Son H, Carpenter D O
Department of Environmental Health and Toxicology, School of Public Health, State University of New York at Albany 12201-0509, USA.
Neuroscience. 1996 May;72(1):1-13. doi: 10.1016/0306-4522(95)00532-3.
The involvement of protein kinase C in long-term potentiation was investigated in the mossy fiber-CA3 pathway in an in vitro slice preparation of rat hippocampus. Tetanic stimulation induced stable long-term potentiation in the mossy fiber-CA3 pathway which was not affected by N-methyl-D-aspartate receptor antagonists. Long-term potentiation was not induced in the presence of a protein kinase C inhibitor, sphingosine. Application of 1 microM phorbol-12, 13-diacetate, an activator of protein kinase C, potentiated the synaptic response by about 400% and this potentiation was completely reversible upon washing. Sphingosine blocked the potentiation when it was applied before protein kinase C activation by phorbol-12, 13-diacetate. However, sphingosine had no effect on the potentiation when it was applied after the synaptic response was potentiated to a plateau following phorbol-12,13-diacetate perfusion. Long-term potentiation and phorbol ester-induced potentiation were not additive when phorbol-12,13-diacetate was applied after induction of long-term potentiation, suggesting that long-term potentiation and phorbol-12, 13-diacetate activate the same protein kinase C pool. The enhanced response caused by phorbol-12,13-diacetate returned to the long-term potentiation level after wash-out of phorbol-12,13-diacetate. Thus the cellular changes underlying long-term potentiation are long-lasting or permanent, while those caused by phorbol-12,13-diacetate are not. However, if tetanic stimulation was induced during prolonged phorbol-12,13-diacetate application (1 h), a potentiation similar in amplitude to long-term potentiation was induced but the population response returned to the control pre-long-term potentiation level after 2 h of washing. The potentiation following tetanic stimulation during prolonged application of phorbol-12,13-diacetate was blocked in the presence of D-2-amino-5-phosphonovaleric acid, a N-methyl-D-aspartate receptor antagonist. Thus, in the presence of phorbol esters the N-methyl-D-aspartate-independent long-term potentiation is occluded but a transient potentiation appears, presumably due to hyperexcitability and activation of N-methyl-D-aspartate receptors in recurrent pathways of area CA3. Normal N-methyl-D-aspartate-independent long-term potentiation could be induced after the 2 h washout period and now was maintained. In conclusion, protein kinase C activation is essential but not sufficient for long-term potentiation in the mossy fiber-CA3 pathway and when stimulated by application of phorbol esters produces a large and reversible synaptic potentiation. These investigations show that long-term potentiation in CA3 is a complex event involving several steps, and that activation of protein kinase C is only one of them.
在大鼠海马体的体外脑片制备中，研究了蛋白激酶C在苔藓纤维-CA3通路长时程增强中的作用。强直刺激在苔藓纤维-CA3通路中诱导出稳定的长时程增强，该增强不受N-甲基-D-天冬氨酸受体拮抗剂的影响。在蛋白激酶C抑制剂鞘氨醇存在的情况下，不能诱导出长时程增强。应用1微摩尔佛波醇-12,13-二乙酸酯（一种蛋白激酶C激活剂）可使突触反应增强约400%，且这种增强在冲洗后完全可逆。当在佛波醇-12,13-二乙酸酯激活蛋白激酶C之前应用鞘氨醇时，它会阻断这种增强作用。然而，当在佛波醇-12,13-二乙酸酯灌注使突触反应增强至平台期后再应用鞘氨醇时，它对这种增强没有影响。当在长时程增强诱导后应用佛波醇-12,13-二乙酸酯时，长时程增强和佛波醇酯诱导的增强不是相加的，这表明长时程增强和佛波醇-12,13-二乙酸酯激活相同的蛋白激酶C池。佛波醇-12,13-二乙酸酯洗脱后，由其引起的增强反应恢复到长时程增强水平。因此，长时程增强所涉及的细胞变化是持久的或永久的，而由佛波醇-12,13-二乙酸酯引起的变化则不是。然而，如果在长时间应用佛波醇-12,13-二乙酸酯（1小时）期间诱导强直刺激，则会诱导出幅度与长时程增强相似的增强，但在冲洗2小时后群体反应恢复到长时程增强前的对照水平。在长时间应用佛波醇-12,13-二乙酸酯期间强直刺激后的增强在N-甲基-D-天冬氨酸受体拮抗剂D-2-氨基-5-膦酰基戊酸存在时被阻断。因此，在佛波醇酯存在的情况下，不依赖N-甲基-D-天冬氨酸的长时程增强被阻断，但会出现短暂的增强，推测这是由于CA3区反复通路中的过度兴奋和N-甲基-D-天冬氨酸受体的激活所致。在2小时冲洗期后可诱导出正常的不依赖N-甲基-D-天冬氨酸的长时程增强，且现在可以维持。总之，蛋白激酶C的激活对于苔藓纤维-CA3通路中的长时程增强是必不可少的，但不是充分条件，并且当通过应用佛波醇酯刺激时会产生大的且可逆的突触增强。这些研究表明，CA3区的长时程增强是一个涉及多个步骤的复杂事件，而蛋白激酶C的激活只是其中之一。
