Individual Differences In Behavioral Responses Research Articles

Lifelong, central corticotropin-releasing factor (CRF) overexpression is associated with individual differences in cocaine-induced conditioned place preference

Stress, through corticotropin-releasing factor (CRF), influences all aspects of cocaine addiction. Earlier studies suggest that individual differences in responsivity to stress affect susceptibility to develop addiction. We have previously found that CRF over-expression alters individual differences in behavioural responses to novelty stress in mice. Therefore, we hypothesised that post-natal, long-term over-expression of brain CRF may alter the rewarding effects of cocaine in a manner that is sensitive to individual differences. In this study we specifically investigated cocaine-induced conditioned place preference (CPP) in transgenic mice over-expressing CRF (CRF-OE) and in wild-type (WT) littermates after determining their individual locomotor and emotional responsivity to inescapable novelty. CRF-OE mice showed decreased overall locomotor activity and increased anxiety-like behaviour in response to novelty compared to WT mice. Low behavioural reactivity to novelty (LR) was associated with heightened anxiety-like behaviour in CRF-OE, but not in WT, mice. WT and CRF-OE mice developed CPP equally to both low (5mg/kg) and high (20mg/kg) doses of cocaine. However, LR CRF-OE mice expressed significantly stronger cocaine CPP than transgenic mice with high locomotor response to novelty (HR). In WT mice, on the other hand, stronger CPP induced by 20mg/kg of cocaine was found in the HR animals. Furthermore, there was a strong negative correlation between locomotor reactivity to novelty and CPP in CRF-OE, but not in WT, mice. Collectively, these results suggest that long-term, post-natal CRF over-expression increases the rewarding effects of cocaine in individuals with high emotional response to stress.

B-36 Free Communication/Poster - Physical Activity and Affect

The inter-individual variability in the effectiveness of structured exercise to achieve expected levels of weight loss or maintenance appears to be due in part to individual differences in behavioral responses that increase energy intake; however, the influence of acute exercise on dietary intake following exercise remains incompletely characterized. PURPOSE: The aim of this study was to evaluate changes in total day and three hour post-exercise (3HR) dietary intake associated with exercise participation among women. METHODS: Previously sedentary women (n=51, 36.1± 6.8y) participated in an 8 week intervention with the goal of 150 min/week of moderate intensity walking exercise (EX). Participation in EX bouts ≥10 min duration was measured via ActiGraph GT3X+. Dietary intake was measured on randomly selected EX and non-EX days via the National Cancer Institute’s ASA24 program with data of interest being total day energy intake in kcals (KCAL) and macronutrient intake; protein (PRO), fat (FAT), and carbohydrate (CHO). RESULTS: No significant mean differences in KCAL (13.2 ± 547.6, p>.05) or macronutrient intake (-6.3 ± 136.4; -12.3 ± 289.5; and 46.9 ± 340.3 for PRO, FAT, and CHO respectively, all p>.05) were observed between EX and non-EX days. Larger, but not statistically significant, differences in 3HR KCAL (101.1 ± 561.6, p>.05) and macronutrient intake (7.1 ± 124.3; 16.0 ± 279.6, and 63.0 ± 270.1 for PRO, FAT, and CHO respectively, all p>.05) were reported on EX versus non-EX days. In sub-group analyses, women who exercised in the morning (n=10) and those classified as obese (BMI≥30; n=17) reported the largest increases in KCAL and all macronutrients on EX days although only differences in 3HR PRO were statistically significant (p=.04). CONCLUSIONS: Acute changes in total daily caloric and macronutrient intake in response to exercise appear to be modest. The potential impact of exercise timing and the role of body composition on modifying dietary responses to acute exercise warrant further study. Supported by NHLBI-1R21HL113742-01

Initial D2 Dopamine Receptor Sensitivity Predicts Cocaine Sensitivity and Reward in Rats

