Further studies on glutamate antagonists in the central nervous system

Abstract

1. 1. Three diaminomonocarboxylic acids which reportedly antagonize the increase in cyclic 3′,5′-adenosine monophosphate in brain slices induced by l-glutamate were tested as glutamate antagonists on the toad ( Bufo marinus) spinal cord and on cerebral cortical neurones in the rat. 2. 2. l-2,4-diaminobutyric acid, dl-2,3-diaminopropionic acid and l-ornithine depressed dorsal root-evoked responses recorded from the dorsal and ventral roots of the amphibian spinal cord and depolarized dorsal root terminals. Associated with these effects there was a reduction in glutamate-evoked depolarization of dorsal root terminals and spinal motoneurones. 3. 3. The three diaminocarboxylic acids depressed the spontaneous, and the l-glutamate-, l-aspartate-and acetylcholine-evoked firing of cerebral cortical neurones. 4. 4. It is concluded that the diaminocarboxylic acids exhibit a similar, albeit less potent, type of action to the monoaminocarboxylic acids, γ-aminobutyric acid (GABA) and β-alanine. They are unlikely to be useful as glutamate antagonists in neuropharmacological experiments.