Ethological Model Research Articles

The association between childhood trauma and motor structure in obsessive-compulsive rituals: An ethological and evolutionary approach.

Ethological models have highlighted a specific motor structure of compulsions in obsessive-compulsive disorder (OCD), based on the rigid repetitions of acts, and with the adaptive significance of facing unpredictable conditions. Such an evolutionary mechanism might explain the robust association between childhood traumatic experiences (CTEs) and OCD. However, a relationship between CTEs and the motor structure of compulsions has not been investigated yet. The first objective of the study was to confirm a specific motor structure of OCD compulsions with respect to control behaviors; the second objective was to assess a possible association between the motor structure of compulsions and CTEs severity. Thirty-two OCD outpatients (13 female, Mage = 44.50 years, SE = 19.71) and 27 healthy controls (10 female, Mage = 37.62 years, SE = 16.20), matched for sex and age, provided a videotape of their compulsions and corresponding ordinary acts, respectively. Behavior was scored with the software "Observer." Participants were administered the Yale-Brown Obsessive Compulsive Scale and the Childhood Trauma Questionnaire. A dependent t test was used to compare the motor structure of behavior between the groups; Pearson's correlations to investigate associations between motor parameters and CTEs. Compulsions showed a specific motor structure due to the repetition of functional and nonfunctional acts. CTEs severity was especially associated with the repetition of functional acts, independently from OCD severity. Our findings, in confirming a peculiar motor structure for OCD compulsions, hint for the first time at a link between CTEs and compulsive repetition of functional acts, which would represent a plastic developmental response to CTEs unpredictability. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Microglia modulate sleep/wakefulness under baseline conditions and under acute social defeat stress in adult mice

Although sleep is tightly regulated by multiple neuronal circuits in the brain, nonneuronal cells such as glial cells have been increasingly recognized as crucial sleep regulators. Recent studies have shown that microglia may act to maintain wakefulness. Here, we investigated the possible involvement of microglia in the regulation of sleep quantity and quality under baseline and stress conditions through electroencephalography (EEG)/electromyography (EMG) recordings, and by employing pharmacological methods to eliminate microglial cells in the adult mouse brain. We found that severe microglial depletion induced by the colony-stimulating factor 1 receptor (CSF1R) antagonist PLX5622 (PLX) reversibly decreased the total wake time and the wake episode duration and increased the EEG slow-wave power during wakefulness under baseline conditions. To examine the role of microglia in sleep/wake regulation under mental stress, we used the acute social defeat stress (ASDS) paradigm, an ethological model for psychosocial stress. Sleep analysis under ASDS revealed that microglial depletion exacerbated the stress-induced decrease in the total wake time and increase in anxiety-like behaviors in the open field test. These results demonstrate that microglia actively modulate sleep quantity and architecture under both baseline and stress conditions. Our findings suggest that microglia may potentially provide resilience against acute psychosocial stress by regulating restorative sleep.

Steady electrocorticogram characteristics predict specific stress-induced behavioral phenotypes.

Depending on the individual, exposure to an intense stressor may, or may not, lead to a stress-induced pathology. Predicting the physiopathological evolution in an individual is therefore an important challenge, at least for prevention. In this context, we developed an ethological model of simulated predator exposure in rats: we call this the multisensorial stress model (MSS). We hypothesized that: (i) MSS exposure can induce stress-induced phenotypes, and (ii) an electrocorticogram (ECoG) recorded before stress exposure can predict phenotypes observed after stress. Forty-five Sprague Dawley rats were equipped with ECoG telemetry and divided into two groups. The Stress group (n = 23) was exposed to an MSS that combined synthetic fox feces odor deposited on filter paper, synthetic blood odor, and 22 kHz rodent distress calls; the Sham group (n = 22) was not exposed to any sensorial stimulus. Fifteen days after initial exposure, the two groups were re-exposed to a context that included a filter paper soaked with water as a traumatic object (TO) reminder. During this re-exposure, freezing behavior and avoidance of the filter paper were measured. Three behaviors were observed in the Stress group: 39% developed a fear memory phenotype (freezing, avoidance, and hyperreactivity); 26% developed avoidance and anhedonia; and 35% made a full recovery. We also identified pre-stress ECoG biomarkers that accurately predicted cluster membership. Decreased chronic 24 h frontal Low θ relative power was associated with resilience; increased frontal Low θ relative power was associated with fear memory; and decreased parietal β2 frequency was associated with the avoidant-anhedonic phenotype. These predictive biomarkers open the way to preventive medicine for stress-induced diseases.

