Patterns of violent aggression-induced brain c-fos expression in male mice selected for aggressiveness

Mice selected for aggressiveness (long and short attack latency mice; LALs and SALs, respectively) constitute a useful tool in studying the neural background of aggressive behavior, especially so as the SAL strain shows violent forms of aggressiveness that appear abnormal in many respects. By using c-Fos staining as a marker of neuronal activation, we show here that agonistic encounters result in different activation patterns in LAL and SAL mice. In LALs, agonistic encounters activated the lateral septum, bed nucleus of stria terminalis, medial amygdala, paraventricular nucleus of the hypothalamus, anterior hypothalamic nucleus and tuber cinereum area (both being analogous with the rat hypothalamic attack area), dorsolateral periaqueductal gray, and locus coeruleus. This pattern is similar with that seen in the territorial aggression of male mice, rats and hamsters, and non-lactating female mice. SALs showed strong fight-induced activations in the central amygdala and lateral/ventrolateral periaqueductal gray. In this strain, no activation was seen in the lateral septum and the dorsolateral periaqueductal gray. This pattern is similar with that seen in other models of violent aggression, e.g., in attacks induced by hypothalamic stimulation in rats, quiet biting in cats, lactating female mice, and hypoarousal-driven abnormal aggression in rats. We suggest here that the excessive activation of the central amygdala and lateral/ventrolateral periaqueductal gray--accompanied by a smaller activation of the septum and dorsolateral periaqueductal gray--underlay the expression of violent attacks under various circumstances.

Long-lasting consequences of a social conflict in rats: behavior during the interaction predicts subsequent changes in daily rhythms of heart rate, temperature, and activity

This study shows that the long-term consequences of a social conflict in rats do not depend on the physical intensity of the fight in terms of aggression received but, especially, on how the subjects deal with it. Experimental rats were introduced into the cage of an aggressive conspecific for 1 hr, and the effects on daily rhythms of heart rate, body temperature, and activity thereafter were measured by means of telemetry. In some rats, the confrontation caused a strong decrease in the daily rhythm amplitude that lasted up to 3 weeks, whereas other subjects showed only minor changes. The changes in rhythm amplitude did not correlate with the number of attacks received from the territory owner. Contrary to this, the changes showed a clear negative correlation with the aggression of the experimental rats themselves. Subjects fighting back and counterattacking the cage owner subsequently had a smaller reduction in rhythm amplitude.

Long-lasting consequences of a social conflict in rats: behavior during the interaction predicts subsequent changes in daily rhythms of heart rate, temperature, and activity

This study shows that the long-term consequences of a social conflict in rats do not depend on the physical intensity of the fight in terms of aggression received but, especially, on how the subjects deal with it. Experimental rats were introduced into the cage of an aggressive conspecific for 1 hr, and the effects on daily rhythms of heart rate, body temperature, and activity thereafter were measured by means of telemetry. In some rats, the confrontation caused a strong decrease in the daily rhythm amplitude that lasted up to 3 weeks, whereas other subjects showed only minor changes. The changes in rhythm amplitude did not correlate with the number of attacks received from the territory owner. Contrary to this, the changes showed a clear negative correlation with the aggression of the experimental rats themselves. Subjects fighting back and counterattacking the cage owner subsequently had a smaller reduction in rhythm amplitude.

Different sympathovagal modulation of heart rate during social and nonsocial stress episodes in wild-type rats

The acute consequences of a social aversive stimulus (defeat) on the autonomic control upon the electrical activity of the heart were measured and compared to those observed in three nonsocial stress paradigms, namely restraint, shock-probe test, and swimming. Electrocardiograms were recorded from rats via radiotelemetry, and the autonomic neural control of the heart was evaluated via measures of heart rate and heart rate variability, such as the average R-R interval (RR), the standard deviation of RR (SD), the coefficient of variance (SD/RR), and the root-mean-square of successive R-R interval differences (r-MSSD). Although all stressors induced significant reductions of average R-R interval, the effect of defeat was significantly larger (p < 0.05). The social stimulus also determined a significant decrease in the variability indexes (p < 0.01 for all), whereas in the other stress conditions they were either unchanged or increased (SD/RR during restraint, p < 0.05; SD and SD/RR during swimming, p < 0.05 and p < 0.01). Cardiac arrhythmias (mostly ventricular premature beats, VPBs) were far more frequent during defeat than during the other challenging situations (p < 0.01), with an average of 33.5 +/- 6.5 VPBs per 15-min test recording. These data suggest that during defeat autonomic control was shifted toward a sympathetic dominance, whereas in rats exposed to nonsocial stressors, although significant heart rate accelerations were also found, sympathovagal balance was substantially maintained. These differences in autonomic stress responsivity explain the different susceptibility to ventricular arrhythmias and indicate that a social challenge can be far more detrimental for cardiac electrical stability than other nonsocial aversive stimuli.

