Lipid peroxidation processes were studied in the striatum during stress in conditions of prior administration of cortisol. Three doses of cortisol (25 mg/kg, daily) had no significant effect on the levels of lipid peroxidation products six days after injections ended. However, lipid peroxidation responses to stress during this period in animals given cortisol were significantly stronger than in controls (there were decreases in the intermediate products of lipid peroxidation and increases in the quantities of Schiff bases). Thus, administration of hormone leads to long-term changes in one of the most important regulatory systems of the body--lipid peroxidation--and has sensitizing effects on changes in the levels of stress-induced lipid peroxidation products.
The behavioral and neuroendocrine responses of the body to external changes are determined by genetically determined programs of individual development, and are established during pre- and post-natal ontogenesis. These responses, however, can be changed by stress or administration of corticosteroid hormones in "critical periods" of the body's development. Mineralo- and glucocorticoid receptors mediate the "inhibition" of particular neuroendocrine or neuromediator systems, promoting behavioral modification.
An enhancement of stress reactivity of the hypophysial-adrenocortical system in response to emotional and physical influence was shown in rats with a low threshold of sensitivity to electrical current. This phenomenon was observed as a rise in the maximum level of blood corticosterone and acceleration of stressor hormonal response. In the high-threshold rats a decrease in sensitivity of the hypophysial adrenocortical system to the feedback signals was observed. Key Words: hypophysial adrenocortical system; stress reactivity; corticosterone; line ratsAnimal experiments confirm that basic properties of the nervous system are determined genetically [6]. Selection according to the excitability threshold of the nerve-muscle apparatus [2] show that not only behavioral characteristics, but also reactivity to stress and ability to adapt to the environment depend on the excitability of the nervous system [1,9,10]. These findings support the hypothesis that the divergence of these properties is determined predominantly by hypophysial-adrenocortical system (HACS). There are data indicating that neuron excitability depends on corticosteroids [13]. We studied functional state of HACS in rats, in which not only the peripheral subdivision of nervous system [2], but also its central structures, the midbrain reticular formation in particular [5], had different threshold of excitability [2]. MATERIALS AND METHODSThe study was carried out on 120 male Wistar rats weighing 350+_.25 g, which were genetieaUy selected according to the threshold of sensitivity of the tibial I.P. Pavlov Institute of Physiology, Russian Academy of Sciences, St. Petersburg nerve to electrical current. Selection was performed from two independent autobred populations: the high sensitivity LT-1 and LT-2 rats (low threshold: first selection program --34th generation and the second selection program --24th generation) and low sensitivity HTol and HT-2 rats (high threshold: the first and second selection programs of the same generations). The rats were grown and maintained on the standard diet at the Laboratory of Genetics of Highest Nervous System (I.P. Pavlov Institute of Physiology).Basal state of HACS was evaluated by plasma content of cortieosterone (CS) at rest. Blood samples were taken from the caudal vein at 4 p.m. Stress response of HACS was estimated by the maximum rise in blood CS. Several types of stressor stimulation were used. Emotional stress caused by new environment was estimated by measuring blood CS after a 30 rain vein (I series). In the 2nd series, the rats were stimulated transeutaneously with electrical current (0.5 rnA, 50 Hz, maximum duration 15 see) which was applied 15 times to the floor of a 20x20x 13 em chamber. Blood was taken from the caudal vein 1, 3, and 24 h after stimulation.The sensitivity of HACS to feedback signals was determined in a 2-day dexamethasone test [4].Two
Using the experimental model of post-traumatic stress disorder (stress-restress paradigm), we studied the dynamics of activity of the hypothalamic-pituitary-adrenal system (HPAS) in adult male rats, whose mothers were daily subjected to restraint stress on days 15-19 of pregnancy. Prenatally stressed males that were subjected to combined stress and subsequent restress exhibited not only increased sensitivity of HPAS to negative feedback signals (manifested under restress conditions), but also enhanced stress system reactivity. These changes persisted to the 30th day after restress. Under basal conditions, the number of cells in the hypothalamic paraventricular nucleus of these animals expressing corticotropin-releasing hormone and vasopressin was shown to decrease progressively on days 1-30. By contrast, combined stress and restress in control animals were followed by an increase in the count of CRH-immunopositive cells in the magnocellular and parvocellular parts of the paraventricular nucleus and number of vasopressin-immunopositive cells in the magnocellular part of the nucleus (to the 10th day after restress). Our results indicate a peculiar level of functional activity of HPAS in prenatally stressed males in the stress-restress paradigm: decreased activity under basal conditions and enhanced reactivity during stress.
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