Roles of the 5-HT1A receptor in zebrafish responses to potential threat and in sociality.

Background: Anxiety is a normal emotion representing a reaction to potential danger, whereas fear can be defined as a reaction to real, explicit danger. Anxiety-like behavior in animal models has been associated with differences in the serotonergic system.

Aims: To understand the roles of the 5-HT1A receptor in zebrafish anxiety-like behavior and sociality.

Methods: Adult zebrafish were treated with 8-OH-DPAT and subjected to the phototaxis (light-dark preference) assay, the novel tank test (NTT), or the social preference test. Separate cohorts were treated with increasing doses of 8-OH-DPAT, while 5-HT1A receptors were blocked with a silent dose of WAY 100635.

Results: 8-OH-DPAT (0.3 mg/kg) decreased anxiety-like behavior in the NTT, but increased it in the phototaxis (light-dark preference) assay, both considered assays for anxiety-like behavior for this species. The same dose decreased social approach in both the social investigation and social novelty phases of the social preference test. Blocking the 5-HT1A receptor with WAY 100635 (0.01 mg/kg) shifted the dose-response curve (0.03-3 mg/kg) for the NTT rightward.

Conclusions: These effects suggest a participation of the 5-HT1A heteroreceptors in zebrafish anxiety and social preference, modulating anxiety in a test-dependent way and decreasing sociality. Thus, the study of this receptor is important for a better understanding of anxiety-like behavior in zebrafish and its relationship with similar phenomena in vertebrates.