Coping styles in animals: current status in behavior and stress-physiology

This paper summarizes the current views on coping styles as a useful concept in understanding individual adaptive capacity and vulnerability to stress-related disease. Studies in feral populations indicate the existence of a proactive and a reactive coping style. These coping styles seem to play a role in the population ecology of the species. Despite domestication, genetic selection and inbreeding, the same coping styles can, to some extent, also be observed in laboratory and farm animals. Coping styles are characterized by consistent behavioral and neuroendocrine characteristics, some of which seem to be causally linked to each other. Evidence is accumulating that the two coping styles might explain a differential vulnerability to stress mediated disease due to the differential adaptive value of the two coping styles and the accompanying neuroendocrine differentiation.

Fear-potentiation in the elevated plus-maze test depends on stressor controllability and fear conditioning

The purpose of the study was to determine which stressor qualities (escapable vs. inescapable stress and unconditioned vs. conditioned stress) can potentiate fear in the elevated plus-maze. While inescapable stress potentiated fear, escapable stress did not, but escapable stress increased the locomotor activity (closed arm entries). Inescapable stress only potentiated fear when re-exposure to the former shock compartment, 24 h after footshock and without further footshock, took place just before to 90 min before testing in the elevated plus-maze. We conclude that fear-potentiation in the plus-maze depends on stressor controllability and contextual conditioning. Fear-potentiation was reduced by the anxiolytic diazepam (0.5, 1.0 and 2.0 mg/kg, s.c.) and was further enhanced by the anxiogenic DMCM (1.0 mg/kg, s.c). The fear-potentiated plus-maze test may be a valuable tool in the search for novel anxiolytics and in the study of the neurobiology of fear-potentiation, fear conditioning and generalization of fear.

Housing familiar male wildtype rats together reduces the long-term adverse behavioural and physiological effects of social defeat

Social stress in rats is known to induce long-lasting, adverse changes in behaviour and physiology, which seem to resemble certain human psychopathologies, such as depression and anxiety. The present experiment was designed to assess the influence of individual or group housing on the vulnerability of male Wildtype rats to long-term effects of inescapable social defeat. Group-housed rats were individually exposed to an aggressive, unfamiliar male conspecific, resulting in a social defeat. Defeated rats were then either individually housed or returned to their group. The changes in their behaviour and physiology were then studied for 3 weeks. Results showed that individually housed rats developed long-lasting, adverse behavioural and physiological changes after social defeat. Their body growth was significantly retarded (p < .05) between 7 and 14 days after defeat. When individually and group-housed rats were exposed to a mild stressor (sudden silence) 2 days after defeat, both groups became highly immobile. However, when exposure was repeated at day 21, individually housed rats were still highly immobile compared to group-housed rats which regained their normal mobility after only 7 days. In an open field test, also regularly repeated, individually housed rats took significantly longer to leave their home base and were also significantly less mobile than group-housed rats over the entire 3-week test period as well as at specific timepoints. When the rats were placed in an elevated plus-maze 14 days after defeat, those that were individually housed were significantly more anxious than those that were group-housed. When tested at 21 days after defeat in a combined dexamethasone (DEX)/corticotrophin-releasing factor (CRF) test, results showed that the hypothalamic-pituitary-adrenocortical (HPA) activity in individually housed rats was higher. This was evidenced in the latter animals by the fact that DEX was significantly less able to suppress the secretion of ACTH and corticosterone, and by a significantly higher release of ACTH after administration of CRF. Although the weights of the spleen and testes of the two groups did not differ, the adrenals of individually housed rats were larger and the thymus and seminal vesicles were smaller. We conclude that when rats are isolated after defeat, they show long-lasting, adverse behavioural and physiological changes that resemble symptoms of stress-related disorders. In contrast, when familiar rats are housed together these effects of a social defeat are greatly reduced. These findings show that housing conditions importantly influence the probability of long-term adverse behavioural and physiological effects of social defeat in male Wildtype rats.

