Tamoxifen - injection/ recombination timeframe

Hello all, I am working with tamoxifen-inducible FosCreERT2 mice as my pain hypersensitivity model. I have already given the dose of Tamoxifen which is 20mg/ml per mice i.p. for 5 consecutive days. I am wondering if anyone knows as to how many days/weeks will it take for the recombination to occur - in order to start the behavioral analyses? I have read several papers- many mentioned - as 1 week to 1 month. Would be helpful if I get some suggestions. Thank you.

@SamineniV - Any thoughts?

I think that it depends on the mouse lines and type of cell you are targeting, but we generally wait 1 week after the first delivery of tamoxifen. To note, we use the same concentration of tamoxifen (20 mg/ml) but delivered by gavage and only for consecutive 3 days. Here our procedure (successfully tested for DRG neurons and microglia):

  1. Dissolve tamoxifen in corn oil at a concentration of 20 mg/ml. Quickly vortex and then place the eppendorf tube to a rotating incubator for 1 hr at 37oC. Tamoxifen is light sensitive, and should be made and stored in a light‐ blocking vessel (amber, or foil wrapped). After tamoxifen is in solution, store at 4°C for the duration of injections.
  2. For adult mice, a oral delivery of 200µl tamoxifen/corn oil solution (above) is effective for inducing recombination.
  3. Administer tamoxifen via gavage once every 24 hours for a total of 3 consecutive days . As a safeguard, sanitize injection site with 70% ethanol prior to injection.
  4. Following the initial delivery, mice should be kept in the chemical room until the end of the experiment (Don’t return to their normal animal room). Generally recombination should take place in 7 days post the initial delivery .
  5. Throughout the course of tamoxifen delivery and any post‐delivery wait period, mice should be closely monitored for any adverse reactions to the treatment.
  • Tamoxifen (Sigma‐Aldrich, cat. no. T5648)
  • Corn Oil (Sigma-Aldrich, cat. no. C8267)
  • Ethanol (for disinfection)
  • 1 ml Syringe (BD)
  • Mice gavage needle
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@Tberta - Thank you for the reply. I am following the protocol which the Jackson’s Laboratory have mentioned on their website. Also I am giving the dose for 5 consecutive days (100 µl tamoxifen/corn oil solution) per adult mice.
but yes thank you for the protocol mentioned.

@Nam - Welcome. To note, we got this protocol from the Dong lab at Hopkins and gavage is used because of the viscosity of the Tamoxifen solution.

Thank you for mentioning that. I know they (Dong’s Lab) really do great work in this field.