al, 2003;.…”