Marble burying is an animal model used in scientific research to depict
anxiety
Anxiety is an emotion characterised by an unpleasant state of inner wikt:turmoil, turmoil and includes feelings of dread over Anticipation, anticipated events. Anxiety is different from fear in that fear is defined as the emotional response ...
or
obsessive–compulsive disorder (OCD) behavior. It is based on the observation that rats and mice will bury either harmful or harmless objects in their bedding. While widely used there is significant controversy over the interpretation of its results.
Difficulty in modeling
Animal behavior modeling is difficult because to create a competent model, the cause of the disease must be known. In the case of OCD and anxiety the causes are
idiopathic
An idiopathic disease is any disease with an unknown cause or mechanism of apparent spontaneous origin.
For some medical conditions, one or more causes are somewhat understood, but in a certain percentage of people with the condition, the cause ...
. The symptoms for both diseases overlap making it difficult to know what disease the animal model is displaying.
OCD is a serious condition with a lifetime prevalence of 1-3%. Common symptoms of OCD include recurrent obsessions or compulsions. These compulsions are time-consuming (more than 1 hr/day) and cause significant stress or impairment in the patient's everyday life. The most common treatment of OCD is serotonin reuptake inhibitors (SSRI) and behavioral treatment.
Anxiety is a complex multi-faceted disorder with many symptoms. Anxiety is difficult to model because psychiatrists who clinically diagnose anxiety follow the
Diagnostic and Statistical Manual (DSM IV) of the American Psychiatric Association, which includes self-reporting from patients. Since animals cannot explain to us how they feel, animals cannot be diagnosed with anxiety disorder. However symptoms of anxiety can be inferred from animal behavior.
Concept
When rodents are put in a cage with marbles they will bury the marbles. This behavior is seen as anxiety related or OCD behavior. When the rodents are injected with drugs used to treat anxiety or OCD, the amount of marbles buried decreases. Marble burying doesn't show any difference between anti-compulsive or
anxiolytic activity. The test is also sensitive to
antidepressant agents.
The test is sensitive to two major classes of drugs: the
Selective Serotonin (5-HT) reuptake inhibitors (SSRIs) and
benzodiazepine
Benzodiazepines (BZD, BDZ, BZs), colloquially known as "benzos", are a class of central nervous system (CNS) depressant, depressant drugs whose core chemical structure is the fusion of a benzene ring and a diazepine ring. They are prescribed t ...
s. Benzodiazepines are commonly used to treat anxiety and SSRIs are used to treat both OCD and anxiety.
Procedure
Rodents are placed for thirty minutes in a standard cage filled with 5 cm depth of wood chip bedding with 10 marbles evenly spaced. After thirty minutes the number of marbles buried are counted. In this procedure a marble is considered buried if 2/3 of the marble is covered with bedding. Within the study there should be two groups of animals, one group
which has been injected with saline and another group which has been injected with the agent being tested.
There are multiple variations of this test. Some experiments use more marbles while other variants place the marbles differently.
It is important to keep the laboratory quiet while performing this experiment to avoid unintended results. Younger mice will bury marbles faster than older mice so the age of the mice being tested must be the same.
Criticisms
There are mixed opinions over the validity of the marble burying test. If the marbles cause anxiety, critics point out that rodents would most likely remain immobile or avoid the side containing marbles.
Critics also point out that the marble burying test reacts to two types of drugs the SSRIs and benzodiazepines. Benzodiazepines have been shown to have no effect on patients with OCD. If the test measured OCD then benzodiazepines would not affect rodent behavior.
The marble burying test measures one acute dose of anti-anxiety agent for thirty minutes. It can be weeks before a noticeable change is observed in patients. There is also a genetic component to this test. Some strains show decreased burying behaviour. This can be counteracted by coating marbles with substances such as Tabasco sauce which will increase burying.
The general consensus when testing potential anxiety and OCD medication is to perform a battery of anxiety tests with a high
predictive validity In psychometrics, predictive validity is the extent to which a score on a scale or test predicts scores on some criterion measure.
For example, the validity of a cognitive test for job performance is the correlation between test scores and, for ...
to determine the potential therapeutic value of a
novel agent.
See also
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Elevated Plus Maze
The elevated plus maze (EPM) is a test measuring anxiety in laboratory animals that usually uses Animal testing on rodents, rodents as a Drug discovery#Screening and design, screening test for putative anxiolytic or anxiogenic compounds and as a ...
*
Open Field (animal test)
*
Animal Models of Depression
Animal models of depression are research tools used to investigate Major depressive disorder, depression and action of antidepressant, antidepressants. They are used as a simulation to investigate the symptomatology and pathophysiology of depress ...
References
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Animal testing techniques
Psychology experiments