INDIVIDUAL-DIFFERENCES IN PLASMA-CATECHOLAMINE AND CORTICOSTERONE STRESS RESPONSES OF WILD-TYPE RATS - RELATIONSHIP WITH AGGRESSION

Plasma noradrenaline (NA), adrenaline (A), and corticosterone (CS) res ponses to social and nonsocial stressors were studied in male members of a strain of wild-type rats, widely differing in their level of aggr ession. The aggressiveness was preliminarily established by measuring the latency time to attack (ALT) a male intruder in a standard residen t-intruder test. Animals were then provided with a jugular vein cannul a for blood sampling during stress exposure. Implanted rats were rando mly assigned to 3 experimental treatments: social stress (defeat exper ience, SD), nonsocial stress (presentation of a shock-prod, SP) and co ntrol (animals undisturbed in their home cages, CTR). A significant co rrelation was found between ALT and the amount of time spent in buryin g the probe in SP rats: the more aggressive the animal, the higher the rate of burying behavior. SD induced a much stronger effect on plasma NA, A, and CS concentrations than SP. A significant negative correlat ion was found between ALT scores and values of the area under the resp onse time curve for NA and A, in both SD and SP situations: the more a ggressive the animal the higher the catecholaminergic reactivity to th e stressors. On the contrary, no evidence of a correlation between agg ressiveness and plasma corticosterone responses was found neither in S D nor in SP rats. These findings in an unselected strain of wild-type rats confirmed that an aggressive/active coping strategy is associated with a high sympathetic-adrenomedullary activation and support the co ncept of individual differentiation in coping styles as a coherent set of behavioral and neuroendocrine characteristics. Copyright (C) 1996 Elsevier Science Inc.