Clinckers Ralph, Gheuens Sarah, Smolders Ilse, Meurs Alfred, Ebinger Guy, Michotte Yvette
Department of Pharmaceutical Chemistry, Drug Analysis and Drug Information, Research Group Experimental Pharmacology, Vrije Universiteit Brussel, Brussels, Belgium.
Epilepsia. 2005 Jun;46(6):828-36. doi: 10.1111/j.1528-1167.2005.57004.x.
Our recent work (Clinckers et al., J Neurochem 2004;89:834-43) demonstrated that intrahippocampal perfusion of 2 nM dopamine or serotonin via a microdialysis probe offered complete protection against focal pilocarpine-induced limbic seizures and did not influence basal extracellular hippocampal glutamate levels. Ten nanomolar dopamine or serotonin perfusion, however, worsened seizures and was accompanied by significant extracellular glutamate increases to approximately 200%. The significance of these glutamate elevations in seizure generation remains unclear. The present microdialysis study investigated the modulatory role of extracellular hippocampal glutamate levels in these monoaminergic protective and proconvulsant effects.
A first group of male Wistar albino rats was perfused intrahippocampally for 240 min with 6.25 microM glutamate alone to increase extracellular levels by 200%. Other animals were perfused with anticonvulsant concentrations of monoamines throughout the experiments while receiving continuous coperfusions of 6.25 microM glutamate either before, during, and after (240 min) or only after (100 min) pilocarpine perfusion (40 min). Rats were scored for epileptic behavior, and the mean scores were compared with those of the control group. Microdialysates were analyzed for monoamine and glutamate content with microbore liquid chromatography.
No convulsions occurred during glutamate perfusion alone. When monoamines and glutamate were coperfused before pilocarpine administration, the anticonvulsant effect of the monoamines was lost. Glutamate addition after pilocarpine administration did not affect monoaminergic seizure protection.
These results indicate that extracellular glutamate increases per se do not necessarily induce seizures but that they can modulate the anticonvulsant effects exerted by hippocampal monoamines.
我们最近的研究工作（Clinckers等人，《神经化学杂志》2004年；89卷：834 - 43页）表明，通过微透析探针向海马内灌注2纳摩尔的多巴胺或血清素，可提供完全保护，防止毛果芸香碱诱导的局灶性边缘叶癫痫发作，且不影响海马基底细胞外谷氨酸水平。然而，灌注10纳摩尔的多巴胺或血清素会使癫痫发作恶化，并伴有细胞外谷氨酸显著增加至约200%。这些谷氨酸升高在癫痫发作产生中的意义仍不清楚。本微透析研究调查了海马细胞外谷氨酸水平在这些单胺能保护和促惊厥作用中的调节作用。
第一组雄性Wistar白化大鼠海马内灌注6.25微摩尔谷氨酸，持续240分钟，以使细胞外水平增加200%。其他动物在整个实验过程中灌注抗惊厥浓度的单胺，同时在毛果芸香碱灌注（40分钟）之前、期间和之后（240分钟）或仅在之后（100分钟）持续共灌注6.25微摩尔谷氨酸。对大鼠的癫痫行为进行评分，并将平均得分与对照组进行比较。用微径液相色谱分析微透析液中的单胺和谷氨酸含量。
单独灌注谷氨酸时未发生惊厥。在毛果芸香碱给药前共灌注单胺和谷氨酸时，单胺的抗惊厥作用丧失。毛果芸香碱给药后添加谷氨酸不影响单胺能癫痫保护作用。
这些结果表明，细胞外谷氨酸增加本身不一定诱发癫痫发作，但它们可以调节海马单胺所发挥的抗惊厥作用。
