State of Stress-Marker Organs in Rats with Various Behavioral Characteristics during Repeated Stress Exposures

Changes in the relative weight of stress-marker organs in rats with various behavioral patterns in the open-field test were studied after repeated stress exposures on the model of daily 4-h immobilization over 8 days. Involution of the thymus and spleen in behaviorally passive specimens was found after single stress, as well as under conditions of 3- and 8-fold immobilizations. The weight of these organs in active animals remained practically unchanged after acute stress, but decreased on day 3 and particularly on day 8 of repeated stress exposures. As differentiated from passive rats (open-field test), behaviorally active specimens were characterized by hypertrophy of the adrenal glands after single and 3-fold stress procedures. Our results complement the data on individual features of the peripheral and central mechanisms for the stress response in mammals. These data illustrate the importance of individual approach to studying systemic organization of physiological functions under normal conditions and during negative emotiogenic exposures.