Instrumental learning within the spinal cord: VI. The NMDA receptor antagonist, AP5, disrupts the acquisition and maintenance of an acquired flexion response.

Prior studies have shown that circuits within the spinal cord can support a simple form of instrumental learning. Spinally transected rats are given shock to one hind leg whenever the leg is extended. This response-outcome contingency causes an increase in flexion duration. The present experiments examine whether the NMDA receptor is involved in the acquisition and maintenance of this instrumental response. Experiment 1 showed that the NMDA receptor antagonist 2-amino-5-phosphonovalerate acid (AP5) reduces instrumental responding in a dose-dependent fashion. Experiment 2 showed that AP5 given after training eliminates the increase in flexion duration. The results implicate the NMDA receptor in the acquisition and maintenance of spinally mediated instrumental behavior.