Vulnerability to arrhythmias during social stress in rats with different sympathovagal balance

An increased activity of the sympathetic nervous system is an important factor in the genesis of ventricular arrhythmias. Changes in average R-R interval, R-R interval variability (indirect measure of sympathovagal balance), occurrence of arrhythmias, and plasma norepinephrine concentrations were measured during a social stress episode (defeat) in two strains of rats, Wistar and wild type, which were supposed to differ in their autonomic stress responsiveness. Electrocardiograms were telemetrically recorded, and blood samples were withdrawn through jugular vein catheters from healthy, freely moving animals. R-R interval variability was estimated by the following time-domain parameters: the standard deviation of the mean R-R interval, the coefficient of variance, and the root mean square of successive differences in R-R interval. Average R-R interval and R-R interval variability measures, as well as plasma norepinephrine concentrations, indicated a higher sympathetic tone, a larger sympathetic responsiveness, and a lower parasympathetic antagonism after sympathetic activation in wild-type animals, which also showed a much higher incidence of arrhythmias (ventricular premature beats), compared with Wistar rats. These two strains might represent a valuable experimental model for studying the mechanisms (cellular/electrophysiological) responsible for the susceptibility to arrhythmias in healthy individuals exposed to stressful situations.

Social stress in rats and mice

This paper summarizes some of the highlights of our current social stress research in rodents as it was inspired by the work of Jim Henry. First, it is argued that social defeat can be considered as one of the most severe stressors among a number of laboratory stressful stimuli in terms of neuroendocrine activation. Moreover, the stress response induced by defeat in particular is characterized by a strong sympathetic dominance. Depending on the stress parameter, the stress response induced by a single social defeat may last from hours to days and weeks. As a long term consequence of a single defeat experience, the animal becomes sensitized to subsequent minor stressors. Finally, the importance of individual differences in coping style in relation to stress vulnerability is discussed.

The temporal dynamics of the stress response

This paper summarises the available evidence that failure of defense mechanisms in (semi)-natural social groups of animals may lead to serious forms of stress pathology. Hence the study of social stress may provide animal models with a high face validity. However, most of the animal models of human stress-disorders have concentrated on the consequences of chronic exposure to stressors. The present paper considers recent data, indicating that a single experience with a major stressor in the form of social defeat may have long-term consequences ranging from hours to days and weeks. It seems that the experience of a major stressor sensitizes the animal to subsequent stressors. The consequences of these long-term temporal dynamics of the stress response to the development of stress-related disorders and stress-vulnerability are discussed.

Orbital bleeding in rats while under diethylether anaesthesia does not influence telemetrically determined heart rate, body temperature, locomotor and eating activity when compared with anaesthesia alone

The question addressed was whether orbital bleeding in rats, while under diethylether anaesthesia, affects their locomotor activity body core temperature, heart rate rhythm and eating pattern. Roman High Avoidance (RHA) and Roman Low Avoidance (RLA) rats were used to enhance generalization of the results. Orbital bleeding when the rats were under diethylether anaesthesia was compared with diethylether anaesthesia alone. To take into account any effects of handling, the rats were also subjected to sham anaesthesia. The RHA rats urinated more during anaesthesia, needed more time to recover from the anaesthesia and showed a greater endocrine stress response to diethylether anaesthesia when compared with the RLA rats. During anaesthesia, the RHA rats showed a greater fall of body temperature and bradycardia than did the RLA rats. Diethylether anaesthesia reduced locomotor activity in the RHA rats, but had no effect in the RLA rats. In neither RHA nor RLA rats did anaesthesia plus orbital puncture, versus anaesthesia alone, influence body temperature, heart rate rhythm, locomotor and eating activity. The lack of effect of orbital puncture occurred both in the short term (within 2h) and long term (within 48 hours) and thus this study indicates that orbital puncture had, at least with respect to variables measured in the present study, no effect superimposed on that of diethylether anaesthesia.

