OPERANT LEARNING AT THE LEVEL OF THE SPINAL CORD IS BLOCKED BY THE NMDA ANTAGONIST APV. R. L. Joynes*, K. R. Janjua, & J. W. Grau. 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. Group) are given shock to one hind leg whenever the leg is extended. Yoked subjects experience the same amount of shock irrespective of leg position. When care is taken to equate flexion force prior to training, subjects in the Exp. Group learn to maintain a flexion response (Barstow et al., Neurosci. Abs., 19, pg. 1001). Yoked rats do not exhibit this learning. Subsequent studies have shown that learning in the Exp. Group is disrupted by: 1) intrathecal lidocaine; and 2) delaying shock onset by as little as 100 msec.

The present experiment looks at whether LTP contributes to this learning. Rats (N=16) received transections at T2 and had catheters (PE-10) lowered to the lumbrosacral enlargement. The next day, subjects received either 20 mM of APV dissolved in 5 ul of saline or the vehicle alone followed by 10 ul of saline. Five min later, shock electrodes were attached to one hind leg and flexion force was set to 0.6 N. All subjects then received 30 min of training. At the start of training, there were no differences in shock reactivity as measured by: flexion force, response duration, or rate of responding. This suggests that the drug did not impair motor functioning. Vehicle treated rats soon learned the operant response, exhibiting a progressive increase in response duration. As a consequence of this learning, these subjects exhibited fewer responses and received less shock. APV-treated rats never acquired the operant response, but instead responded in the same mechanical fashion throughout training. Supported by MH48994 to J.W.G.

Published in Society for Neuroscience Abstracts, 21, 1995, 415.

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