Neuroendocrinology of coping styles: towards understanding the biology of individual variation

Serotonin and arginine-vasopressin mediate sex differences in the regulation of dominance and aggression by the social brain

There are profound sex differences in the incidence of many psychiatric disorders. Although these disorders are frequently linked to social stress and to deficits in social engagement, little is known about sex differences in the neural mechanisms that underlie these phenomena. Phenotypes characterized by dominance, competitive aggression, and active coping strategies appear to be more resilient to psychiatric disorders such as posttraumatic stress disorder (PTSD) compared with those characterized by subordinate status and the lack of aggressiveness. Here, we report that serotonin (5-HT) and arginine-vasopressin (AVP) act in opposite ways in the hypothalamus to regulate dominance and aggression in females and males. Hypothalamic injection of a 5-HT1a agonist stimulated aggression in female hamsters and inhibited aggression in males, whereas injection of AVP inhibited aggression in females and stimulated aggression in males. Striking sex differences were also identified in the neural mechanisms regulating dominance. Acquisition of dominance was associated with activation of 5-HT neurons within the dorsal raphe in females and activation of hypothalamic AVP neurons in males. These data strongly indicate that there are fundamental sex differences in the neural regulation of dominance and aggression. Further, because systemically administered fluoxetine increased aggression in females and substantially reduced aggression in males, there may be substantial gender differences in the clinical efficacy of commonly prescribed 5-HT-active drugs such as selective 5-HT reuptake inhibitors. These data suggest that the treatment of psychiatric disorders such as PTSD may be more effective with the use of 5-HT-targeted drugs in females and AVP-targeted drugs in males.

Characterization of stress coping style in Senegalese sole (Solea senegalensis) juveniles and breeders for aquaculture

The aim of this work was to characterize stress coping styles of Senegalese sole (Solea senegalensis) juveniles and breeders and to select an operational behavioural screening test (OBST) that can be used by the aquaculture industry to classify and select between behavioural phenotypes in order to improve production indicators. A total of 61 juveniles and 59 breeders were subjected to five individual behavioural tests and two grouping tests. At the end of the individual tests, all animals were blood sampled in order to measure cortisol, glucose and lactate. Three tests (restraining, new environment and confinement) characterized the stress coping style behaviour of Senegalese sole juveniles and breeders and demonstrated inter-individual consistency. Further, the tests when incorporated into a principal components analysis (PCA) (i) identified two principal axes of personality traits: 'fearfulness-reactivity' and 'activity-exploration', (ii) were representative of the physiological axis of stress coping style, and (iii) were validated by established group tests. This study proposed for the first time three individual coping style tests that reliably represented proactive and reactive personalities of Senegalese sole juveniles and breeders. In addition, the three proposed tests met some basic operational criteria (rapid testing, no special equipment and easy to apply and interpret) that could prove attractive for fish farmers to identify fish with a specific behaviour that gives advantages in the culture system and that could be used to establish selection-based breeding programmes to improve domestication and production.

Non-invasive assessment of adrenocortical activity as a measure of stress in giraffe (Giraffa camelopardalis)

Background

Numbers of giraffes are declining rapidly in their native habitat. As giraffe research and conservation efforts increase, the demand for more complete measures of the impact of conservation interventions and the effects of captive environments on animal health and welfare have risen. We compared the ability of six different enzyme immunoassays to quantify changes in fecal glucocorticoid metabolites (FGM) resulting from three sources: adrenocorticotropic hormone stimulation test, transport, and time of day that samples were collected.

Results

Two male giraffes underwent ACTH injections; all six assays detected FGM increases following injection for Giraffe 1, while only three assays detected FGM increases following injection for Giraffe 2. Consistent with other ruminant species, the two 11-oxoetiocholanolone assays (one for 11,17-dioxoandrostanes and the other for 3α,11-oxo metabolites) measured the most pronounced and prolonged elevation of FGM, while an assay for 3β,11β-diol detected peaks of smaller magnitude and duration. Both of the 11-oxoetiocholanolone assays detected significant FGM increases after transport in Giraffes 3–7, and preliminary data suggest FGM detected by the assay for 11,17-dioxoandrostanes may differ across time of day.

Conclusions

We conclude the assay for 11,17-dioxoandrostanes is the most sensitive assay tested for FGM in giraffes and the assay for FGM with a 5β-3α-ol-11-one structure is also effective. 11-oxoetiocholanolone enzyme immunoassays have now been demonstrated to be successful in a wide variety of ruminant species, providing indirect evidence that 5β-reduction may be a common metabolic pathway for glucocorticoids in ruminants. As FGM peaks were detected in at least some giraffes using all assays tested, giraffes appear to excrete a wide variety of different FGM. The assays validated here will provide a valuable tool for research on the health, welfare, and conservation of giraffes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0864-8) contains supplementary material, which is available to authorized users.

