Manahan-Vaughan D, Reiser M, Pin J P, Wilsch V, Bockaert J, Reymann K G, Riedel G
Federal Institute for Neurobiology, Department of Neurophysiology, Magdeburg, Germany.
Neuroscience. 1996 Jun;72(4):999-1008. doi: 10.1016/0306-4522(95)00594-3.
In this study, we biochemically analysed the effects of the novel metabotropic glutamate receptor agonist trans-azetidine-2,4-dicarboxylic acid and examined its role in hippocampal long-term potentiation. In cell lines expressing metabotropic receptor 1 or 5 subtypes, the compound stimulated phosphoinositide hydrolysis with EC50 values of 189.4 +/- 6.4 and 32.2 +/- 8.3 microM, respectively. In hippocampal slices, trans-azetidine-2,4-dicarboxylic acid also increased phosphoinositide hydrolysis, yet failed to show any effect on forskolin-stimulated formation of cyclic AMP, even if 1 mM azetidine was applied. Since trans-azetidine-2,4-dicarboxylic acid (20 mM in 5 microliters) injected cerebroventricularly prolongs long-term potentiation induced by weak tetanization, a possible interaction with N-methyl-D-aspartate receptors was investigated using patch-clamp techniques. Neither facilitation of N-methyl-D-aspartate (500 microM) currents nor induction of non-specific currents was observed in the presence of 50 and 500 microM azetidine. Strong tetanus-induced long-term potentiation in the dentate gyrus of freely moving rats was not influenced by azetidine. In combination with the antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (200 mM in 5 microliters), however, the potentiation was attenuated and returned to baseline within 90 min. Blockade of N-methyl-D-aspartate receptors using 2-amino-5-phosphonopentanoate (20 mM in 5 microliters) prevented the potentiation in controls, but not in the azetidine group, where normal potentiation was observed for both the population spike amplitude and the excitatory postsynaptic potential. These data suggest that (i) trans-azetidine-2,4- dicarboxylic acid is an agonist at glutamate metabotropic receptors; (ii) a facilitation of induction and maintenance of long-term potentiation via N-methyl-D-aspartate receptors seems unlikely; and (iii) pharmacological activation of metabotropic receptors prior to tetanization appears to bypass the N-methyl-D-aspartate receptor dependence of the potentiation. In conclusion, a role for metabotropic glutamate receptors in both short-term and long-term potentiation is indicated by these data.
在本研究中，我们对新型代谢型谷氨酸受体激动剂反式氮杂环丁烷-2,4-二羧酸进行了生化分析，并研究了其在海马体长期增强效应中的作用。在表达代谢型受体1或5亚型的细胞系中，该化合物刺激磷酸肌醇水解，其半数有效浓度（EC50）值分别为189.4±6.4微摩尔和32.2±8.3微摩尔。在海马体切片中，反式氮杂环丁烷-2,4-二羧酸也增加了磷酸肌醇水解，但即使施加1毫摩尔氮杂环丁烷，对福斯高林刺激的环磷酸腺苷形成也未显示出任何影响。由于经脑室注射反式氮杂环丁烷-2,4-二羧酸（5微升中含20毫摩尔）可延长由弱强直刺激诱导的长期增强效应，因此使用膜片钳技术研究了其与N-甲基-D-天冬氨酸受体的可能相互作用。在存在50和500微摩尔氮杂环丁烷的情况下，未观察到N-甲基-D-天冬氨酸（500微摩尔）电流的促进作用或非特异性电流的诱导。自由活动大鼠齿状回中强强直刺激诱导的长期增强效应不受氮杂环丁烷影响。然而，与拮抗剂（R,S）-α-甲基-4-羧基苯基甘氨酸（5微升中含200毫摩尔）联合使用时，这种增强效应减弱，并在90分钟内恢复到基线水平。使用2-氨基-5-磷酸戊酸（5微升中含20毫摩尔）阻断N-甲基-D-天冬氨酸受体可阻止对照组中的增强效应，但在氮杂环丁烷组中则不然，在该组中群体峰电位幅度和兴奋性突触后电位均观察到正常的增强效应。这些数据表明：（i）反式氮杂环丁烷-2,4-二羧酸是谷氨酸代谢型受体的激动剂；（ii）通过N-甲基-D-天冬氨酸受体促进长期增强效应的诱导和维持似乎不太可能；（iii）在强直刺激之前对代谢型受体进行药理学激活似乎绕过了增强效应对N-甲基-D-天冬氨酸受体的依赖性。总之，这些数据表明代谢型谷氨酸受体在短期和长期增强效应中均发挥作用。
