Acute stress differentially affects grooming subtypes and ultrasonic vocalisations in the open-field and home-cage test in rats

Grooming behaviour in rodents has been associated with emotional distress, especially in unfamiliar and aversive contexts. However, the biological function of grooming in such situations is still unclear. We hypothesised that particular grooming subtypes are differentially associated with the stress response. Here, we investigated the effects of an acute stress exposure on grooming and ultrasonic vocalisations (USVs) assessed on different testing contexts varying in the level of familiarity. To this aim, footshocked and non-footshocked rats were tested for 20 min on one of the following conditions: an unfamiliar open-field test, a familiar open-field test, and an individual home cage filled with bedding. We found that footshock stress slightly decreased complex grooming sequences while increased cephalic grooming. Stress induced a negative affective state inferred from an increase and decrease of 22-kHz and 50-kHz calls, respectively. The latter USVs correlated positively with the complex grooming subtypes. Altogether, a detailed analysis of grooming seems necessary for elucidating its diverse biological functions. Nevertheless, footshock stress and testing conditions produced weaker-than-expected effects, possibly because the time elapsed between footshocks and behavioural testing was too short for eliciting a full stress response, and because the simple footshock-chamber experience may have impeded detecting stronger effects of familiarity.