In search of a conditioned place preference test for mice to assess the severity of experimental procedures

Summary To compare the severity of experimental procedures and behavioural tests from an animal’s perspective, novel methods are required. Theoretically, one feasible approach could be the use of a conditioned place preference test (CPP). This test employs the preference for a certain area in a test apparatus being associated with an experimental treatment. Traditionally, the CPP is used to investigate, for example, the effects of drugs. Instead we aimed to develop a protocol that would enable us to compare the effects of different experimental procedures conducted with mice. Nine experiments with C57BL/6J mice were performed, varying the setup, the procedure duration, the stimuli as well as the presentation order. None of the tested protocols resulted in a distinct preference. Moreover, even simple protocols using food reward as a treatment failed to result in a conditioned place preference. In summary, none of the protocols was sufficient to form a reliable association between conditioned and unconditioned stimulus. We have scrutinized the experimental setup in detail, and we cannot present a solution yet. However, hopefully, our findings will help to create a working CPP to compare the severity of different experimental procedures for mice.