The activation of dopamine receptors within the mesolimbic dopamine system is known to be involved in the initiation and maintenance of cocaine use. Expression of the D2 dopamine receptor subtype has been implicated as both a predisposing factor and consequence of chronic cocaine use. It is unclear whether there is a predictive relationship between D2 dopamine receptor function and cocaine sensitivity that would enable cocaine abuse. Therefore, we exploited individual differences in behavioral responses to D2 dopamine receptor stimulation to test its relationship with cocaine-mediated behaviors. Outbred, male Sprague-Dawley rats were initially characterized by their locomotor responsiveness to the D2 dopamine receptor agonist, quinpirole, in a within-session ascending dose-response regimen (0, 0.1, 0.3 & 1.0 mg/kg, sc). Rats were classified as high or low quinpirole responders (HD2 and LD2, respectively) by a median split of their quinpirole-induced locomotor activity. Rats were subsequently tested for differences in the psychostimulant effects of cocaine by measuring changes in cocaine-induced locomotor activity (5 and 15 mg/kg, ip). Rats were also tested for differences in the development of conditioned place preference to a low dose of cocaine (7.5 mg/kg, ip) that does not reliably produce a cocaine conditioned place preference. Finally, rats were tested for acquisition of cocaine self-administration and maintenance responding on fixed ratio 1 and 5 schedules of reinforcement, respectively. Results demonstrate that HD2 rats have enhanced sensitivity to the locomotor stimulating properties of cocaine, display greater cocaine conditioned place preference, and self-administer more cocaine compared to LD2 animals. These findings suggest that individual differences in D2 dopamine receptor sensitivity may be predictive of cocaine sensitivity and reward.

Can we predict personality in fish? Searching for consistency over time and across contexts.

The interest in animal personality, broadly defined as consistency of individual behavioural traits over time and across contexts, has increased dramatically over the last years. Individual differences in behaviour are no longer recognised as noise around a mean but rather as adaptive variation and thus, essentially, raw material for evolution. Animal personality has been considered evolutionary conserved and has been shown to be present in all vertebrates including fish. Despite the importance of evolutionary and comparative aspects in this field, few studies have actually documented consistency across situations in fish. In addition, most studies are done with individually housed fish which may pose additional challenges when interpreting data from social species. Here, we investigate, for the first time in fish, whether individual differences in behavioural responses to a variety of challenges are consistent over time and across contexts using both individual and grouped-based tests. Twenty-four juveniles of Gilthead seabream Sparus aurata were subjected to three individual-based tests: feed intake recovery in a novel environment, novel object and restraining and to two group-based tests: risk-taking and hypoxia. Each test was repeated twice to assess consistency of behavioural responses over time. Risk taking and escape behaviours during restraining were shown to be significantly consistent over time. In addition, consistency across contexts was also observed: individuals that took longer to recover feed intake after transfer into a novel environment exhibited higher escape attempts during a restraining test and escaped faster from hypoxia conditions. These results highlight the possibility to predict behaviour in groups from individual personality traits.

Social context of bullying: Do misperceptions of group norms influence children's responses to witnessed episodes?

This study explores the association between norm misperception and behavioral responses to witnessed bullying episodes. We hypothesized that pluralistic ignorance (PI) could explain individual differences in behavioral responses. According to PI theory, children who believe that victims deserve protection may inhibit defending behavior if they assume their attitudes are out of step with their peers. A total of 446 fourth and eighth graders described their personal attitudes and perceptions of peers’ attitudes about bullying, as well as their behavioral responses when they witnessed a bullying episode. Consistent with PI theory, children perceived their personal attitudes as more prosocial than those of their classmates. Further, misperception of group norms was associated with children's reports of behavioral responses to bullying; children who overestimated peers’ approval of bullying reported lower levels of defending the victim and higher levels of joining in. This material is based on work supported by the National Science Foundation under Grant No. 0841897. The authors are grateful to the students, teachers, and school administrators who participated in this study. We extend special thanks to Meredith Craven, Meg Macdonald, and Colleen Fitzpatrick, who helped to orchestrate the data collection process.

