Altered Left / Right Brain Asymmetry Disrupts Normal Behavior of Ciona Larvae

Abstract

With 177 neurons, the tunicate Ciona intestinalis are wonderfully simple. Its mapped connectome and concise behavioral repertoire let us investigate the relationship between brain and behavior. The Ciona brain is anatomically asymmetrical. We found that dechorionation, a common procedure that removes the egg’s protective membrane, disrupts this asymmetry. Ciona larvae display gravitaxis, a reorientation and upwards swimming behavior relying upon a disinhibitory circuit, in response to dimming ambient light. Using gravitaxis assays, we discovered that larvae dechorionated earlier in development, which possess considerably altered brain asymmetry, also display significantly impaired behavior compared to larvae dechorionated later and undechorionated larvae. Researchers should therefore use caution when drawing conclusions from experimental manipulations, if they dechorionate larvae early. We have found it possible to behaviorally sort early-dechorionated larvae and obtain animals with normal gravitactic responses. This may provide an alternative to tedious microinjections of gene constructs in future experiments that explore Ciona neurobiology.