Social environment modulates anxiogenic effects of caffeine in zebrafish

Zebrafish has recently become a species of choice in a number of preclinical studies to examine whether and how psychoactive compounds modulate individual and social behaviors. Here, we sought to contribute an improved understanding of the effects of caffeine, a well-known anxiogenic compound, on the swimming activity and the collective response of zebrafish. To investigate how the social environment influences individual response to acute caffeine treatment, we measured the behavior of a caffeine-treated subject swimming in isolation or in the presence of a group of untreated conspecifics. The experimental paradigm used a recently developed automatic tracking system to extract individual trajectories of zebrafish and preserve their identities over time. Our results indicate that caffeine reduces the swimming activity of fish tested in isolation, and that this effect is mitigated by the presence of untreated conspecifics. The collective response is also influenced by caffeine exposure at low doses, whereby caffeine-treated subjects may act as group leaders by taking anticipatory turning manoeuvres that are followed by the rest of the group. While anxiogenic effects of caffeine could explain the reduction in the swimming activity, the observed variation in the collective response is likely related to the interplay between anxiogenic and psychostimulant properties of caffeine.