Tamoxifen Preparation and Treatment in Mice for Genetic Recombinations

Rationale: Tamoxifen is used to kick-start genetic recombinations in genetically engineered mouse models (GEMMs) and to activate genes through a cascade of events.

Here is a detailed step-by-step guideline on how to prepare and inject Tamoxifen into mice. Please ensure you are properly trained and authorized to handle laboratory mice before proceeding. Always follow animal welfare laws and your facility’s study protocol.

Tamoxifen Preparation

1. Calculate the appropriate concentration of tamoxifen for your experiment; the dose usually falls in the range of 40–100 mg/kg/day, but adjust according to the specifics of your study.

2. Tamoxifen is soluble in ethanol at 50 mg/mL. To create this stock solution, dissolve the required amount of tamoxifen in 100% ethanol.

3. After completely dissolved, dilute the stock solution with corn or sunflower oil to reach the intended final concentration.

4. Store it at -20 degrees Celsius for long-term storage.

Intraperitoneal Injection

1. Allow the tamoxifen solution to reach room temperature before the injection or warm at 37⁰C (recommended) before use to match the internal body temperature of mice for improved function.

2. Load a sterile insulin syringe (1 mL) with the appropriate volume to achieve the desired dosage.

3. For intraperitoneal (IP) injection, the mouse is restrained manually or using a suitable restrainer. Applying gentle pressure on both sides of the lower part of the abdomen makes the injection easier and more accurate.

4. Hold the syringe and needle like a dart and puncture the skin and peritoneum on the lower right side of the abdomen, avoiding vital organs.

5. Once inserted, depress the syringe slowly to inject the solution. Do not force it if you meet resistance.

6. Properly manage the needle after injection to prevent injuries and infections.

7. Monitor mice after the injection and record any changes in their behavior, weight, or appearance.

Be aware that tamoxifen administration can induce some side effects in mice, such as weight loss or pyometra in females; monitor them regularly.

Usage Example:

At 6 weeks of age, mice were intraperitoneally injected with 75 mg per kg (body weight) of tamoxifen (Sigma-Aldrich, T5648-5G) dissolved in corn oil once a day for 5 consecutive days (Yin et al., 2023, Nat. Immunol.).

This procedure must be done accurately and carefully. Future adjustments must be made based on the observed results. Always follow your Institutional Animal Care and Use Committee regulations and guidelines. If any issues occur, consult with your attending veterinarian.

Remember, this guide does not replace professional training, and an experienced investigator or veterinarian should supervise all steps until proficiency is achieved.