Burrowing in rodents: a sensitive method for detecting behavioral dysfunction.

Virtually all rodents display burrowing behavior, yet measurement of this behavior has not yet been standardized or formalized. Previously, parameters such as the latency to burrow and the complexity of the burrow systems in substrate-filled boxes in the laboratory or naturalistic outdoor environments have been assessed. We describe here a simple protocol that can quantitatively measure burrowing in laboratory rodents, using a simple apparatus that can be placed in the home cage. The test is very cheap to run and requires minimal experimenter training, yet seems sensitive to a variety of treatments, such as the early stages of prion disease in mice, mouse strain differences, lesions of the hippocampus and prefrontal cortex in mice, also effects of lipopolysaccharide and IL-1beta in rats. Other species such as hamsters, gerbils and Egyptian spiny mice also burrow in this apparatus, and with suitable size modification probably almost any burrowing animal could be tested in it. The simplicity, sensitivity and robustness of burrowing make it ideal for assessing genetically modified animals, which in most cases would be mice. The test is run from late afternoon until the next morning, but only two measurements need to be taken.