Natural animal models of human psychiatric conditions: assessment of mechanism and validity

Evaluation of animal models of neurobehavioral disorders

Animal models play a central role in all areas of biomedical research. The process of animal model building, development and evaluation has rarely been addressed systematically, despite the long history of using animal models in the investigation of neuropsychiatric disorders and behavioral dysfunctions. An iterative, multi-stage trajectory for developing animal models and assessing their quality is proposed. The process starts with defining the purpose(s) of the model, preferentially based on hypotheses about brain-behavior relationships. Then, the model is developed and tested. The evaluation of the model takes scientific and ethical criteria into consideration.Model development requires a multidisciplinary approach. Preclinical and clinical experts should establish a set of scientific criteria, which a model must meet. The scientific evaluation consists of assessing the replicability/reliability, predictive, construct and external validity/generalizability, and relevance of the model. We emphasize the role of (systematic and extended) replications in the course of the validation process. One may apply a multiple-tiered 'replication battery' to estimate the reliability/replicability, validity, and generalizability of result.Compromised welfare is inherent in many deficiency models in animals. Unfortunately, 'animal welfare' is a vaguely defined concept, making it difficult to establish exact evaluation criteria. Weighing the animal's welfare and considerations as to whether action is indicated to reduce the discomfort must accompany the scientific evaluation at any stage of the model building and evaluation process. Animal model building should be discontinued if the model does not meet the preset scientific criteria, or when animal welfare is severely compromised. The application of the evaluation procedure is exemplified using the rat with neonatal hippocampal lesion as a proposed model of schizophrenia.In a manner congruent to that for improving animal models, guided by the procedure expounded upon in this paper, the developmental and evaluation procedure itself may be improved by careful definition of the purpose(s) of a model and by defining better evaluation criteria, based on the proposed use of the model.

Diagnosis of rapid eye movement sleep disorder with electroencephalography and treatment with tricyclic antidepressants in a dog

A 9-month-old, female Labrador retriever mix was presented for two types of seizure-like episodes, one of which occurred only during sleep. The two types of episodes were morphologically distinct. An electroencephalogram (EEG) demonstrated that the sleep-associated episodes occurred during rapid eye movement (REM) sleep, supporting a diagnosis of a REM behavior disorder. Based on their morphology and response to antiseizure medications, the waking episodes were diagnosed as seizures. The animal was also diagnosed with an obsessive-compulsive and generalized anxiety disorder. The REM behavior disorder and anxiety-related behaviors improved with tricyclic antidepressant therapy.

Big thoughts in small brains? Dogs as a model for understanding human social cognition

In this review we argued that dogs can provide a good model for both the evolution of human social-cognitive abilities and studying the underlying neural and genetic structures of these behavioural features. The key difference between the present and other approaches for modelling human social evolution lies in the assumption that there is a large overlap between the human and dog behaviour complex because during their evolution in close contact with human groups dogs evolved functionally similar social skills. Thus the parallel investigation of the human and dog behaviour complex widens our possibility for understanding human social cognition because it allows the modelling of the interaction between various components in contrast to other models which are often restricted to modelling a single aspect of human social cognitive skills.

What's wrong with my mouse model?

Stress plays a key role in pathogenesis of anxiety and depression. Animal models of these disorders are widely used in behavioral neuroscience to explore stress-evoked brain abnormalities, screen anxiolytic/antidepressant drugs and establish behavioral phenotypes of gene-targeted or transgenic animals. Here we discuss the current situation with these experimental models, and critically evaluate the state of the art in this field. Noting a deficit of fresh ideas and especially new paradigms for animal anxiety and depression models, we review existing challenges and outline important directions for further research in this field.

