Functioning of hypophysial adrenocortical system in rats selected by the threshold of sensitivity to electrical current

Abstract

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

Effects of psychogenic stress on some peripheral and central inflammatory markers in rats with the different level of excitability of the nervous system

“…It is known that subcutaneous administration of corticosterone in mice for 14 days leads to hyperactivity of the amygdala, as well as to disturbances of amygdala-mediated memory of a traumatic event [29]. Previously, it was shown that strains of highly excitable rats with a low threshold of sensitivity to electric current are characterized by increased stress reactivity of the HPA, accelerated development of the hormonal response, and reduced sensitivity of the HPA to feedback signals [30]. It makes animals of this strain more susceptible to immune dysfunctions in response to chronic stress and may lead to excessive activation of the amygdala.…”

Genome response of hippocampal cells to stress in male rats with different excitability of the nervous system

“…Presumably, LT rats are more sensitive to genotoxic action due to the selection in favor of a low nerve excitability threshold, which is somehow connected with the genome response to stress in cells of different brain structures. Previously, it was shown that LT rats are characterized by increased stress reactivity of the HPA, accelerated development of the hormonal response, and reduced sensitivity of the HPA to feedback signals (Ordyan et al, 1998).…”

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“…Stress experienced by mothers during various terms of gestation can have a negative impact on physiological functions in their progeny [10], but biochemical mechanisms of these disorders are still unclear. On the one hand, we know the important role of the psychotype in the development of pathological reaction to stress [2,[5][6][7]. Study of biochemical processes in animals with genetically determined differences in the CNS function will help to understand the mechanisms and regularities in the formation of pathological states.…”

“…Study of biochemical processes in animals with genetically determined differences in the CNS function will help to understand the mechanisms and regularities in the formation of pathological states. Rats with high and low excitability threshold (HET and LET, respectively) selected at I. P. Pavlov Institute of Physiology are models of opposite types of the nervous system functioning [6].…”