INESCAPABLE SHOCK DISRUPTS SPINAL LEARNING: EVIDENCE FOR SPINAL MEDIATION AND NALTREXONE REVERSIBILITY. J.W. Grau*, R.L. Joynes & H. Penland. Dept. of Psychology, Texas A&M University, College Station, TX 77843.
Prior work suggests that spinal neurons can support a simple form of operant learning. In a typical experiment, spinal rats (Exp.) are given shock to one hind leg whenever the leg is extended. Yoked subjects experience the same amount of shock irrespective of leg position. Rats in the Exp., but not the Yoked, group learn to maintain a flexion response. In a subsequent test phase, all subjects receive controllable shock. Rats in the Exp. group show facilitated learning (positive transfer), while subjects that previously experienced inescapable shock fail to learn (a learned helplessness-like interference effect).
Experiment 1 examines whether operant training of one hind leg affects learning when shock is applied to the contralateral leg. Spinal rats (N=36) received 30 min of controllable shock, uncontrollable shock, or no shock. Half the subjects then received 30 min of controllable shock applied to the ipsilateral leg, while the other half were trained using the contralateral leg. Prior exposure to inescapable shock disrupted learning irrespective of whether the ipsi- or contralateral leg was tested. An analysis of the data collected during the first 3 min of testing indicated that prior exposure to controllable shock facilitated learning when shock was applied to either hind leg. These results rule out a variety of peripheral explanations of the transfer effects and suggest that both depend on spinal neurons.
Experiment 2 looked at whether inescapable shock undermines learning by inducing an opioid mediated antinociception. Spinal rats (N=36) were given saline or the opioid antagonist naltrexone (14 mg/kg) followed by 30 min of escapable, inescapable or no shock. All subjects then received 30 min of testing with controllable shock applied to the same leg. Exposure to inescapable shock produced a small, but significant, antinociception. Naltrexone attenuated the antinociception observed after training and eliminated the interference effect during testing. Supported by MH48994 to J.W.G.
Published in Society for Neuroscience Abstracts, 22, 1996,1840.