Changes in daily rhythms of body temperature and activity after a single social defeat in rats

The long-term consequences of social stress on daily rhythms of body temperature and activity in rats were studied by means of radiotelemetry with intraperitoneally implanted transmitters. Rats were subjected to a single social defeat by placing them into the territory of a male conspecific for 1 h. Social defeat caused a sharp subsequent reduction in the amplitude of the daily temperature rhythm, which lasted for at least 4 days. The reduced amplitude was mainly due to higher temperatures during the circadian rest phase, i.e., the light period. Movement activity was less affected, but the decrease in activity during the dark phase after defeat correlated significantly with the temperature increase during the light phase. The stress-induced changes in daily rhythms of body temperature and activity are discussed in terms of their relevance to the role of rhythm-disturbances in the pathogenesis of affective disorders.

Counterregulatory hormone responses during graded hyperinsulinemic euglycemia in conscious rats

It has been suggested that hyperinsulinemia per se may affect the levels of some counterregulatory hormones in the absence of hypoglycemia. We studied the effect of graded hyperinsulinemia and concomitant increased glucose metabolism on the levels of counterregulatory hormones by means of the 5-step sequential hyperinsulinemic euglycemic clamp technique, combined with [3-3H]-glucose infusion, in conscious rats. Insulin infusion rates (IIR) of 0, 0.5, 1, 3, and 16 mU/min, resulted in steady-state plasma insulin levels (mean +/- SEM) of 24 +/- 4, 44 +/- 3, 98 +/- 8, 418 +/- 48, and 6626 +/- 361 microU/ml, peripheral glucose uptake (PGU) of 3.1 +/- 0.2, 3.6 +/- 0.3, 5.4 +/- 0.3, 9.2 +/- 0.4, and 12.4 +/- 0.2 mg/min and hepatic glucose production (HGP) of 3.1 +/- 0.2, 2.4 +/- 0.4, 0.8 +/- 0.3, -0.1 +/- 0.2, and -0.5 +/- 0.3 mg/min, respectively. Plasma glucagon levels were half maximally suppressed between IIRs of 0.5 and 1 mU/min and maximally suppressed at 3 mU/min. The suppression exactly paralleled the inhibition of HGP (r = 0.87 +/- 0.04, p < 0.02) but not the stimulation of PGU (r = -0.66 +/- 0.12, p = NS). This suggests that the inhibition of HGP by insulin is at least partially mediated by a simultaneous suppression of plasma glucagon levels. The adrenal hormones corticosterone and epinephrine were not influenced during the clamp.(ABSTRACT TRUNCATED AT 250 WORDS)

Common mechanisms underlying the proconflict effects of corticotropin-releasing factor, a benzodiazepine inverse agonist and electric foot-shock

The effects of corticotropin-releasing factor (CRF), a benzodiazepine inverse agonist (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate; DMCM) and electric foot-shock on rat conflict behavior were characterized and compared. Rats were trained to lever press under a multiple fixed-ratio schedule (FR 20) of food reinforcement in which responses during the first component were not punished, and the first response of each FR during the second component produced electric shock of an intensity sufficient to suppress responding by 10% to 15%. Intracerebroventricular injection of CRF (0.1-5.6 micrograms) caused a dose-dependent decrease in the rate of responding in both components of the schedule. However, CRF was more potent in decreasing rates of punished responding (proconflict effect). DMCM (10-100 micrograms; i.c.v.) also decreased rates of punished and nonpunished responding and was more potent during the punishment component. The suppression of punished and nonpunished responding by CRF and DMCM was mimicked by increasing the shock intensity (delta = 0.1 to 0.6 mA) during the punishment component. To determine whether CRF, DMCM and electric shock shared common mechanisms for these effects, rats were pretreated with i.c.v. injections of either a CRF antagonist (alpha helical CRF9-41, 50 micrograms), a benzodiazepine agonist (chlordiazepoxide, 10 micrograms) or a benzodiazepine antagonist (flumazenil, 10 micrograms) before the administration of equieffective doses of CRF or DMCM or an increase in shock intensity. Chlordiazepoxide attenuated the effects of all three stimuli. Flumazenil antagonized DMCM and CRF, but not shock, implicating a pharmacologic interaction between CRF and benzodiazepine systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of buspirone and chlordiazepoxide on plasma catecholamine and corticosterone levels in stressed and nonstressed rats

