INSTRUMENTAL LEARNING IN SPINALIZED RATS: THE GABA ANTAGONIST BICUCULLINE PREVENTS THE BEHAVIORAL DEFICIT OBESERVED AFTER NONCONTINGENT SHOCK. A. R. Ferguson* , E. D. Crown, S. Dhruv, S. N. Washburn and J. W. Grau, Dept. of Psychology, Texas A&M Univ., College Station, TX 77843.

We have previously shown that the spinal cord can support a simple form of instrumental learning. In a typical experiment, rats are transected at the second thoracic vertebra and are tested 24 hours later. During testing subjects receive shock to one hindleg when that leg is extended. They quickly learn to maintain the leg in a flexed position, decreasing net shock exposure. Interestingly, rats that have previously received shock independent of leg position (noncontingent shock) fail to learn. This behavioral deficit lasts 1-2 days and can be induced by just 6 minutes of noncontingent shock to the leg or tail. The expression of the deficit seems to depend on a kappa opioid, for a kappa antagonist blocks the expression (but not the induction) of the deficit. Experiment 1 showed noncontingent legshock induces a local allodynia that increases reactivity to mechanical (von Frey hair) stimulation. The allodynia observed in other preparations has been linked to an increase in GABAergic inhibition and enhanced expression of dynorphin A. Given this, we hypothesized that noncontingent shock may induce a behavioral deficit by enhancing GABA-mediated inhibition. If so, pretreatment with a GABA antagonist should eliminate the deficit. Intrathecal bicuculline was given prior to noncontingent tailshock and subjects were tested 30 minutes later (Exp. 2). The GABA antagonist eliminated the behavioral deficit. To determine whether the drug could block the induction of the deficit subjects were pretreated with intrathecal bicuculline or its vehicle prior to noncontingent tailshock and were tested 24 hours later (Exp. 3). Vehicle treated rats failed to learn. Pretreatment with bicuculline blocked the induction of the behavioral deficit. Supported by MH60157 to J.W.G.

Published in Society for Neuroscience Abstracts, 26, 2000, 2207.

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