A system to measure thermal nociception

Hyperalgesia is commonly demonstrated by measuring the difference in latency to thermal nociception between a control and injured condition. Historically these tests have been conducted using either a hot plate or radiant heat source to stimulate thermal receptors in the foot. The design of a simple and inexpensive circuit to measure thermal nociception based on a method originally introduced by Hargreaves et al. (1988) is described. The design uses a movable, high-intensity light source to heat either the right or left footpad of the test animal. The advantage of this method is that it permits each animal to serve as its own control since the experimental and control footpads can be tested independently. The design possesses greater sensitivity than mechanical hyperalgesia test procedures and provides an automated endpoint that electronically records the latency to removal of the foot from the heat source. Additional features of this design which reduce variability include a constant temperature floor to reduce the effect of altered footpad temperature that may be caused by autonomic dysfunction in the experimental limb and a method of reproducibly locating the heat source prior to testing. The response to a unilateral lesion is demonstrated with this device.