Exertional Heat Stroke Mouse Model: A Protocol to Study Mechanisms Underlying Exertional Heat Stroke

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1. EHS Protocol

1. The night before the EHS protocol, place the mouse in the environmental chamber at room temperature (~25 °C, ≈30% relative humidity) to acclimate to the chamber.
2. Use a data acquisition system to collect continuous core temperature (Tc), averaged over 30 s intervals overnight.
3. On the morning of the EHS protocol, make sure the mouse is at or below a normal range of diurnal temperature before increasing the chamber temperature (i.e., 36–37.5 °C). This ensures the mouse does not have a fever and has not experienced undue stress during this period.
4. Once the mouse is stable and within a range of normal resting core temperature, remove the food and water and weigh the animal. Shut the chamber door and increase the chamber temperature to a target of 37.5 °C and 40%–50% relative humidity, or the desired environmental temperature and humidity. Verify the chamber temperature and humidity with a calibrated temperature and humidity monitor.
5. Surround the chamber with a black-out curtain to keep light and disturbances minimal during the protocol. Monitor the mouse continuously during the protocol via remote IR illuminated cameras. Focus a second camera on the temperature and humidity monitor, placed close to the running wheel. Make any adjustments to the controller for the environmental chamber set-point to ensure accurate temperature readings near the animal.
6. Once the chamber has reached its target temperature as measured by the second camera on the temperature monitor (this can take ~30 min), quickly open the chamber door and place the mouse in the forced running wheel.
7. Initiate the forced running wheel protocol at a speed of 2.5 m/min and increase the speed 0.3 m/min every 10 min until the mouse reaches a Tc of 41 °C. Once the mouse has reached this core temperature, allow the speed to remain constant until symptom limitation, characterized by an apparent loss of consciousness, a backward fall or fainting, and the inability to continue to run or hold on to the wheel. Confirm this time point when the mouse has three backward rotations on the wheel without signs of a physical response. Alternatively, identify a humane endpoint following local IACUC rules to determine when to stop the protocol (e.g., when Tc ~43 °C). This endpoint is slightly above symptom limitation in essentially all mice.
8. To perform the Rapid Cooling protocol (R), once the mouse reaches symptom limitation, stop the wheel, and remove it immediately from the forced running wheel. Weigh the mouse and place it back in its home cage to recover at room temperature. During this time, leave the chamber door open and return the incubator set point to room temperature to allow the chamber to cool rapidly. This procedure results in >99% long-term survival.