The importance of tail temperature monitoring during tail-flick test in evaluating the antinociceptive action of volatile anesthetics.

Abstract

Tail-flick (TF) latency can be influenced by tail-skin temperature (TT), and treatments that raise TT can mimic hyperalgesia on a TF test. As volatile anesthetics can raise TT via heat redistribution, their antinociceptive action can be hidden or obscured in a TF test. We tested the hypothesis that TT monitoring improves the efficiency of TF tests in evaluating the antinociceptive action of volatile anesthetics. The relationship between TT and TF latency was first explored under varied TTs in 12 rats. Then, TT and TF latency were measured before and during isoflurane exposure (1.2%). In the low temperature group (n=6), rats were prewarmed mildly to increase TT during isoflurane exposure. In the high temperature group (n=6), rats were prewarmed enough to prevent a TT increase during isoflurane exposure. There was a highly significant correlation between TT and TF latency, that is, TF latency decreased as TT increased. In the low temperature group, there was a significant increase in TT during isoflurane exposure, while an increase in TF latency did not reach statistical significance. Tail-flick latency corrected by a change in TT showed a significant increase. In the high temperature group, TF latency increased significantly during isoflurane exposure without an increase in TT. Isoflurane inhalation can induce an increase in TT, which can obscure its antinociceptive action as evaluated by a TF test. Monitoring TT during a TF test is important to efficiently evaluate the antinociceptive action of volatile anesthetics.