title: Kynurenic acid distinguishes kainate and quisqualate receptors in the vertebrate retina.
abstract: Excitatory amino acid receptors (EAARs) underlie major synaptic pathways in the brain, retina and spinal cord. Several subclasses of EAARs have been proposed, based on pharmacological studies using a variety of agonists and antagonists. Kynurenic acid (Kyn), a metabolite of tryptophan, has been recently proposed as a potent EAAR antagonist. In this report, we show that Kyn can be used to separate two distinct classes of EAAR in the vertebrate retina: it blocks kainic acid (KA) responses but has minimal effects on responses mediated by quisqualate (QQ). At concentrations which block the KA responses, Kyn also blocks the light-evoked synaptic responses of all types of third-order neurons in the retina. These results suggest that KA receptors are the major receptor subtypes which underlie synaptic transmission and that QQ receptors are minimally utilized by light-activated pathways under the conditions of our experiments.
mesh_terms: D000818:Animals; D007608:Kainic Acid / Q000037:antagonists & inhibitors*; D007736:Kynurenic Acid / Q000494:pharmacology*; D009337:Necturus; D010069:Oxadiazoles / Q000037:antagonists & inhibitors*; D010775:Photic Stimulation; D016318:Quisqualic Acid; D011817:Rabbits; D018091:Receptors, AMPA; D011955:Receptors, Drug / Q000187:drug effects*; D018092:Kainic Acid Receptors; D017981:Receptors, Neurotransmitter / Q000187:drug effects*; D012160:Retina / Q000187:drug effects*; D013045:Species Specificity
chemical_list: D007608:Kainic Acid; D007736:Kynurenic Acid; D010069:Oxadiazoles; D016318:Quisqualic Acid; D018091:Receptors, AMPA; D011955:Receptors, Drug; D018092:Kainic Acid Receptors; D017981:Receptors, Neurotransmitter