Imagine two different people: one spends nearly all of their time in a small apartment. The walls are white and lacking decor, and the rest of the space is bare, except for the basic necessities of food and water. The other individual lives in a space of a similar size, but in addition to food and water has a large window, vivid paintings on the walls, a treadmill, and a television that emits a constant stream of novel images and flashing lights.
Now imagine, after spending weeks at a time in these apartments, how the individuals will respond when they walk out onto a busy city street. The person who receives constant stimuli at home will probably adapt differently, and more favorably than the person without regular environmental enrichment.
Laboratory rodents are no different. The environmental conditions of their home cage can have a profound effect on how they behave outside of the cage. As increased efforts are being made to provide laboratory rodents with enriched environments to better mimic their natural habitats and promote improved health, researchers must consider how these environmental conditions will affect experimental outcomes and reproducibility.
Variables in Animal Housing Conditions
The following are some of the variables in animal housing:
- Single vs. group housing
- Different cage materials and ventilation methods
- Different cage bedding types (corn cob bedding, wood chips, etc.)
- Provision of enrichment materials (igloos, shepherd shacks, nestlets, etc.)
- Provision of running wheels, climbing walls, and other apparatuses for physical exercise
Numerous studies have demonstrated how such housing conditions can modify rodent behavior. For example, mice with environmental enrichment have been shown to eat and weigh more and to be calmer and easier to handle. Specific behavioral tests have also been performed on rodents housed in different conditions.
In one study, mice from standard and enriched housing conditions were studied in the open-field test, elevated plus maze, and barrier test. The enriched conditions included a wooden climbing frame and a plastic inset for use as a hiding place. In the barrier test, the latency to climb over the barrier was shorter in the mice with enriched housing. Other studies have confirmed that rodents with physical enrichment perform better in behavioral tests with a climbing component.
Studies of environmental enrichment on anxiety have produced varying results. The results may be strain-dependent, as van de Weerd et al. found that BALB/c mice provided with nesting material, a nestbox, and a tube in their home cage had reduced locomotion in the open-field test, whereas this outcome was not seen in C57BL/6 mice provided this same enrichment.
Conversely, another study showed that the effect on elevated plus maze activity was sex-dependent, where enriched males had increased locomotion in the elevated plus maze, and enriched females had reduced locomotion. Other studies have demonstrated that enrichment reduces anxiety-related behavior in mice[4, 7].
There has been considerable research into the effects of various cage ventilatory systems on rodent behavior. A recent study compared the effect of housing in open-top cages (OTC), motor free ventilated cages (MFVC) and individually ventilated cages (IVC) on exploratory and anxiety-like behavior in mice. Mice were tested in the open-field test and elevated plus maze, respectively. Mice housed in the MFVCs had increased exploratory and reduced anxiety-like behavior.
Other studies have shown that IVC housing increases social activity and anxiety, but does not affect locomotion or cognition[9, 10]. IVC housing may cause these behavioral changes by altering the levels of the neurotransmitters serotonin and dopamine.
These are just some examples of how variations in cage conditions can affect rodent behavior. Standardization of housing conditions is an important aspect of preclinical research, and careful consideration should be given to the habitat (and any changes thereto) of animals to be used in behavioral testing.
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- van de Weerd HA, Van Loo PL, Van Zutphen LF, Koolhaas JM, Baumans V. Nesting material as environmental enrichment has no adverse effects on behavior and physiology of laboratory mice. Physiol Behav. 1997 Nov;62(5):1019-28.
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- Polissidis A, Zelelak S, Nikita M, Alexakos P, Stasinopoulou M, Kakazanis ZI, Kostomitsopoulos N. Assessing the exploratory and anxiety-related behaviors of mice. Do different caging systems affect the outcome of behavioral tests? Physiol Behav. 2017 177:68-73.
- Logge W, Kingham J, Karl T. Behavioural consequences of IVC cages on male and female C57BL/6J mice. Neuroscience. 2013 237:285-93.
- Burman O, Buccarello L, Redaelli V, Cervo L. The effect of two different Individually Ventilated Cage systems on anxiety-related behaviour and welfare in two strains of laboratory mouse. Physiol Behav. 2014 124:92-9.
- Pasquarelli N, Voehringer P, Henke J, Ferger B. Effect of a change in housing conditions on body weight, behavior and brain neurotransmitters in male C57BL/6J mice. Behav Brain Res. 2017 Aug 30;333:35-42.