Personality and plasticity: consistent responses within-, but not across-temperature situations in crabs

Recent research suggests that repeated assays of behaviour, conducted both within and across situations, could reveal important insights into two traditionally distinct areas of study: animal personality and individual differences in behavioural plasticity. However, at present relatively few studies present such data, and few consider how changing abiotic conditions affect behavioural plasticity. Individual differences in metabolic rate have been suggested as a proximate mechanism promoting personality, leading one to speculate that individual differences in metabolic sensitivity to temperature may affect behavioural responses in ectotherms. At present, only one study (out of two) has tested for and shown individual differences in behavioural responses to temperature. Here, we repeatedly assayed the behaviour of a marine crab across a narrow range of temperatures to test for individual differences in responses to temperature. We observed large inter-individual differences in behaviour that were consistent over time at a given temperature (evidence for personality), and individual differences in responses to temperature (evidence for plasticity). This study adds to the very scant literature on ectotherm behavioural sensitivity to temperature, and suggests the phenomenon might be widespread. We speculate about the role of metabolism as a proximate mechanism that might explain these individual differences in plasticity and make suggestions for future research to test this hypothesis.

Boldness as a consistent personality trait in the noble crayfish, Astacus astacus

Consistent individual differences in behavioural responses to perceived predation risk may have extensive ecological and evolutionary implications. We studied the repeatability of boldness across time and its relation to resource holding potential in the noble crayfish, Astacus astacus L., using predator-naive immature individuals. We followed individual’s shelter use both with and without exposure to the chemical and physical cues of predators, and with and without the presence of a conspecific. In addition, we examined if armament, i.e. relative chelae size, would be correlated with individual differences in behaviour. Individuals showed repeatable behaviours across time and context. Individuals that occupied the shelter in competitive dyadic tests also spent more time in the shelter during individual control observations, suggesting that boldness is a personality trait that does not necessarily relate positively to high resource holding potential in the noble crayfish. The relative size of chelae did not correlate with any of the measured behavioural variables. Our results suggest that boldness can be considered as individually consistent and ecologically important personality trait in the noble crayfish.

Relevance of structural brain connectivity to learning and recovery from stroke.

The physical structure of white matter fiber bundles constrains their function. Any behavior that relies on transmission of signals along a particular pathway will therefore be influenced by the structural condition of that pathway. Diffusion-weighted magnetic resonance imaging provides localized measures that are sensitive to white matter microstructure. In this review, we discuss imaging evidence on the relevance of white matter microstructure to behavior. We focus in particular on motor behavior and learning in healthy individuals and in individuals who have suffered a stroke. We provide examples of ways in which imaging measures of structural brain connectivity can inform our study of motor behavior and effects of motor training in three different domains: (1) to assess network degeneration or damage with healthy aging and following stroke, (2) to identify a structural basis for individual differences in behavioral responses, and (3) to test for dynamic changes in structural connectivity with learning or recovery.

Individual Differences in Novelty-Seeking and Behavioral Responses to Nicotine: A Review of Animal Studies

Individual differences in the behavioral responses to a novel environment have been proposed as a research tool to predict responsiveness to other behavioral tasks, response to certain events and individual vulnerability to nicotine addiction. In rats and mice, novelty seeking (defined as enhanced specific exploration of novel situations) is a complex behavior confirmed by a large body of neurochemical, endocrinological and behavioral data. We review the main standardized procedures employed to measure the novelty seeking trait in rodents and the ontogeny of this behavior throughout the life-span taking into account that novelty seeking can be permanently modified as a consequence of particular early experiences, maternal care, and environmental enrichment. Studies in animal models suggest that individual differences in the sensitivity to nicotine depend on different variables such as basal locomotor activity of the experimental subjects, their response to novel environments (open-field, hole-board) and level of impulsivity. It is concluded that these basic findings contribute to a better understanding of smoking behavior and to the establishment of improved pharmacological treatments if individual differences are borne in mind.