Pathological anxiety in animals

Selective breeding programmes in domestic and laboratory animals generally focus on physiological and/or anatomical characteristics. However, selection may have an (unintended) impact on other characteristics and may lead to dysfunctional behaviour that can affect biological functioning and, as a consequence, compromise welfare and quality of life. In this review it is proposed that various behavioural dysfunctions in animals are due to pathological anxiety. Although several approaches have been undertaken to specify the diagnostic criteria of pathological anxiety as a behavioural disorder in animals, the causal aetiology largely remains unknown. This is mainly due to the fact that integrated concepts, combining the behavioural syndrome and (neuro-) physiological processes, are widely lacking. Moreover, even the term anxiety itself represents a poorly defined concept or category. A definition is suggested and the potential causes of pathological anxiety are explored with a plea for developing adequate diagnostic tools and therapies to fight pathological anxiety in animals based on insight from scientific research.

Relationship between paw preference strength and noise phobia in Canis familiaris

The authors investigated the relationship between degree of lateralization and noise phobia in 48 domestic dogs (Canis familiaris) by scoring paw preference to hold a food object and relating it to reactivity to the sounds of thunderstorms and fireworks, measured by playback and a questionnaire. The dogs without a significant paw preference were significantly more reactive to the sounds than the dogs with either a left-paw or right-paw preference. Intense reactivity, therefore, is associated with a weaker strength of cerebral lateralization. The authors note the similarity between their finding and the weaker hand preferences shown in humans suffering extreme levels of anxiety and suggest neural mechanisms that may be involved.

Selection, acclimation, training, and preparation of dogs for the research setting

Dogs have made and will continue to make valuable contributions as animal models in biomedical research. A comprehensive approach from time of breeding through completion of in-life usage is necessary to ensure that high-quality dog models are used in studies. This approach ensures good care and minimizes the impact of interanimal variability on experimental results. Guidance related to choosing and developing high-quality laboratory dogs and managing canine research colonies is provided in this article. Ensuring that dogs are healthy, well adapted, and cooperative involves good communication between vendors, veterinarians, care staff, and researchers to develop appropriate dog husbandry programs. These programs are designed to minimize animal stress and distress from the postweaning period through the transfer and acclimation period within the research facility. Canine socialization and training programs provided by skilled personnel, together with comprehensive veterinary health programs, can further enhance animal welfare and minimize interanimal and group variability in studies.

Animal models of behavioral dysfunctions: Basic concepts and classifications, and an evaluation strategy

In behavioral neurosciences, such as neurobiology and biopsychology, animal models make it possible to investigate brain-behavior relations, with the aim of gaining insight into normal and abnormal human behavior and its underlying neuronal and neuroendocrinological processes. Different types of animal models of behavioral dysfunctions are reviewed in this article. In order to determine the precise criteria that an animal model should fulfill, experts from different fields must define the desired characteristics of that model at the neuropathologic and behavioral level. The list of characteristics depends on the purpose of the model. The phenotype-abnormal behavior or behavioral dysfunctions-has to be translated into testable measures in animal experiments. It is essential to standardize rearing, housing, and testing conditions, and to evaluate the reliability, validity (primarily predictive and construct validity), and biological or clinical relevance of putative animal models of human behavioral dysfunctions. This evaluation, guided by a systematic strategy, is central to the development of a model. The necessity of animal models and the responsible use of animals in research are discussed briefly.

Animal models of obsessive-compulsive disorder: rationale to understanding psychobiology and pharmacology

