Mechanical threshold testing after CFA in hindpaw -> Edema in mid hindpaw makes the mice less sensitive?

Hi all,

So I’m working with the CFA inflammatory model in the hindpaw. I inject 20 ul of CFA subcutaneously. By 24 hours, the hindpaw is very edematous and much larger than the contralateral. I’ve noticed though that when I test von Frey on the mid hindpaw, where it is most swollen, the mice are actually pretty insensitive, which is not what I expect. They seem most sensitive very anteriorly, just behind the toes.

Have you noticed this?
@ram_kandasamy @LegakisL @tberta @jmogil @fmoehring @thicunha

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Where do you usually test the animals?
We usually try to target the areas between the pads closer to the toes, so our animals are very sensitized and stay that way for quite a few weeks.

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The pads closer to the toes is indeed the right region to test. Alternatively you can also inject CFA dorsally and test in the middle of the paw.

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You are totally right. We also observed insensitivity with 20 microL of CFA in mechanical (von
frey filament) and thermal (Hargreaves). We have reduced the amount of CFA (10 microL) and
the results are better for mechanical but unfortunately, thermal we never had
good results.

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Thanks all. @thicunha I’m glad to hear I’m not seeing totally crazy things. These are the small details that make all the difference. Precisely the reason I created Pain Researcher. I’ll try 10 ul in the future.

Thank @tberta for the confirmation

@achamess I forgot to say that in earlier time points (2-7 h) von frey filament and Hargreaves work very well, but in latter times 24 h, we also detected the insensitivity with 20 microL.

I have seen similar phenomena. I tried to avoid the swollen area, tested on the area posterior to the footpads. Also, is some mice, they tend to lift the paw with the filament.

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Thanks for letting us know. Yeah, I do the anterior toe area, but even that can be ambiguous. I will likely use 10 ul about @thicunha suggested and see what happens.

I want to revisit this. I did another CFA experiment with 10 ul instead of 20 ul. I injected as posteriorly as possible to give sufficient area in the anterior paw.

A colleague performed and scored the behavior and I analyzed. At 1,3 and 9 days, we saw only a mild difference vehicle (PBS) and CFA, despite the CFA paw being quite enlarged.

I’ve had much better results with Zymosan. The mice get very sensitive quickly and it’s evident.

From some of the earlier responses in this thread, we’re not the only ones who’ve noticed this. Perhaps we’re doing something wrong…

Any insights would be greatly appreciated.

@thicunha @tberta @liz @jmogil @runDRG @ShanTan