Individual Differences in Fear and Social Reinstatement Behaviours in Laying Hens

Individual differences in behavioural responses are of growing interest in behavioural studies. The present study investigated the consistency of the individual differences over time and across social (social reinstatement responses) and non social test situations (tonic immobility response). Three breeds of commercial hybrid layers (ISA Brown, Lohmann Tradition and Lohmann Silver) were reared from hatch to 37 weeks of age. Individual birds were subjected to tonic immobility test at 3, 5, 7, 10, 11, 15, 16, 20, 24, 35 and 37 wk old and to runway test of sociality at 3, 5, 10, 16, 20 and 37 wk old. Fearfulness did not show breed differences either in the overall means or in a certain tested age. However, ISA Brown had a higher latency to emerge to a runway than LT (16 and 20 wk) and LS (at 37 wk). In addition, ISA Brown hens had a higher latency to reinstate with their companion than LS (10 and 37 wk). The individual ranks for behavioural traits of fear and sociality were consistent over time. These results indicate fear and sociality responses are behavioural strategies used by individuals in certain test situation when repeated. Moreover, the duration of TI response was positively correlated to both sociality traits (latency to emerge and reinstate with a companion) indicating that birds had overall behavioural traits that were consistent across different contexts. This suggests that hens can be categorized into behavioural types or styles based on their test responses. The highly fearful birds (longer TI duration) had a higher latency to emerge and reinstate with their companions (reactive style) and the less fearful birds (shorter TI duration) had a lower latency to emerge and socially reinstate with their companions (proactive style). In conclusion, these individual differences are consistent over time and the behaviour of hens in one test can predict their behaviour in other test situation. Thus it could be used to assess individual hens and potentially be used in a breeding program to select a hen with more desirable personality traits.

Repeated social defeat stress-induced sensitization to the locomotor activating effects of d-amphetamine: role of individual differences

In this study, we sought to examine individual differences in stress-induced behavioral sensitization to d-amphetamine after repeated social defeat stress. In an effort to understand what mechanisms underlie stress-induced sensitization to d-amphetamine, we examined striatal gene expression of the dopamine receptor D(2). Additionally, we investigated if repeated social defeat was associated with changes in dendritic spine density in the hippocampus, prefrontal cortex, and nucleus accumbens of rats that exhibit stress-induced sensitization. Male rats were classified into high responders (HR) and low responders (LR) based on their locomotor response to a novel environment. Then, rats were either handled as a control or defeated on four occasions by aggressive rats. Two weeks after the last defeat, animals were challenged with one of three doses of d-amphetamine and their locomotor activity was recorded. Non-defeated HR rats exhibited higher locomotor activity in response to d-amphetamine when compared to LR non-defeated rats. Fourteen days from the last repeated social defeat, LR rats and HR rats were behaviorally identical in response to acute injections of amphetamine. Furthermore, HR non-defeated rats had less D(2) mRNA expression in the nucleus accumbens core and dorsal striatum than do LR non-defeated rats. However, after repeated social defeat, HR and LR rats had identical D(2) mRNA expression in both the core and dorsal striatum. Finally, there were no changes in dendritic spine density in any of the brain areas examined in LR rats. Repeated social defeat abolishes individual differences in behavioral responses to d-amphetamine which may be due to a down-regulation of striatal dopamine D(2) receptors in LR rats.

Behavioural reactivity of heifer calves in potentially alarming test situations: a multivariate and correlational analysis

The aim of the present study was to determine the degree of consistency of individual differences in behavioural responses of heifer calves over time and across different situations. Twenty-five Holstein Friesian heifer calves were individually subjected to the same set of four behavioural tests at 3, 16 and 29 weeks of age. The tests involved measuring the calves’ responses to a stationary human, a novel object, an open field (novel environment), and to tethering restraint. Principal component analysis (PCA) of measures recorded at each age was used to identify independent dimensions underlying the calves’ reactivity to these situations. The consistency of individual differences was established by ranking the behavioural scores and the scores of factors extracted by PCA and then estimating the correlations between the ranks of each individual calf at each of the test ages. At each age, PCA revealed four factors that could be labelled: “locomotion”, “vocalisation”, “interaction with a novel object”, and “interaction with a human”. Individual differences in 7 of 13 behavioural measures and in scores of all factors except “interaction with a human” were consistent between 16 and 29 weeks of age. Rank orders for scores of the factor labelled “interaction with a novel object” were significantly correlated across all three ages. Our results support the existence in calves of stable characteristics mediating reactivity to challenge. Multiple behavioural dimensions obtained with PCA suggest that behavioural responsiveness of calves to challenge is governed by a number of underlying factors rather than univariate phenomena, such as fearfulness or coping style.