Personality and problem-solving in common mynas (Acridotheres tristis)

Animals show consistent individual differences in behaviour across time and/or contexts. Recently, it has been suggested that proactive personality types might also exhibit fast cognitive styles. The speed with which individuals sample environmental cues is one way in which correlations between personality and cognition might arise. Here, we measured a collection of behavioural traits (competitiveness, neophobia, neophilia, task-directed motivation and exploration) in common mynas (Acridotheres tristis) and measured their relationship with problem solving. We predicted that fast solving mynas would interact with (i.e. sample) the problem solving task at higher rates, but also be more competitive, less neophobic, more neophilic, and more exploratory. Mynas that were faster to solve a novel foraging problem were no more competitive around food and no more inclined to take risks. Unexpectedly, these fast-solving mynas had higher rates of interactions with the task, but also displayed lower levels of exploration. It is possible that a negative relation between problem solving and spatial exploration arose as a consequence of how inter-individual variation in exploration was quantified. We discuss the need for greater consensus on how to measure exploratory behaviour before we can advance our understanding of relationships between cognition and personality more effectively.

Are coping styles consistent in the teleost fish Sparus aurata through sexual maturation and sex reversal?

Individual differences in behaviour and physiological responses to stress are associated with evolutionary adaptive variation and thus raw material for evolution. In farmed animals, the interest in consistent trait associations, i.e. coping styles, has increased dramatically over the last years. However, one of limitations of the available knowledge, regarding the temporal consistency, is that it refers always to short-term consistency (usually few weeks). The present study used an escape response during a net restraining test, previously shown to be an indicative of coping styles in seabream, to investigate long-term consistency of coping styles both over time and during different life history stages. Results showed both short-term (14 days) consistency and long-term (8 months) consistency of escape response. However, we did not found consistency in the same behaviour after sexual maturation when the restraining test was repeated 16, 22 and 23 months after the first test was performed. In conclusion, this study showed consistent behaviour traits in seabream when juveniles, and a loss of this behavioural traits when adults. Therefore, these results underline that adding a life story approach to data interpretation as an essential step forward towards coping styles foreground. Furthermore, a fine-tuning of aquaculture rearing strategies to adapt to different coping strategies may need to be adjusted differently at early stages of development and adults to improve the welfare of farmed fish.

Maladaptive choices by defeated rats: link between rapid approach to social threat and escalated cocaine self-administration

RATIONALE

Intermittent social defeat stress engenders persistent neuroadaptations and can result in later increased cocaine taking and seeking. However, there are individual differences in stress-escalated cocaine self-administration behavior, which may be a direct result of individual differences in the manner in which rats experience social defeat stress.

OBJECTIVE

The present study dissected the discrete behavioral phases of social defeat and analyzed which behavioral characteristics may be predictive of subsequent cocaine self-administration.

METHODS

Male Long-Evans rats underwent nine intermittent social defeat episodes over 21 days in a three-compartment apparatus permitting approach to and escape from a confrontation with an aggressive resident rat. Rats then self-administered intravenous cocaine, which culminated in a 24-h unlimited access "binge." Behaviors during social defeat and cocaine self-administration were evaluated by principal component analysis (PCA).

RESULTS

PCA revealed that the latency to enter the threatening environment was highly predictive of later cocaine self-administration during the 24-h binge. This behavior was not associated with other cocaine-predictive traits, such as reactivity to novelty in an open field, saccharin preference, and motor impulsivity. Additionally, there was no effect of latency to enter a threatening environment on physiological measures of stress, including plasma corticosterone and corticotropin releasing factor (CRF) in the extended amygdala. However, latency to enter the threatening environment was negatively correlated with brain-derived neurotropic factor (BDNF) and its receptor, tyrosine kinase B (TrkB) in the hippocampus.

CONCLUSION

These data suggest that latency to enter a threatening environment is a novel behavioral characteristic predictive of later cocaine self-administration.

Adrenocortical Expression Profiling of Cattle with Distinct Juvenile Temperament Types

Temperament affects ease of handling, animal welfare, and economically important production traits in cattle. The use of gene expression profiles as molecular traits provides a novel means of gaining insight into behavioural genetics. In this study, differences in adrenocortical expression profiles between 60 F₂ cows (Charolais × German Holstein) of distinct temperament types were analysed. The cows were assessed in a novel-human test at an age of 90 days. Most of the adrenal cortex transcripts which were differentially expressed (FDR <0.05) were found between temperament types of 'fearful/neophobic-alert' and all other temperament types. These transcripts belong to several biological functions like NRF2-mediated oxidative stress response, Glucocorticoid Receptor Signalling and Complement System. Overall, the present study provides new insight into transcriptional differences in the adrenal cortex between cows of distinct temperament types. Genetic regulations of such molecular traits facilitate uncovering positional and functional gene candidates for temperament type in cattle.

Consistent inter-individual differences in common marmosets (Callithrix jacchus) in Boldness-Shyness, Stress-Activity, and Exploration-Avoidance

The study of animal personality, defined as consistent inter-individual differences in correlated behavioral traits stable throughout time and/or contexts, has recently become one of the fastest growing areas in animal biology, with study species ranging from insects to non-human primates. The latter have, however, only occasionally been tested with standardized experiments. Instead their personality has usually been assessed using questionnaires. Therefore, this study aimed to test 21 common marmosets (Callithrix jacchus) living in three family groups, in five different experiments, and their corresponding controls. We found that behavioral differences between our animals were not only consistent over time, but also across different contexts. Moreover, the consistent behaviors formed a construct of four major non-social personality components: Boldness-Shyness in Foraging, Boldness-Shyness in Predation, Stress-Activity, and Exploration-Avoidance. We found no sex or age differences in these components, but our results did reveal differences in Exploration-Avoidance between the three family groups. As social environment can have a large influence on behavior of individuals, our results may suggest group-level similarity in personality (i.e., "group personality") in common marmosets, a species living in highly cohesive social groups. Am. J. Primatol. 78:961-973, 2016. © 2016 Wiley Periodicals, Inc.

