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

The night before the exertional heatstroke protocol, place the mouse in the environmental chamber at room temperature to acclimate to the chamber. Use the data acquisition system to collect continuous core temperature or Tc, averaged over 30-second intervals overnight. On the morning of the exertional heatstroke protocol, make sure the mouse is at or below the normal range of diurnal temperature of 36 to 37.5 degrees Celsius before increasing the chamber temperature to ensure that the mouse does not have a fever or has experienced undue stress during this period.

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 degrees Celsius and 40% to 50% relative humidity or the desired environmental temperature and humidity. Verify the chamber temperature and humidity with a calibrated temperature and humidity monitor.

Surround the chamber with a blackout curtain to keep light and disturbances minimal during the protocol. Monitor the mouse continuously during the protocol via remote IR illuminated cameras. Focus the second camera on the temperature and humidity monitor placed close to the running wheel. Make adjustments to the controller for the environmental chamber set-point to ensure accurate temperature readings near the animal.

Once the chamber has reached its target temperature as measured by the second camera on the temperature monitor, quickly open the chamber door and place the mouse in the forced running wheel. Initiate the forced running wheel protocol at a speed of 2.5 meters per minute and increase the speed by 0.3 meters per minute every 10 minutes until the mouse reaches a core temperature of 41 degrees Celsius.

Once the core temperature has been achieved, allow the speed to remain constant until symptom limitation occurs characterized by an apparent loss of consciousness, a backward fall or fainting, and the inability to continue running or holding on to the wheel. Confirm the 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. This endpoint is slightly above symptom limitation in essentially all mice.

To perform the rapid cooling protocol, stop the wheel once the mouse reaches symptom limitation and remove the mouse 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, which results in greater than 99% long-term survival.