{'fraction_non_alphanumeric': 0.056383668178872325, 'fraction_numerical': 0.026571613739468567, 'mean_word_length': 5.954954954954955, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Pharmacology and Regional Distribution of the Binding of 6‐[3H]Nitro‐7‐Sulphamoylbenzo[f]‐Quinoxaline‐2,3‐Dione to Rat Brain

Abstract: 6‐Nitro‐7‐sulphamoylbenzo[f]quinoxaline‐2,3‐dione (NBQX) is a competitive antagonist selective for α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate (AMPA) receptors. Here we report the pharmacological characteristics and anatomical distribution of [3H]NBQX binding to rat brain. The association rate of [3H]NBQX to rat cerebrocortical membranes was rapid, with peak binding occurring within 10 min at 0°C. The off‐rate was also rapid, with near‐complete dissociation of the radioligand within 5 min of addition of 1 mM unlabelled l‐glutamate. [3H]NBQX bound to a single class of sites with KD and Bmax values of 47 nM and 2.6 pmol mg−1 of protein, respectively. The rank order of inhibition of [3H]NBQX binding by AMPA receptor ligands was NBQX ≫ 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) ≥ (S)‐5‐fluorowillardiine ≥ AMPA ≫l‐glutamate. The chaotrope KSCN had no effect on the IC50 value of unlabelled NBQX displacement of [3H]NBQX binding. The kainate receptor‐selective ligands NS102 and kainate were only very weak displacers. It is interesting that NBQX and CNQX displaced significantly more [3H]NBQX than any of the agonists tested. Autoradiographic analysis of the binding of [3H]NBQX to coronal sections showed a distribution compatible with that of [3H]AMPA binding. These data indicate that [3H]NBQX provides a useful novel tool to characterise the antagonist binding properties of AMPA receptors.