Role of brain serotonin in modulating fish behavior

Abstract

The organization of the brain serotonergic system appears to have been highly conserved across the vertebrate subphylum. In fish as well as in other vertebrates, brain serotonin (5-HT), mainly acts as a neuromodulator with complex effects on multiple functions. It is becoming increasingly clear that acute and chronic increase in brain 5-HT neurotransmission have very different effects. An acute 5-HT activation, which is seen in both winners and losers of agonistic interactions, could be related to a general arousal effect, whereas the chronic activation observed in subordinate fish is clearly linked to the behavioral inhibition displayed by these individuals. Fish displaying divergent stress coping styles (proactive vs. reactive) differ in 5-HT functions. In teleost fish, brain monoaminergic function is also related to life history traits.

Keywords: aggression; dominance; monoamines; plasticity; stress; zebrafish.

Figure 1.

Open field test. Four different behavioral parameters recorded for 20 min following 2 h of immersion in 2 different fluoxetine doses compared to controls (A–D). A Kruskal–Wallis analysis revealed an effect of fluoxetine on time spent in the center zone. Subsequent pairwise comparison reported an adjusted significance (P = 0.022) between the 0.5 mg/L and 1.5 mg/L group (B). Frequency of transitions between the center and outer zone (A), distance moved (C), and immobility duration (D) were all significantly decreased in females in comparison to males, Mann–Whitney U-test comparisons (see text for statistical analysis). All data are presented as mean ± SEM. *P < 0.05.

Figure 2.

Brain serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) concentrations following 2 h of immersion in 2 different doses of fluoxetine in comparison to controls. Whole brain 5-HIAA/5-HT ratio (A) and 5-HIAA concentration (B) were both significantly lower in treatment groups. All data are presented as mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001 (2-way ANOVA).