Acute Exposure to Fluoxetine Alters Aggressive Behavior of Zebrafish and Expression of Genes Involved in Serotonergic System Regulation

Abstract

Zebrafish, Danio rerio, is an emerging model organism in stress and neurobehavioral studies. In nature, the species forms shoals, yet when kept in pairs it exhibits an agonistic and anxiety-like behavior that leads to the establishment of dominant-subordinate relationships. Fluoxetine, a selective serotonin reuptake inhibitor, is used as an anxiolytic tool to alter aggressive behavior in several vertebrates and as an antidepressant drug in humans. Pairs of male zebrafish were held overnight to develop dominant—subordinate behavior, either treated or non-treated for 2 h with fluoxetine (5 mg L−1), and allowed to interact once more for 1 h. Behavior was recorded both prior and after fluoxetine administration. At the end of the experiment, trunk and brain samples were also taken for cortisol determination and mRNA expression studies, respectively. Fluoxetine treatment significantly affected zebrafish behavior and the expression levels of several genes, by decreasing offensive aggression in dominants and by eliminating freezing in the subordinates. There was no statistically significant difference in whole-trunk cortisol concentrations between dominant and subordinate fish, while fluoxetine treatment resulted in higher (P = 0.004) cortisol concentrations in both groups. There were statistically significant differences between dominant and subordinate fish in brain mRNA expression levels of genes involved in stress axis (gr, mr), neural activity (bdnf, c-fos), and the serotonergic system (htr2b, slc6a4b). The significant decrease in the offensive and defensive aggression following fluoxetine treatment was concomitant with a reversed pattern in c-fos expression levels. Overall, an acute administration of a selective serotonin reuptake inhibitor alters aggressive behavior in male zebrafish in association with changes in the neuroendocrine mediators of coping styles.

A quantitative trait locus on chromosome 1 modulates intermale aggression in mice

“…HTR2B mutations are also associated with aggression in other species, such as pigs (Chu et al , 2017) and zebrafish (Theodoridi et al , 2017). In humans, a specific 5-HT2B receptor stop codon (HTR2B Q20*) observed in a Finnish male population segregates with severe impulsivity, psychosis, and early-onset schizophrenia (Bevilacqua et al , 2010).…”

“…37 HTR2B mutations are also associated with aggression in other species, such as pigs 38 and zebrafish. 39 In humans, a specific 5-HT2B receptor stop codon (HTR2B Q20*) observed in a Finnish male population segregates with severe impulsivity, psychosis and early-onset schizophrenia. 16 These individuals exhibit increased aggressive behavior toward themselves and others, as well as criminal activity, substance abuse, suicide and depression, 18 especially after alcohol use.…”

Effects of monoamine manipulations on the personality and gene expression of three-spined sticklebacks

“…SSRI drugs inhibit the reuptake of the neurotransmitter serotonin from the synaptic cleft during signaling between neurons, by blocking the serotonin transporter; this results in serotonin remaining in the cleft for longer, prolonging the stimulation of serotonin receptors (Vaswani et al, 2003). Exposure to fluoxetine reduces aggression (Perreault et al, 2003;Bell et al, 2007;Clotfelter et al, 2007;Carere and Maestripieri, 2013;Eisenreich et al, 2017;Theodoridi et al, 2017;Barbosa et al, 2018;Kellner et al, 2018). Dopamine levels, polymorphisms in dopamine receptor and transporter genes, and differential methylation of dopamineassociated genes are related to novelty-seeking and exploratory behavior in mammals and birds (Schinka et al, 2002;Fidler et al, 2007;Egan et al, 2009;Filby et al, 2010;van Oers and Mueller, 2010;Shaw and Øverli, 2012;Caramaschi et al, 2013;Carere and Maestripieri, 2013;Holtmann et al, 2016;Abbey-Lee et al, 2018a).…”

“…The monoamine systems can work in conjunction, with both serotonin and dopamine involved in physiological stress responses (Winberg and Nilsson, 1993;Øverli et al, 1999;Höglund et al, 2001;Lillesaar, 2011;Melnyk-Lamont et al, 2014). Additionally, fluoxetine can influence more than just the serotonin system; it has been shown to decrease whole-body cortisol concentrations in zebrafish (Egan et al, 2009) and upregulate gene expression of serotonin receptor 5HT-2B, as well as glucocorticoid brain receptors (GRs) and mineralocorticoid brain receptors (MRs) (elements of the stress response system) in proactive zebrafish (Theodoridi et al, 2017). Thus, monoamine profiles can be linked to changes in stress response, indicating an interaction between monoaminergic systems and the hypothalamicpituitary-adrenal (HPA) axis [hypothalamic-pituitary-interrenal (HPI) axis in fish].…”

“…Specifically, we focused on behavior describing variation in the personality traits exploration, aggression, sociability and boldness. Based on previous work, we predicted that our serotonin manipulation would increase serotonin levels in the brain, thus decreasing individual aggressiveness (Perreault et al, 2003;Bell et al, 2007;Clotfelter et al, 2007;Carere and Maestripieri, 2013;Eisenreich et al, 2017;Theodoridi et al, 2017;Barbosa et al, 2018;Kellner et al, 2018) and increasing boldness and exploration behavior (Egan et al, 2009). Our dopamine manipulation should increase dopamine receptor activity in the brain, and thus we predicted it would decrease exploration, boldness, aggressiveness and sociability (Schinka et al, 2002;Fidler et al, 2007;Egan et al, 2009;Filby et al, 2010;van Oers and Mueller, 2010;Carere and Maestripieri, 2013;Holtmann et al, 2016).…”