Kayadjanian N, Gioanni H, Ménetrey A, Besson M J
Laboratoire de Neurochimie-Anatomie, Institut des Neurosciences, CNRS URA 1488, Université Pierre, Paris, France.
Neuroscience. 1994 Dec;63(4):989-1002. doi: 10.1016/0306-4522(94)90567-3.
The effect of muscarinic agonists on the spontaneous release of [3H]GABA was investigated in vitro on rat substantia nigra slices. Acetylcholine (5 x 10(-5) M) in the presence of eserine (5 x 10(-5) M) induced a 12.3% increase of the spontaneous release of [3H]GABA. Similarly, carbachol (5 x 10(-4) M) enhanced by 9% the release of [3H]GABA. This effect was Ca(2+)-dependent, it was abolished in the presence of 0.4 mM Ca2+ and enhanced from 9 to 17% when Ca(2+)-concentration of the superfusion medium was increased from 1.3 to 2.4 mM. The carbachol effect was mediated by muscarinic receptors since it was abolished by atropine (2 x 10(-6) M). The pharmacologically M2 muscarinic receptor subtypes seems to be involved as the carbachol-induced effect was abolished by AF-DX384MS (10(-6) M), an M2 antagonist and was only partially reversed by pirenzepine (10(-5) and 10(-4) M), an M1 antagonist which at these doses also block the M2 receptors. The absence of effect of SCH23390 (10(-6) M) a D1 antagonist as well as the lack of effect of CNQX (10(-5) M) and dizocilpine maleate (10(-6) M), two glutamate antagonists, on the carbachol-induced effect indicated that neither dopamine (through D1 receptors) nor glutamate (through ionotropic receptors) were involved in the response. In addition, the persistence of the carbachol-induced effect in the presence of tetrodotoxin (2 x 10(-7) M) suggests a direct muscarinic-mediated modulation of [3H]GABA. The localization of muscarinic receptors on striatonigral fibres was confirmed by autoradiographic studies showing a decrease of [3H]pirenzepine binding in the substantia nigra after a unilateral striatal lesion induced by kainic acid injection. This latter result provides evidence of the presence of M1 receptors on striatonigral terminals as the concentration of [3H]pirenzepine used (10 nM) is M1-selective. These results indicate a cholinergic modulation of GABA release in the rat substantia nigra mediated by muscarinic receptors localized on striatonigral terminals. The involvement of the m4 muscarinic receptor subtype that have a M1/M2 pharmacology is discussed.
在体外对大鼠黑质切片研究了毒蕈碱激动剂对[3H]GABA自发释放的影响。在存在毒扁豆碱（5×10(-5)M）的情况下，乙酰胆碱（5×10(-5)M）使[3H]GABA的自发释放增加了12.3%。同样，卡巴胆碱（5×10(-4)M）使[3H]GABA的释放增加了9%。这种效应依赖于Ca(2+)，在0.4mM Ca2+存在时被消除，当灌流液中Ca(2+)浓度从1.3mM增加到2.4mM时，该效应从9%增强到17%。卡巴胆碱的效应由毒蕈碱受体介导，因为它被阿托品（2×10(-6)M）消除。药理学上的M2毒蕈碱受体亚型似乎参与其中，因为卡巴胆碱诱导的效应被M2拮抗剂AF-DX384MS（10(-6)M）消除，并且仅被M1拮抗剂哌仑西平（10(-5)和10(-4)M）部分逆转，而在这些剂量下哌仑西平也阻断M2受体。D1拮抗剂SCH23390（10(-6)M）以及两种谷氨酸拮抗剂CNQX（10(-5)M）和马来酸二氢麦角碱（10(-6)M）对卡巴胆碱诱导的效应无影响，这表明多巴胺（通过D1受体）和谷氨酸（通过离子型受体）均不参与该反应。此外，在存在河豚毒素（2×10(-7)M）的情况下卡巴胆碱诱导的效应持续存在，提示对[3H]GABA存在直接的毒蕈碱介导的调节。通过放射自显影研究证实了毒蕈碱受体在纹状体黑质纤维上的定位，该研究显示在注射 kainic 酸诱导单侧纹状体损伤后，黑质中[3H]哌仑西平结合减少。后一结果提供了纹状体黑质终末存在M1受体的证据，因为所使用的[3H]哌仑西平浓度（10nM）具有M1选择性。这些结果表明，位于纹状体黑质终末的毒蕈碱受体介导了大鼠黑质中GABA释放的胆碱能调节。文中讨论了具有M1/M2药理学特性的m4毒蕈碱受体亚型的参与情况。