On the Role of Neurogenesis and Neural Plasticity in the Evolution of Animal Personalities and Stress Coping Styles

Individual variation in how animals react to stress and environmental change has become a central topic in a wide range of biological disciplines, from evolutionary ecology to biomedicine. Such variation manifests phenotypically as correlated trait-clusters (referred to as coping styles, behavioral syndromes, shyness-boldness, or personality traits). Thresholds for switching from active coping (fight-flight) to inhibition and passive behavior when exposed to stress depend on experience and genetic factors. Comparative research has revealed a range of neuroendocrine-behavioral associations which are conserved throughout the vertebrate subphylum, including factors affecting perception, learning, and memory of stimuli and events. Here we review conserved aspects of the contribution of neurogenesis and other aspects of neural plasticity to stress coping. In teleost fish, brain cell proliferation and neurogenesis have received recent attention. This work reveals that brain cell proliferation and neurogenesis are associated with heritable variation in stress coping style, and they are also differentially affected by short- and long-term stress in a biphasic manner. Routine-dependent and inflexible behavior in proactive individuals is associated with limited neural plasticity. These evolutionarily conserved relationships hold the potential to illuminate the biological background for stress-related neurobiological disorders.

Acute embryonic exposure to corticosterone alters physiology, behaviour and growth in nestlings of a wild passerine

Maternally-derived glucocorticoids can modify the normal development of young animals. To date, little is known about maternal effects that are mediated by acute embryonic exposure to glucocorticoids. In birds, elevated maternal transmission of corticosterone (CORT) to egg albumen is mainly dependent on acute stress. In this study, we increased CORT levels in the egg albumen of a wild passerine, the great tit (Parus major), breeding in favourable deciduous and less suitable coniferous habitat. Subsequently we measured the somatic growth, baseline and acute glucocorticoid responses, immunity and behaviour of prenatally manipulated offspring with respect to control siblings. We found that prenatally CORT-exposed nestlings had lower baseline CORT levels, a more rapid decline in CORT during recovery from a standardized stressor, and a reduced heterophil/lymphocyte ratio compared with controls. Although stress-induced total CORT levels remained unchanged, free CORT levels were significantly lower and the levels of corticosteroid binding globulins (CBG) significantly higher in experimental offspring. Prenatally CORT-exposed offspring begged longer after hatching than controls. Stress-induced behavioural activity of fledglings did not differ between treatments, while its association with baseline CORT levels was significant in the control group only. The body mass and tarsus length of fledglings was positively affected by manipulation in unfavourable coniferous habitat only. We conclude that maternal effects related to elevated levels of albumen CORT modify diverse aspects of offspring phenotype and potentially increase offspring performance in resource poor environments. Moreover, our results indicate that maternal glucocorticoids may suppress the effect of hormones on behavioural responses.

Novel Primate Model of Serotonin Transporter Genetic Polymorphisms Associated with Gene Expression, Anxiety and Sensitivity to Antidepressants

Genetic polymorphisms in the repeat upstream region of the serotonin transporter gene (SLC6A4) are associated with individual differences in stress reactivity, vulnerability to affective disorders, and response to pharmacotherapy. However, the molecular, neurodevelopmental and psychopharmacological mechanisms underlying the link between SLC6A4 polymorphisms and the emotionally vulnerable phenotype are not fully understood. Thus, using the marmoset monkey Callithrix jacchus we characterize here a new neurobiological model to help to address these questions. We first sequenced the marmoset SLC6A4 promoter and identified a double nucleotide polymorphism (-2053AC/CT) and two single-nucleotide polymorphisms (-2022C/T and -1592G/C) within the repeat upstream region. We showed their association with gene expression using in vivo quantitative PCR and with affective behavior using a primate test of anxiety (human intruder test). The low-expressing haplotype (AC/C/G) was linked with high anxiety while the high-expressing one (CT/T/C) was associated with an active coping strategy in response to threat. Pharmacological challenge with an acute dose of the selective serotonin reuptake inhibitor, citalopram, revealed a genotype-dependent behavioral response. While individuals homozygous for the high anxiety-related haplotype AC/C/G exhibited a dose-dependent, anxiogenic response, individuals homozygous for the low anxiety-related haplotype CT/T/C showed an opposing, dose-dependent anxiolytic effect. These findings provide a novel genetic and behavioral primate model to study the molecular, neurodevelopmental, and psychopharmacological mechanisms that underlie genetic variation-associated complex behaviors, with specific implications for the understanding of normal and abnormal serotonin actions and the development of personalized pharmacological treatments for psychiatric disorders.

