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

To compare the severity of experimental procedures and behavioural tests from an animal’s perspective novel methods are needed. In theory, one feasible approach could be the use of a conditioned place preference test (CPP). In this test the preference for a certain area in a test apparatus is associated with an experimental treatment. Traditionally, the CPP is used to investigate, for example, the effects of drugs. Here, we wanted to develop a protocol, which instead 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 neutral to be conditioned stimuli (NS → CS; visual and/or textual), and the unconditioned stimuli (US; fixation, food reward, or weighing) as well as the presentation order (NS before, after, or parallel to US). Unfortunately, none of the tested protocol resulted in a distinct preference. Moreover, even simple protocols using food reward as a treatment failed to result in a conditioned place preference. Overall, none of the protocols was sufficient to form a reliable association between NS and US. 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. ### Competing Interest Statement The authors have declared no competing interest.