EFFECT OF ENVIRONMENTAL STRESSORS ON TIME-COURSE, VARIABILITY AND FORM OF SELF-GROOMING IN THE RAT - HANDLING, SOCIAL CONTACT, DEFEAT, NOVELTY, RESTRAINT AND FUR MOISTENING

Grooming is often related to dearousal following stressors. Interestingly, electrical and chemical stimulation of the paraventricular nucleus of the hypothalamus (PVH), at levels that are known to activate the hypothalamus-pituitary adrenal axis (HPA), also elicits grooming. At the level of the PVH, the neuroendocrine stress response is apparently still linked to the behavioural response to stressors. However the precise nature of this relation is not fully understood. Here we report on grooming in rats following exposure to different stressors which are known to activate the HPA axis. Stressors such as handling, restraint, novelty, encounters with aggressive or non-aggressive conspecifics, or moistening the fur, change the amount and time course of grooming upon return in the home cage, as compared with controls that are just handled. However the amount of grooming is not directly related to the strength of the stressor. Defeated intruders groom less upon return in their home cage. Novelty and non-aggressive encounters with conspecifics reduce the variation in the amount of grooming between rats. The time course of grooming over the 20-min observation period also differs between treatments. Following restraint, or exposure to non-aggressive conspecifics, grooming first increases and then decreases. Moistened rats immediately start grooming which subsequently decreases. Rats used as intruders in the territory of another rat maintain a constant low level of grooming. Rats placed in a novel cage steadily increase grooming during the 20-min observation period. These results suggest that grooming cannot be simply understood as an immediate response necessary to reduce arousal following stressors. Following exposure to a stressor, grooming rather seems temporary suppressed. If grooming has a restorative function, it is a delayed function, which is not directly related to the strength of the stressor.