Hypothalamic-pituitary-adrenal and cardiac autonomic responses to transrectal examination differ with behavioral reactivity in dairy cows

Behavior, hypothalamic-pituitary-adrenal axis, and cardiac autonomic nervous system (ANS) activity were evaluated in response to transrectal examination in nonlactating Holstein-Friesian cows with different behavioral reactivity. According to behavioral reactions shown to the procedure of fixing the heart rate (HR) monitors, the 20 cows with the highest and the 20 cows with the lowest behavioral reactivity were involved in the study (high responder, n=20; and low responder, n=20, respectively). Activity of the ANS was assessed by HR and HR variability parameters. Blood and saliva were collected at 5 min before (baseline) and 0, 5 10, 15, 20, 30, 40, 60, and 120 min after the examination to determine cortisol concentrations. The examination lasted for 5 min. Cardiac parameters included HR, the root mean square of successive differences between the consecutive interbeat intervals, the high frequency (HF) component of heart rate variability, and the ratio between the low frequency (LF) and HF parameter (LF/HF). Following the examination, peak plasma and saliva cortisol levels and the amplitude of the plasma and saliva cortisol response were higher in high responder cows than in low responders. Areas under the plasma and saliva cortisol response curves were greater in high responder cows. Plasma and salivary cortisol levels correlated significantly at baseline (r=0.91), right after examination (r=0.98), and at peak levels (r=0.96). Area under the HR response curve was higher in low responder cows; however, maximum HR and the amplitude of the HR response showed no differences between groups. Minimum values of both parameters calculated for the examination were higher in high responders. Following the examination, response parameters of root mean square of successive differences and HF did not differ between groups. The maximum and the amplitude of LF/HF response and area under the LF/HF response curve were lower in low responder cows, suggesting a lower sympathetic activation of the ANS. Although changes in behaviors indicated that the procedure was painful for the animals, no differences were observed either in vocalization or in attendant behavior between groups during the examination. Our results demonstrate that behaviorally more reactive animals exhibit increased plasma and salivary cortisol concentrations and higher cardiac autonomic responsiveness to transrectal examination than less reactive cows. Salivary cortisol may substitute for plasma cortisol when assessing response of cattle to stress.

A novel role for pigment genes in the stress response in rainbow trout (Oncorhynchus mykiss)

In many vertebrate species visible melanin-based pigmentation patterns correlate with high stress- and disease-resistance, but proximate mechanisms for this trait association remain enigmatic. Here we show that a missense mutation in a classical pigmentation gene, melanocyte stimulating hormone receptor (MC1R), is strongly associated with distinct differences in steroidogenic melanocortin 2 receptor (MC2R) mRNA expression between high- (HR) and low-responsive (LR) rainbow trout (Oncorhynchus mykiss). We also show experimentally that cortisol implants increase the expression of agouti signaling protein (ASIP) mRNA in skin, likely explaining the association between HR-traits and reduced skin melanin patterning. Molecular dynamics simulations predict that melanocortin 2 receptor accessory protein (MRAP), needed for MC2R function, binds differently to the two MC1R variants. Considering that mRNA for MC2R and the MC1R variants are present in head kidney cells, we hypothesized that MC2R activity is modulated in part by different binding affinities of the MC1R variants for MRAP. Experiments in mammalian cells confirmed that trout MRAP interacts with the two trout MC1R variants and MC2R, but failed to detect regulation of MC2R signaling, possibly due to high constitutive MC1R activity.

Correlated evolution of personality, morphology and performance

Evolutionary change in one trait can elicit evolutionary changes in other traits due to genetic correlations. This constrains the independent evolution of traits and can lead to unpredicted ecological and evolutionary outcomes. Animals might frequently exhibit genetic associations among behavioural and morphological-physiological traits, because the physiological mechanisms behind animal personality can have broad multitrait effects and because many selective agents influence the evolution of multiple types of traits. However, we currently know little about genetic correlations between animal personalities and nonbehavioural traits. We tested for associations between personality, morphology and locomotor performance by comparing zebrafish (Danio rerio) collected from the wild and then selectively bred for either a proactive or reactive stress coping style ('bold' or 'shy' phenotypes). Based on adaptive hypotheses of correlational selection in the wild, we predicted that artificial selection for boldness would produce correlated evolutionary responses of larger caudal regions and higher fast-start escape performance (and the opposite for shyness). After four to seven generations, morphology and locomotor performance differed between personality lines: bold zebrafish exhibited a larger caudal region and higher fast-start performance than fish in the shy line, matching predictions. Individual-level phenotypic correlations suggested that pleiotropy or physical gene linkage likely explained the correlated response of locomotor performance, while the correlated response of body shape may have reflected linkage disequilibrium, which is breaking down each generation in the laboratory. Our results indicate that evolution of personality can result in concomitant changes in morphology and whole-organism performance, and vice versa.

