The prediction of resistance to emotional stress based on the individual testing of behavior

On the basis of the elaborated experimental model for testing of emotional interaction of animals individual typification of behaviour was established according to which all experimental male rats of August line were subdivided into groups: I--rats manifesting behaviour of avoidance, "victims" of electrocutaneous stimulation; II--without definite behaviour with respect to the "victim" rat; III--rats, preferring the behaviour determining electrocutaneous stimulation of the "victim" rat. All typified animals were subjected to emotional stress with the use of the elaborated experimental model of aggressive-conflict behaviour. Stability against emotional stress of each group of animals was studied. Significant differences were established of stability degree to emotional stress of the rats of three groups manifesting different types of behavioural reaction in conditions of emotional interaction. The most stable were rats of the I group, the least--of the III group; rats of the II group were in the middle position. Typification on the basis of testing of emotional interaction of animals allows to prognosticate individual stability against emotional stress.     

Increasing resistance to emotional stress by endogenous peptide prolactin

In real work we studied ability of endogenic peptide prolactin to raise the resistance of emotional stress under existing conditions of experimental model. Emotional stress was formed in the course of 5 days during 5 hours with fixation of groups of rats. All experimental animals were divided into three groups. The experiments showed the ability of the prolactin to raise the resistance of emotional stress.     

Cooperation among Norway Rats: The Importance of Visual Cues for Reciprocal Cooperation,and the Role of Coercion

Some animals reciprocate help, but the underlying proximate mechanisms are largely unclear. Norway rats (Rattus norvegicus) have been shown to cooperate in a variant of the iterated prisoner's dilemma paradigm, yet it is unknown which sensory modalities they use. Visual information is often implicitly assumed to play a major role in social interactions, but primarily nocturnal species such as Norway rats may rely on different cues when deciding to reciprocate received help. We used an instrumental cooperative task to compare the test rats' propensity to reciprocate received help between two experimental conditions, with and without visual information exchange between social partners. Our results show that visual information is not required for reciprocal cooperation among social partners because even when it was lacking, test rats provided food significantly earlier to partners that had helped them to obtain food before than to those that had not done so. The mean decision speed did not differ between the two experimental conditions, with or without visual information. Social partners sometimes showed aggressive behaviour towards focal test individuals. When including this in the analyses to assess the possible role of aggression as a trigger of cooperation, aggression received from cooperators apparently reduced the cooperation propensity, whereas aggression received from defectors increased it. Hence, in addition to reciprocity, coercion seems to provide additional means to generate altruistic help in Norway rats.     

Brain monoamine oxidase in mink selected for their reaction to man]

Monoamineoxidase activity was studied in minks of three behavioural groups--those bred for absence of aggression towards man, those bred for high aggression to man, and those of non-selected population. Breeding for the absence of aggression was accompanied by a decrease of MAO-B activity with unchanged MAO-A activity. The minks bred for aggressive behaviour towards man, as compared to those bred for the absence of aggression, were characterised by increased MAO-A and MAO-B activities in the brain stem. The effect of emotional stress on MAO-A and MAO-B was similar in aggressive, non-aggressive and unselected minks and was expressed in a decrease of both MAO-A and MAO-B activity. The MAO activity of cerebral hemispheres remained unaffected both by selection for behaviour and by the emotional stress.     

Increased illumination level during gestation and offspring emotionality in the rat

Open-field defecation, ambulation and HR were recorded from a group of rats whose mothers had been exposed to high intensity illumination during pregnancy. Compared with controls, experimental animals showed reduced defecation, increased HR, and no significant differences in ambulation. No significant sex differences in open-field measures were found. It was concluded that illumination level is a more satisfactory independent variable in prenatal maternal stress studies, than the traditional ‘conditioned anxiety’ technique. The findings were compared with those of other studies in the area, and discussed in relation to theories of autonomic functioning in emotional behaviour.     

Genetical aspects of hormonal modification of the stress reactivity. II. Modification in early ontogenesis of the stress reactivity of adult gray rats selected for behavior toward man

Inherited and modificational changes of the stress reactivity in two outbreed stocks of wild Norway rats trapped in nature and selected for behaviour were studied. During 18 generations the rats of one stock were selected for the lack of defensive behaviour in the glove test (tame), while in another stock the aggressiveness was maintained by the selection (aggressive). Interstock differences in the brain noradrenaline mechanisms were observed. The emotional stress reactivity of the tame animals was decreased, in comparison with the aggressive ones. Definitive stress reactivity of adult rats was modified by injections of hydrocortisone to their mothers on the 16 and 18 days of gestation. Hormonal treatment changed noradrenaline mechanisms and decreased the reaction to emotional stressor in aggressive rats. The modified level of the stress reactivity of aggressive rats was similar to the definitive level of the tame ones. Hormonal treatment did not modify stress reactivity in tame rats. Thus, the phenotype only emerging in aggressive rats, as a result of hormonal modification, is the inherited norm of the tame animals. However, due to rat selection for the lack of defensive behaviour towards the man, high corticosteroid level in the blood of pregnant females, an external developmental factor, in respect to the fetus, loses regulatory function during the development of the neuroendocrine mechanisms of the stress reaction.     

