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Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) increases were determined in individual rats subjected to either 20 regularly or irregularly scheduled white-noise stimulations (4 min, 100 dBA). Blood was frequently sampled during the first and twentieth noise exposure, and during a reexposure after 24 hr. During the sampling periods, behavioral activities of the rats were recorded. The initial noise-induced CS release was partially reduced following the regular noise presentations. The increase after irregular presentations remained high. The difference in adrenocortical responsiveness between regular and irregular exposure persisted for 24 hr. The NA response to noise was partially attenuated following irregular administration of noise. However, regular exposure produced increased NA levels prior to noise presentation and a subsequent decrease during stimulation. After 24 hr, noise evoked an exaggerated initial NA release in the regular group. The noise-elicited rise in A was completely abolished after 20 noise presentations irrespective of whether these were applied regularly or irregularly. Reexposure after 24 hr evoked again a significant A response in both groups. No differences were observed in the habituation pattern of behavioral reactions among the regular and irregular groups. The results show that the sympathetic neural, adrenomedullary and adrenocortical systems differ in degree and speed of adaptation to intermittent stressful stimuli and in sensitivity to the predictability of stressors.

Plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) concentrations were determined in rats before, during and after 15-min exposure to a constantly electrified (2 mA) or nonelectrified prod which was mounted on the wall of the home cage either with or without bedding material on the floor. Concomitantly, exploration of the prod, freezing and prod-burying behavior were recorded. Both in the presence and absence of bedding material, rats explored the nonelectrified prod and showed a small increase in plasma NA and CS contents. Exploration of the prod was strongly reduced when the prod was electrified. In the presence of bedding material, shocked rats typically displayed burying behavior (active avoidance), whereas in the absence of bedding (i.e., burying option eliminated) shocked rats engaged in freezing behavior (passive avoidance). The passive avoidance situation was accompanied by larger A and CS increases but a lower NA rise as compared to the hormonal responses associated with the active avoidance situation. Administration of the anxiolytic chlordiazepoxide (CDP; 9 mg/kg intragastrically) attenuated the shock-induced suppression of prod exploration, decreased prod-burying behavior but, paradoxically, increased freezing behavior. Irrespective of bedding condition, the prod shock-induced elevations in plasma CS and A contents were completely abolished in CDP-treated rats. The rise in plasma NA was attenuated only in CDP-treated rats tested on a bedding-floor. The results indicate that passive (e.g., freezing) and active (e.g., burying) behavioral coping are each accompanied by specific and dissociated patterns of neurosympathetic, adrenomedullary and adrenocortical outflow. CDP-treatment shifts an animal's behavioral coping style from an active to a passive form of avoidance responding, but abolishes the accompanying adrenocortical and adrenomedullary activation.

Frequency-dependent transfer from EOG to EEG may be insufficiently accounted for by simple time domain regression methods (Gasser, Sroka, & Möcks, 1986; Woestenburg, Verbaten, & Slangen, 1983). In contrast, a multiple-lag time domain regression analysis, using lagged regression of EEG on EOG, must theoretically account for both frequency dependence and independence. Two data sets were constructed, in which the transfer from EOG to EEG was either frequency-independent (constant gain) or frequency-dependent. Subsequently, three different correction methods were applied: 1) a simple regression analysis in the time domain; 2) a multiple-lag regression analysis in the time domain; and 3) a regression analysis in the frequency domain. The major results were that, for data set 1, the three methods constructed the original EEG equally well. With data set 2, reconstruction of the original EEG was achieved reasonably well with the frequency domain method and the time domain multiple-lag method, but not with simple time domain regression. These three correction procedures were also applied to real data, consisting of concomitantly recorded EEG and high-variance EOG series. No appreciable differences in outcome of the three methods were observed, and estimated transfer parameters suggested that these data were marked by weak frequency dependence only, which can be accounted for by simple time domain regression (and also by the other two methods).