The effects of intragastric administration of the prototypical benzodiazepine (BDZ) anxiolytic drug chlordiazepoxide (CDP) and the non-BDZ anxiolytic agent buspirone (BUSP) on basal and stress-elevated plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) contents were investigated. Acute dosing of CDP (1-27 mg/kg) produced dose-related increases in basal CS secretion but was without effect on basal NA levels. The high dose of CDP caused a slight short-term A increase. Dose-dependent increases in plasma A, NA and CS contents were observed after acute treatment with BUSP (2 and 20 mg/kg). A medium dose of CDP (9 mg/kg) attenuated the stress-induced CS and A elevations. High doses of CDP that elevated basal CS release prevented a further increase of CS by stress and inhibited the NA and A response to stress. BUSP (2 and 20 mg/kg) was not effective in decreasing the stress-elicited rise of CS, NA or A. Conversely, the 20 mg/kg dose of BUSP enhanced the stress-induced A response. Repeated administration of CDP (9 mg/kg/day for six days) produced tolerance to the elevation of basal CS triggered by acute CDP treatment, but increased the efficacy of the drug's CS and A attenuating action in stressed rats. Repeated administration of BUSP (2 mg/kg/day for six days) also produced tolerance to the acute BUSP-induced effect on basal CS release, but did not affect the stress-induced CS, NA and A responses. It is concluded that the clinically effective anxiolytic BUSP does not have the BDZ-like property to inhibit stress-induced elevations in CS, NA and A. Furthermore, the present data support other evidence that activation of 5-HT1A receptor mechanisms increases plasma catecholamine and corticosterone concentrations.

Effects of chlordiazepoxide, flumazenil and DMCM on plasma catecholamine and corticosterone concentrations in rats

The effects of drugs representing three classes of benzodiazepine (BDZ) receptor-acting agents on circulating corticosterone (CS), noradrenaline (NA) and adrenaline (A) were examined in unstressed rats. Intragastric administration of a single-dose of the inverse agonist 3-carbomethoxy-4-ethyl-6,7-dimethoxy-beta-carboline (DMCM; 10 mg/kg) evoked 15-, 4- and 1.5-fold increases in plasma CS, A and NA, respectively, as compared to control values. The DMCM-induced CS, A and NA rises were completely blocked by combined treatment with the BDZ antagonist flumazenil (Ro 15-1788; 20 mg/kg). Flumazenil given alone did not affect plasma hormone levels. Administration (either intragastrically or intraperitoneally) of a single-dose of the BDZ agonist chlordiazepoxide (CDP; 20 mg/kg) produced a 10- to 15-fold increase in plasma CS but caused no change in plasma NA and A contents. Pretreatment with flumazenil blocked the CDP-elicited release of CS. The findings indicate that the CNS mechanisms controlling pituitary-adrenocortical and sympatho-adrenal outflow under basal conditions are functionally linked to central-type BDZ receptor system(s). Drugs with agonist or inverse-agonist actions at these receptor sites can be differentiated from each other by their distinct effects on plasma NA and A, but not CS, release.

Plasma catecholamine and corticosterone levels during active and passive shock-prod avoidance behavior in rats: effects of chlordiazepoxide

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.

Brain benzodiazepine receptor-mediated effects on plasma catecholamine and corticosterone concentrations in rats

The effects of the benzodiazepine (BDZ) receptor agonist chlordiazepoxide (CDP) and antagonist flumazenil (Ro 15-1788), given alone and in combination, on basal and novel environment stress (NES)-elevated plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) contents were investigated. When administered on their own, a medium dose of CDP (2.5 mg/kg) and a moderate dose of flumazenil (5 mg/kg) did not affect basal hormone levels. However, flumazenil potentiated the NES-induced CS elevation and suppressed the NA rise in response to NES. The 2.5 mg/kg dose of CDP attenuated the NES-elicited rise of CS and A, without changing the NES-enhanced NA concentrations. High doses of CDP (10 and 12.5 mg/kg), which elevated basal CS levels, prevented a further CS increase by NES and completely abolished the NA and A response to NES. The CDP effects on CS and NA were antagonized by pretreatment with flumazenil, in contrast to the CDP effect on A which was not blocked. The data indicate that brain (central-type) BDZ receptor systems are involved in regulating the neurosympathetic and adrenocortical, but not adrenomedullary, responses to mild stress.

