Burrowing: a sensitive behavioural assay, tested in five species of laboratory rodents

In the burrowing test, mice or rats spontaneously empty a tube filled with food pellets, gravel or other substances. The test is extremely simple to perform, the apparatus is inexpensive and readily constructed. It exploits a natural rodent behaviour, provides quantitative data under controlled laboratory conditions, and has proved extremely sensitive to prion disease in mice (Mus musculus), cytokines in rats (Rattus norvegicus), lipopolysaccharide in mice and rats, strain differences and brain lesions in mice. However, it has not been used in other, less common, laboratory species, and might, e.g. be useful in detecting scrapie infection in hamsters (Mesocricetus auratus), a commonly used species in prion disease research. Therefore, the present study systematically investigated burrowing behaviour in five rodent species, using five different burrowing substrates. It also enquired whether rats are unique among rodents in showing little burrowing of food pellets, yet burrow gravel and other earth-like substrates vigorously. The results showed that all the species (rats, mice, hamsters and gerbils (Meriones unguiculatus)), except one (Egyptian spiny mice, Acomys cahirinus, which does not dig burrows in the wild) burrowed earth-like substrates well. However, laboratory mice were the only species that burrowed food pellets vigorously, without prior exposure to other substrates. These results show that burrowing, with an appropriate substrate, can be used as a simple behavioural test in many rodent species. It is an excellent detector of neurobehavioural toxicity with applications in many areas of research, especially when long-term behavioural monitoring is required, e.g. to track changes in chronic disease models.