Psychopharmacological effects of acute exposure to kynurenic acid (KYNA) in zebrafish

A metabolite of the kynurenine pathway, kynurenic acid (KYNA) is an important endogenous neuromodulator and neuroprotector, that also exerts neurotropic effects following exogenous administration. In humans and animals, KYNA regulates affective and cognitive responses, acting mainly as an antagonist of glutamatergic receptors. However, the complete psychopharmacological profile of KYNA (which includes the activity of several neurotransmitter receptors) is poorly understood, and merit further studies. Aquatic models are rapidly emerging as useful tools in translational psychopharmacology research. Here, we exposed adult zebrafish (Danio rerio) to exogenous KYNA for 20 min, and assessed their behavior in the novel tank test. Exposure to KYNA (20 mg/L) in this paradigm evoked overt effects in fish, including decreased latency to enter the top half of the tank, increased number of top entries and longer top duration. In contrast, locomotor activity indices (swimming distance and velocity) were not affected by KYNA in this study. Overall, our results show KYNA has an anxiolytic-like pharmacological effect in zebrafish, and therefore strongly support the utility of zebrafish models in neurotropic drug screening, including drugs acting at central glutamatergic system. Robust phenotypic differences evoked by KYNA, revealed here using three-dimensional (3D) reconstructions of zebrafish locomotion in X, Y and time (Z) coordinates, confirm this notion, also demonstrating the value of 3D-based phenotyping approaches for high-throughput drug screening using zebrafish models.