A Preclinical Model of Exertional Heat Stroke in Mice

Summary

The protocol describes the development of a standardized, repeatable, preclinical model of exertional heat stroke (EHS) in mice free from adverse external stimuli such as electric shock. The model provides a platform for mechanistic, preventative, and therapeutic studies.

Abstract

Heat stroke is the most severe manifestation of heat-related illnesses. Classic heat stroke (CHS), also known as passive heat stroke, occurs at rest, whereas exertional heat stroke (EHS) occurs during physical activity. EHS differs from CHS in etiology, clinical presentation, and sequelae of multi-organ dysfunction. Until recently, only models of CHS have been well established. This protocol aims to provide guidelines for a refined preclinical mouse model of EHS that is free from major limiting factors such as the use of anesthesia, restraint, rectal probes, or electric shock. Male and female C57Bl/6 mice, instrumented with core temperature (Tc) telemetric probes were utilized in this model. For familiarization with the running mode, mice undergo 3 weeks of training using both voluntary and forced running wheels. Thereafter, mice run on a forced wheel inside a climatic chamber set at 37.5 °C and 40%-50% relative humidity (RH) until displaying symptom limitation (e.g., loss of consciousness) at Tc of 42.1-42.5 °C, although suitable results can be obtained at chamber temperatures between 34.5-39.5 °C and humidity between 30%-90%. Depending on the desired severity, mice are removed from the chamber immediately for recovery in ambient temperature or remain in the heated chamber for a longer duration, inducing a more severe exposure and a higher incidence of mortality. Results are compared with sham-matched exercise controls (EXC) and/or naïve controls (NC). The model mirrors many of the pathophysiological outcomes observed in human EHS, including loss of consciousness, severe hyperthermia, multi-organ damage as well as inflammatory cytokine release, and acute phase responses of the immune system. This model is ideal for hypothesis-driven research to test preventative and therapeutic strategies that may delay the onset of EHS or reduce the multi-organ damage that characterizes this manifestation.

Introduction

Heat stroke is characterized by central nervous system dysfunction and subsequent organ damage in hyperthermic subjects¹. There are two manifestations of heatstroke. Classic heat stroke (CHS) affects mostly elderly populations during heat waves or children left in sun-exposed vehicles during hot summer days¹. Exertional heat stroke (EHS) occurs when there is an inability to thermoregulate adequately during physical exertion, typically, but not always, under high ambient temperatures resulting in neurological symptoms, hyperthermia, and subsequent multi-organ dysfunction and damage². EHS occurs in ....

Protocol

All procedures have been reviewed and approved by the University of Florida IACUC. C57BL/6J male or female mice, ~4 months old, weighing within a range of 27-34 g and 20-25 g, respectively, are used for the study.

1. Surgical implantation of the telemetric temperature monitoring system

1. Upon arrival from the vendor, allow the animals to rest in the vivarium for at least 1 week prior to surgery to minimize the stress of transportation.
2. Group house the mice (maximum of 5 per.......

Discussion

This technical review aims to provide guidelines for the performance of a preclinical model of EHS in mice. Detailed steps and materials required for the execution of a reproducible EHS episode of variable severities are provided. Importantly, the model largely mimics the signs, symptoms, and multi-organ dysfunction observed in human EHS victims^11,19. Furthermore, this model allows for the examination of the mechanism underlying short- and long-term EHS recovery<.......

Materials

Name	Company	Catalog Number	Comments
1080P HD 4 Security Cameras 4CH Home Video Security Camera System w/ 1TB HDD 2MP Night View Cameras CCTV Surveillance Kit	LaView
5-0 Coated Vicryl Violet Braided	Ethicon
5-0 Ethilon Nylon suture Black Monofilament	Ethicon
Adhesive Surgical Drape with Povidone 12x18	Jorgensen Labset al.
BK Precision Multi-Range Programmable DC Power Supplies Model 9201	BK Precision
DR Instruments Medical Student Comprehensive Anatomy Dissection Kit	DR Instruments
Energizer Power Supply	Starr Life Sciences
G2 Emitteret al.	Starr Life Sciences
Layfayette Motorized Wheel Model #80840B	Layfayette
Patterson Veterinary Isoflurane	Patterson Veterinary
Platform receiveret al.	Starr Life Sciences
Scientific Environmental Chamber Model 3911	ThermoForma
Training Wheels	Columbus Inst.