THE EFFECT OF SOCIAL EXPERIENCE ON BRAIN MORPHOLOGY IN ZEBRAFISH (DANIO RERIO)

Abstract

Adult male Zebrafish form stable dominance relationships that consist of dominant and subordinate animals. The long-term effects of social dominance on nervous system function remain poorly understood. Here, we investigated how social stress affects the morphological architecture of the hypothalamic dopaminergic nuclei implicated in social regulation and aggression. The dopaminergic system is a prime target of social factors given dopamine’s (DA) involvement in aggression, depression, stress and anxiety. We tested the hypothesis that social dominance induces morphological reorganization of the hypothalamic dopaminergic Posterior Tubercular rostral (PTar) and Caudal (PTac) nuclei. Both nuclei receive visual and olfactory social cues and relay the integrated information to spinal cord locomotor circuits to modulate locomotor activity. To test the effect of social dominance on the number of DA neurons we used the transgenic zebrafish line Tg(dat:EGFP) that expresses EGFP in all CNS dopaminergic neurons. Using confocal imaging of brain slices coupled with digital analysis, we compared the number of DA neurons in the PT nuclei between dominant and subordinate animals after two weeks of continuous social interactions; while group-housed (6 communally housed males) served as a control group. Our results show a significant increase in the number of DA neurons in dominants compared subordinate animals, while the number of DA neurons in communals was not statistically significant from neither dominants nor subordinates. Our results demonstrate that social dominance induces morphological reconfiguration of the hypothalamic DA system in a social status-dependent manner, and likely to have broader implications on other vertebrate social species.