Quantitative Assessment of Quinolinic Acid-induced Striatal Toxicity in Rats Using Radioligand Binding Assays

To validate specific, sensitive and quantitative markers of the rat model of Huntington's disease produced by the intrastriatal injection of quinolinic acid, we used striatal homogenate binding assays for [H-3]MK-801-labelled N-methyl-D-aspartate receptors, [H-3]SCH 23390-labelled D1 and [H-3]sulpiride-labelled D2 dopamine receptors, [H-3]CGS 21680-labelled adenosine A2 receptors, [H-3]GBR 12935-labelled dopamine uptake sites, [H-3]hemicholinium-3-labelled high affinity choline uptake sites and [H-3]PK 11195-labelled glial cells, in 3 groups of rats: 1) lesioned only, 2) pretreated with MK-807, an antagonist of the N-methyl-D-aspartate receptor, to assess the non-N-methyl-D-aspartate-mediated toxicity of quinolinic acid, and 31 pretreated with MK-801 plus scopolamine, an anticholinergic drug that prevents MK-801 neuronal toxicity, [H-3]MK-801 and [H-3]PK 11195 are sensitive markers of quinolinic acid toxicity. In addition, [H-3]SCH 23390, [H-3]CGS 21680 and [H-3]hemicholinium-3, are found to be specific markers of quinolinic acid-induced toxicity on striatonigral and striatopallidal projecting neurons, and on large interneurons, respectively. MK-801 pretreatment prevented the quinolinic acid-induced reduction in binding of [H-3]MK-801, [H-3]SCH 23390 and [H-3]CGS 21680 but failed to do so for [H-3]sulpride and [H-3]hemicholinium-3, suggesting that quinolinic acid may act by mechanisms other than direct activation of N-methyl-D-aspartate receptors. Combined pretreatment with MK-801 and scopolamine increased the protection against quinolinic acid, suggesting an involvement of the cholinergic system.