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.

Stress-sensitive organs and blood corticosterone after immobilization of active and passive rats immunized with glutamate-bovine serum albumin conjugate.

We studied stress-induced organ and hormonal responses in behaviorally active and passive rats against the background of immunization with glutamate-BSA conjugate. The relative weight of the adrenal glands after immobilization was lower in rats immunized with the conjugate in comparison with non-immunized animals. The weight of the adrenal glands in behaviorally active rats decreased in parallel with the decrease in blood corticosterone. In behaviorally active and passive rats immunized with the conjugate, ulcer formation in the stomach was slightly intensified after immobilization. It was hypothesized that immunization with glutamate-BSA conjugate suppresses activity of the hypothalamic-pituitary-adrenal feedback mechanism underlying the production of glucocorticoid hormones, which is manifested in slightly increased ulceration due to attenuation of the gastroprotective action of corticosterone under stress.

Changes in ß-endorphin level in the cingulate cortex in rats after peripheral loperamide and methylnaloxone administration at rest and during emotional stress.

ß-Endorphin content in the extracellular space of rat cingulate cortex was measured using intravital microdialysis followed by ELISA. Intragastric administration of µ-opioid ligands loperamide and methylnaloxone not crossing the blood-brain barrier produced different effects on ß-endorphin level: loperamide reduced and methylnaloxone significantly increased the release of ß-endorphin into the extracellular space of rat cingulate cortex. Emotional stress caused by immobilization resulted in slight increase in ß-endorphin level in the cingulate cortex. Peripheral administration of loperamide (but not methylnaloxone) significantly increased the release of the neuropeptide during stress. These findings support our hypothesis of reciprocal interaction between the central and peripheral compartments of the endogenous opioid system and provide explanations for the anti-stress effects of loperamide.