Cuprizone in mice
Animals are used to study demyelinating diseases of the nervous system, in which the myelin sheath that insulates neurons (nerve cells) is damaged. These include multiple sclerosis, Charcot-Marie-Tooth disease and central nervous system neuropathies. In a commonly used model, mice are fed cuprizone, which causes neurons to degenerate throughout the nervous system including the brain. Potential drugs and therapies can then be evaluated for the disease under study.
Six weeks of 0.2 per cent cuprizone in the diet causes a significant level of reversible demyelination in mice, which becomes irreversible if exposure to cuprizone is continuous for up to 12 weeks. Mice treated with cuprizone invariably exhibit spontaneous seizures (fits) and mortality can be up to 50 per cent in males. Treatment with cuprizone can therefore be severe.
A pharmaceutical establishment wanted to refine the use of cuprizone and, after evaluating the literature, they set up this protocol:
- Female mice weighing at least 25g were used - according to the literature, female mice are less susceptible to cuprizone
- 0.2 per cent cuprizone was incorporated into chow pellets, which mice prefer to powdered diet and find easier to handle
- Animals were housed in a 'quiet' area of the animal facilities with low traffic
- The number of interventions was reduced by combining various activities within a single handling session, e.g. by weighing and checking the animals during cage clean
- MRI techniques were used to assess demyelination more accurately and refine humane endpoints. Scanning sessions lasted 15 minutes, under isoflurane anaesthesia
As a result, the actual severity was mild for all animals and the animal model was robust. MRI was also used to implement reduction, as longitudinal data was obtained from a single animal.