Regression modeling of rodent locomotion data

We present the case for a model-based approach to the statistical analysis of rodent locomotion data for which previous research has established that the time course of behavioral change follows a specified parametric form. Inadequacies of statistical methods commonly applied to such data are described. Regression models can reveal time-dependent aspects of response that might escape more elementary analyses, as we illustrate with experimental data regarding the locomotion response to amphetamine. Inter-individual variation in response profiles is incorporated through the use of random coefficients (i.e. mixed effects models). These models provide an effective means of quantifying the extent of individual differences in behavioral response to stimulant drugs not attributable to treatment. The need to adjust for multiple comparisons when searching for regions of significant difference is discussed. We present specific models that we have found useful for characterizing responses to low doses of amphetamine or cocaine (the log-logistic random effects model) and higher or repetitive doses of amphetamine or cocaine (the polynomial random effects model). Code for performing these analyses with standard statistical software is provided.

Individual differences in behavioral responses to novelty and amphetamine self-administration in male and female rats.

Previous work has shown that individual differences in locomotor activity in an inescapable novel environment can predict acquisition of amphetamine self-administration. The current study examined whether individual differences in approach to novelty in a free choice test could also predict amphetamine self-administration. Further, the current study examined whether individual differences in either free choice or inescapable novelty tests could predict responding for a nondrug reinforcer (sucrose) in the presence and absence of amphetamine. Male and female rats were first tested for their response to free choice novelty (playground maze and novelty-induced place preference tests) and inescapable novelty. They were then tested for acquisition of sucrose-reinforced responding, amphetamine-induced changes in maintenance of sucrose-reinforced responding, and amphetamine self-administration. Based on the inescapable novelty test, acquisition of sucrose-reinforced responding was more rapid in male high responders (HR) compared to low responders (LR). This effect in males did not generalize to females. None of the novelty tests predicted the ability of amphetamine to decrease sucrose-maintained responding. However, using the inescapable novelty test, both male and female HRs self-administered more amphetamine than LRs within the dose range tested (0.03-0.16 mg/kg/infusion). Neither the playground maze nor the novelty-induced place preference test predicted amphetamine self-administration. These results indicate that responses to free choice novelty and inescapable novelty predict different components of amphetamine-induced behavior.

Maternal care during infancy regulates the development of neural systems mediating the expression of fearfulness in the rat.

The mothers of infant rats show individual differences in the frequency of licking/grooming and arched-back nursing (LG-ABN) of pups that contribute to the development of individual differences in behavioral responses to stress. As adults, the offspring of mothers that exhibited high levels of LG-ABN showed substantially reduced behavioral fearfulness in response to novelty compared with the offspring of low LG-ABN mothers. In addition, the adult offspring of the high LG-ABN mothers showed significantly (i) increased central benzodiazepine receptor density in the central, lateral, and basolateral nuclei of the amygdala as well as in the locus ceruleus, (ii) increased alpha2 adrenoreceptor density in the locus ceruleus, and (iii) decreased corticotropin-releasing hormone (CRH) receptor density in the locus ceruleus. The expression of fear and anxiety is regulated by a neural circuitry that includes the activation of ascending noradrenergic projections from the locus ceruleus to the forebrain structures. Considering the importance of the amygdala, notably the anxiogenic influence of CRH projections from the amygdala to the locus ceruleus, as well as the anxiolytic actions of benzodiazepines, for the expression of behavioral responses to stress, these findings suggest that maternal care during infancy serves to "program" behavioral responses to stress in the offspring by altering the development of the neural systems that mediate fearfulness.

Individual differences and their relation to social structure in domestic cats.

