Domoic and quisqualic acids as potent amino acid excitants of frog and rat spinal neurones

The anions of domoic and quisqualic acids were found to be at least two orders of magnitude more potent than L-glutamate, and equal to or stronger than kainate, whereas α-allo-kainate was a considerably weaker excitant.

Abstract

THE finding that kainic acid (Fig. 1a) is a potent glutamate-like excitant of rat cerebral1 and cat spinal2 neurones has led us to test domoic acid (Fig. 1b), which is structurally related to kainic acid and wnich also occurs in certain marine algae and has similar anthelmintic properties3,4. We have also compared the actions of these two compounds with those of α-allo-kainic acid (Fig. 1c), a stereo-isomer of kainic acid and a weaker excitant of rat cerebral neurones1, and with quisqualic acid (Fig. 1d), an ascaricidal compound isolated from seeds of the plant genus Quisqualis5. Quisqualic acid is highly potent as a glutamate agonist at the crayfish neuromuscular junction6. Compounds were tested on rat spinal interneurones by micro-electrophoresis7 and on frog spinal motoneurones by superfusion of the procaine-blocked8 hemisected spinal cord in vitro9. On both these preparations (see Table 1), the anions of domoic and quisqualic acids were found to be at least two orders of magnitude more potent than L-glutamate, and equal to or stronger than kainate, whereas α-allo-kainate was a considerably weaker excitant.