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
✍ Scribed by A. Hatziefthimiou; A. Mitsacos; E. D. Kouvelas
- Publisher
- John Wiley and Sons
- Year
- 1994
- Tongue
- English
- Weight
- 819 KB
- Volume
- 37
- Category
- Article
- ISSN
- 0360-4012
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✦ Synopsis
Using quantitative autoradiography, we have characterized the binding properties of the non-N-methyl-D-aspartate (NMDA) glutamate receptor antagonist ["H]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 f 6.4and83.3 k 9.9nM, respectively). The maximum number of [3H]CNQX binding sites was much higher in the molecular compared to the granule cell layer (B,,, = 16.2 f 1.1 and 2.8 f 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)a -amino-3-hydroxy -5methyl-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 (Kj: 2.8 f 0.8 nM and 12.5 f 0.8 pM) was 4-to 6-fold greater than the corresponding potency of kainate (Ki: 18.1 f 5.7 nM and 48.7 f 9.3 pM). 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.