Widdowson P S, Wyatt I, Gyte A, Simpson M G, Lock E A
Neurotoxicology Group, ZENECA Central Toxicology Laboratory, Macclesfield, Cheshire, United Kingdom.
Toxicol Appl Pharmacol. 1996 Jan;136(1):138-45. doi: 10.1006/taap.1996.0017.
We have demonstrated that following a single oral dose of L-2-chloropropionic acid (L-CPA) to rats (750 mg/kg; pH 7) there was a marked and widespread loss of granule cells in the cerebellum as assessed by neuropathology by 48 hr. There also appeared to be limited damage to Purkinje cells, whereas stellate, Golgi, and basket cells were not affected by L-CPA administration. The L-CPA-mediated cerebellar neuropathology was accompanied by a significant increase in the cerebellar water content and sodium concentration, 48 hr following L-CPA administration, suggesting an edematous reaction. After 36 hr, the animals displayed marked locomotor dysfunction and had to be terminated at 54 hr due to marked weight loss. We did not observe any neuropathology in forebrain regions nor was the water content in the forebrain significantly different from controls in animals which had been treated with L-CPA. Cerebellar aspartate concentrations were reduced 48 hr following L-CPA administration becoming marked at 54 hr and accompanied by a significant reduction in cerebellar glutamate concentrations. The density of N-methyl-D-aspartate (NMDA) receptors in the granular layer of the cerebellar cortex was also significantly reduced at 48 and 54 hr following L-CPA administration. Prior administration of MK-801 (dizocilpine) (5 mg/kg/i.p.), an irreversible NMDA receptor antagonist, 30 min before an oral dose of L-CPA (750 mg/kg) prevented the loss of both granule and Purkinje cells. There was no abnormal locomotor activity in the L-CPA rats treated with MK-801 except for the first 4 hr following dosing when animals were severely sedated. Animals which received L-CPA plus MK-801 were normal 96 hr post dosing showing that MK-801 did not delay the onset of L-CPA toxicity. There was no alteration in cerebellar water content or sodium concentrations in rats which had been administered MK-801 with L-CPA. The reductions in cerebellar aspartate and glutamate concentrations were totally prevented by administration of MK-801, as was the reduction in L(-)[3H]glutamate binding to cerebellar NMDA receptors. Administration of MK-801 alone (5 mg/kg/i.p.) did not alter the water content, sodium concentrations, aspartate or glutamate concentrations, or the density of NMDA receptors in the cerebellum. In conclusion, we suggest that L-CPA-induced neurotoxicity leading to loss in granule cells and an accompanying cerebellar edema can be prevented by MK-801, suggesting that a subpopulation of NMDA receptors found on cerebellar granule cells play a pivotal role in mediating the toxicity of this compound.
我们已经证明，给大鼠单次口服L-2-氯丙酸（L-CPA）（750mg/kg；pH7）后，通过神经病理学评估，48小时时小脑颗粒细胞出现明显且广泛的损失。浦肯野细胞似乎也有有限的损伤，而星状细胞、高尔基细胞和篮状细胞不受L-CPA给药的影响。L-CPA介导的小脑神经病理学伴随着L-CPA给药后48小时小脑含水量和钠浓度的显著增加，提示存在水肿反应。36小时后，动物表现出明显的运动功能障碍，由于体重显著减轻，在54小时时不得不将其处死。我们在脑前叶区域未观察到任何神经病理学变化，在用L-CPA处理的动物中，脑前叶的含水量与对照组也无显著差异。L-CPA给药后48小时小脑天冬氨酸浓度降低，在54小时时变得明显，并伴有小脑谷氨酸浓度的显著降低。L-CPA给药后48小时和54小时，小脑皮质颗粒层中N-甲基-D-天冬氨酸（NMDA）受体的密度也显著降低。在口服L-CPA（750mg/kg）前30分钟预先给予不可逆的NMDA受体拮抗剂MK-801（地佐环平）（5mg/kg/i.p.）可防止颗粒细胞和浦肯野细胞的损失。在用MK-801处理的L-CPA大鼠中，除给药后的最初4小时动物严重镇静外，没有异常的运动活动。接受L-CPA加MK-801的动物在给药后96小时正常，表明MK-801没有延迟L-CPA毒性的发作。同时给予MK-801和L-CPA的大鼠小脑含水量或钠浓度没有改变。给予MK-801可完全防止小脑天冬氨酸和谷氨酸浓度的降低，以及L-（-）-[3H]谷氨酸与小脑NMDA受体结合的减少。单独给予MK-801（5mg/kg/i.p.）不会改变小脑的含水量、钠浓度、天冬氨酸或谷氨酸浓度，也不会改变小脑NMDA受体的密度。总之，我们认为MK-801可以预防L-CPA诱导的导致颗粒细胞损失和伴随的小脑水肿的神经毒性，这表明在小脑颗粒细胞上发现的NMDA受体亚群在介导该化合物的毒性中起关键作用。
