A work, published in Science by French researchers from Université de Bordeaux (France), shows the presence of a neural mechanism of an anxiety-like behavior in animal, specifically crayfish, throughout evolution. It is claimed that anxiety has only been found in human and a few other vertebrates. This is the first case discovered in the history that anxiety-like behavior also exists in invertebrates. Additionally, they have also found that this emotion weakens and disappears as anxiolytic is injected (suggesting a similar mechanism as in human).
Figure 1: Photo of a crayfish used in the experiment (in the cross-shaped mazed)
First of all, anxiety is a form of behavioral response to stress, including lasting fear and nervousness. This involuntary response raises awareness and the ability of detecting threats in individuals, consequently, increasing their life expectancy.
During experiment, researchers repeatedly exposed crayfish to an electric field (stress environment) for thirty minutes before placing them in an aquatic cross-shaped maze. The maze was set up in a way that two of its arms were lit up and the other two were kept dark. Dark area was found to be reassuring for crayfish. Results of the experiments illustrate a tendency that those that are anxious stay in the dark arms of the maze and those who are not anxious (in the control group) remain throughout the whole maze.
From a neuro-biological standpoint, this anxiety response is related to an increase in serotonin level in brain. This neurotransmitter, is responsible for the feelings of well-being and happiness is released when body experiences stress, suppressing anxious feelings. Researchers have also injected a dose of anxiolytic, commonly used in human (benzodiazepine), to crayfish and found similar effects as if in human: weakening the symptoms of anxiety.
Researchers believe that this analysis of this ancestral behavior will essential for studying the neuronal bases of this emotion. This is also a behavioral study on a unique model, which is invertebrates. Further studies can be done based upon the finding from this experiment.
Posted by Phi Duong (Group A)