Acoustic signalling reflects personality in a social mammal

Social interactions among individuals are often mediated through acoustic signals. If acoustic signals are consistent and related to an individual's personality, these consistent individual differences in signalling may be an important driver in social interactions. However, few studies in non-human mammals have investigated the relationship between acoustic signalling and personality. Here we show that acoustic signalling rate is repeatable and strongly related to personality in a highly social mammal, the domestic pig (Sus scrofa domestica). Furthermore, acoustic signalling varied between environments of differing quality, with males from a poor-quality environment having a reduced vocalization rate compared with females and males from an enriched environment. Such differences may be mediated by personality with pigs from a poor-quality environment having more reactive and more extreme personality scores compared with pigs from an enriched environment. Our results add to the evidence that acoustic signalling reflects personality in a non-human mammal. Signals reflecting personalities may have far reaching consequences in shaping the evolution of social behaviours as acoustic communication forms an integral part of animal societies.

The effects anandamide signaling in the prelimbic cortex and basolateral amygdala on coping with environmental stimuli in rats

RATIONALE

Several lines of recent evidence suggest that endocannabinoids affect behavior by influencing the general patterns of challenge responding.

OBJECTIVES

Here, we investigated the brain mechanisms underlying this phenomenon in rats.

METHODS

The anandamide hydrolysis inhibitor URB597 was condensed into the tip of stainless steel cannulae, which were chronically implanted slightly above the prelimbic cortex (PRL) or the basolateral amygdala (BLA), two important regions of coping and endocannabinoid action. Thereafter, we investigated behavioral responsiveness to ambient light level in the elevated plus-maze and conditioned fear tests.

RESULTS

URB597 concentration was ~30 μg/mg protein in target areas; local brain anandamide levels increased threefold, without significant changes in 2-arachidonoylglycerol. High levels of illumination halved the time spent by controls in the open arms of the plus-maze. No similar decrease was observed in rats with URB597 implants in the PRL. High light decreased conditioned fear by 30 % in controls, but not in rats with prelimbic URB597 implants. Unresponsiveness to environmental challenges was not attributable to the anxiolytic effects of anandamide enhancement, as implants induced paradoxical anxiogenic-like effects under low light, which could be explained by effects on stimulus responsiveness rather than by effects on anxiety. URB597 implants targeting the BLA did not affect stimulus responsiveness.

CONCLUSIONS

Our findings show that elevated prelimbic anandamide signaling leads to less environment-dependent (more autonomous) behavioral responses to challenges, which is an attribute of active coping styles. These findings are discussed in light of two emerging concepts of endocannabinoid roles, particularly "emotional homeostasis" and "active coping."

Failure to upregulate Agrp and Orexin in response to activity based anorexia in weight loss vulnerable rats characterized by passive stress coping and prenatal stress experience

We hypothesize that anorexia nervosa (AN) poses a physiological stress. Therefore, the way an individual copes with stress may affect AN vulnerability. Since prenatal stress (PNS) exposure alters stress responsivity in offspring this may increase their risk of developing AN. We tested this hypothesis using the activity based anorexia (ABA) rat model in control and PNS rats that were characterized by either proactive or passive stress-coping behavior. We found that PNS passively coping rats ate less and lost more weight during the ABA paradigm. Exposure to ABA resulted in higher baseline corticosterone and lower insulin levels in all groups. However, leptin levels were only decreased in rats with a proactive stress-coping style. Similarly, ghrelin levels were increased only in proactively coping ABA rats. Neuropeptide Y (Npy) expression was increased and proopiomelanocortin (Pomc) expression was decreased in all rats exposed to ABA. In contrast, agouti-related peptide (Agrp) and orexin (Hctr) expression were increased in all but the PNS passively coping ABA rats. Furthermore, DNA methylation of the orexin gene was increased after ABA in proactive coping rats and not in passive coping rats. Overall our study suggests that passive PNS rats have innate impairments in leptin and ghrelin in responses to starvation combined with prenatal stress associated impairments in Agrp and orexin expression in response to starvation. These impairments may underlie decreased food intake and associated heightened body weight loss during ABA in the passively coping PNS rats.

Environmental Enrichment Effect on Fecal Glucocorticoid Metabolites and Captive Maned Wolf (Chrysocyon brachyurus) Behavior

Environmental enrichment is a technique that may reduce the stress of nonhuman animals in captivity. Stress may interfere with normal behavioral expression and affect cognitive decision making. Noninvasive hormonal studies can provide important information about the stress statuses of animals. This study evaluated the effectiveness of different environmental enrichment treatments in the diminution of fecal glucocorticoid metabolites (stress indicators) of three captive maned wolves (Chrysocyon brachyurus). Correlations of the fecal glucocorticoid metabolite levels with expressed behaviors were also determined. Results showed that environmental enrichment reduced fecal glucocorticoid metabolite levels. Furthermore, interspecific and foraging enrichment items were most effective in reducing stress in two of the three wolves. No definite pattern was found between behavioral and physiological responses to stress. In conclusion, these behavioral and physiological data showed that maned wolves responded positively from an animal well being perspective to the enrichment items presented.

Role of brain serotonin in modulating fish behavior

The organization of the brain serotonergic system appears to have been highly conserved across the vertebrate subphylum. In fish as well as in other vertebrates, brain serotonin (5-HT), mainly acts as a neuromodulator with complex effects on multiple functions. It is becoming increasingly clear that acute and chronic increase in brain 5-HT neurotransmission have very different effects. An acute 5-HT activation, which is seen in both winners and losers of agonistic interactions, could be related to a general arousal effect, whereas the chronic activation observed in subordinate fish is clearly linked to the behavioral inhibition displayed by these individuals. Fish displaying divergent stress coping styles (proactive vs. reactive) differ in 5-HT functions. In teleost fish, brain monoaminergic function is also related to life history traits.

