CONDITIONED ANTINOCICEPTION IN THE SPINALIZED RAT: THE ROLE OF NONASSOCIATIVE MECHANISMS. R.L. Joynes*, T.W. Prentice, and J.W. Grau. Dept. of Psychology, Texas A&M Univ., College Station, TX 77843.

Conditioned antinociception can be demonstrated in spinalized rats by pairing stimulation (10-s, 1-mA shock) to one hind leg (the conditioned stimulus, or CS+) with an intense (2-s, 3-mA) tailshock (the unconditioned stimulus, or US). In these same subjects, a second CS (the CS-) is presented alone. An hour after rats have experienced 30 presentations of the CS+ and CS-, they exhibit longer tail-flick latencies during the CS+. The present study explores whether a nonassociative mechanism, habituation, contributes to this effect.

Experiment 1 assessed whether nociceptive thresholds during a CS are affected by prior exposure to the CS alone. Twenty-four hrs after rats were spinalized at T2 (N=12), one CS (CS-habit) was presented alone 30 times (ITI=2min). Tail-flick latencies during CS-habit, as well as a novel CS (stimulation of the opposite hindleg), were tested either immediately after training or one hour later. At both test points, the novel CS induced a slight antinociception, while CS-habit did not. Experiment 2 showed that presenting a US during the preexposure phase enhanced the antinociception elicited by both CSs and eliminated the habituatio effect. Supported by MH48994 to J.W.G.

Published in Society for Neuroscience Abstracts, 20, 1994, 762.

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