Effects of prenatal disturbance in the brain testosterone metabolism on anxiety level and behavior of rats in a novel environment

The effects of maternal administration of the aromatase inhibitor 1,4,6-androstatrien-3,17-dione (ATD) during the last week of gestation on formation of behavior in a novel environment were studied in male and female offspring. The "open field" and the elevated plus-maze tests were used. The results showed that there were a significant elevation of the anxiety level and emotionality in ATD-treated 30-day-old female rats, whereas at the age of 90 days, the elevation of these behavioral parameters was observed both in males and females. There was no a sexual dimorphism in behavioral response to a novel environment such as locomotor activity, time of immobilization, total duration of grooming reaction, and anxiety level between adult control male and treated female rats. These data suggest that prenatal inhibition of the brain testosterone metabolism alters the formation of sexual dimorphism of the anxiety and behavioral response to a novel environment in adulthood.     

Common variations in the pretest environment influence genotypic comparisons in models of anxiety

The behavioral characterization of rodent strains in different studies and laboratories can provide unreplicable results even when genotypes are kept constant and environmental control is maximized. In the present study, the influence of common laboratory environmental variables and their interaction with genotype on the results of behavioral tests of anxiety/emotionality were investigated. To this end, the inbred rat strains Lewis (LEW) and spontaneously hypertensive rats (SHR), which are known to differ for numerous emotionality-related behaviors, were tested in the open field (OF), elevated plus maze (EPM) and black/white box (BWB), while three environmental factors were systematically controlled and analyzed: (1) the experimenter handling the animal (familiar or unfamiliar); (2) the position of the home cage (top or bottom shelf of the rack) and (3) the behavioral state of the animal immediately before the test (arousal or rest). Experimenter familiarity did not alter the behavior of rats in the OF. Cage position, on the other hand, influenced the behavior in the OF and BWB, with rats housed in top cages appearing less anxious than those housed in the bottom. In the BWB (but not in the OF), these effects were genotype dependent. Finally, the behavioral state of the animals prior to testing altered the results of the EPM in a strain-dependent manner, with some anxiety-related genotypic differences being found only among rats that were aroused in their home cages. This study showed that common variations in the laboratory environment interact with genotype in behavioral tests of anxiety/emotionality. Recognizing and understanding such variations can help in the design of more effective experiments.     

Latent Variables Affecting Behavioral Response to the Human Intruder Test in Infant Rhesus Macaques (Macaca mulatta)

The human intruder test is a testing paradigm designed to measure rhesus macaques’ behavioral responses to a stressful and threatening situation. In the test, an unfamiliar human positions him/herself in various threatening positions relative to a caged macaque. This paradigm has been utilized for over 20 years to measure a variety of behavioral constructs, including fear and anxiety, behavioral inhibition, emotionality, and aggression. To date, there have been no attempts to evaluate comprehensively the structure of the behavioral responses to the test. Our first goal was to identify the underlying latent factors affecting the different responses among subjects, and our second goal was to determine if rhesus reared in different environments respond differently in this testing paradigm. To accomplish this, we first performed exploratory and confirmatory factor analyses on the behavioral responses of 3‐ to 4‐month‐old rhesus macaques, utilizing data from over 2,000 separate tests conducted between 2001–2007. Using the resulting model, we then tested to see whether early rearing experience affected responses in the test. Our first analyses suggested that most of the variation in infant behavioral responses to the human intruder test could be explained by four latent factors: “activity,” “emotionality,” “aggression,” and “displacement.” Our second analyses revealed a significant effect of rearing condition for each factor score (P < 0.001); most notable socially reared animals had the lowest activity score (P < 0.001), indoor mother‐reared animals had the highest displacement score (P < 0.001), and nursery‐reared animals had the highest emotionality (P < 0.001) and lowest aggression scores (P < 0.001). These results demonstrate that this standardized testing paradigm reveals multiple patterns of response, which are influenced by an animal's rearing history. Am. J. Primatol. 75:314‐323, 2013. © 2012 Wiley Periodicals, Inc.     

