Hermenegildo C, Montoliu C, Llansola M, Muñoz M D, Gaztelu J M, Miñana M D, Felipo V
Laboratory of Neurobiology, Instituto de Investigaciones Citologicas, Fundación Valenciana de Investigaciones Biomédicas, Spain.
Eur J Neurosci. 1998 Oct;10(10):3201-9. doi: 10.1046/j.1460-9568.1998.00329.x.
The aim of this work was to assess whether ammonia concentrations similar to the increase found in the brain of hyperammonemic rats (100 microM), impair N-methyl-D-aspartate (NMDA) receptor-mediated signal transduction. We first measured glutamate neurotoxicity, which in these neurons is mediated by activation of NMDA receptors, as an initial parameter reflecting activation of NMDA receptor-mediated pathways. Long-term treatment of cultured neurons with ammonia prevents glutamate-induced neuronal death. The EC50 was 20 microM, and at 100 microM the protection was complete. The induction of the protective effect was not immediate, but took several hours. Treatment with 100 microM ammonia did not prevent a glutamate- or NMDA-induced rise of intracellular calcium. Ammonia impaired the glutamate-nitric oxide-cGMP (3',5'-cyclic guanosine monophosphate) pathway in a dose- and time-dependent manner. Glutamate-induced formation of cGMP was reduced by 42%, while activation of nitric oxide synthase was not affected. Ammonia reduced by 31% cGMP formation induced by S-nitroso-N-acetyl-penicillamine (SNAP), a NO-generating agent, confirming that the interference occurs at the level of guanylate cyclase activation by nitric oxide. To assess whether chronic moderate hyperammonemia in vivo also impairs the glutamate-nitric oxide-cGMP pathway, we determined by in vivo brain microdialysis in freely moving rats the formation of cGMP induced by NMDA. In hyperammonemic rats, the formation of cGMP induced by NMDA and SNAP was reduced by ca. 60 and 41%, respectively, indicating that chronic hyperammonemia in the animal in vivo also impairs the glutamate-nitric oxide-cGMP pathway. Impairment of this pathway can contribute to the neurological alterations found in hyperammonemia and hepatic encephalopathy.
本研究旨在评估与高氨血症大鼠大脑中发现的氨浓度升高（100微摩尔）相似的氨浓度是否会损害N-甲基-D-天冬氨酸（NMDA）受体介导的信号转导。我们首先测量谷氨酸神经毒性，在这些神经元中，谷氨酸神经毒性是由NMDA受体激活介导的，作为反映NMDA受体介导途径激活的初始参数。用氨对培养的神经元进行长期处理可预防谷氨酸诱导的神经元死亡。半数有效浓度（EC50）为20微摩尔，在100微摩尔时保护作用完全。保护作用的诱导不是立即发生的，而是需要几个小时。用100微摩尔氨处理并不能预防谷氨酸或NMDA诱导的细胞内钙升高。氨以剂量和时间依赖性方式损害谷氨酸-一氧化氮-环磷酸鸟苷（cGMP）途径。谷氨酸诱导的cGMP形成减少了42%，而一氧化氮合酶的激活不受影响。氨使一氧化氮供体S-亚硝基-N-乙酰青霉胺（SNAP）诱导的cGMP形成减少了31%，证实这种干扰发生在一氧化氮激活鸟苷酸环化酶的水平。为了评估体内慢性中度高氨血症是否也会损害谷氨酸-一氧化氮-cGMP途径，我们通过对自由活动大鼠进行体内脑微透析来测定NMDA诱导的cGMP形成。在高氨血症大鼠中，NMDA和SNAP诱导的cGMP形成分别减少了约60%和41%，表明动物体内慢性高氨血症也会损害谷氨酸-一氧化氮-cGMP途径。该途径的损害可能导致高氨血症和肝性脑病中发现的神经学改变。