Gene c-Fos expression in brain of rats resistant and predisposed to emotional stress after intraperitoneal injection of the ACTH(4-10)analog--semax

The effect of the ACTH(4-10) analog Semax on immediate early gene c-Fos expression was studied in Wistar rats with high and low resistance to emotional stress under the usual conditions and during psychoemotional loading. Fos-immunoreactive cells in the were counted automatically with the help of a computer. It was shown that under the usual conditions the intraperitoneal Semax injection induced immediate early gene c-Fos expression in the lateral septal region in rats predisposed to emotional stress and in the paraventricular hypothalamus in rats of both groups. Preliminary Semax injection decreased the stress-induced c-Fos expression in the paraventricular hypothalamus and medial septum in rats predisposed to emotional stress and tended to reduce the number of stress-induced c-Fos-immunopositive cells in the lateral septum and basolateral amygdala in both groups of animals. The obtained data suggest that Semax differently affects the immediate early c-Fos gene expression in the brain of rats resistant and predisposed to emotional stress and this effect reflects the antistressor properties of the regulatory peptide.     

Pharmacological correction of emotional stress after exposure to ionizing radiation and treatment with a radioprotector indralin

A possibility to use tranquilizers (aphobazole, phenazepamum) for reducing symptoms of prolonged emotional stress influencing rats after irradiation under treatment with a radioprotector indralin was investigated. It was found that indralin showed the protective effect and activated regenerative processes in the hemopoietic system of animals exposed to doses of 6.0 and 7.0 Gy. The prolonged emotional stress developing in the early periods after the exposure, essentially reduced the favourable action of the radioprotector on restoration of hemopoiesis. The application of tranquilizers stopped the inhibiting action of the emotional stress on the hemopoietic system of the irradiated animals in conditions of radioprotective administering.     

Biogenic amines in the brain structures of rats from genetically diverse strains under stress]

The content was studied of biogenic amines and their metabolites (by the method of high-effective fluid chromatography electrochemical detection) in the reticular formation of the midbrain, locus coeruleus and sensorimotor cortex in the rats of Wistar and August lines, differing in the behaviour in the open field, in conditions of immobilization stress. The dependence was revealed of the biogenic amines level on the animals genotype and individual characteristics. Most probably, the level of biogenic amines metabolism in central brain structures determines the stability of the animals against emotional stress.     

Correlation of hippocampal theta-rhythm with behavior in rabbits]

Dynamics of the hippocampal theta-activity was studied during performance of a stably elaborated habit with drinking reinforcement. It has been shown that during running and in other forms of behaviour, belonging to the class of voluntary movements, the theta-activity takes place within the band of 7.5--12 c/s; during emotional stress without locomotion its frequency amounts to 6--7.5 c/s, during lapping movements it is equal to 5-6 c/s, during emotionally motivated and behavioral inactivation--to 2.5--5 c/s. In accordance with the data obtained in conditions of spontaneous behaviour, the observed facts allow to consider the wide spectrum of the hippocampal theta-rhythm not as a continuous, one-band, functionally uniform frequency, reflecting the continuum of arousal by its intensity,--but as consisting of discrete frequency bands which are functionally connected with different forms of behavior.     

Domestication affects the structure,development and stability of biobehavioural profiles

