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

1. The responses to glutamate and amino acid antagonists of cells in the cuneate nucleus of anaesthetized rats have been examined.2. 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.3. Spike activity of cuneate cells was evoked by stimulating the cerebral cortex. Spikeswhich 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 neurones.4. HA-966 reversibly blocked the evoked activity in twenty-eight (70%) of forty units in which monosynaptically evoked spikes were induced.5. The results raise the possibility that the neurotransmitter released by neurones of the pyramidal tract may be an excitatory amino acid.