EN
Responsiveness to novelty is often used as a measure of inter-individual vulnerability to stress loads and drug abuse. The aim of this study was to determine the relationship between individual behavioral profile and brain structures activation. Possible influence of stressful laboratory routines on manifestation of these individual differences was investigated. Male Wistar rats (n=21) were subjected to the novelty test and divided into high (HR) and low (LR) responders to a new environment according to median. Randomly chosen 6 LRs and 5 HRs rats were handled and carried out from the vivarium to the laboratory for nine days (carried group), remaining rats stayed in their home cages (control group, 5 HRs and 5 LRs). One week after the last carrying, an immunohistochemical detection of Fos protein in selected brain areas was performed. Carried HRs showed significantly higher Fos expression in all studied nuclei of the amygdala and most of the hypothalamic areas as compared to LRs and also to control rats. Carried LRs showed elevated density of Fos+ cells only in the stressrelated paraventricular and supraoptic hypothalamic nuclei. Surprisingly, inter-individual (HR vs LR) differences in brain activation was found in carried rats only. We conclude that mild stress evoked by some laboratory routines reveals constitutive differences between the individuals reflected by an increased activity of the amygdala and hypothalamus.