Estrogen receptor beta in the central amygdala regulates the deleterious behavioral and neuronal consequences of repeated social stress in female rats

While over 95% of the population has reported experiencing extreme stress or trauma, females of reproductive age develop stress-induced neuropsychiatric disorders at twice the rate of males. This suggests that ovarian hormones may facilitate neural processes that increase stress susceptibility and underlie the heightened rates of these disorders, like depression and anxiety, that result from stress exposure in females. However, there is contradicting evidence in the literature regarding estrogen's role in stress-related behavioral outcomes. Estrogen signaling through estrogen receptor beta (ERβ) has been traditionally thought of as anxiolytic, but recent studies suggest estrogen exhibits distinct effects in the context of stress. Furthermore, ERβ is found abundantly in many stress-sensitive brain loci, including the central amygdala (CeA), in which transcription of the vital stress hormone, corticotropin releasing factor (CRF), can be regulated by an estrogen response element. Therefore, these experiments sought to identify the role of CeA ERβ activity during stress on behavioral outcomes in naturally cycling, adult, female Sprague-Dawley rats. Rats were exposed to an ethological model of vicarious social stress, witness stress (WS), in which they experienced the sensory and psychological aspects of an aggressive social defeat encounter between two males. Following WS, rats exhibited stress-induced anxiety-like behaviors in the marble burying taskand brain analysis revealed increased ERβ and CRF specifically within the CeA following exposure to stress cues. Subsequent experiments were designed to target this receptor in the CeA using microinjections of the ERβ antagonist, PHTPP, prior to each stress session. During WS, estrogen signaling through ERβ was responsible for the behavioral sensitization to repeated social stress. Sucrose preference, acoustic startle, and marble burying tasks determined that blocking ERβ in the CeA during WS prevented the development of depressive-, anxiety-like, and hypervigilant behaviors. Additionally, brain analysis revealed a long-term decrease of intra-CeA CRF expression in PHTPP-treated rats. These experiments indicate that ERβ signaling in the CeA, likely through its effects on CRF, contributes to the development of negative valence behaviors that result from exposure to repeated social stress in female rats.

Animal models of anxiety: a review

Anxiety is a disorder that affects the quality of life and also imposes a huge economic burden. Animal models of anxiety have widened our understanding of the pathophysiology behind anxiety and to identify newer pharmacological compounds. Every behavioral test has its own limitations, and there are ways to minimize these like environment and handling. This review lists various experimental models of anxiety based on unlearned ethological models, learned responses like the Vogel conflict test, and psychological and physical stress models.

A specific circuit in the midbrain detects stress and induces restorative sleep.

In mice, social defeat stress (SDS), an ethological model for psychosocial stress, induces sleep. Such sleep could enable resilience, but how stress promotes sleep is unclear. Activity-dependent tagging revealed a subset of ventral tegmental area GABA-somatostatin (VTAVgat-Sst) cells that sense stress and drive NREM and REM sleep via the lateral hypothalamus, and also inhibit corticotropin-releasing factor (CRF) release in the paraventricular hypothalamus. Transient stress enhances the activity of VTAVgat-Sst cells for several hours, allowing them to exert their sleep effects persistently. Lesioning of VTAVgat-Sst cells abolished SDS-induced sleep; without it, anxiety and corticosterone levels remained elevated after stress. Thus, a specific circuit allows animals to restore mental and body functions via sleeping, potentially providing a refined route for treating anxiety disorders.

