Reuben M, Louis M, Clarke P B
Department of Pharmacology and Therapeutics, McGill University, Montreal, Canada.
Br J Pharmacol. 1998 Nov;125(6):1218-27. doi: 10.1038/sj.bjp.0702215.
Chlorisondamine (CHL) blocks behavioural responses to nicotine for several weeks or months in rats. Persistent blockade has also been demonstrated ex vivo, in assays of nicotine-evoked striatal dopamine release. Central administration of [3H]-CHL leads to long-term retention of radiolabel in nigrostriatal dopaminergic neurons and in few other cell groups. We investigated whether an analogous blockade also occurs in noradrenergic neurons in the brain and in cultured pheochromocytoma (PC12) cells, which have a similar noradrenergic phenotype. Administration of CHL (10 mg kg(-1) s.c. or 10 microg i.c.v.), 21 days prior, resulted in a near-total block of nicotine-evoked release of hippocampal [3H]-noradrenaline ([3H]-NA) from superfused rat synaptosomes; NMDA-evoked [3H]-NA release was unaffected. Three weeks after administration of [3H]-CHL (10 microg i.c.v.), preferential accumulation of radiolabel was observed in the locus coeruleus, which provides the entire noradrenergic innervation to hippocampus, as well as in previously noted structures. In rat pheochromocytoma (PC12) cells, nicotine evoked [3H]-NA release (EC50 approximately 30 microM). This effect was blocked by co-incubation with mecamylamine (10 microM) or CHL (1 microM) but was not affected by alpha-bungarotoxin. As in the hippocampus, the nicotinic agonist cytisine was at least as efficacious as nicotine. Acute exposure of PC12 cells to CHL 10 or 100 microM (but not 1 microM), followed by 90 min wash-out, almost completely blocked release evoked by 30 microM nicotine. More prolonged (24 h) exposure to CHL 100 microM (but not 1 or 10 microM), followed by 3 days of wash-out, partially inhibited release evoked by nicotine, leaving responses to high K+ unchanged. A significant (30%) reduction was also seen 5 days after exposure. We conclude that persistent nicotinic blockade by CHL is neither restricted to mesostriatal dopamine neurons, nor to the CNS, nor to neurons possessing the same nicotinic receptor pharmacology. In addition, the persistent blockade does not appear to result from an acute blocking action, but may be dependent upon intracellular accumulation of the antagonist.
氯异吲哚铵（CHL）可在数周或数月内阻断大鼠对尼古丁的行为反应。在尼古丁诱发的纹状体多巴胺释放试验中，也已在体外证实了持续的阻断作用。脑室内注射[3H]-CHL会导致黑质纹状体多巴胺能神经元以及其他少数细胞群中长期保留放射性标记。我们研究了在脑内的去甲肾上腺素能神经元以及具有相似去甲肾上腺素能表型的培养嗜铬细胞瘤（PC12）细胞中是否也会发生类似的阻断作用。提前21天皮下注射CHL（10 mg kg(-1)）或脑室内注射CHL（10 μg），可使灌注的大鼠突触体中尼古丁诱发的海马[3H]-去甲肾上腺素（[3H]-NA）释放几乎完全被阻断；NMDA诱发的[3H]-NA释放不受影响。脑室内注射[3H]-CHL（10 μg）三周后，在蓝斑中观察到放射性标记的优先积累，蓝斑为海马提供了全部去甲肾上腺素能神经支配，以及在先前提到的结构中也有积累。在大鼠嗜铬细胞瘤（PC12）细胞中，尼古丁可诱发[3H]-NA释放（EC50约为30 μM）。与美加明（10 μM）或CHL（1 μM）共同孵育可阻断此效应，但不受α-银环蛇毒素影响。与在海马中的情况一样，烟碱激动剂金雀花碱的效力至少与尼古丁相同。PC12细胞急性暴露于10或100 μM CHL（但不是1 μM），随后冲洗90分钟，几乎完全阻断了30 μM尼古丁诱发的释放。更长时间（24小时）暴露于100 μM CHL（但不是1或10 μM），随后冲洗3天，部分抑制了尼古丁诱发的释放，而对高钾的反应不变。暴露5天后也观察到显著（30%）的降低。我们得出结论，CHL引起的持续性烟碱阻断作用既不限于中脑纹状体多巴胺神经元，也不限于中枢神经系统，也不限于具有相同烟碱受体药理学的神经元。此外，持续性阻断似乎不是由急性阻断作用引起的，而是可能依赖于拮抗剂在细胞内的积累。