Domestication is an evolutionary process during which the biobehavioural profile (comprising e.g. social and emotional behaviour, cognitive abilities, as well as hormonal stress responses) is substantially reshaped. Using a comparative approach, and focusing mainly on the domestic and wild guinea pig, an established model system for the study of domestication, we review (a) how wild and domestic animals of the same species differ in behaviour, emotion, cognition, and hormonal stress responses, (b) during which phases of life differences in biobehavioural profiles emerge and (c) whether or not animal personalities exist in both the wild and domestic form. Concerning (a), typical changes with domestication include increased courtship, sociopositive and maternal behaviours as well as decreased aggression and attentive behaviour. In addition, domestic animals display more anxiety-like and less risk-taking and exploratory behaviour than the wild form and they show distinctly lower endocrine stress responsiveness. There are no indications, however, that domestic animals have diminished cognitive abilities relative to the wild form. The different biobehavioural profiles of the wild and domestic animals can be regarded as adaptations to the different environmental conditions under which they live, i.e., the natural habitat and artificial man-made housing conditions, respectively. Concerning (b), the comparison of infantile, adolescent and adult wild and domestic guinea pigs shows that the typical biobehavioural profile of the domestic form is already present during early phases of life, that is, during early adolescence and weaning. Thus, differences between the domestic and the wild form can be attributed to genetic alterations resulting from artificial selection, and likely to environmental influences during the pre- and perinatal phase. Interestingly, the frequency of play behaviour does not differ between the domestic and wild form early in life, but is significantly higher in domesticated guinea pigs at later ages. Concerning (c), there is some evidence that personalities occur in both wild and domestic animals. However, there may be differences in which behavioural domains – social and sexual behaviour, emotionality, stress-responsiveness – are consistent over time. These differences are probably due to changing selection pressures during domestication.     

The effect of ablation in the n. medianus raphe on the aggressive and sexual behavior of white rats]

A study was made of a change in the aggressive and sexual behaviour of albino rats under the influence of ablation of the n. medianus raphe whose serotonin-containing units send ascending projections to the forebrain. Ablation of the nucleus produced a drop in the serotonin level in the forebrain, and aggressiveness to mice, which was much more pronounced in the male than in the female animals. Intraspecial aggressiveness between animals of the same sex and the sexual behaviour of the male rats did not change. It has been assumed that n. medianus raphe exerts an inhibitory influence on the manifestation of aggression of the "predatory" animal.     

Acute and chronic restraint stress alter the incidence of social conflict in male rats

Stress and elevated stress hormone levels are known to alter cognition, learning, memory, and emotional responses. Three weeks of chronic stress or glucocorticoid exposure is reported to alter neuronal morphology in the hippocampus, the amygdala, and the prefrontal cortex, and to decrease neurogenesis in the dentate gyrus. Here we examine the effects of acute and chronic restraint stress exposure on the incidence of emotional responses throughout a 3-week period among adult rat conspecifics. Our data indicate that acute restraint stress (i.e., a single 6-h exposure) results in a significant reduction in aggressive conflicts among stressed males compared to experimental controls. In contrast, on Days 14 and 21, repeatedly restrained rats exhibited significantly more aggressive behaviors than controls. Blood samples taken 18 h after the last restraint session indicate that plasma concentrations of the stress hormone corticosterone (CORT) in stressed rats were equivalent to those of unstressed rats; however, the number of individually initiated aggressive acts observed positively correlated with plasma CORT measures taken at the end of the study. In contrast to studies of psychosocial stress or intruder paradigms, here we observe spontaneous emotional responses to an uncontrollable stressor in the homecage. This study provides a novel examination of the effects of chronic restraint stress on emotional responses in the home environment among cagemates. These results indicate that acute and chronic restraint stress alter the incidence of aggression, and emphasize the relevance of this model of chronic stress to studies of stress-responsive disorders characterized by aggressive behavior.     

Is pain-induced aggression actually a defensive form of that behavior?

25-minute testing of aggressive reactions in constant pairs of male rats, elicited by electric shocks shows that electro-pain aggression of rats is not a homogeneous process, but consists of three successive stages: orienting-investigatory activity and attempts to get out of the chamber; defensive aggression; establishing of relations of domination-subordination and attacking aggression. Division in attacking rats and defending themselves, occurs mainly at final stages of testing (15-25 min); in some pairs reactions of attacking aggression are accomplished by the same rats. It is supposed that rats pain aggression is not a purely defensive form of this behaviour, but a modification of intermale aggression caused by specificity of laboratory conditions.     

"Sensitive periods" in the systemogenesis of intraspecific aggression in rats

As a result of experiments conducted on male outbred white rats, approximate limits were established of two sensitive periods for the formation of intraspecies aggression of rats under the influence of contacts with the animals of the same age: sensitive period from 12th to 21st postnatal day for changing from playing behaviour into the aggressive one; and 40-60 days for differentiation of the aggressivity against the males and females. It was shown, that despite considerable change in the spectrum of aggressive reactions of early isolated rats towards intruders and low effect of these reactions, judging by response behaviour of intruders, these reactions were based on the emotionally-motivational state, typical for the formed aggressive behaviour. It was also found, that disturbances of the aggression formation in rats isolated in early age, were caused by deprivation of contacts with rats of the same age and not by general informational impoverishment of the environment where rat pups were bred.     

