Anxiolytic effects of diazepam in Trinidadian guppies exposed to chemical cues indicating predation risk

The fear of predation is pervasive among vertebrate prey species, being characterized by neurobiological and behavioral changes induced by risk exposure. To understand the acquisition and attenuation of fearful phenotypes, such as dimensions of posttraumatic stress, researchers often use animal models, with prey fishes recently emerging as a nontraditional but promising model. Much is known about fear acquisition in prey fishes such as the Trinidadian guppy, Poecilia reticulata, which inhabit high and low predation sites. Little is known, however, about whether a guppy model shows fear attenuation via therapeutic treatments, such as commonly prescribed anxiolytic drugs, like benzodiazepines. In this study, we used Trinidadian guppies from wild populations to explore the interactive effects of exposure to the anxiolytic drug, diazepam, and exposure to predation risk in the form of injured conspecific cues (i.e. alarm cues) that reliably indicate a predator attack. In Experiment 1, juvenile guppies from both high- and low-predation populations were given a 10-min exposure to diazepam (160 µg/l), resulting in the loss of fear behavior when simultaneously presented with alarm cues. In Experiment 2, we found that a prior 10-min exposure to diazepam (160 µg/l) for adult guppies significantly reduced their subsequent fear behavior toward a separate exposure to alarm cues, revealing that diazepam was having direct effects on guppy cognition rather than simply inactivating the alarm cues via chemical alteration. These anxiolytic effects thus add to the growing support for the predictive validity of prey fishes as animal models for exploring fear attenuation in humans.