Stereotypies in the Autism Spectrum Disorder: Can We Rely on an Ethological Model?

Background: Stereotypic behaviour can be defined as a clear behavioural pattern where a specific function or target cannot be identified, although it delays on time. Nonetheless, repetitive and stereotypical behaviours play a key role in both animal and human behaviour. Similar behaviours are observed across species, in typical human developmental phases, and in some neuropsychiatric conditions, such as Autism Spectrum Disorder (ASD) and Intellectual Disability. This evidence led to the spread of animal models of repetitive behaviours to better understand the neurobiological mechanisms underlying these dysfunctional behaviours and to gain better insight into their role and origin within ASD and other disorders. This, in turn, could lead to new treatments of those disorders in humans. Method: This paper maps the literature on repetitive behaviours in animal models of ASD, in order to improve understanding of stereotypies in persons with ASD in terms of characterization, pathophysiology, genomic and anatomical factors. Results: Literature mapping confirmed that phylogenic approach and animal models may help to improve understanding and differentiation of stereotypies in ASD. Some repetitive behaviours appear to be interconnected and mediated by common genomic and anatomical factors across species, mainly by alterations of basal ganglia circuitry. A new distinction between stereotypies and autotypies should be considered. Conclusions: Phylogenic approach and studies on animal models may support clinical issues related to stereotypies in persons with ASD and provide new insights in classification, pathogenesis, and management.

Криминалистический потенциал заимствования коммуникативных моделей в тактику проведения допроса

The article deals with the problem of interdisciplinary research related to the borrowing of communication models from related sciences into the forensic tactic of investigative actions. The subject matter of the research is the interpersonal interaction of interrogation participants. The study used the general research methods of analysis, synthesis, abstraction, system analysis, as well as the specific modeling and comparative-historical research methods. The article contains the following conclusions. Communication models are a field of interdisciplinary research that has significant potential for borrowing into forensic science in order to improve the efficiency of preliminary investigation. The existing definitions of communication that are based on the allocation of semantic components are grouped into the following approaches: cybernetic, semiotic, etho-logical, and psychological. Semantic components were established for each approach to the definition of communication by abstracting: in the cybernetic approach, it is a system of information transmission; in the semiotic approach, it is a meaningful message; in the ethological approach, it is a coordinated activity; in the psychological approach, it is an individual. The final conclusion is the idea that the forensic potential of borrowing communication models into the tactic of interrogation is based on the extent to which the approach to defining communication, within which a specific model was created, corresponds to the tasks solved by means of a certain forensic toolkit. The cybernetic approach abstracts communication into a system of information, the content of which is blocks of data. Accordingly, the sphere of forensic characterization of crimes, used as a system for grouping information contained in the testimony of the interrogated, has the greatest p otential for borrowing cybernetic models of communication. The semiotic approach focuses on the meaning that is embedded in the behavior of interrogation participants and the ways in which it is conveyed. Respectively, the sphere of overcoming the interrogated person's opposition and the tactic of targeted influence have the greatest potential for borrowing semiotic communication models. The ethological approach is focused on interaction as the need for coordinated actions of the participants in communication. Accordingly, the greatest potential for borrowing ethological models of communication belongs to the sphere of coordinating the actions of the participants in the investigation team, as well as developing tactical combinations. The psychological approach is based on the unique personality of the offender. Respectively, the sphere of establishing psychological contact and personification of tactical methods of interrogation has the greatest potential for borrowing ethological models of communication.

