An improved method for tail-flick testing with adjustment for tail-skin temperature.

The tail-skin temperature is an important factor in determining tail-flick latency to noxious radiant heat in rats and mice. A simple, non-invasive method for recording the tail-skin temperature during conventional tail-flick testing is described. The method is conveniently performed during conventional tail-flick testing. It does not require additional handling of the animals, and it is not stressful. The method utilizes a small-sized thermocouple which is brought in contact with the dorsal surface of the tail close to the area exposed to the radiant heat stimulus. A computer based system is used to record the temperature and control the tail-flick apparatus. Continuous monitoring of skin temperature showed that the temperature as measured 23 mm from the tip of the tail agreed well with skin temperature in the position where the beam was focused during tail-flick testing (13 mm from the tip). The skin temperature closer to the base of the tail (100 mm from the tip) showed considerably more deviation from the temperature 13 mm from the tip. Temperature measurements close to the heated area gave a higher degree of correlation between recorded temperature and tail-flick latencies than did temperature measurements closer to the base of the tail. These results provide further support for the contention that tail-skin temperature is an important factor when assessing nociception by means of the tail-flick test, and demonstrate that the temperature should be measured as close to the heated area as possible.