Descending fibre-mediated release of endogenous glutamate and glycine from the perfused cat spinal cord in vivo.

The release of endogenous amino acids into the perfused central canal of the cat spinal cord in vivo was studied using a [3H]dansyl chloride assay procedure. Perfusion of 0.1 mM p-chloromercuriphenyl-sulphonate (pCMS), an uptake inhibitor, augmented the efflux of most amino acids studied. The large increases in glycine, glutamate and GABA efflux (9.9, 5.3 and 4.1-fold, respectively) suggest that the membrane fluxes of these amino acids were particularly high, a finding consistent with their putative neurotransmitter functions. Subsequent electrical stimulation of descending spinal tracts increased the efflux of glycine, glutamate, GABA and leucine (1.8, 2.2, 1.9 and 1.3-fold, respectively), although only the release of glycine and glutamate was clearly independent of the concomitant rise in blood pressure. The evoked amino acid release, which was accompanied by a substantial ventral root discharge, was not observed in the absence of pCMS, nor in the presence of a low concentration (0.01 mM) of this compound. These results have been discussed in relation to the putative neurotransmitter roles for amine acids in the spinal cord.