Behavioral changes across novelty habituation: Contextual modulation of self-grooming after a stress event

Abstract

Grooming is a widespread behavior in the animal kingdom primarily geared towards the care of the body surface; nonetheless, other behavioral functions have been investigated and postulated. For example, rodents display high levels of grooming in contexts of potential threat, a fact usually interpreted as a sign of stress and anxiety. Conversely, new evidence suggests that during the process of habituation to novel and threatening contexts, particular sequences of grooming would act as a behavioral feedback facilitating emotional de-arousal. To test those opposing hypotheses about grooming interpretation, we assessed how testing contexts with different gradients of familiarity would affect exploratory activity and risk-assessment behaviors, and grooming subtypes of stressed and non-stressed rats. For that purpose, different groups of male Wistar rats were tested in one of the follow conditions: (1) in an unfamiliar open-field arena, (2) in a familiar open-field arena, (3) and in a home cage. Prior to the 20-minutes testing session, half of the animals within each testing condition were stressed by receiving three foot shocks of 1 mA 5 seconds apart. If grooming indicates stress and anxiety, it should increase at the beginning of tests, with stressed rats displaying even higher levels of grooming as compared with their non-stressed counterparts. However, if grooming facilitates emotional de-arousal, it should increase as exploration and risk-assessment decrease. In such scenario, unstressed animals tested in the familiar contexts should display the greater levels of grooming, in contrast to pre-stressed animals tested in unfamiliar contexts. Evidence will be presented about how the degree of novelty and threat associated with the testing context, may modulate defensive behaviors after an acute stress. Furthermore, the detailed analysis of the kinetic changes in grooming sequences will provide new insights into the understanding of grooming and its informative value in preclinical research. We propose that the richness of grooming interpretation lies in the careful analysis of its sub-components over time. Here, we will bring new evidence that support the hypothesis that long and complex sequences of grooming would facilitate emotional de-arousal, whereas short and head-directed sequences would be more related with ongoing stress states.