大鼠尾状核内注射高剂量L-( )-2-氨基-3-磷酸基丙酸的神经毒性

目的:观察代谢型谷氨酸受体部分激动剂/拮抗剂L-( )-2-氨基-3-磷酸基丙酸(L-AP_3)脑内注射引起的神经毒性作用,并探讨其机制。方法:大鼠尾状核内微量注射药物后,观察动物意识状态和活动情况,测定脑组织含水量、Na~ 、K~ 、Ca~(2 )含量及血脑屏障(BBB)通透性变化,并进行组织学研究。结果:L-AP_3 600nmol脑内注射后动物出现嗜睡,并引起脑组织含水量、Na~ 和Ca~(2 )含量增加,K~ 含量减少,同时BBB通透性增加P<0.01,L-AP_3 60nmol未产生上述变化。电镜检查发现L-AP_3引起星形胶质细胞高度肿胀,神经元变性坏死。D-( )-2-氨基-3-磷酸基丙酸和L-( )2-氨基-4-磷酸丁酸不能模拟L-AP_3引起的变化,DL-2-氨基-5-磷酸基戊酸可以减轻L-AP_3的作用,(±)-α-甲基-(4-羧基苯基)甘氨酸不能减轻L-AP_3的作用。结论:脑内注射高剂量的L-AP_3引起神经毒性作用,以血管源性脑水肿、神经元损伤及脑组织高Ca~(2 )含量为特征,此作用是立体构型特异的,可能与磷脂酶C激活有关,部分通过NMDA受体介导。

Neurotoxic effect of high dose of L-( )-2-amino-3-phosphono- propionic acid in rats after intracaudatal injection

AIM: To investigate neurotoxic effect of L-(+)-2-amino-3-phosphonopropionic acid (L-AP3), a partial agonist/antagonist of metabotropic glutamate receptors (mGluRs), and explore the underlying mechanisms. METHODS: Consciousness and behavior of rats were evaluated after injection of L-AP3, D-(+)-2-amino-3-phosphonopropionic acid (D-AP3, an isomer of L-AP3) or L-(+)-2-amino-4-phosphonobutyric acid (L-AP4, an agonist of mGluRs) into right caudatum. Brain water, Na+, K+, and Ca2+ contents as well as the permeability of blood brain barrier (BBB) were determined 6 h after treatment of these chemicals. Histological changes at the same time point were also observed. RESULTS: Rats treated with L-AP3 600 nmol but not 60 nmol became somnolentia. Inject ion of L-AP3 600 nmol induced a great increase of brain water, Na+, and Ca2+ contents, and a decrease of brain K+ content (P < 0.01). Meanwhile, the permeability of BBB was also increased (P < 0.01). Electron microscopic study revealed remarkable swelling of astrocytes and degenerative changes of neurons in chemical-treated caudatum. The neurotoxic effect of L-AP3 was not mimicked by D-AP3 or L-AP4 (P < 0.05). DL-2-Amino-5-phosphonovaleric acid, an antagonist of N-methyl-D-aspartate (NMDA) receptors, attenuated the changes induced by L-AP3 (P < 0.05), whereas (+/-)-alpha-methyl-(4-carboxyphenyl)glycine, a non-subtype specific antagonist of mGluRs, failed to block the effect of L-AP3. CONCLUSION: Intracaudatal injection of L-AP3 induced neurotoxic effect characterized by vasogenic brain edema, neuronal degeneration, and high brain Ca2+ content. Neurotoxic effect of L-AP3 was stereoselective and might be mediated by phospholipase C activation and partially involvement of NMDA receptors.