The effect of D-alpha-aminoadipate on excitatory amino acid responses recorded intracellularly from motoneurones of the frog spinal cord.

The excitatory responses to amino acids were recorded intracellularly from motoneurones in the isolated frog spinal cord and the effect of the antagonist D-alpha-aminoadipate examined. An unusual profile of antagonism was obtained in that with 50-100 microM D-alpha-aminoadipate the depolarization to quisqualate was unaffected (or slightly potentiated) while those to L-glutamate, L-aspartate and N-methyl-D-aspartate were all considerably attenuated. D-alpha-aminoadipate did not influence passive membrane properties although a small hyperpolarization was sometimes evident. Dorsal root evoked excitations of motoneurones, particularly those using low strength stimulation, were also susceptible to antagonism by D-alpha-aminoadipate. These data suggest a separate neuroeffector/receptor mechanism for quisqualate compared to L-glutamate, L-aspartate and N-methyl-D-aspartate.