Variability in emotional responsiveness and coping style during active avoidance as a window onto psychological vulnerability to stress

Individual differences in coping styles are associated with psychological vulnerability to stress. Recent animal research suggests that coping styles reflect trade-offs between proactive and reactive threat responses during active avoidance paradigms, with proactive responses associated with better stress tolerance. Based on these preclinical findings, we developed a novel instructed active avoidance paradigm to characterize patterns of proactive and reactive responses using behavioral, motoric, and autonomic measures in humans. Analyses revealed significant inter-individual variability not only in the magnitude of general emotional responsiveness but also the likelihood to specifically express proactive or reactive responses. In men but not women, individual differences in general emotional responsiveness were linked to increased trait anxiety while proactive coping style was linked to increased trait aggression. These patterns are consistent with preclinical findings and suggest that instructed active avoidance paradigms may be useful in assessing psychological vulnerability to stress using objective behavioral measures.

The endocannabinoid system in guarding against fear, anxiety and stress

The endocannabinoid (eCB) system has emerged as a central integrator linking the perception of external and internal stimuli to distinct neurophysiological and behavioural outcomes (such as fear reaction, anxiety and stress-coping), thus allowing an organism to adapt to its changing environment. eCB signalling seems to determine the value of fear-evoking stimuli and to tune appropriate behavioural responses, which are essential for the organism's long-term viability, homeostasis and stress resilience; and dysregulation of eCB signalling can lead to psychiatric disorders. An understanding of the underlying neural cell populations and cellular processes enables the development of therapeutic strategies to mitigate behavioural maladaptation.

Animals can tell us more

From a behavioural biologist's point of view, we argue: (1) The study of resilience in animals should not be restricted to neuronal mechanisms. Rather, questions of ontogeny, function, and evolution also should be addressed to achieve a comprehensive understanding. (2) Implementing new paradigms from animal welfare research in studies of resilience would allow an assessment of appraisal styles in animals.

Individual variation in corticosterone and personality traits in the blue tit Cyanistes caeruleus

Variation in personality traits is predicted to reflect physiology, but the extent to which variations in stress hormones derive from differences in personality and/or state-dependent factors remains unclear. To investigate this, wild blue tits (Cyanistes caeruleus) were briefly brought into captivity and scored for personality and corticosterone (Cort) concentrations. More active females had lower baseline Cort than less active individuals. Exploratory tendency and neophobia did not co-vary with baseline Cort. Stress-induced Cort concentrations were correlated negatively with exploratory tendency and haematocrit, but positively with mass gain in captivity. Therefore, baseline and stress-induced Cort concentrations in wintering blue tits were associated with state-dependent variables, sex, age and personality traits. Key to interpreting the physiology of personality traits seems to be their interactions with other traits that mediate ability to utilise resources, and thus influence an individual’s perception of its current and future energy balance.

Cognitive appraisal of aversive stimulus differs between individuals with contrasting stress coping styles; evidences from selected rainbow trout (Oncorhynchus mykiss) strains

In animals, personality variations in response to stress and energy demands have been established. Cognitive processing of negative stimuli correlates with stress response patterns. Still, the relative contribution of cognitive appraisal or physiological demands to the behavioural output needs to be clarified. In this study we utilized reactive (high-responsive, HR) and proactive (low-responsive, LR) rainbow trout strains to investigate how contrasting reactions to hypoxia are related to individual variation in metabolism and/or cognition. The HR-LR strains did not differ in standard metabolic rate or hypoxia tolerance. HR trout displayed more pronounced avoidance to a signal cue after being conditioned with hypoxia, suggesting that they experienced this stimulus more aversive than LR trout. Together with differences in forebrain c-fos activation patterns in dorsomedial pallium, these results suggest cognitive differences between the strains. These results demonstrate that differences in personality/stress coping style can be related to contrasts in cognition, which are independent of metabolic differences.

To boldly climb: behavioural and cognitive differences in migrating European glass eels

European eel (Anguilla anguilla) is a catadromous fish species that received substantial attention as its population has markedly declined in the last three decades. The possible causes of this decline include habitat fragmentation factors such as dams and weirs. In some cases, these obstacles are equipped with fish friendly passage devices that may select young eels according to their climbing behaviour. We tested how individual climbing tendency was related to the event of fishway passage experienced in the field and classified fish climbing profiles as climbing 'leaders', 'followers', 'finishers' and 'no climbers'. Moreover, we analysed the brain transcription level of genes related to neurogenesis and synaptic plasticity and compared it to climbing profiles. We found that fish from the upstream segments of an impounded river had a higher climbing propensity. Their behaviour was also more repeatable throughout the whole test than the obstacle-naive fish from the downstream segment. Moreover, we found that boldly climbing 'leaders' had lower levels of transcription of synapse-related genes than the climbing 'followers'. These differences could be related to coping styles of fish, where proactive 'leaders' express a routine and risky behaviour, whereas reactive fish need an environmental assessment before exploratory behaviour. Our study showed that differences in climbing propensity exist in glass eels separated by water obstacles. Moreover, eels could adopt climbing different strategies according to the way they deal with environmental stress and to the cognitive abilities they possess.

