Serotonin, but not dopamine, controls stress response and anxiety-like behavior in crayfish, <i>Procambarus clarkii.</i>

Abstract

In the animal kingdom, biogenic amines are widespread modulators of nervous system that frequently interact in the control of mood. Our previous investigations in crayfish (Procambarus clarkii) have established that stress induces changes in brain serotonin (5-HT) concentrations that are responsible for the appearance of anxiety-like behavior (ALB). The following study further analyzes the roles of 5-HT and of another biogenic amine, dopamine (DA), on crayfish response to stress. Results showed that the intensity of crayfish ALB depended on the intensity of stressful stimulation and was associated with increased concentrations of 5-HT in the brain. These 5-HT levels were significantly correlated, before, as well as after stress, with those of DA, which were approximately 3-5 times less abundant. However, whereas ALB intensity was clearly correlated with brain 5-HT concentrations, it was not significantly correlated with those of DA. Moreover, contrary to 5-HT, DA injections were not able to elicit stress response and ALB. Incidentally, 5-HT and DA levels were not modified by treatment with the anxiolytic chlordiazepoxide, confirming that ALB suppression by this ligand of GABA-A receptors acted downstream and independently from changes in crayfish bioamine levels. Our study also provided evidence that the anxiogenic effect of 5-HT injections can be prevented by a preliminary injection of 5-HT antagonists. Altogether, our results emphasize that the rises in the brain concentrations of 5-HT, but not of DA, play a role in controlling the induction and the intensity of crayfish ALB.