Autoradiographic characterization of the non-N-methyl-D-aspartate binding sites in human cerebellum using the antagonist [3H]6-cyano-7-nitroquinoxaline-2,3-dione.
Using quantitative autoradiography, we have characterized the binding properties of the non-N-methyl-D-aspartate (NMDA) glutamate receptor antagonist [3H]6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in adult human cerebellum. Saturation experiments revealed [3H]CNQX binding to a single class of sites with similar affinity in the molecular and granule cell layer (Kd = 89.0 +/- 6.4 and 83.3 +/- 9.9 nM, respectively). The maximum number of [3H]CNQX binding sites was much higher in the molecular compared to the granule cell layer (Bmax = 16.2 +/- 1.1 and 2.8 +/- 0.5 pmol/mg protein, respectively). Inhibition experiments were performed in order to examine the pharmacological profile of [3H]CNQX binding in the molecular layer. [3H]CNQX labeled sites with high affinity for both non-NMDA agonists, (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate. Dose-response curves for inhibition of [3H]CNQX by AMPA and kainate were biphasic. The potency of AMPA for displacement of [3H]CNQX binding (Ki: 2.8 +/- 0.8 nM and 12.5 +/- 0.8 microM) was 4- to 6-fold greater than the corresponding potency of kainate (Ki: 18.1 +/- 5.7 nM and 48.7 +/- 9.3 microM). In conclusion, the pharmacological analysis of [3H]CNQX binding in the human cerebellar molecular layer reflects the existence of multiple binding sites of the non-NMDA receptor that have different affinities for both AMPA and kainate.
Hatziefthimiou
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Department of Physiology, Medical School, University of Patras, Greece.
Mitsacos
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Kouvelas
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D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000328:Adult; D001345:Autoradiography; D001667:Binding, Competitive / Q000187:drug effects; D002525:Cerebellar Cortex / Q000187:drug effects / Q000378:metabolism; D002531:Cerebellum / Q000033:anatomy & histology / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D011810:Quinoxalines / Q000493:pharmacokinetics / Q000494:pharmacology*; D016318:Quisqualic Acid / Q000378:metabolism; D018091:Receptors, AMPA / Q000187:drug effects / Q000378:metabolism; D017459:Receptors, Amino Acid / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018092:Kainic Acid Receptors / Q000187:drug effects / Q000378:metabolism
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D011810:Quinoxalines; D016318:Quisqualic Acid; D018091:Receptors, AMPA; D017459:Receptors, Amino Acid; D018092:Kainic Acid Receptors