HPI reactivity does not reflect changes in personality among trout introduced to bold or shy social groups

Physiological stress responses often correlate with personalities (e.g., boldness). However, this relationship can become decoupled, although the mechanisms underlying changes in this relationship are poorly understood. Here we quantify (1) how an individual’s boldness (response to novel objects) in rainbow trout,Oncorhynchus mykiss, changes in response to interactions with a population of either bold or shy conspecifics and we (2) measured associated post-stress cortisol levels. Initially-bold trout became shyer regardless of group composition, whereas shy trout remained shy demonstrating that bold individuals are more plastic. Stress-induced plasma cortisol reflected the original personality of fish but not the personality induced by the treatment, irrespective of population personality. Change in boldness of bold trout may indicate preference towards initially subordinate behaviour when joining a new population. However, here we provide further evidence that behavioural and physiological parameters of coping styles may become uncoupled whereby behavioural changes are not correlated with stress responsiveness.

Non-Invasive Measurement of Adrenocortical Activity in Blue-Fronted Parrots (Amazona aestiva, Linnaeus, 1758)

Parrots kept in zoos and private households often develop psychological and behavioural disorders. Despite knowing that such disorders have a multifactorial aetiology and that chronic stress is involved, little is known about their development mainly due to a poor understanding of the parrots' physiology and the lack of validated methods to measure stress in these species. In birds, blood corticosterone concentrations provide information about adrenocortical activity. However, blood sampling techniques are difficult, highly invasive and inappropriate to investigate stressful situations and welfare conditions. Thus, a non-invasive method to measure steroid hormones is critically needed. Aiming to perform a physiological validation of a cortisone enzyme immunoassay (EIA) to measure glucocorticoid metabolites (GCM) in droppings of 24 Blue-fronted parrots (Amazona aestiva), two experiments were designed. During the experiments all droppings were collected at 3-h intervals. Initially, birds were sampled for 24 h (experiment 1) and one week later assigned to four different treatments (experiment 2): Control (undisturbed), Saline (0.2 mL of 0.9% NaCl IM), Dexamethasone (1 mg/kg IM) and Adrenocorticotropic hormone (ACTH; 25 IU IM). Treatments (always one week apart) were applied to all animals in a cross-over study design. A daily rhythm pattern in GCM excretion was detected but there were no sex differences (first experiment). Saline and dexamethasone treatments had no effect on GCM (not different from control concentrations). Following ACTH injection, GCM concentration increased about 13.1-fold (median) at the peak (after 3-9 h), and then dropped to pre-treatment concentrations. By a successful physiological validation, we demonstrated the suitability of the cortisone EIA to non-invasively monitor increased adrenocortical activity, and thus, stress in the Blue-fronted parrot. This method opens up new perspectives for investigating the connection between behavioural disorders and stress in this bird species, and could also help in their captive management.

Turtle hatchlings show behavioral types that are robust to developmental manipulations

There can be substantial variation among individuals within a species in how they behave, even under similar conditions; this pattern is found in many species and across taxa. However, the mechanisms that give rise to this behavioral variation are often unclear. This study investigated the influence of environmental manipulations during development on behavioral variation in hatchlings of the red-eared slider turtle (Trachemys scripta). First, we examined the effects of three manipulations during incubation (estrone sulfate exposure, corticosterone exposure, and thermal fluctuations) on hatchling righting response and exploration. Second, we determined whether hatchlings showed consistent differences (i.e. behavioral types) in their righting response and exploration across days and months, and whether these behaviors were correlated with one another. Finally, we examined whether righting response was predictive of ecologically relevant behaviors such as habitat choice and dispersal. Hatchling behavior was robust to our early manipulations; none of the pre-hatch treatments affected later behavior. There were significant clutch effects, which due to the split-clutch design suggests genetic underpinnings and/or maternal effects. We found evidence for behavioral types in turtles; both righting response and exploration were strongly repeatable and these behaviors were positively correlated. Righting response was not predictive of dispersal ability in the field, necessitating a revision in the general interpretations of righting response as a proxy for dispersal ability in turtles. Thus, turtle hatchlings show consistent behavioral differences that are robust to early developmental manipulations, and while not necessarily predictive of dispersal, these behavioral types can have important consequences throughout ontogeny.