Two groups of domesticated cats with established social structures were tested for their response to novel stimuli in a variety of test situations. Clear individual differences in responses were consistent over a series of test sessions and remained stable despite regular environmental changes. Individual differences in behavioral response were not related to object dominance (food competition) or social dominance (freedom of movement in social encounters) unlike similar studies with social animals. No relationship was found in either group between a cat's rank in object dominance and its rank in social dominance. Significant correlations were demonstrated in the individual cat's latency to approach a novel stimulus, behavioral rank in test situations, and attention span in both groups of cats. Comparisons were made between similar studies with wolves, and inferences were drawn about the relationship between individual differences and social structure in social and nonsocial species.

Individual behavioural differences in pigs: intra-and inter-test consistency

Individual differences in behavioural responses are of increasing interest in the behavioural sciences. There could be enormous benefits for animal husbandry if a test could be developed that would identify categories or types of individuals unlikely to cope with subsequent challenges. The present study compared the behavioural responses of two series of 16 groups ( n = 6 or 7 gilts) under four different circumstances: Situation 1, an open field with a novel stimulus (bucket or human); Situation 2, individual access to food for 15 min after a 20-h period of food deprivation; Situation 3, competition for food after food deprivation; Situation 4, general activity and feeding behaviour in a group over a 24-h period. Situations 1 and 2 were assessed four and three times over a 2- and 1-week period, respectively. Both showed high levels of consistency in the behavioural responses of the gilts. Principal component analyses were used to reduce the number of variables per test situation and facilitate measurement of consistency across test situations. The amount of variation explained by the first component was generally more than twice that explained by any subsequent components. The only significant correlation between factor scores calculated from the first components was found between Situations 1 and 2 in the first series. None of the calculated factor scores showed bi- or multimodal distributions. We conclude that, whilst over a short period of time gilts respond consistently to a specific challenge, they do not display the same consistency when challenged in a different context. This lack of inter-situation correlations, plus the absence of multimodal distributions, fails to support the view that behavioural ‘types’ of gilts exist.

Responses of pigs to social and non-social challenges in the abattoir

Conditions at die abattoir are such that pigs are exposed to social stress (mixing with unfamiliar pigs) and non-social stress (rough handling). Individual differences in behavioural responses to stress in pigs have been well documented (Hessing et al., 1994; Jensen, 1994; Mendl et al., 1992) and can result in considerable variation in their ability to cope. In this experiment, we studied whether individual differences in behaviour and physiology in home pen conditions are related to subsequent reactions during periods of transport, driving and mixing.

Responses of pigs to social and non-social challenges in the abattoir

Conditions at die abattoir are such that pigs are exposed to social stress (mixing with unfamiliar pigs) and non-social stress (rough handling). Individual differences in behavioural responses to stress in pigs have been well documented (Hessing et al., 1994; Jensen, 1994; Mendl et al., 1992) and can result in considerable variation in their ability to cope. In this experiment, we studied whether individual differences in behaviour and physiology in home pen conditions are related to subsequent reactions during periods of transport, driving and mixing.

Individual differences in behavioral responses to novelty in rats. Possible relationship with the sensation-seeking trait in man

Sensation-seeking is a human personality trait characterized by the need for varied, novel and complex sensations, and a general liking for risk-taking activities. Analogies can be drawn with some behavioral tendencies shown in animals. In studies on rats, certain individuals labeled as high-responders (HR), opposed to low-responders (LR), have been shown to be highly reactive in a novel environment and also predisposed to drug taking. Given that the response to novelty is the basis of the definition of sensation-seeking, the present study was designed to obtain more detailed information on the exploratory tendencies of HR rats in behavioral tasks involving a free-choice response to various novel environments differing in levels of complexity and aversiveness. The animals' preferences for novelty and familiarity were tested in a Y-maze, and for a variety of novel places in a 16-arm radial maze. The animals' exploratory tendencies in a well illuminated area were evaluated in a dark-light emergence test. The HR rats visited one (Y-maze) or many (16-arm radial maze) novel places more frequently than the LR animals did. The visits in the 16-arm radial maze by HR rats were also of shorter duration, indicating a more rapid habituation to novelty. Finally, HR rats entered more often and more rapidly an area considered as stressful. In conclusion, HR rats appear to seek novelty, variety and emotional stimulation. These characteristics may be analogous to some of the factors found in human high-sensation seekers.