Fighting Females: Neural and Behavioral Consequences of Social Defeat Stress in Female Mice

BackgroundDespite the twofold higher prevalence of major depressive and posttraumatic stress disorders in women compared with men, most clinical and preclinical studies have focused on male subjects. We used an ethological murine model to study several cardinal symptoms of affective disorders in the female targets of female aggression. MethodsIntact Swiss Webster (CFW) female resident mice were housed with castrated male mice and tested for aggression toward female intruders. For 10 days, aggressive CFW female residents defeated C57BL/6J (B6) female intruders during 5-minute encounters. Measures of corticosterone, c-Fos activation in hypothalamic and limbic structures, and species-typical behaviors were collected from defeated and control females. Ketamine (20 mg/kg) was tested for its potential to reverse stress-induced social deficits. ResultsHoused with a castrated male mouse, most intact resident CFW females readily attacked unfamiliar B6 female intruders, inflicting >40 bites in a 5-minute encounter. Compared with controls, defeated B6 females exhibited elevated plasma corticosterone and increased c-Fos activation in the medial amygdala, ventral lateral septum, ventromedial hypothalamus, and hypothalamic paraventricular nucleus. Chronically defeated females also showed vigilance-like behavior and deficits in social interactions, novel object investigation, and nesting. The duration of social interactions increased 24 hours after chronically defeated female mice received a systemic dose of ketamine. ConclusionsThese findings demonstrate that CFW female mice living with male conspecifics can be used as aggressive residents in an ethological model of female social defeat stress. These novel behavioral methods will encourage further studies of sex-specific neural, physiological, and behavioral adaptations to chronic stress and the biological bases for interfemale aggression.

Procreative well-being and pornography – analyzing the script. Public health implications revealed through an ethological lens

An ethological model of human procreative well-being is proposed and the goodness-of-fit of pornography’s script to that model is considered. Deducing an evolutionary template for procreative well-being from an ethological analysis links attachment dynamics to procreative success. Alongside parent–child attachment, pair-bond attachment in the procreative couple looms large as an element of optimal procreative relationship structure and quality. Key elements of pair-bond attachment are documented. Turning next to an empirical examination of the sexual behavioral system in humans, we see evidence of an evolutionary design supportive of attachment as well as reproductive exigencies of procreative well-being. Sexual system mechanisms promoting both reproduction and attachment are evident in the evolutionary design. We next employ script theory to identify key elements of the sexual script promulgated by pornography. Joining these two analyses, we compare the evolutionary, attachment-based template for procreative success in juxtaposition to pornography’s sexual script to evaluate the goodness-of-fit of pornography use to attachment success and, by extension, procreative well-being. We conclude that there is an ethological case to be made for considering pornography use as a public health risk. Implications of the model of procreative well-being for the practice of couple therapy are given mention.

The self and depression: Four psychological theories and their potential neural correlates.

We review theory and research pertaining to psychodynamic, social, humanistic, and ethological models of the self and depression and examine research into the neurobiological bases of the self and depression. We provide a narrative review of classic and recent empirical evidence pertaining to these four models of the relation of the self to depression as well as exemplar relevant neurobiological research. Evidence stemming from each of the four theories reviewed here shows a robust relationship between deficits in the sense of self and depressive symptoms, as well as increases in depressive symptoms over time. A smaller body of literature has linked one's sense of self to onsets of depressive episodes. A growing body of literature has linked self-relevant variables to functioning in various prefrontal and cortical midline brain regions as well as emotion and reward processing brain regions which have in turn been linked to depression. Evidence has therefore converged across all four theories and confirmed that a deficit in one's sense of self confers risk for depression and that there is substantial overlap in the brain areas associated with one's sense of self and depression.