Integrated Genome-wide association and hypothalamus eQTL studies indicate a link between the circadian rhythm-related gene PER1 and coping behavior

Animal personality and coping styles are basic concepts for evaluating animal welfare. Struggling response of piglets in so-called backtests early in life reflects their coping strategy. Behavioral reactions of piglets in backtests have a moderate heritability, but their genetic basis largely remains unknown. Here, latency, duration and frequency of struggling attempts during one-minute backtests were repeatedly recorded of piglets at days 5, 12, 19, and 26. A genome-wide association study for backtest traits revealed 465 significant SNPs (FDR ≤ 0.05) mostly located in QTL (quantitative trait locus) regions on chromosome 3, 5, 12 and 16. In order to capture genes in these regions, 37 transcripts with significant SNPs were selected for expressionQTL analysis in the hypothalamus. Eight genes (ASGR1, CPAMD8, CTC1, FBXO39, IL19, LOC100511790, RAD51B, UBOX5) had cis- and five (RANGRF, PER1, PDZRN3, SH2D4B, LONP2) had trans-expressionQTL. In particular, for PER1, with known physiological implications for maintenance of circadian rhythms, a role in coping behavior was evidenced by confirmed association in an independent population. For CTC1 a cis-expression QTL and the consistent relationship of gene polymorphism, mRNA expression level and backtest traits promoted its link to coping style. GWAS and eQTL analyses uncovered positional and functional gene candidates for coping behavior.

Sex differences in risk-taking and associative learning in rats

In many species, males tend to have lower parental investment than females and greater variance in their reproductive success. Males might therefore be expected to adopt more high-risk, high-return behaviours than females. Next to risk-taking behaviour itself, sexes might also differ in how they respond to information and learn new associations owing to the fundamental link of these cognitive processes with the risk-reward axis. Here we investigated sex differences in both risk-taking and learned responses to risk by measuring male and female rats' (Rattus norvegicus) behaviour across three contexts in an open field test containing cover. We found that when the environment was novel, males spent more time out of cover than females. Males also hid less when exposed to the test arena containing predator odour. By contrast, females explored more than males when the predator odour was removed (associatively learned risk). These results suggest that males are more risk-prone but behave more in line with previous experiences, while females are more risk-averse and more responsive to changes in their current environment. Our results suggest that male and female rats differ in how they cope with risk and highlight that a general link may exist between risk-taking behaviour and learning style.

Dissociated neural effects of cortisol depending on threat escapability

Evolution has provided us with a highly flexible neuroendocrine threat system which, depending on threat imminence, switches between active escape and passive freezing. Cortisol, the "stress-hormone", is thought to play an important role in both fear behaviors, but the exact mechanisms are not understood. Using pharmacological functional magnetic resonance imaging we investigated how cortisol modulates the brain's fear systems when humans are under virtual-predator attack. We show dissociated neural effects of cortisol depending on whether escape from threat is possible. During inescapable threat cortisol reduces fear-related midbrain activity, whereas in anticipation of active escape cortisol boosts activity in the frontal salience network (insula and anterior cingulate cortex), which is involved in autonomic control, visceral perception and motivated action. Our findings suggest that cortisol adjusts the human neural threat system from passive fear to active escape, which illuminates the hormone's crucial role in the adaptive flexibility of fear behaviors.

Shaking the myth: Body mass, aggression, steroid hormones, and social dominance in wild house mouse

In social mammals, the position of a male in the group's hierarchy strongly affects his reproductive success. Since a high social rank is often gained through competition with other males, selection should favour bigger males over smaller ones. We may therefore predict faster growth and/or delayed sexual maturity in dominant males. Likewise, dominants should have higher levels of testosterone, hormone important in many aspects of male dominance. Less obvious is the relationship between dominance and levels of corticosterone but generally higher concentrations are expected in subordinate individuals. We studied body growth, sexual maturation and endocrinal changes in males of two house mouse subspecies, raised in fraternal pairs. Since Mus musculus domesticus is the subspecies which dominates mutual encounters with Mus musculus musculus we predicted higher growth rate, delayed puberty and aggression, and higher testosterone and corticosterone levels in domesticus males compared to musculus. In all comparisons, no differences were found between dominant and subordinate musculus brothers. On the other hand, in M. m. domesticus, dominant males revealed a different growth trajectory and lower corticosterone levels than subordinate males but not delayed puberty and higher testosterone concentrations, thus contradicting our predictions. In inter-subspecific comparisons, musculus males matured earlier but became aggressive at the same time as domesticus males. The musculus testosterone ontogeny suggests that social positions in this subspecies remain unfixed for an extended period and that the increasing levels probably reflect prolonged hierarchy contests. It appears that the ontogeny of behaviour and physiological traits diverge cryptically between the two subspecies.

Chronic stress and brain plasticity: Mechanisms underlying adaptive and maladaptive changes and implications for stress-related CNS disorders

Stress responses entail neuroendocrine, autonomic, and behavioral changes to promote effective coping with real or perceived threats to one's safety. While these responses are critical for the survival of the individual, adverse effects of repeated exposure to stress are widely known to have deleterious effects on health. Thus, a considerable effort in the search for treatments to stress-related CNS disorders necessitates unraveling the brain mechanisms responsible for adaptation under acute conditions and their perturbations following chronic stress exposure. This paper is based upon a symposium from the 2014 International Behavioral Neuroscience Meeting, summarizing some recent advances in understanding the effects of stress on adaptive and maladaptive responses subserved by limbic forebrain networks. An important theme highlighted in this review is that the same networks mediating neuroendocrine, autonomic, and behavioral processes during adaptive coping also comprise targets of the effects of repeated stress exposure in the development of maladaptive states. Where possible, reference is made to the similarity of neurobiological substrates and effects observed following repeated exposure to stress in laboratory animals and the clinical features of stress-related disorders in humans.