10 August 2017

Shiratori and colleagues

Shiratori C, Suzuki N, Momohara Y, Shiraishi K, Aonuma H Nagayama T. 2017. Cyclic AMP-regulated opposing and parallel effects of serotonin and dopamine on phototaxis in the Marmorkrebs (marbled crayfish). European Journal of Neuroscience 46(3): 1863–1874. http://dx.doi.org/10.1111/ejn.13632

Abstract

Phototactic behaviors are observed from prokaryotes to amphibians and are a basic form of orientation. We show that the marbled crayfish displays phototaxis in which the behavioral response reverse from negative to positive depending on external light conditions. Animals reared in a 12L/12D light cycle showed negative phototaxis during day-time and positive phototaxis during night-time. Animals reared under constant light conditioning showed negative phototaxis during day- and night-time, while animals reared under constant dark conditioning showed positive phototaxis during day- and night-time. Injection of serotonin leads to a reversal of negative to positive phototaxis in both light/dark-reared and light/light-reared animals while injection of dopamine induced reversed negative phototaxis in dark/dark-reared animals. Four hours of dark adaptation were enough for light/dark-reared animals to reverse phototaxis from negative to positive. Injection of a serotonin 5HT1 receptor antagonist blocked the reverse phototaxis while serotonin 5HT2 receptor antagonists had no effects. Similarly, dark/dark-reared animals reversed to showing negative phototaxis after 4 hours of light adaptation. Injection of a dopamine DA1 receptor antagonist blocked this reverse phototaxis, while dopamine DA2 receptor antagonists had no effects. Injection of a cAMP analogue into light/dark-reared animals blocked reverse phototaxis after dark adaptation, while adenylate cyclase inhibitor in dark/dark-reared animals blocked reverse phototaxis after light adaptation. These results strongly suggest that serotonin mediates positive phototaxis owing to decreased cAMP levels, while dopamine-mediated negative phototaxis occurs due to increased cAMP levels. Supporting this, the ratio of serotonin to dopamine in the brain was much higher in dark/dark-reared than light/dark-reared animals

Keywords: crayfish • taxis • biogenic amines • second messenger • circadian rhythm

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