Kamat Pradip K, Rai Shivika, Swarnkar Supriya, Shukla Rakesh, Nath Chandishwar
Division of Physiology and Biophysics, University of Louisville, KY 40202, USA.
Division of Pharmacology and Toxicology, CSIR-Central Drug Research Institute (CDRI), P.O. Box 173, Lucknow, U.P. 226001, India.
Neurochem Int. 2014 Oct;76:32-41. doi: 10.1016/j.neuint.2014.06.012. Epub 2014 Jun 28.
The N-methyl-D-aspartate (NMDA) receptor is a subtype of ionotropic glutamate receptor that is involved in synaptic mechanisms of learning and memory, and mediates excitotoxic neuronal injury. In this study, we tested the hypothesis that NMDA receptor subunit gene expression is altered in cortex and hippocampus of OKA induced memory impairment. Therefore in the present study, we checked the effect of OKA (ICV) on NMDA receptor regulation and synapse function. The memory function anomalies and synaptosomal calcium ion (Ca(2+)) level were increased in OKA treated rats brain; which was further protected by MK801 (0.05mg/kg. i.p) treatment daily for 13days. To elucidate the involvement of NMDA receptor, we estimated NR1, NR2A and NR2B (subunits) expression in rat brain. Results showed that expression of NR1 and NR2B were significantly increased, but expression of NR2A had no significant change in OKA treated rat brain. We also observed decrease in synapsin-1 mRNA and protein expression which indicates synapse dysfunction. In addition, we detected an increase in MDA and nitrite levels and a decrease in GSH level in synapse preparation which indicates synapse altered redox stress. Moreover, neuronal loss was also confirmed by nissl staining in periventricular cortex and hippocampus. Altered level of oxidative stress markers along with neuronal loss confirmed neurotoxicity. Further, MK801 treatment restored the level of NR1, NR2B and synapsin-1 expression, and protected from neuronal loss and synapse redox stress. In conclusion, Okadaic acid (OKA) induced expression of NR1 and NR2B deteriorates synapse function in rat brain which was confirmed by the neuroprotective effect of MK801.
N-甲基-D-天冬氨酸（NMDA）受体是离子型谷氨酸受体的一种亚型，参与学习和记忆的突触机制，并介导兴奋性毒性神经元损伤。在本研究中，我们检验了以下假设：在鹅膏蕈氨酸（OKA）诱导的记忆损伤模型中，NMDA受体亚基基因表达在皮层和海马中发生改变。因此，在本研究中，我们检测了脑室内注射OKA对NMDA受体调节和突触功能的影响。在经OKA处理的大鼠脑中，记忆功能异常和突触体钙离子（Ca(2+)）水平升高；每日腹腔注射MK801（0.05mg/kg），连续13天，可进一步保护大鼠。为阐明NMDA受体的作用，我们评估了大鼠脑中NR1、NR2A和NR2B（亚基）的表达。结果显示，在经OKA处理的大鼠脑中，NR1和NR2B的表达显著增加，但NR2A的表达无显著变化。我们还观察到突触素-1 mRNA和蛋白表达下降，这表明突触功能障碍。此外，我们在突触制剂中检测到丙二醛（MDA）和亚硝酸盐水平升高，谷胱甘肽（GSH）水平降低，这表明突触氧化还原应激发生改变。此外，通过尼氏染色在脑室周围皮层和海马中也证实了神经元丢失。氧化应激标志物水平的改变以及神经元丢失证实了神经毒性。此外，MK801治疗恢复了NR1、NR2B和突触素-1的表达水平，并保护大鼠免受神经元丢失和突触氧化还原应激的影响。总之，冈田酸（OKA）诱导的NR1和NR2B表达导致大鼠脑突触功能恶化，MK801的神经保护作用证实了这一点。
