Battery-Powered Homeothermic Warming Pad for Maintaining Core Temperature in Mice and Rats

Anesthesia decreases core body temperature and this seriously compromises the physiological status of an experimental animal. Importantly, hypothermia alters many aspects of neural function. When recording nervous system activity in anesthetized animals, the core temperature of the animal must be stabilized. Although commercial heating pads for small animals are readily available, they typically are expensive, somewhat bulky, and require power cords and a 120/240V source. Consequently, transporting an anesthetized animal from one location (e.g., surgical suite) to another (e.g., imaging rig) involves moving power cords. Moreover, commercial devices are not always compatible with custom stereotaxic frames, microscope stages, or holding boxes. This report describes a low-cost, battery-powered, temperature-controlled warming pad for mice and rats and documents its validity and utility. The device monitors an animal's core temperature continuously and automatically adjusts the heating pad to maintain normothermia. It can be constructed in under 30 min, the components are readily available, and the cost is less than $100. The device is portable, making it convenient for researchers who conduct procedures such as surgical preparations in one location and transport the anesthetized animal to another location for experimental recordings. The device can keep an anesthetized mouse normothermic ±0.7° for over 6 h without supplemental warmth (e.g., heat lamp), despite >15° differential between ambient room temperature and core body temperature. This report demonstrates how the warming pad can be used for in vivo imaging of neuronal activity for a prolonged period in mice.