Are People Attracted to Others Who Resemble Their Opposite-Sex Parents? An Examination of Mate Preferences and Parental Ethnicity Among Biracial Individuals

It is generally believed that people tend to be attracted to and pair with others who resemble their opposite-sex parents. Studies 1A (n = 1,025) and 1B (n = 3,105) tested this assumption by examining whether biracial adults were more likely to be paired with partners who matched their opposite-sex parent’s ethnicity. Study 2 (n = 516) examined whether biracial adults were more likely to be attracted to targets whose ethnicity matched that of their opposite-sex parent. Although biracial adults were more likely to pair with and be attracted to others who resembled their parents compared to those who did not, the sex of the parent was largely inconsequential. These findings have implications for models of mate preferences, including the traditional perspectives (which assume that the opposite-sex parent has greater influence on adult mating preferences) and ethological models (which assume that the sex of the parent is irrelevant with regard to influence on mating preferences).

Predator odor evokes sex-independent stress responses in male and female Wistar rats and reduces phosphorylation of cyclic-adenosine monophosphate response element binding protein in the male, but not the female hippocampus.

Post-traumatic stress disorder (PTSD) is characterized by memory disturbances following trauma. Acute predator threat has emerged as an ethological model of PTSD, yet the effects of predator odor on signaling cascades associated with long-term memory remain poorly understood. In this study, we exposed male and female Wistar rats to the synthetic predator odor 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) to assess behavioral and physiological responses as well as rapid modulation of signal transduction cascades associated with learning and memory in the male and female hippocampus. During exposure to TMT in the homecage, both male and female animals displayed robust immobility, avoidance, and altered activity as a function of time. Physiologically, TMT exposure increased circulating corticosterone and blood glucose in both male and female rodents, suggesting that TMT evokes sex-independent behavioral and physiological responses. With respect to signal transduction, TMT exposure rapidly reduced phosphorylation of cyclic-adenosine monophosphate response element binding protein (CREB) in the male, but not the female hippocampus. Furthermore, TMT exposure reduced phosphorylation of extracellular signal-regulated kinase 1/2 and increased nuclear expression of the synapto-nuclear messenger protein Jacob in the male hippocampus, consistent with activation of the CREB shut-off pathway. In a follow-up behavioral experiment, post-training exposure to TMT did not affect spatial water maze performance of male rats. However, male rats re-introduced to the context in which TMT had previously been presented displayed avoidance and hyperactivity, but not freezing behavior or elevated corticosterone responses, suggesting that TMT exposure supports a form of contextual conditioning which is not characterized by immobility. Taken together, our findings suggest that TMT evokes similar behavioral and physiological responses in male and female Wistar rats, but affects distinct signaling cascades in the male and female hippocampus which may contribute to behavioral disruptions associated with predator exposure.

PTSD after childbirth: A predictive ethological model for symptom development

BackgroundChildbirth can be a traumatic experience occasionally leading to posttraumatic stress disorder (PTSD). This study aimed to assess childbirth-related PTSD risk-factors using an etiological model inspired by the transactional model of stress and coping. Methods348 out of 505 (70%) Dutch women completed questionnaires during pregnancy, one week postpartum, and three months postpartum. A further 284 (56%) also completed questionnaires ten months postpartum. The model was tested using path analysis. ResultsAntenatal depressive symptoms (β=.15, p<.05), state anxiety (β=.17, p<.01), and perinatal psychoform (β=.17, p<.01) and somatoform (β=.17, p<.01) dissociation were identified as PTSD symptom risk factors three months postpartum. Antenatal depressive symptoms (β=.31, p<.001) and perinatal somatoform dissociation (β=.14, p<.05) predicted symptoms ten months postpartum. LimitationsAlmost a third of our sample was lost at three months postpartum, and 44% at ten months. The sample size was relatively small. The present study did not control for prior PTSD. The PTSD A criterion was not considered an exclusion criteria for model testing, and the fit index of the ten months model was just below suggested cut-off values. ConclusionsScreening for high risk pregnant women should focus on antenatal depression, anxiety and dissociative tendencies. Hospital staff and midwives are advised to be vigilant for perinatal dissociation after intense negative emotions. To help regulate perinatal negative emotional responses, hospital staff and midwifes are recommended to provide information about birth procedures and be attentive to women's birth-related needs.

