433 © 2008, Japanese Society for Alternatives to Animal Experiments Alternative application route in the LLNA provides crucial environmental enrichment and broadens the usability of vehicles

The Local Lymph Node Assay (LLNA), OECD Guideline 429, is the preferred animal model for assessment of skin sensitizing chemicals. A disadvantage of the OECD Guideline is that single housing of animals is required, which causes distress and discomfort to the mice. The aim of the present work was therefore to refine housing and treatment conditions of animals in the LLNA and furthermore improve the application of water-soluble substances. Instead of applying the test material to the dorsum of the ears, we applied the test material into the ear canal. Otherwise, the standard OECD protocol with groups of CBA/Ca mice (n=5) was used. Application into the ears has several advantages: The animals can be housed in groups; the dosing procedure can be performed by one person only; the procedure itself is gentle as the mouse does not have to be restrained. Moreover, if water is used as a vehicle it will not run off when dosed into the ears. Conclusion: Results obtained from the application on the ear dorsum compare favorably to direct application into the ear canal. Furthermore, the alternative dosing procedure provides significant animal welfare benefits compared to the standard procedure