Plasma catecholamine, corticosterone and glucose responses to repeated stress in rats: effect of interstressor interval length

Plasma noradrenaline (NA), adrenaline (A), corticosterone (CS) and glucose concentrations were determined in blood frequently sampled via a cardiac catheter from freely behaving rats exposed to five successive trials of water-immersion stress (WIS) with an interval between successive trials (interstressor interval; ISI) of either 24 hr or 72 hr. The first, acute exposure to WIS was accompanied by increased levels of plasma NA, A, CS and glucose which were substantially higher than those associated with handling or placement into a new cage. The magnitudes of the WIS-induced plasma NA, A, CS and glucose responses gradually declined across trials. However, five WIS exposures at a 24-hr ISI resulted in a faster and greater decrement of the plasma A, CS and glucose responses than five exposures at a 72-hr ISI. The data indicate that frequency of stressor presentation (i.e., length of interstressor interval) affects the adaptation pattern of neuroendocrine and metabolic responses to chronic intermittent stress. This finding supports the hypothesis that neuroendocrine adaptation to stress is (at least partly) similar to the process of behavioral or neurophysiological habituation to a sensory stimulus.

Effects of fasting on plasma catecholamine, corticosterone and glucose concentrations under basal and stress conditions in individual rats

Plasma noradrenaline (NA), adrenaline (A), corticosterone (CS) and glucose concentrations were determined in blood sampled via a cardiac catheter from freely moving male rats under ad lib fed and 24 hr food deprived conditions using a repeated measures within-subject design. Resting plasma NA and glucose levels were lower in the fasted condition as compared to the fed situation. One day of refeeding reinstated the decreased NA and glucose values to prefasting level. Exposing 24 hr food deprived animals to the psychological stress of a novel environment resulted in larger NA and glucose increases, an unchanged A release and a lower CS rise in comparison with the responses during the free feeding state. The results show the usefulness of a within-subject design to detect subtle changes in plasma NA contents. Additionally, the data support the concept of selective control of the sympathetic nervous system and adrenal medullae. It is argued that hypothalamic noradrenergic mechanisms may be linked to the fasting-induced effects on the sympatho-adrenal system.

Plasma catecholamine and corticosterone responses to predictable and unpredictable noise stress in rats

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.

Endotoxin-induced reduction of beta-adrenergic binding sites on splenic lymphocytes in vivo and in vitro: its modulation by anterior hypothalamic lesions

Bacterial endotoxin induced a 38% decrease in the number of beta-adrenergic binding sites (Bmax) on splenic lymphocytes, four days after intraperitoneal administration to guinea pigs. No change in the affinity (Kd) for [125-I]-cyanopindolol ([125-I]-CYP) binding was observed. Incubation of guinea pig splenocytes in vitro with different concentrations of bacterial endotoxin for 24 hours resulted in an increased incorporation of [3H]-thymidine, a parameter for lymphocyte activation. Activation of splenic lymphocytes with the optimal endotoxin concentration of 100 micrograms/ml for 24 hours induced a 27% decrease in the Bmax whereas the Kd for [125-I]-CYP binding was not changed. Based on these findings, we speculate that activation of lymphocytes with endotoxin in vitro and in vivo is associated with a reduction in the number of beta-adrenergic binding sites on these cells. Anterior hypothalamic (AHA) lesions protected against the endotoxin-induced reduction in the number of beta-adrenergic binding sites on lymphocytes. The protective effect of these lesions could not be related to alterations in the plasma levels of cortisol, triiodothyronine (T3), thyroxine (T4), adrenaline and noradrenaline or to splenic noradrenaline content. Since AHA lesions have been shown to inhibit several lymphocyte functions, it is suggested that these lesions prevent lymphocyte activation after in vivo endotoxin administration and through this abrogate the reduction of the beta-adrenergic binding sites.

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.