Behavioral and adrenal relationships to audiogenic-seizure susceptibility in BALB-cJ mice

This study reports behavioral, biochemical and endocrine differences in audiogenic-seizure susceptible and resistant male mice (BALB/cJ) observed at 6 to 11 weeks of age. The various findings (total leukocyte and adrenal corticosterone) indicated hypoadrenal function in the audiogenic-seizure susceptible mice. The evaluation demonstrated that locomotor activity and emotionality were significantly increased in the audiogenic-seizure susceptible mice with suggestions of increased timidity. The interrelationships of hypoadrenocortical function and audiogenic-seizure susceptibility with locomotor activity, emotionality and timidity in the BALB/cJ mice merit further investigation.     

Genetic variations of noradrenaline synthesis and reception in the mouse brain and the animal behavior in the new environment]

C57BL mice were found to have the highest locomotion and the lowest emotionality under novel environment out of three strains of mice. Their brain stem TH activity was increased whereas the density of alpha2-ARs and beta-ARs were decreased in their cortex and hypothalamus. The BALB mice were twice as virulent as the CBA mice whereas the emotionality was the same in both strains. In general, low emotionality and high locomotion in novel environment were found in mice with increased activity of norepinephrine synthesis and decreased amount of adrenergic receptors in the brain.     

Behavioral alterations induced by repeated testing in C57BL/6J and 129S2/Sv mice: implications for phenotyping screens

The C57BL/6JOlaHsd and 129S2/SvHsd mice were tested in a battery designed for behavioral phenotyping of genetically modified mice. The study was performed in order to reveal the effect of training history on the behavior by comparison with the experimentally naïve mice in the same tests. Significant strain differences were obtained in all experiments. Previous handling and testing reduced exploratory activity and emotionality significantly in the mice. The coordination ability was better and nociceptive sensitivity was increased in the trained mice. The contextual fear was reduced whereas the cued fear was enhanced in the experienced mice. The training history did not alter initial learning in the water maze. However, after reversal learning the naïve mice displayed significant preference for both old and new platform locations, whereas the battery animals did not exhibit preference to the old location. The experienced mice appeared to be less active in the forced swimming test and exhibited decreased conditioned taste aversion. The influence of test history was strain-dependent in certain cases. Therefore, the experience has substantial consequences on the behavior, mainly by reducing exploratory activity, and the previous experience of the animals has always to be considered in the analysis of genetically modified mice.     

Circadian patterns of basic emotional reactivity and stress related events revisited in mice treated with lithium: behavioral rhythmometric analyses

This research dealt with rhythmometric methods for estimating and comparing the main temporal parameters characterizing the circadian structure of behavioral events in mice with and without lithium treatment. Such comparative chronobiologic studies would tend to demonstrate in psychophysiology that this drug does not displace the circadian patterns of basic emotionality, but does displace some behavioral circadian rhythms associated with more corticalized integrations. The present behavioral observations would tend to support the hypothesis that lithium salts modify the circadian structure of emotionality by cortical modulation rather than only by physiological subcortical integrations. Such circadian studies show also that behavioral chronobiology raises some working hypotheses in comparative ethology and permits the development of new heuristic concepts in the field of biological psychiatry.     

Behavioral and physiological characteristics of nonagouti mutation in gray rats during selection for aggressiveness

The goal of this work was to find out to which degree the black coat color mutation nonagouti that appears in wild Norway rat in the course of breeding for the maintenance and enhancement of aggressiveness towards a human affects selected and other behavioral traits as well as stress reactivity and brain neurochemistry. Nonagouti rats displayed increased emotionality in the open-field and forced-swimming tests as compared to agouti animals, whereas there were no differences in anxiety estimated in the elevated plus-maze. Neither were there any differences in glucocorticoid reactions to a combined stressful procedure such as forced swimming. The dopamine content in the frontal cortex and striatum and noradrenaline content in the frontal cortex were increased in black rats as compared to gray rats. The result suggest that the nonagouti mutation in gray aggressive rats enhances the effects of selection for aggressiveness on some behavioral traits and brain catecholamine level.     

