Rodent marble-burying behavior in the marble-burying test (MBT) is employed as a model or measure to study anxiety-and compulsive-like behaviors or anxiolytic and anticompulsive drug action. However, the test responds variably to a range of pharmacological interventions, and little consensus exists regarding specific methodologies for its execution. Regardless, the test is widely applied to investigate the effects of pharmacological, genetic, and behavioral manipulations on purported behaviors related to the said neuropsychiatric constructs. Therefore, in the present review we attempt to expound the collective translational significance of the MBT. We do this by (1) reviewing burying behavior as a natural behavioral phenotype, (2) highlighting key aspects of anxiety and obsessive-compulsive disorder from a translational perspective, (3) reviewing the history and proof of concept of the MBT, (4) critically appraising potential methodological confounds in execution of the MBT, and (5) dissecting responses of the MBT to various pharmacological interventions. We conclude by underlining that the collective translational value of the MBT will be strengthened by contextually valid experimental designs and objective reporting of data.

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Burying forms part of the normal behavioral routine of rodents, although its expression is species-specific. However, it has been suggested that aberrant burying behavior, of which marble-burying (MB) is an example, may represent neophobic and/or compulsive-like behavior. In the present investigation, we assessed MB in an established animal model of obsessive-compulsive disorder (OCD)-namely, spontaneous stereotypy in the deer mouse-to establish whether high (H) stereotypy is associated with neophobia and/or another compulsive endophenotype, i.e. MB, as compared to nonstereotypical (N) controls. A three-trial, one-zone MB test was performed over three consecutive evenings both before and after chronic treatment with high-dose (50 mg/kg/ day) oral escitalopram. Neophobia was measured via the number of marbles buried during the first pre-and posttreatment MB trials, and compulsive-like behavior via the number of marbles buried over all pre-and posttreatment MB trials. The data from the present study support earlier findings that burying is a normal behavioral routine (inherent burying behavior, IBB) that is expressed by all deer mice, irrespective of stereotypical cohort, and is not associated with either neophobia or compulsiveness. Indeed, chronic escitalopram treatment, which is similarly effective in treating clinical anxiety and OCD, as well as in attenuating H behavior, failed to influence IBB. Although 11 % of the animals presented with a unique burying endophenotype (high burying behavior), escitalopram also failed to attenuate said behavior, necessitating further investigation as to its relevance. In conclusion, MB cannot be regarded as a measure of anxiety-like or compulsive behavior in the deer mouse model of OCD.Keywords Marble-burying . Obsessive-compulsive disorder . Neophobia . Deer mouse . Animal model . Escitalopram Burying, burrowing, and digging form part of the normal behavioral repertoire of rodents, in both the wild and the laboratory (Deacon, 2006;Smithers, 1983). These strain-specific behaviors are mostly aimed at searching for food, burying both noxious and harmless objects, and building adequate nurseries capable of protecting individuals against predators and providing suitable environments to breed (Smithers, 1983). Evidently, burying and digging are expressed in relatively nonanxiogenic scenarios (e.g., nesting, hoarding, foraging), as well as under anxiogenic circumstances (e.g., burying of noxious objects, confronting predators).Defensive burying (Pinel & Treit, 1978) can be defined as the process of moving loose bedding material vertically upward and over potentially harmful stimuli or sources of aversive stimulation (e.g., a shock prod). Due to the stressprovoking nature of an electric shock, defensive burying has been used as a measure of avoidance-dependent anxiety in a Electronic supplementary material The online version of this article

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Obsessive-compulsive disorder (OCD) is a phenotypically heterogeneous condition characterised by time-consuming intrusive thoughts and/or compulsions. Irrespective of the symptom type diagnosed, the severity of OCD is characterised by heterogeneity in symptom presentation that complicates diagnosis and treatment. Heterogeneity of symptoms would be invaluable in an animal model. Nest building behaviour forms part of the normal behavioural repertoire of rodents and demonstrates profound between-species differences. However, it has been proposed that within-species differences in nest building behaviour (i.e. aberrant vs. normal nest building) may resemble obsessive-compulsive-like symptoms. In an attempt to investigate whether other obsessive-compulsive-like behaviours are present in an animal model of OCD, or if aberrant nest building behaviour may represent a unique obsessive-compulsive phenotype in such a model, the current study assessed nest building behaviour in high (H, viz obsessive-compulsive) and non (N, viz normal) stereotypical deer mice. Subsequently, 12 N and H animals, respectively, were provided with an excess of cotton wool daily for one week prior to and following four weeks of high-dose oral escitalopram treatment (50 mg/kg/day). Data from the current investigation demonstrate daily nesting activity to be highly variable in deer mice, with stereotypy and nest building being independent behaviours. However, we identified unique aberrant large nest building behaviour in 30% of animals from both cohorts that was attenuated by escitalopram to pre-treatment nesting scores of the larger group. In summary, behavioural and drug-treatment evidence confirms that deer mouse behaviour does indeed resemble symptom heterogeneity related to OCD, and as such expands its face and predictive validity for the disorder.