Testing ethological hypotheses of the trace fossil Zoophycos based on Quaternary material from the Greenland and Norwegian Seas

Despite the fact that the trace fossil Zoophycos has been found in rocks from most of the Phanerozoic, little consensus has been reached on how and why this intricate burrow was constructed. The Cenozoic morphotypes of Zoophycos typically include a helically coiled spreite arranged around a vertical shaft connected to the sediment surface. Morphological details and environmental preferences of the Zoophycos producer were studied using 156 cores from the Norwegian and Greenland Seas in order to test the different ethological hypothesis proposed for this trace fossil. The spreiten were constructed during interglacial or interstadial intervals and consist of a repeated alternation of lamellae consisting of fine-grained pelleted material, and coarse-grained unpelleted material, respectively. Spreiten were encountered in vigorously bioturbated sediment, in turbidite layers, and in layers dominated by coarse ice-rafted debris. This indifference to the composition of the substrate effectively rules out ethological models based on different forms of deposit-feeding, and the large size and wide spacing of the whorls of the spreiten also make the cesspit model unlikely. Rather, the observed features best agree with a cache behaviour, where the main purpose of the deep penetration was to store food and to prevent access by other burrowers, likely combined with some gardening of microbes. However, no indubitable evidence of a reworking of the cached material could be found, and probably the answer to how the cache was accessed by the producer is to be found in the marginal tube. The difference in diameter between marginal tube and spreiten lamellae, together with the presence of both open and filled marginal tubes indicate that the marginal tube is the result of a far more complex behaviour than simply a lateral shift through the sediment.

Etho-robotics: What kind of behaviour can we learn from the animals?

The trends of robotics changes as service robots gain more ground and become part of our daily lives. Service or social robots have to function in less controlled and more dynamically changing environments than industrial robots, and the users of social robots are generally less technologically literate than the users of industrial robots, therefore social robots have to be able to interact naturally with humans and to fit in the human social environment. Social robotics faces new challenges that require an interdisciplinary approach. In contrast to previous approaches where the communication and behaviour of social robots were based on human-human interactions, ethorobotics offer a new direction. Today robotics is not advanced enough to reach the physical and cognitive capabilities of humans thus human-animal interaction can serve as a better model for designing the behaviour of social robots. Human-dog relationship is a good example for this paradigm as dogs have similar roles as social robots will have in the future. Dogs acquired social cognitive skills during domestication that enhances the interspecific relationship with humans and helps their interactions. Etho-robotics research uses ethological principles and methods to derive complex behavioural models which can be transcribed to mathematical form and implemented into robots. Human-robot interaction studies can be conducted to evaluate and refine the implemented models. Etho-robotics research was already used to create behavioural models for attachment and for multiple aspects of human-robot interactions. The application of Fuzzy Rule Interpolation methods fits well the conceptually “spare rule-based” structure of the existing descriptive verbal ethological models, as in case of the descriptive verbal ethological models the “completeness” of the rule-base is not required. The main benefit of the FRI method adaptation in ethological model implementation is the fact, that it has a simple rule-based knowledge representation format. Because of this, even after numerical optimization of the model, the rules are still “human readable”, and helps the formal validation of the model by the ethological experts. On the other side due to the FRI base, the model has still low computational demand and fits directly the requirements of the embedded implementations.

Division of labour in honey bees: age- and task-related changes in the expression of octopamine receptor genes.

