A SUPRA-THRESHOLD TAIL-FLICK TRIAL INDUCES HYPERALGESIA IN PENTOBARBITAL ANESTHETIZED RATS BUT NOT IN AWAKE RATS. C.F. Kallina*, T.E. King, & J.W. Grau, Dept. of Psychol., Texas A&M Univ., College Station, TX 77843.

The tail-flick test is frequently used to measure pain reactivity in rats. In an effort to reduce variability, and to monitor the time course of effects, researchers often repeatedly test the same subjects. This poses little problem as long as the test per se has no impact on pain reactivity. However, Baldwin et al. (Neurosci. Abstracts, 18, 292) recently showed that a single supra-threshold exposure to radiant heat can induce hyperalgesia in pentobarbital anesthetized rats. Experiment 1 was designed to replicate this effect and evaluate whether it was due to a change in tail temperature. Pentobarbital anesthetized (40 mg/kg) rats were placed in restraining tubes and administered 5 tail-flick tests at 1 m intervals (mean=4.7). Half the subjects (n=10) then received a supra-threshold exposure by manually holding their tail under the heat source for 6 s. Ten more tail-flick tests were given at 1 m intervals. Tail temperature was also monitored. We found a supra-threshold exposure induced hyperalgesia and that this effect could not be accounted for by a change in tail temperature. Experiment 2 assessed whether a similar effect could be observed in spinally transected (T2) rats. No change in tail-flick latencies were observed suggesting the hyperalgesic effect is supraspinally mediated. Experiment 3 tested whether a supra-threshold exposure to radiant heat affects pain reactivity in intact/awake rats. We found it had no effect on pain reactivity in intact subjects.

Published in Society for Neuroscience Abstracts, 19, 1993, 966.

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