ADRENOCEPTORS IN CRYPTIC PATTERNING OF A FLATFISH, PLEURONECTES-AMERICANUS

Cryptic patterns of winter flounder, Pleuronectes americanus, possess general background: dark band and white spot components that display differential chromatic responsiveness which has been studied pharmacologically in the current work. In vitro experiments with catecholamines and phentolamine demonstrate that cc-adrenoceptors mediate melanosome aggregation in each pattern component. There was pattern-related differential responsiveness to noradrenaline, with EC50 values between 5.2 x 10(-7) M for dark bands and 2.6 x 10(-6) M for white spots. Phentolamine (10(-4) M) completely dispersed melanosomes, previously aggregated by noradrenaline (10(-5) M), in 9 min for the white spots compared with approximately 82.5% dispersion in 15 min for the other two components. High degrees of melanosome aggregation induced in vitro by isoproterenol (3.15 x 10(-5) M) were reversed differentially by propranolol (10(-4) M) indicating beta-adrenoceptor involvement, white spots displaying complete melanosome dispersion in 15 min with partial or no dispersion in the other two components. Phentolamine (10(-4) M) also reversed the effect of isoproterenol, so that the apparent beta-adrenoceptor synergism can be explained in terms of pattern-related presynaptic neuromodulation.