Omega-3 fatty acids and rodent behavior

This paper reviews the role of the n-3 fatty acids in the regulation of cognitive functions, locomotor and exploratory activity and emotional status in rodents. There are disparate data on the performance of n-3 fatty acid deficient animals in the open field test and elevated plus maze. Results obtained in our laboratory indicated slower habituation to the open field in deficient mice, which affects total locomotor and exploratory parameters. We also observed no change in plus maze performance of deficient mice under low-stress but elevated anxiety under high-stress conditions. There is some evidence of elevated aggression and increased immobility time in the forced swimming test caused by n-3 fatty acid deficiency in rodents. Effects of n-3 fatty acid deficiency and supplementation on learning in several tests such as the Morris water maze, two odor olfactory discriminations, radial arm maze performance and avoidance tasks are reviewed in detail. There is some evidence of an enhanced vulnerability to stress of n-3 fatty acid deficient animals and this factor can influence performance in a variety of tests. Thus, behavioral tasks that involve a higher level of stress may better differentiate behavioral effects related to brain docosahexaenoic acid (DHA) status. It is suggested that a fruitful area for future investigations of functional alterations related to brain DHA status will be the delineation of the factors underlying changes in performance in behavioral tasks. The possible role of non-cognitive factors like emotionality and attention in the impaired performance of n-3 fatty acid deficient animals also requires further investigation.     

Lifelong hyperarousal in the spontaneously hypertensive rat indicated by operant behavior

Instrumental conditioning techniques were used to obtain objective evidence of differences in behavioral arousal between the spontaneously hypertensive rat (SHR) and the normotensive ancestral Wistar Kyoto (WKY) strain. Subjective emotionality ratings previously indicated that the genetically hypertensive rats were more active and aggressive than their normotensive cousins. In a lengthy series of operant conditioning sessions using a small number of adult female SHR and WKY rats, hyperarousal in the SHR was confirmed by their significantly higher response outputs on either response contingent or time contingent schedules of reinforcement. Conditioned emotionality tests during this series of experiments also suggested hyperarousal and aggressiveness in the SHR, since the fear-conditioned stimulus suppressed bar-pressing in the SHR much less than in the WKY. Further experiments with young prehypertensive SHR rats provided the same evidence of hyperresponsivity in the SHR compared to the WKY strain. Furthermore, these young SHR failed to develop hypertension by the end of the study (14 weeks of age), while their nonconditioned SHR cousins had become clearly hypertensive by the same age. This suggests that factors related to the conditioning methods modified the development of high blood pressure in this animal model of essential hypertension.     

Different data from different labs: lessons from studies of gene-environment interaction

It is sometimes supposed that standardizing tests of mouse behavior will ensure similar results in different laboratories. We evaluated this supposition by conducting behavioral tests with identical apparatus and test protocols in independent laboratories. Eight genetic groups of mice, including equal numbers of males and females, were either bred locally or shipped from the supplier and then tested on six behaviors simultaneously in three laboratories (Albany, NY; Edmonton, AB; Portland, OR). The behaviors included locomotor activity in a small box, the elevated plus maze, accelerating rotarod, visible platform water escape, cocaine activation of locomotor activity, and ethanol preference in a two-bottle test. A preliminary report of this study presented a conventional analysis of conventional measures that revealed strong effects of both genotype and laboratory as well as noteworthy interactions between genotype and laboratory. We now report a more detailed analysis of additional measures and view the data for each test in different ways. Whether mice were shipped from a supplier or bred locally had negligible effects for almost every measure in the six tests, and sex differences were also absent or very small for most behaviors, whereas genetic effects were almost always large. For locomotor activity, cocaine activation, and elevated plus maze, the analysis demonstrated the strong dependence of genetic differences in behavior on the laboratory giving the tests. For ethanol preference and water escape learning, on the other hand, the three labs obtained essentially the same results for key indicators of behavior. Thus, it is clear that the strong dependence of results on the specific laboratory is itself dependent on the task in question. Our results suggest that there may be advantages of test standardization, but laboratory environments probably can never be made sufficiently similar to guarantee identical results on a wide range of tests in a wide range of labs. Interpretations of our results by colleagues in neuroscience as well as the mass media are reviewed. Pessimistic views, prevalent in the media but relatively uncommon among neuroscientists, of mouse behavioral tests as being highly unreliable are contradicted by our data. Despite the presence of noteworthy interactions between genotype and lab environment, most of the larger differences between inbred strains were replicated across the three labs. Strain differences of moderate effects size, on the other hand, often differed markedly among labs, especially those involving three 129-derived strains. Implications for behavioral screening of targeted and induced mutations in mice are discussed.     

