Experimental Study: Youth vs. Life Experience of Adulthood in Terms of Acute Stress Response

Age differences in the response to acute stress were studied in young and mature reproductive-age inbred male Wistar rats. Stress was found to increase the corticosterone level in both age groups, while the testosterone level decreased and the leptin concentration increases. In response to stress, young rats showed a classic decrease in the mass coefficients (MCs) of the thymus and liver and an increase in the MCs of the adrenal glands and heart. In contrast, mature rats showed a decrease in the MC of the adrenal glands and stability of the MC of other visceral organs under all experimental conditions. The rats were tested in the elevated plus maze (EPM), and opposite behavioral changes were observed in the two groups after stress exposure. Exploratory activity decreased in the young rats and increased in the mature rats. It was assumed that neurons of the dorsal part of the periaqueductal grey and the cerebellum were in an excited state as a result of accumulated life experience in the mature rats and that this was expressed as more intense locomotor activity (LA) and a higher efficiency of decision-making mechanisms in choosing the direction of movement in the EPM. Lack of such experience in the young rats inhibited the LA speed and decision-making mechanisms, inducing a feeling of uncertainty during navigation in the EPM. The data can have a wide range of applications in preclinical studies related to health, aging, stress, and modeling of various diseases.