Anxiogenic and anxiolytic modulators differentially affect thigmotaxis and thrashing behavior in adult zebrafish during habituation to the open field test

The Open Field Test (OFT) is a valuable paradigm to study the effects of distinct anxiety-like states on exploratory dynamics. Zebrafish responds to anxiogenic and anxiolytic protocols in the OFT, but the influence of such manipulations on the habituation process is still unclear. Here, we aimed to elucidate how distinct anxiety modulators influence thigmotaxis over time and thrashing behavior. For this, adult zebrafish (Danio rerio) were submitted to the morphine (1.5 mg/L) withdrawal protocol (MOR) and acute conspecific alarm substance (CAS) at 3.5 mL/L for 5 min as anxiogenic exposures. For anxiolytic treatments, we selected acute ethanol (ETOH) at 0.5 % (v/v) for 1 h and acute fluoxetine (FLU) at 100 µg/L for 15 min. Then, fish were individually transferred to a 10-min OFT trial, with posterior analysis of behavioral activity. While MOR responses comprised hyperactivity, higher thigmotaxis, and increased thrashing, CAS showed heightened total immobility. ETOH exposure decreased time spent and distance traveled in the periphery, thrashing behavior, and locomotion. FLU group spent less time in the periphery, showing decreased thigmotaxis and thrashing. Pearson analyses contributed to elucidate how endpoint data correlate to each other, reinforcing the distinct responses observed. Overall, our study reinforces the differential effects evoked by anxiogenic and anxiolytic protocols regarding thigmotaxis. Moreover, our results suggest that thrashing behavior configures a valuable tool to improve behavioral analyses in the OFT, contributing to further in-depth investigations related to distinct anxiety-like states.