Ketamine modulates the exploratory dynamics and homebase-related behaviors of adult zebrafish

Anxiety can be a protective emotion when animals face aversive conditions, but is commonly associated with various neuropsychiatric disorders when pathologically exacerbated. Drug repurposing has emerged as a valuable strategy based on utilizing the existing pharmaceuticals for new therapeutic purposes. Ketamine, traditionally used as an anesthetic, acts as a non-competitive antagonist of the glutamate N-methyl-D-aspartate (NMDA) receptor, and shows potential anxiolytic and antidepressant effects at subanesthetic doses. However, the influence of ketamine on multiple behavioral domains in vertebrates is not completely understood. Here, we evaluated the potential modulatory effect of ketamine on the spatio-temporal exploratory dynamics and homebase-related behaviors in adult zebrafish using the open field test (OFT). Animals were exposed to subanesthetic concentrations of ketamine (0, 2, 20, and 40 mg/L) for 20 min and their locomotion-, exploration- and homebase-related behaviors were assessed in a single 30-min trial. Our data revealed that acute ketamine (20 and 40 mg/L) induced hyperlocomotion, as verified by the increased total distance traveled. All concentrations tested elicited circling behavior, a stereotyped-like response which gradually reduced across the periods of test. We also observed modulatory effects of ketamine on the spatio-temporal exploratory pattern, in which the reduced thigmotaxis and homebase activity, associated with the increased average length of trips, suggest anxiolytic-like effects. Collectively, our findings support the modulatory effects of ketamine on the spatio-temporal exploratory activity, and corroborate the utility of homebase-related measurements to evaluate the behavioral dynamics in zebrafish models.