Pharmacological Modulation of Adrenoreceptors Regulating Melanophore Dynamics in the Freshwater Teleost Fish, Balantiocheilos melanopterus

Abstract

In the present study, the dorso-lateral trunk scales of Balantiocheilos melanopterus (Bleeker) were used as a model to investigate sympathetic–neural melanophore responses. Pharmacological modulation was examined using adrenergic agonists such as norepinephrine, salbutamol, terbutaline, and ephedrine, alongside adrenergic antagonists including yohimbine, propranolol, phenoxybenzamine, and metoprolol. The adrenergic agonists induced pigment dispersion in melanophores in a dose-dependent manner, indicating strong stimulation of pigment innervation. In contrast, adrenergic antagonists—particularly those blocking α2-adrenoceptors—effectively inhibited this action, suggesting a regulatory role of these receptors. The responses were quantified using the Melanophore Index (MI) in isolated scale preparations. The findings support that melanophores in B. melanopterus possess functionally active adrenoreceptors, including α2-subtypes, which mediate bidirectional pigment translocation through microtubule-associated mechanisms.