Perception of fight outcome is needed to activate socially driven changes in brain transcriptome

Group living animals must be able to express different behavior profiles depending on their social status. This implies that the same genotype may translate into different behavioral phenotypes through socially driven differential gene expression. Here we show for the first time that what triggers the switch between status-specific neurogenomic states is not the objective structure of the social interaction but rather the subjects’ perception of its outcome. For this purpose we had male zebrafish fight either a real opponent or their own image on a mirror. Massive changes in the brain transcriptome were observed in real opponent fighters, which experience either a victory or a defeat. In contrast, mirror fighters, which had no information on fight outcome despite expressing aggressive behavior, failed to activate a neurogenomic response. These results indicate that, even in cognitively simple organisms such as zebrafish, neurogenomic responses underlying changes in social status rely on cognitive appraisal. Brain samples from zebrafish, Danio rerio were collected after experimental manipulations generated 4 phenotypes regarding social experience: mirror fighters (M), winners of a real opponent fight (W), losers of a real opponent fight (L); and socially isolated fish (I). After 30 minutes of experimental manipulation animals were anesthetized with a lethal dose of MS-222 (1000-1500 mg/l) and decapitated. Brains were rapidly collected, homogenized and RNA extracted following standard methods of RNeasy Lipid Tissue Mini Kit, Qiagen. RNA was then treated with DNase (RNase-free DNase set, Qiagen) to remove possible contaminations with genomic DNA and concentration and purity was estimated by spectrophotometric absorbance in a NanoDrop ND-1000 UV-Vis Spectrophotometer (Nano-Drop Technologies).