Effect of 2-amino-5-phosphopentanoic acid (AP5), a glutamate NMDA receptor blocker, on neuron activity in the cat motor cortex during performance of a paw placement conditioned reflex.

Two types of stimulus-associated response were recorded in the contralateral motor cortex during performance of a condition reflex consisting of placing the forepaw on a support in response to a short electrical stimulus (4 msec, 500 Hz) applied to the contralateral parietal cortex (field 5). Primary short-latency responses (peak latent period about 10 msec, duration 30-50 msec) showed little sensitivity to the application of AP5, a blocker of glutamate NMDA receptors; secondary long-latency responses (peak latent period 65 msec, duration 150-200 msec) were inhibited in 44% of cases. Excitatory neuron responses associated with movement were inhibited by AP5 in 18% of cases. Increases in the latent period of the movement itself were seen in 19% of cases. AP5 decreased background activity in 46% of background-active neurons. The number of cases in which individual components of the response and neuron background activity were increased and latent periods of movement were decreased after application of AP5 was no more than expected from a random spread of data.