Animal models have shown progressive development and have undoubtedly proven their supportive value in OCD research. Thus, various animal models have confirmed the importance of the 5-HT [72-74] and dopamine systems [104,111] in the neurobiology and treatment of OCD. Given the neurochemical, emotional, and cognitive complexity of the disorder, how-ever, animal models are being used to investigate more and more complicated neurochemical and behavioral theories purported to underlie OCD. The lever-press model, for example, has implicated deficient response feed-back in a neural system that regulates operant behavior [74]. Studies on stereotypic movement disorder [89] have opened a new avenue of investigation into the neurobiology of stereotypy that may be applicable to more complex syndromes such as OCD. Models that have focused on specific neuropsychologic aspects of OCD such as reward [74], displacement behavior[63,101], perseveration and indecisiveness [73,102], and spontaneous stereotypy [90,94] are important in their attempt to unify the diverse behavioral manifestations of this disorder. It is clear that for a deeper, more holistic understanding of OCD, multiple animal models will be needed to allow investigation of the various aspects of the disorder and to provide convergent validation of the research findings. The heterogeneous nature of OCD, the various subtypes that exist within the disorder, and the range of obsessive-compulsive spectrum disorders suggest that particular questions regarding OCD may be addressed best by us-ing a particular ethologic model, whereas other questions might require a pharmacologic model or a combination of both for meaningful results[62,115]. Genetic models will be extremely useful for studying the genetics of pathologic behavior and for relating these findings to neuroanatomic and neurochemical changes in the model (eg, DICT-7 mice as a model for Tourette's syndrome and OCD). Neither ethologic nor pharmacologic models, however, can assess whether the "compulsive" behavior is a response to an "obsessive" anxiety or fear. Perhaps the symptoms seen in patients who have OCD, which may be exacerbated by everyday stress, are analogous to displacement behaviors in animals and also reflect some form of anxiety or stress [98]. In this regard, the bank vole model [116]has provided evidence that previously developed stereotypies increase markedly after acute stress and argues that healthy individuals "habituate" to everyday stress, whereas patients who have OCD do not. Interindividual variation in behavioral response and attempts to replicate studies in different laboratories often is the nemesis of the behavioral scientist. Small within- and between-subject variability is usually desirable, how-ever, because there are cases in which the study of the variability of the model could lead to a better understanding of the disorder. Variability can-not always be considered an error; it is possible that previously disregarded neuronal systems may have a place in the observed variation and, indeed, in the pathophysiology of OCD. In this regard, SRIs are not always effective for OCD [6,29,30] such that a lack of effect in a model may reflect an un-known neurobiological basis for compulsive behavior in a sub-group of SRI refractory patients. Similarly, separating the afflicted (ie, working with animals that show greater behavioral change in a model and/or after drug treatment) would have distinct benefits. To increase successful implementation of an ethologic animal model, especially when reinforcement models or signal attenuation models are used,the laboratory must be equipped with the essential behavioral testing apparatus as well as the operant chambers/rooms in which to conduct the train-ing and data collection. Quantification of certain stereotypy behaviors also requires experienced or trained observers. An illustration of the difficulty in measuring behavioral changes is that in the rewarded alternation model,a good response to behavioral treatment (alternation training) may lead to a floor effect [73] which, after successful drug treatment of the animal,produces no residual persistence (ie, measurable behavioral change) on which a drug treatment can be tested. Clearly, the choice of ethologic, pharmacologic, or genetic models should be considered carefully. A well-validated model may quell many of the limitations and considerations described previously. Noninvasive neuroimaging(eg, the use of small-animal single-photon emission CT) to explore the neuroanatomic basis of OCD offers an exciting future challenge, especially if combined with pharmacologic or ethologic models, and could confirm or ex-tend knowledge of the neuroanatomy of OCD. Although studies to investigate further the interactive role of 5-HT, dopamine, GABA, and glutamate are still needed, the role of neuroactive peptides such as cholecystokinin, corticotrophin-releasing factor, neuropeptide Y, tachykinins (ie, substance P),and natriuretic peptides in OCD should also be considered. Genetically engineered animal models will become increasingly valuable in combination with new technologies such as gene-chip microarrays, RNA interference, and advanced proteomics that will help further the understanding of OCD. Animal models of OCD are poised to play a vital role in extending the knowledge of the disorder now and in the future.

The genetic contribution to canine personality

The domestic dog may be exceptionally well suited for behavioral genetic studies owing to its population history and the striking behavior differences among breeds. To explore to what extent and how behavioral traits are transmitted between generations, heritabilities and genetic correlations for behavioral traits were estimated in a cohort containing over 10,000 behaviorally tested German shepherd and Rottweiler dogs. In both breeds, the pattern of co-inheritance was found to be similar for the 16 examined behavioral traits. Furthermore, over 50% of the additive genetic variation of the behavioral traits could be explained by one underlying principal component, indicating a shared genetic component behind most of the examined behavioral traits. Only aggression appears to be inherited independently of the other traits. The results support a genetic basis for a broad personality trait previously named shyness-boldness dimension, and heritability was estimated to be 0.25 in the two breeds. Therefore, breeds of dogs appear to constitute a valuable resource for behavioral genetic research on the normal behavioral differences in broad personality traits.

