Topical application of capsaicin to mouse skin

Currently, our lab is working on the topical application of capsaicin to the mouse neck area, followed by an examination of allodynia in this region. We are encountering a challenge in ensuring the effective absorption of capsaicin by the skin while preventing inadvertent contact by the mouse forepaw during grooming.

Does anyone have experience with topical capsaicin application to mouse skin and could kindly provide some guidance on the process? For instance, are the mice subjected to anesthesia, or is any form of restraint employed? Additionally, I am curious to know whether the capsaicin solution needs to be rubbed for a specific duration until the skin fully absorbs it, and if so, for how long?

The paper I found on topical capsaicin on animals lacks details on how the capsaicin was applied topically. I have come across papers with human subjects where gelform or patches were used. However, mice cannot control themselves from grooming and touching the application region.

Any insights or advice you can share on these matters would be greatly appreciated.

Good question. I haven’t done this. Calling in some other experts
@thicunha @tberta @tonellor @liz @CandlerPaige

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Your best bet for all of your criteria is probably to inject the capsaicin s.c., that will get around the issues of penetration and getting it on the paws through grooming. We had a tough time with this issue using mustard oil on the hindpaw, the mice lick it, rub it, etc. If you really want to use topical I would think you would want to shave the area and/or Nair it, which can also break down the epidermal barrier and make the skin more sensitive to it. We have used OTC capsaicin ointment (0.1%) on human volunteers for med school demonstrations of secondary allodynia, which works well and is fun if you aren’t the subject, but as I’m sure you know it’s a big pain to use ointment on fur. If you are dealing with short time periods you could put them in a restraint tube to keep them from getting the capsaicin on their paws.