AUTORADIOGRAPHIC CHARACTERIZATION OF THE NON-N-METHYL-D-ASPARTATE BINDING-SITES IN HUMAN CEREBELLUM USING THE ANTAGONIST [H-3] 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 a ntagonist [H-3]6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in adult hu man cerebellum. Saturation experiments revealed [H-3]CNQX binding to a single class of sites with similar affinity in the molecular and gran ule cell layer (K-d = 89.0 +/- 6.4 and 83.3 +/- 9.9 nM, respectively). The maximum number of [H-3]CNQX binding sites was much higher in the molecular compared to the granule cell layer (B-max = 16.2 +/- 1.1 and 2.8 +/- 0.5 pmol/mg protein, respectively). Inhibition experiments we re performed in order to examine the pharmacological profile of [H-3]C NQX binding in the molecular layer. [H-3]CNQX labeled sites with high affinity for both non-NMDA agonists, (RS)-alpha-amino-3-hydroxy-5-meth yl-4-isoxazole propionic acid (AMPA) and kainate. Dose-response curves for inhibition of [H-3]CNQX by AMPA and kainate were biphasic. The po tency of AMPA for displacement of [H-3]CNQX binding (K-i: 2.8 +/- 0.8 nM and 12.5 +/- 0.8 mu M) was 4- to 6-fold greater than the correspond ing potency of kainate (K-i: 18.1 +/- 5.7 nM and 48.7 +/- 9.3 mu M). I n conclusion, the pharmacological analysis of [H-3]CNQX binding in the human cerebellar molecular layer reflects the existence of multiple b inding sites of the non-NMDA receptor that have different affinities f or both AMPA and kainate. (C) 1994 Wiley-Liss, Inc.