The honey bee (Apis mellifera L.) has developed into an important ethological model organism for social behaviour and behavioural plasticity. Bees perform a complex age-dependent division of labour with the most pronounced behavioural differences occurring between in-hive bees and foragers. Whereas nurse bees, for example, stay inside the hive and provide the larvae with food, foragers leave the hive to collect pollen and nectar for the entire colony. The biogenic amine octopamine appears to play a major role in division of labour but the molecular mechanisms involved are unknown. We here investigated the role of two characterized octopamine receptors in honey bee division of labour. AmOctαR1 codes for a Ca(2+) -linked octopamine receptor. AmOctβR3/4 codes for a cyclic adenosine monophosphate-coupled octopamine receptor. Messenger RNA expression of AmOctαR1 in different brain neuropils correlates with social task, whereas expression of AmOctβR3/4 changes with age rather than with social role per se. Our results for the first time link the regulatory role of octopamine in division of labour to specific receptors and brain regions. They are an important step forward in our understanding of complex behavioural organization in social groups.

Social domination and reproductive success in male laboratory mice (Mus musculus)

The goal of the present study was to evaluate effect of social status and genotype on success of reproduction of male laboratory mice with use of ethological model of social hierarchy of "minimal socium". The model represents the paired maintenance of two male mice of different genotype (PT and CBA/Lac). The mice lived for 30 days in one experimental cage males, two females of the DD/He strain were supplemented. Regardless of genotype, the dominants became fathers more often than the subordinants and got more progeny. It was established that in subordinates there did not occur the complete suppression of fertility. This is suggested to allow them to realize the genetical contribution to the next generation and to remain in the gene pool of population.

Animal models of obsessive-compulsive spectrum disorders

Obsessive-compulsive disorder (OCD) and related conditions (trichotillomania, pathological skin-picking, pathological nail-biting) are common and disabling. Current treatment approaches fail to help a significant proportion of patients. Multiple tiers of evidence link these conditions with underlying dysregulation of particular cortico-subcortical circuitry and monoamine systems, which represent targets for treatment. Animal models designed to capture aspects of these conditions are critical for several reasons. First, they help in furthering our understanding of neuroanatomical and neurochemical underpinnings of the obsessive-compulsive (OC) spectrum. Second, they help to account for the brain mechanisms by which existing treatments (pharmacotherapy, psychotherapy, deep brain stimulation) exert their beneficial effects on patients. Third, they inform the search for novel treatments. This article provides a critique of key animal models for selected OC spectrum disorders, beginning with initial work relating to anxiety, but moving on to recent developments in domains of genetic, pharmacological, cognitive, and ethological models. We find that there is a burgeoning literature in these areas with important ramifications, which are considered, along with salient future lines of research.

Towards an Ethological Animal Model of Depression? A Study on Horses

BackgroundRecent reviews question current animal models of depression and emphasise the need for ethological models of mood disorders based on animals living under natural conditions. Domestic horses encounter chronic stress, including potential stress at work, which can induce behavioural disorders (e.g. “apathy”). Our pioneering study evaluated the potential of domestic horses in their usual environment to become an ethological model of depression by testing this models’ face validity (i.e. behavioural similarity with descriptions of human depressive states).Methodology/Principal FindingsWe observed the spontaneous behaviour of 59 working horses in their home environment, focusing on immobility bouts of apparent unresponsiveness when horses displayed an atypical posture (termed withdrawn hereafter), evaluated their responsiveness to their environment and their anxiety levels, and analysed cortisol levels. Twenty-four percent of the horses presented the withdrawn posture, also characterized by gaze, head and ears fixity, a profile that suggests a spontaneous expression of “behavioural despair”. When compared with control “non-withdrawn” horses from the same stable, withdrawn horses appeared more indifferent to environmental stimuli in their home environment but reacted more emotionally in more challenging situations. They exhibited lower plasma cortisol levels. Withdrawn horses all belonged to the same breed and females were over-represented.Conclusions/SignificanceHorse might be a useful potential candidate for an animal model of depression. Face validity of this model appeared good, and potential genetic input and high prevalence of these disorders in females add to the convergence. At a time when current animal models of depression are questioned and the need for novel models is expressed, this study suggests that novel models and biomarkers could emerge from ethological approaches in home environments.