Do you test male and female mice/rats at the same time in the same place, or separate over time?

When doing nociceptive behavioral assays, for example the von Frey assay or formalin-test, do you test the male and female animals at the same time in the same apparatus, or do you separate the testing of the different sexes so that male and females aren’t in the same space at the same time? I am using both male and female mice now, rather than just all males, as I used to do, since sexual dimorphism in pain phenotypes is increasingly appreciated, among other reasons.

But I’m wondering whether I should do my testing of both sexes simultaneously (both sexes on the testing apparatus at the same time), or staggered in time (so that only one sex is on the apparatus at a time). My concern is potential male-female influence (via odors or sounds). What do you think? Potential concerns are that the close proximity of the animals could influence their behavior, through sounds or smells, as is suggested from this intriguing paper from the Mogil group.

Taking into account that animals are housed together in separate cages and assuming you have availability of two apparatus you could do the testing of both sexes in the same room at the same time in two different apparatus. As long as you maintain your acclimation period about 30 min to 1 hour all of the measurements should be ok.

Thanks for the response. So for the von frey assay, for example, do you think it’s important to have the mice separated on different racks, or would you be comfortable putting male and female mice in different compartments on the same rack. So they’re separated by their containers, but they’re still close to one another.

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.

I would rather use different racks as they are used to smell each other in the same room but not necessarily next to each other. This as Ram points allows me to test the whole cage together and might be closer to their housing conditions. In the end I believe the most important component is acclimation.

Bump - 2020-03-10
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I always separate males and females for testing

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Great discussion to this thread on Twitter as well

It’s not as cut and dried as I thought it might be. Seems like some significant variance here, although majority sentiment is keep them separate.