What I gathered from the paper is that these changes appear to be related to stress-induced analgesia. Luis’ approach seems like it would cause the least amount of stress. My thinking is that testing animals in the manner that they are housed (i.e., with cage mates) will be the least stressful. Alex’s point of testing females on the same rack may or may not introduce a variety of issues. However, this is just my overly simple way of getting at this issue.