Effects Of Chronic Stress Exposure Research Articles

Coping strategies in male and female rats exposed to multiple stressors

Because of the pathogenic effects of chronic stress exposure, it is important to identify factors, such as effective coping strategies, that mitigate stress-induced pathology. Of interest in the present study was the consistency of behavioral responses across a diverse array of stressors. Sixteen male and 16 female Long–Evans rats were assigned to either a stress or control group. The stressed animals were subsequently exposed to a battery of ecologically relevant stressors (e.g., predator odor, novel stimuli, and immunological challenge) to determine trends in coping strategies. Blood was collected for corticosterone (CORT) assay and brains were harvested for assessment of fos immunoreactivity in the paraventricular hypothalamus (PVH) and central amygdala (CEA) following exposure to the final stressor of fox urine. A correlational analysis indicated that certain response strategies (e.g., latency to respond in different stress tests such as the open-field and novel item tests) persist across several behavioral tests, especially those tests involving exploratory components. A subsequent principal component factor analysis revealed the following four components: initiative to explore, low reactivity, variable reactivity, and high reactivity. Females exhibited higher recovery CORT levels than males; however, sex only affected one behavioral response measure (i.e., females demonstrated more attempts to climb the wall in the forced-swim test than their male counterparts). In conclusion, these results support the importance and prevalence of initiative to explore as a common factor in many stress tests; additionally, the principal component analysis indicated that physiological correlates of stress are more closely associated with more challenging environments and stimuli such as forced swimming, immunological challenges, and exposure to predator odors.

Circadian differences in stress-induced pressor reactivity in mice.

The objective of this study was to determine the effect of chronic stress exposure on the circadian pattern of cardiovascular responses in mice. Using male C57BL6 mice with carotid arterial catheters, we tested the effect of 7 days of intermittent shaker stress on body weight, food intake, drinking activity, plasma corticosterone, mean arterial pressure (MAP), and heart rate. The stress was delivered automatically for 2-minute periods (150 cycles/min), 45 times/d for 7 days. Plasma corticosterone was significantly increased in acutely and chronically stressed mice, with a partial attenuation in the chronic condition. Stress increased water intake, produced no change in food intake, and significantly decreased body weight (5% change). MAP and heart rate were measured continuously on stress days 1, 3, and 7 and during the basal and recovery periods. Chronic stress did not produce a sustained increase in MAP; however, there was an increase in MAP during the first stress day and a decrease during the recovery period. There was a circadian pattern in the pressor responses, with greater increases seen during the light period (nonactive phase) than in the dark period (+24% versus +11% on stress day 3, light versus dark). The results suggest that a stress delivered during the nonactive phase represents a higher cardiovascular risk.

Long‐term behavioral and neurochemical effects of chronic stress exposure in rats

Rats exposed to acute unavoidable stress develop a deficit in escaping avoidable aversive stimuli that lasts as long as unavoidable stress exposure is repeated. A 3-week exposure to unavoidable stress also reduces dopamine (DA) output in the nucleus accumbens shell (NAcS). This study showed that a 7-day exposure to unavoidable stress induced in rats an escape deficit and a decrease in extraneuronal DA basal concentration in the NAcS. Moreover, animals had reduced DA and serotonin (5-HT) accumulation after cocaine administration in the medial pre-frontal cortex (mPFC) and NAcS, compared with control animals. After a 3-week exposure to unavoidable stress, escape deficit and reduced DA output in the NAcS were still significant at day 14 after the last stress administration. In the mPFC we observed: (i) a short-term reduction in DA basal levels that was back to control values at day 14; (ii) a decrease in DA accumulation at day 3 followed by a significant increase beyond control values at day 14; (iii) a significant reduction in 5-HT extraneuronal basal levels at day 3, but not at day 14. Finally, a significant decrease in 5-HT accumulation following cocaine administration was present in the NAcS and mPFC at day 3, but not at day 14. In conclusion, a long-term stress exposure induced long-lasting behavioral sequelae associated with reproducible neurochemical modifications.

Effects of acute and chronic stress on the neural retina of young, mid-age, and aged Fischer-344 rats

Male Fischer-344 rats at 5 (young), 11 (mid-age) and 18 (aged) months of age were exposed either to a single, 1-h period of acute stress, or to daily 4-h periods (chronic) of escapable footshock stress for 6 months, and subsequently allowed a one month interval without stress. The influence of age and exposure to stress on the neural retina was examined by histopathologic and morphometric methods. Age changes in the retina of unstressed control animals included reduction in the thickness of the outer nuclear layer (ONL; photoreceptor nuclei) and of the retina, especially in the peripheral areas. The superior hemisphere was more severely affected than the inferior retina. Exposure to acute stress did not influence retinal histopathology. However, in mid-age and aged rats exposed to chronic stress, the ONL and retinal thicknesses were reduced significantly. Our results indicate for the first time that exposure of rats to chronic stress produces changes in retinal morphology that are associated commonly with aging, such as extensive loss of peripheral photoreceptor cells. In addition, the results show that the effects of chronic stress exposure are greatest in aged rats. The effect of light exposure on the aging retina was not investigated since all rats were exposed to the same total photoperiod.

Gender and chronic stress effects on the neural retina of young and mid-aged Fischer-344 rats

Young (5 months) and mid-aged (11 months) male and female Fischer rats were exposed to daily (5 days/week) chronic escapable foot-shock stress for 6 months. Following a subsequent 1-month rest period, by which time the animals were 12 and 18 months old, neural retinas were evaluated histopathologically and morphometrically. A significant reduction in t the thickness of the retina occurred in the mid-aged, as compared to the young animals. A severe age-related loss in photoreceptor cells, particularly in the peripheral zones of the retina, occurred in a pattern resembling that described for aging humans. The effect of stress was to increase photoreceptor loss in a pattern resembling that of age-related cell loss. Stress-associated photoreceptor cell death was observed in males and females of both ages, but was more pronounced and statistically significant for mid-aged males (a five-fold increase in cell loss over females). The results demonstrated that exposure of rats to chronic escapable foot-shock stress exacerbates retinal changes commonly associated with aging and that the deleterious effects of chronic stress exposure were greater in the older age, male group.