Physiological manifestations of action of a gene regulating predisposition to a pendulum-like movements in rodents

Physiological effects of the gene determining predisposition to a stereotypical hyperkinesis in the form of pedulum movements (PM) are manifested in some behavioral peculiarities (total motor activity, emotionality, intensity of the startle reflex, sensitivity of the 5-HT2 receptors, predisposition to catalepsy). High frequency of the PM occurring in Wistar rat stock suggests that the gene determining the PM expression is not a pathological one but controls some adaptive properties of the nervous system. Relationships between the PM expression and the degree of predisposition to catalepsy are biphasic and may be described by an inverted U-shaped curve.     

Exposure to environmental enrichment elicits differential hippocampal cell proliferation: role of individual responsiveness to anxiety

Environmental enrichment (EE) is a largely employed behavioral procedure in which animals are exposed to high stimulation compared with conventional housing conditions. Animal exposure to an EE exerts beneficial effects on the performance of different learning tasks and induces a number of behavioral, neurochemical, and neuroanatomical changes including hippocampal cell proliferation. However, the importance of voluntary interaction with the environment in these changes has not been clearly resolved yet. Moreover, the effects of a complex environment on animal emotionality still remains questionable and has not been explored in detail under conditions that allow unmasking individual responses among subjects in a group. The present study was aimed at exposing groups of rats to an EE, and analyzing individual differences in activity levels during EE sessions. We observed differences with respect to the activity level displayed by rats during the enriched sessions, which correlated with differences in the rate of hippocampal cell proliferation. It is suggested that exposure to EE may reduce anxiety-like behaviors and may elicit individual differences on emotional reactions positively linked with hippocampal neurogenesis and testosterone levels.     

Sex differences in behavioral and corticosterone responses to mild stressors in ICR mice are altered by ovariectomy in peripubertal period

Among rodents, females are generally considered to be highly responsive in terms of emotionality under stressful conditions, and have higher corticosterone levels and activity. In this study, we examined sex differences in mice by evaluating anxiety behaviors and corticosterone responses to mild stressors. In our first experiment, we analyzed the behavioral and corticosterone responses to the elevated plus-maze test and open-field test in male and female mice, and compared sex differences. Principal component analysis (PCA) was used to investigate the correlation of these responses between males and females. The corticosterone level was higher in females under both basal and stressed conditions. In the behavioral response, higher locomotor activity was seen in females in the elevated plus-maze test. PCA showed little association among anxiety behavior, locomotor activity, and corticosterone secretion. In our second experiment, we examined the activational effects of sex steroids on the corticosterone response to the elevated plus-maze test by gonadectomizing male and female mice and using testosterone or estrogen capsules as hormonal replacements. Sex differences at the basal corticosterone level were not altered by the hormonal milieu in adults, however the higher corticosterone level of females in response to stress was diminished by ovariectomy, although replacement with neither testosterone nor estrogen had any effect. These results suggest that the sex difference in novelty exposure observed in the form of a greater hypothalamic-pituitary-adrenal (HPA) axis response in female ICR mice is controlled by ovary-derived factors in adults.     

