N-methyl-D-aspartate-sensitive receptors expressed in Xemopus oocytes by guinea-pig cerebellar messenger RNA are not potentiated by glycine

The properties of the excitatory postsynaptic potential evoked by focal stimulation and of the responses to excitatory amino acids were examined by intracellular recording from sympathetic preganglionic neurons in upper thoracic spinal cord slices of the adult cat. Single stimuli to the region dorsal to the intermedio-lateral nucleus evoked short-latency, presumably monosynaptic, excitatory postsynaptic potentials. The reversal potential of this response was −2.2 mV and became more negative when external Na+ or K+ concentration was decreased. The excitatory postsynaptic potential was depressed by the non-selective excitatory amino acid receptor antagonistcis-2,3-piperidine dicarboxylic acid and enhanced by a glutamate uptake inhibitor. Thenon-N-methyl-d-aspartate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione abolished the excitatory postsynaptic potential in 72% of neurons. In the remaining neurons, this antagonist only depressed the potential and unmasked a slower component which was abolished by theN-methyl-d-aspartate receptor antagonistd,l-2-amino-5-phosphonovaleric acid. In the presence of tetrodotoxin all neurons tested were depolarized by glutamate or aspartate, as well as by the selective agonists quisqualate, alpha-amino-3-hydroxy-5-methylisoxazole propionic acid, kainate andN-methyl-d-aspartate. The glutamate-evoked depolarization reversed at a membrane potential of −2.0 mV and at a more negative value when external Na+ or K+ concentration was decreased. The response to alpha-amino-3-hydroxy-5-methylisoxazole propionic acid was abolished by 6-cyano-7-nitro-quinoxaline-2,3-dione in all neurons tested and that to kainate in only one-third of the cells. In the remainder the response to kainate was only slightly depressed by this antagonist. The responses to glutamate and aspartate were only slightly depressed by the combined action of the various amino acid receptor antagonists used. The responses toN-methyl-d-aspartate were abolished byd,l-2-amino-5-phosphonovaleric acid. The punched-out region of the intermedio-lateral nucleus, maintainedin vitro, released glutamate and aspartate in the absence of stimulation. Field stimulation (20 Hz) enhanced release by between 40 and 100%. The increase was prevented by superfusion with calcium-free Krebs.It is concluded that excitatory amino acids, acting on bothN-methyl-d-aspartate andnon-N-methyl-d-aspartate receptors, but mainly on the latter, are likely mediators of the monosynaptic excitatory postsynaptic potential evoked in sympathetic preganglionic neurons by the stimulated region. The efflux data suggest that glutamate and aspartate are among the mediators.