STIZOLOBIC ACID ON FROG SPINAL-CORD - POSSIBLE SPECIES-DEPENDENT ACTIVATION OF EXCITATORY AMINO-ACID RECEPTORS

1. We examined the effects of stizolobic acid, an amino acid isolated from a plant, Stizolobium hassjoo, on the binding of [H-3]glutamic acid and [H-3]kainic acid to synaptosomes from frog spinal cords and on the depolarization at the ventral roots of frog spinal cords. 2. Stizolobic acid inhibited the binding of [H-3]kainic acid more potently than that of [H-3]glutamic acid. 3. Among stizolobic acid derivatives, 3-Br-stizolobic acid was the most potent inhibitor of the binding of [H-3]kainic acid, but the inhibitory potency was 100 times weaker than that of kainic acid. 4. Stizolobic acid and its derivatives could cause depolarization of the ventral root of frog spinal cord in a dose dependent manner, and 3-Br-stizolobic acid was a more potent inducer of depolarization than kainic acid, but the dose dependency of 3-Br-stizolobic acid was a little different from that of kainic acid. 5. The results suggest that stizolobic acid and its analogues act as a kainic acid agonist in frog spinal cord. 6. The present results and others indicate that stizolobic acid may interact with the different types of excitatory amino acid receptors dependent on the species of animals.