Sex- and lineage-specific inheritance of depression-like behavior in the rat

The Wistar–Kyoto (WKY) rat exhibits physiological and behavioral similarities to endophenotypes of human depression. In the forced swim test (FST), a well-characterized antidepressant-reversible test for behavioral despair in rodents, WKYs express characteristics of behavioral despair; increased immobility, and decreased climbing. To map genetic loci linked to behavior in the FST, we conducted a quantitative trait loci (QTL) analysis of the segregating F2 generation of a WKY × Fisher 344 (F344) reciprocal intercross. Using linear-model-based genome scans to include covariate (sex or lineage)-by-QTL interaction effects, four significant QTL influencing climbing behavior were identified. In addition, we identified three, seven, and two suggestive QTL for climbing, immobility, and swimming, respectively. One of these loci was pleiotropic, affecting both immobility and climbing. As found in human linkage studies, several of these QTL showed sex- and/or lineage-dependent effects. A simultaneous search strategy identified three epistatic locus pairs for climbing. Multiple regression analysis was employed to characterize the joint contributions of these QTL and to clarify the sex- and lineage-dependent effects. As expected for complex traits, FST behavior is influenced by multiple QTL of small effect, each contributing 5%–10%, accounting for a total 10%–30% of the phenotypic variance. A number of loci mapped in this study share overlapping candidate regions with previously identified emotionality QTL in mice as well as with susceptibility loci recognized by linkage or genome scan analyses for major depression or bipolar disorder in humans. The presence of these loci across species suggests that these QTL may represent universal genetic factors contributing to mood disorders.     

Statistical analysis of measures of arousal in ovariectomized female mice

In preparation for evaluating hormone effects and hormone receptor gene influences on fundamental processes of behavioral arousal, we subjected 48 ovariectomized female mice to a rigid protocol of several tests bearing on arousal concepts. The central hypothesis was that results would organize themselves according to capacities for sensory alertness, motor activity, and emotional reactivity. The large table of across-mouse correlation was subjected to factor analysis and cluster analysis. Results provided evidence for a general arousal (one-factor solution) which, however, accounted for only 29.72% of the variance. Four-factor (72.03%) matched four-cluster and six-factor (84.38%) matched six-cluster lineups of behavior components quite well, but did not conform to the main hypothesis; e.g., home cage exploration frequency and duration variables did not covary, and locomotor wheel activity grouped with fear indices. Besides providing a baseline for ongoing estrogen/thyroid and related genetic experiments, this statistical approach should be useful for a variety of hormonal studies of complex behaviors in mice.     

Spatial organization of EEG in rats with genetically determined emotionality

In order to study the possibility of EEG discrimination of genetically determined emotionality (increased propensity to emotional and stress reactions and anxiety) brain electrical activity was recorded in rats of two strains: Maudsley Reactive and Maudsley Nonreactive (24 derivations from the convexital skull surface were used). The program package "Synchro-EEG" was used for EEG processing. It was demonstrated that the two rat strains were significantly different in 120 EEG parameters of 840 ones analyzed. On the basis of 37 parameters, each rat was correctly recognized as belonging to the respective group with the error of 4.89%. The analysis of the detected signs allowed their classification to be performed in accordance with the peculiarities of the emotional and cognitive processes and the level of nonspecific activation. Specific forms of interaction between these components in the system of emotional reactions were revealed.     

The significance of the genotype and individual behavioral characteristics for the manifestation of the dominant phenotype in mouse micropopulations]

Influence of genotype and such individual characteristics as locomotor and exploratory activity, aggressiveness and emotionality, was studied in male mice. Males F1 and males of the parent line PT had high level of social dominance. F1 had high level of aggressiveness, and low emotionality, medium level of locomotor and exploratory activity. Significance of these individual behavioural characteristics for dominant behaviour is discussed.     

Behavioural studies in different strains of mice and the problem of heterosis

Significant differences between strains were found for open field activity and emotionality, exploratory activity, initial reaction to shock, conditioned avoidance learning, and weight for three inbred strains (Balb/c, C57Bl and C3H), such that the heaviest strain (Balb/c) was the least active and most emotional in the open field, gave the lowest score for exploratory activity and longest reaction to shock times, and was the poorest at conditioned avoidance learning.The hybrids from crosses with C57Bl tended more towards complete dominance and overdominance than did the Balb/c × C3H hybrid, probably because the Balb/c and C3H strains have some common ancestry.Heterosis was most marked for traits involving exploration or learning. Variability of the hybrids for these traits was often lower than the parents, i.e. they showed behavioural homeostasis. For other traits variability of the hybrids tended towards the parent whose genotype was dominant for the trait.Of the non-genetic factors studied, age and litter size were found to have the greatest effect on the behavioural traits. Parity was found only to affect weight. Sex differences were found for weight and emotionality.