The action of kainic acid and quisqualic acid on the glutamate receptors of three identifiable neurones from the brain of the snail, Helix aspersa

Abstract

1. Intracellular recordings were made from three identifiable neurons in the suboesophageal ganglionic mass of Helix aspersa. 2. The three cells gave different responses to glutamic acid; cell F1 was hyperpolarised and its activity inhibited by glutamate; cell F30 was depolarised and its activity increased by glutamate; cell E4 displayed a biphasic response to glutamate, inhibition followed by excitation. 3. The interaction of kainic acid and quisqualic acid with the glutamate receptors of these three cells was investigated. 4. Kainic acid was an agonist of the excitatory action of glutamate on cell F30 and E4 with an EPMR of 500 and 10 respectively, i.e. less active than glutamate. Low doses of kainic acid, 4.7−47 nmoles, potentiated the action of glutamate while higher doses, 470 nmoles, reduced the size of standard doses of glutamate on cell F30. Kainic acid had no effect on the inhibitory glutamate responses of cells E4 and F1. 5. Quisqualic acid was a glutamate agonist on all three cells. It was 10 times more active than glutamate on cell F30 and 100 times more active than glutamate on cell F1. On cell E4 quisqualic acid was 10 times less active on the glutamate inhibitory receptor but 1000 times more active than glutamate on the glutamate excitatory receptor. 6. It is suggested that both kainic acid and quisqualic acid exeert their excitatory effect in a partly folded conformation although quisqualic acid unlike kainic acid can also act in an extended conformation on the inhibitory glutamate receptors of cell E4.