Blockade by amino acid antagonists of neuronal excitation mediated by the pyramidal tract.

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Abstract
The responses to glutamate and amino acid antagonists of cells in the cuneate nucleus of anesthetized rats were examined. 1-hydroxy-3-amino-pyrrolidone-2 (HA-966) and glutamic acid diethylester applied by micro-iontophoresis reduced glutamate excitation of the neurons. HA-966 was effective on more cells than glutamic acid diethylester and was more potent. HA-966 did not affect excitatory responses to acetylcholine. Spike activity of cuneate cells was evoked by stimulating the cerebral cortex. Spikes which could be attributed to monosynaptic activation of the cells were studied. The pyramidal tract is the only corticofugal pathway known to be capable of short latency activation of dorsal column nucleus neurons. HA-966 reversibly blocked the evoked activity in 28 (70%) of 40 units in which monosynaptically evoked spikes were induced. The neurotransmitter released by neurons of the pyramidal tract may be an excitatory amino acid.