Rituals, stereotypy and compulsive behavior in animals and humans

From a survey of the behavior of animals in the wild, in captivity, under the influence of psychoactive drugs and in a model of obsessive-compulsive disorder (OCD), we identify that the behavioral repertoire invariably includes motor rituals, and that such rituals are performed at a few specific locations/objects in the environment with an orderly transition amongst locations/objects. The concept and parameters of this stable organization of rituals in time and space were used to analyze rituals of OCD patients, compared with control individuals performing the same actions (e.g. car locking). It was found that human rituals also converged to a few places/objects where repetitive acts were performed in a regular order, with the acts in OCD patients overlapping with those of control individuals. Across a very diverse range of animals and conditions, motor rituals are thus characterized by their close linkage to a few environmental locations and the repeated performance of relatively few acts. Such similarity in form may reflect a similarity in the mechanisms that control motor rituals in both animals and humans.

Enrichment Strategies for Laboratory Animals from the Viewpoint of Clinical Veterinary Behavioral Medicine: Emphasis on Cats and Dogs

Behavioral wellness has become a recent focus for the care of laboratory animals, farm and zoo animals, and pets. Behavioral enrichment issues for these groups are more similar than dissimilar, and each group can learn from the other. The emphasis on overall enhancement for laboratory dogs and cats in this review includes an emphasis on behavioral enrichment. Understanding the range of behaviors, behavioral choices, and cognitive stimulation that cats and dogs exhibit under non-laboratory conditions can increase the ability of investigators to predict which enrichments are likely to be the most successful in the laboratory. Many of the enrichment strategies described are surprisingly straightforward and inexpensive to implement.

Dog star rising: the canine genetic system

Purebred dogs are providing invaluable information about morphology, behaviour and complex diseases, both of themselves and humans, by supplying tractable populations in which to map genes that control those processes. The diversification of dog breeds has led to the development of breeds enriched for particular genetic disorders, the mapping and cloning of which have been facilitated by the availability of the canine genome map and sequence. These tools have aided our understanding of canine population genetics, linkage disequilibrium and haplotype sharing in the dog, and have informed ongoing efforts of the need to identify quantitative trait loci that are important in complex traits.

Medical differentials with potential behavioral manifestations

Boundaries between behavioral conditions and medical differentials are likely to blur more rather than less as we learn more about genomic, cellular, and subcellular effects on common conditions. These changes should lead to better treatment but may also require a paradigm shift in how we view behavioral conditions and the mechanisms that contribute to them.

Clinical features and outcome in dogs and cats with obsessive-compulsive disorder: 126 cases (1989-2000)

OBJECTIVE

To determine clinical features and outcome in dogs and cats with obsessive-compulsive disorder (OCD).

DESIGN

Retrospective study.

ANIMALS

103 dogs and 23 cats.

PROCEDURES

Records of patients with OCD were analyzed for clinical features, medication used, extent of behavior modification, and outcome.

RESULTS

Most dogs affected with OCD had been obtained from breeders. Male dogs significantly outnumbered females (2:1). Female cats outnumbered male cats by 2:1 in a small sample. Most affected dogs lived in households with 2 or more humans and other dogs or cats, and had some formal training. Client compliance with behavior modification was high. A combination of behavior modification and medication resulted in a large decrease in intensity and frequency of OCD in most animals. Clomipramine was significantly more efficacious for treatment in dogs than was amitriptyline. Only 1 dog and 1 cat were euthanatized because of OCD during the study.

CONCLUSIONS AND CLINICAL RELEVANCE

OCD in dogs does not appear to be associated with lack of training, lack of household stimulation, or social confinement. In cats, OCD may be associated with environmental and social stress. Obsessive-compulsive disorder appears at the time of social maturity and may have sporadic and heritable forms. With appropriate treatment (consistent behavior modification and treatment with clomipramine), frequency and intensity of clinical signs in most dogs and cats may decrease by > 50%. Success appears to depend on client understanding and compliance and the reasonable expectation that OCD cannot be cured, but can be well controlled.