Anxiety is a serious mental disorder, and recent statistics have determined that 35.12% of the global population had an anxiety disorder during the COVID-19 pandemic. A mechanism associated with anxiolytic effects is related to nicotinic acetylcholine receptor (nAChR) agonists, principally acting on the α4β2 nAChR subtype. nAChRs are present in different animal models, including murine and teleosteos ones. Zebrafish has become an ideal animal model due to its high human genetic similarities (70%), giving it high versatility in different areas of study, among them in behavioral studies related to anxiety. The novel tank diving test (NTT) is one of the many paradigms used for studies on new drugs related to their anxiolytic effect. In this work, an adult zebrafish was used to determine the behavioral effects of 3- and 5-halocytisine derivatives, using the NTT at different doses. Our results show that substitution at position 3 by chlorine or bromine decreases the time spent by the fish at the bottom compared to the control. However, the 3-chloro derivative at higher doses increases the bottom dwelling time. In contrast, substitution at the 5 position increases bottom dwelling at all concentrations showing no anxiolytic effects in this model. Unexpected results were observed with the 5-chlorocytisine derivative, which at a concentration of 10 mg/L produced a significant decrease in bottom dwelling and showed high times of freezing. In conclusion, the 3-chloro and 3-bromo derivatives show an anxiolytic effect, the 3-chlorocytisine derivative being more potent than the 3-bromo derivative, with the lowest time at the bottom of the tank at 1mg/L. On the other hand, chlorine, and bromine at position 5 produce an opposite effect.

Background/Objective: Serotonin and dopamine are key neurotransmitters involved in regulating mood, anxiety, and locomotor activity. Specific transporters mediate their reuptake, SERT and DAT, making them targets for drugs such as Fluoxetine and Methylphenidate. Zebrafish (Danio rerio), due to their genetic and neurochemical similarity to humans, serve as a valuable model for studying the behavioral effects of these drugs. This study aimed to compare the behavioral phenotypes induced by SERT and DAT blockers in adult zebrafish using the Novel Tank Diving Test (NTT), thereby generating a swimming profile for drugs acting on these monoamine transporters that can be utilized in drug discovery and behavior. Methods: Adult zebrafish were administered Fluoxetine or Methylphenidate and subjected to the NTT. Behavioral endpoints measured included bottom-dwelling time (anxiety-like behavior), swimming velocity (locomotor activity), and transitions to the upper zone (exploratory behavior). Results: Fluoxetine treatment significantly reduced bottom-dwelling behavior, increased transitions to the upper zone, and decreased erratic swimming, indicating reduced anxiety and enhanced exploration. In contrast, Methylphenidate administration led to prolonged bottom-dwelling and reduced exploration, suggesting increased anxiety-like behavior and decreased exploration. These findings highlight distinct behavioral profiles resulting from selective modulation of serotonergic and dopaminergic pathways. Conclusions: The study demonstrates that SERT and DAT blockades produce divergent behavioral effects in adult zebrafish, with Fluoxetine exhibiting anxiolytic and exploratory-promoting actions. At the same time, Methylphenidate induces anxiety-like and less exploratory behaviors. These results underscore the utility of zebrafish as a valuable translational model for neuropharmacological research and drug discovery, providing insights into the differential impact of serotonergic and dopaminergic modulation on behavior.