Anxiety-like behavior in crayfish is controlled by serotonin

Abstract

The crayfish that was afraid of the dark We tend to assume that complex emotions, such as anxiety, only occur in mammals or other cognitively complex vertebrates. But a heightened sense of awareness and the avoidance of novel or dangerous environments could be helpful for any animal species. Fossat et al. show that crayfish exposed to a stressful electric field refuse to enter dark arms in a light/dark maze, even after the electric field has been removed. The animals calmed down when they were injected with an anxiolytic drug used to treat anxiety in humans, and they entered the dark as normal. The stressed animals had increased levels of the neurotransmitter serotonin in the brain, and injections of serotonin induced anxiety-like behavior in control animals. Thus, these invertebrates display a primitive form of anxiety that shares a mechanism with the more complex emotions displayed by vertebrates. Science , this issue p. 1293