Stress: behavioral and biological interactions

Behavior and corticosteroid response of Maudsley reactive and nonreactive rats in the open field and forced swimming test

Maudsley reactive (MR) and nonreactive (MNRA) male rats were tested in the open field and in the forced swimming test. MR rats defecated more and were less active than MNRA rats in the open field. MR rats also defecated more, but were more immobile in the forced swim test. The two strains did not differ significantly in basal corticosteroid levels or corticosteroid levels in response to either test. These results suggest that the increased defecation rates exhibited by MR rats in various tests are not indicative of a general increase in "emotionality" or stress level.

Adaptation of plasma catecholamine and corticosterone responses to short-term repeated noise stress in rats

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations were determined in blood frequently sampled via a cardiac catheter from freely moving rats exposed to three successive trials of white-noise stimulation (10 min, 100 dBA) with an intertrial interval of 30 min. During the sampling period, behavioral activities of the rats were recorded. It was demonstrated that the first exposure to noise induced a specific temporal pattern of neuroendocrine changes: Plasma A and NA contents increased rapidly and peaked early after stimulus onset but their peak-latencies were different (1 and 5 min, respectively). Noise offset was followed by quick return to basal levels. The changes in plasma CS concentrations were considerably slower in onset and slower in decline. The second and third exposure to this type of stressor resulted in attenuated hormonal responses and a reduced decrement of the NA/A-ratio, concurrent with a gradually less intense behavioral reaction. This differential pattern of plasma NA, A and CS responses following repetitive exposure to identical stressors, referred to as adaptation, is discussed with regard to the biochemical changes at various levels of the neuroendocrine systems involved.

Daily variations in plasma noradrenaline, adrenaline and corticosterone concentrations in rats

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations were determined in blood samples taken once every hour during a 12-hr light/12-hr dark period from freely moving rats with a permanent heart cannula. Before, during and shortly after each blood sampling, behavioral activity was recorded. All rats exhibited a very pronounced peak in CS concentrations at the end of the light period, indicating normal circadian rhythmicity. Plasma NA and A contents varied significantly over the 24-hr sampling period. During nighttime, the behaviorally active phase, mean levels of circulating A and NA were significantly higher than during daytime resting period. Significant correlations between the daily NA, A and behavioral activity patterns were found only when uncorrected data were considered. In contrast, no significant correlations were found for values corrected for circadian trends, indicating that circadian patterns of NA, A and behavioral activity rather than their short-term fluctuations are similar. It is concluded that the circadian variations in plasma NA and A reflect a common activation of both the neural and adrenomedullary parts of the sympathetic autonomic nervous system, most likely associated with the daily patterning of behavior activities. On short-term basis through the day however, a dissociation between these two parts can occur suggesting separate regulating mechanisms for the fine tuning of physiological processes.