THE EFFECTS OF A SERIES OF ω‐PHOSPHONIC α‐CARBOXYLIC AMINO ACIDS ON ELECTRICALLY EVOKED AND EXCITANT AMINO ACID‐INDUCED RESPONSES IN ISOLATED SPINAL CORD PREPARATIONS

Abstract

1 The depressant actions on evoked electrical activity and the excitant amino acid antagonist properties of a range of omega-phosphonic alpha-carboxylic amino acids have been investigated in the isolated spinal cord preparations of the frog or immature rat. 2 When tested on dorsal root-evoked ventral root potentials, members of the homologous series from 2- amino-5-phosphonovaleric acid to 2-amino-8-phosphonooctanoic acid showed depressant actions which correlated with the ability of the substances to antagonize selectivity motoneuronal depolarizations induced by N-methyl-D-aspartate. 3 2-Amino-5-phosphonovalerate was the most potent substance of the series giving an apparent KD of 1.4 microM for the antagonism of responses to N-methyl-D-aspartate. 4 A comparison of the (+)- and (-)-forms of 2-amino-5-phosphonovalerate indicated that the N-methyl-D-aspartate antagonist activity and the neuronal depressant action of this substance were both due mainly to the (-)-isomer. 5 The (-)- and (+)-forms of 2-amino-4-phosphonobutyrate had different actions. The (-)-forms of this substance had a relatively weak and non-selective antagonist action on depolarizations induced by N-methyl-D-aspartate, quisqualate and kainate and a similarly weak depressant effect when tested on evoked electrical activity. The (+)-form was more potent than he (-)-form in depressing electrically evoked activity but did not antagonize responses to amino acid excitants. At concentrations higher than those required to depress electrically evoked activity, the (+)-form produced depolarization. This action was blocked by 2-amino-5-phosphonovalerate.