An in vitro study of α and β adrenoreceptors in melanosome differential aggregation and dispersion associated with cryptic patterning in winter flounder (Pleuronectes americanus)

Mayo, Dennis Joseph (1996) An in vitro study of α and β adrenoreceptors in melanosome differential aggregation and dispersion associated with cryptic patterning in winter flounder (Pleuronectes americanus). Masters thesis, Memorial University of Newfoundland.

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Abstract

The remarkable cryptic patterning capability of flatfish gives rise to important questions about the regulatory processes which must be involved in the differential control of melanophores. Winter flounder, Pleuronectes americanus, possess three distinct pattern components on its dark upper (ocular) surface that are important for cryptic patterning. These are the white spot, general background and dark band components that display differential chromatic responsiveness which has been studied using electrophysiological and pharmacological methods in the current work. -- In vitro experiments with K⁺ rich aggregating fluid (AF) or noradrenaline and phentolamine demonstrate that α-adrenoceptors mediate melanosome aggregation. Studies examining the effects of increasing concentrations of prazosin and yohimbine on melanosome aggregation evoked by electrical stimulation indicate that both α₁- and α₂-adrenoceptors play a role in melanosome aggregation, but there is a predominance of the latter. Experiments with atenolol suggest that there may be some β-adrenoceptor synergism involved in pigment aggregation. -- Topical application of low concentrations of soproterenol and noradrenaline enhance rates of in vitro melanosome dispersion in balanced salt solution which could be depressed with propranolol and suggests β-adrenoceptor mediation. The subtype of this adrenoceptor appears to be most likely the β₂ conformation based on studies with terbutaline. Denervation of scale slips in 6-OH dopamine followed by incubation in a high concentration of isoproterenol and propranolol results in complete melanosome aggregation. Incubation of denervated scale slips in the same concentration of isoproterenol and phentolamine results in the blockade of pigment aggregation. -- This study shows that α- and β₂-adrenoceptors play roles in pigment aggregation and dispersion respectively and that the melanophore response that is initiated is dependent upon neurotransmitter concentration. High concentrations of noradrenaline or isoproterenol evoke melanosome aggregation via α-adrenoceptors while low concentrations induce melanosome dispersion via β₂-adrenoceptors.

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