Aversão ao contexto associado ao estresse de derrota social em camundongos : um estudo etológico

Abstract

Aggressive interactions between conspecific animals have been used as an ethological source of social stress to study some aspects of social anxiety. Through this work we used a new experimental protocol in order to develop a new behavioural paradigm in the study of social anxiety. Mice were exposed to an apparatus adapted from rat exposure test (RET) and it consisted of three interconnected regions: home chamber, tunnel and surface area. Animals were exposed to the experimental apparatus for five consecutive days, being the first three days for habituation to the apparatus (habituation 1 , 2 and 3) and on the fourth day occurred the social interaction between conspecifics (not aggressive for animals from "non-defeated group" and aggressive for animals from "defeated group"). On the fifth and final experimental day the animals were re-exposed to the apparatus for 10 minutes and the following behaviors were assessed: frequency of entries and time spent in the three regions of the apparatus (home chamber/tunnel/surface area), frequency of the stretched attend posture (SAP) behaviour in the three regions, time spent on self-grooming in the three regions, frequency of rearing in the surface area and latency to reach the surface area once the animals were re-exposed to the experimental apparatus. Factor analysis was used in this study to trace the behavioural profile of socially defeated mice (n=90) when re-exposed to the apparatus where the aggressive interaction occurred; we also compared the behavioural profile of non-defeated (n=89) and defeated (n=90) mice when re-exposed to the context where social (non-aggressive or aggressive) interaction occurred, using Student’s t test. Final factor analysis yielded 4 factors that together represent 72.09% of total variance: factor 1 was loaded with time spent in the home chamber and in the surface area and self-grooming in the home chamber, while factor 2 loaded on time spent in the tunnel and total entries in the three compartments of the apparatus (home chamber, tunnel and surface area). Factor 3 was loaded with SAP frequency in the tunnel and in the surface area; and factor 4 was loaded only with latency to reach the surface area. Student’s t test showed that socially defeated mice spent more time to reach the surface area and performing self-grooming in the home chamber when compared to non-defeated mice. Together, these results suggest that the increase in the latency to reach the surface area and self-grooming in the home chamber were conditioned to a single social defeat, but there were no conditioning for classical measures such as: place aversion and risk assessment behaviour (SAP).