The action of tropic adenohypophyseal hormones when administered intraventricularly on rat behavioral reactions

In experiments on rats the influence was studied of tropic hormones of adenohypophysis--somatotropin, thyrotropin and adrenocorticotropin (STH, ThTN and ACTH respectively) on the elaboration and extinction of conditioned reaction of active avoidance (CRAA) in Y-maze and behaviour in the open field under microinjections of hormones into the brain lateral ventricle (0.001-0.002 ME). It has been shown that all studied hormones improve animals learning at negative pain reinforcement; ThTH and ACTH retard it in contrast to STH, which accelerates the extinction of the elaborated CRAA; tropic hormones exert differentiated influence on rats behaviour in the open field. No distinct correlation was found between behavioural manifestation and the level of catecholamines in the rats hypothalamus.     

Effect of dipeptide vilon on emotional stress resistance in rats

Effects of synthetic thymomimetic vilon on open field behaviour, immediate early gene c-Fos expression in paraventricular hypothalamus properties of organs sensitive to emotional stress, and characteristics of albumin in the blood plasma in male Wistar rats, were investigated and are discussed in the article. It is shown that intraperitoneal vilon injection rises the resistance against emotional stress according to prognostic indexes open field behaviour. Vilon administration also inhibits hypertrophy of the adrenals, involution of the thymus, and elevates concentration of albumin in the blood plasma. The number of Fos-immunoreactive neurons in the paraventricular hypothalamus was lower after vilon administration especially in rats resistant against emotional stress.     

The Effects of Juvenile Stress on Anxiety,Cognitive Bias and Decision Making in Adulthood: A Rat Model

Stress experienced in childhood is associated with an increased risk of developing psychiatric disorders in adulthood. These disorders are particularly characterized by disturbances to emotional and cognitive processes, which are not currently fully modeled in animals. Assays of cognitive bias have recently been used with animals to give an indication of their emotional/cognitive state. We used a cognitive bias test, alongside a traditional measure of anxiety (elevated plus maze), to investigate the effects of juvenile stress (JS) on adulthood behaviour using a rodent model. During the cognitive bias test, animals were trained to discriminate between two reward bowls based on a stimulus (rough/smooth sandpaper) encountered before they reached the bowls. One stimulus (e.g. rough) was associated with a lower value reward than the other (e.g. smooth). Once rats were trained, their cognitive bias was explored through the presentation of an ambiguous stimulus (intermediate grade sandpaper): a rat was classed as optimistic if it chose the bowl ordinarily associated with the high value reward. JS animals were lighter than controls, exhibited increased anxiety-like behaviour in the elevated plus maze and were more optimistic in the cognitive bias test. This increased optimism may represent an optimal foraging strategy for these underweight animals. JS animals were also faster than controls to make a decision when presented with an ambiguous stimulus, suggesting altered decision making. These results demonstrate that stress in the juvenile phase can increase anxiety-like behaviour and alter cognitive bias and decision making in adulthood in a rat model.     

Imaging Conditioned Fear Circuitry Using Awake Rodent fMRI

Functional magnetic resonance imaging (fMRI) is a powerful method for exploring emotional and cognitive brain responses in humans. However rodent fMRI has not previously been applied to the analysis of learned behaviour in awake animals, limiting its use as a translational tool. Here we have developed a novel paradigm for studying brain activation in awake rats responding to conditioned stimuli using fMRI. Using this method we show activation of the amygdala and related fear circuitry in response to a fear-conditioned stimulus and demonstrate that the magnitude of fear circuitry activation is increased following early life stress, a rodent model of affective disorders. This technique provides a new translatable method for testing environmental, genetic and pharmacological manipulations on emotional and cognitive processes in awake rodent models.     

Sex differences in response to stress in conscious and anesthesized rats during surgical stress]

Adrenal and plasma corticosterone levels under conditions of preoperative stress (removal from animal to experimental rooms, removal from a home cage, handling, weighing and injecting with saline) were more than 2-fold higher in female rats than in male ones. Females, compared with males, showed more pronounced decrease in corticosterone responses to preoperative stress and laparotomy under nembutal anesthesia, which blocked stress-induced emotional activation. One hour after recovery from anesthesia laparotomized females but not males, demonstrated a significant (5-fold) increase in plasma corticosterone level. The absolute values of plasma corticosterone in laparotomized females, compared with males, were 2-fold lower under anesthesia but 2-fold higher after recovery from anesthesia. It is supposed that in females, compared with males, stress-induced emotional tension plays more considerable role in endocrine stress responses. This provides higher adrenocortical sensitivity to stress in conscious female rats than in male animals.