Song Jun, Shen Guofu, Greenfield L John, Tietz Elizabeth I
Department of Physiology and Pharmacology, University of Toledo College of Medicine, Health Science Campus Formerly Medical University of Ohio, Toledo, OH 43614, USA.
J Pharmacol Exp Ther. 2007 Aug;322(2):569-81. doi: 10.1124/jpet.107.121798. Epub 2007 May 17.
Modification of glutamatergic synaptic function, a mechanism central to neuronal plasticity, may also mediate long-term drug effects, including dependence and addiction. Benzodiazepine withdrawal results in increased glutamatergic strength, but whether alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors (AMPARs) are functionally and structurally remodeled during benzodiazepine withdrawal is uncertain. Whole-cell recordings of rat hippocampal CA1 neurons, either acutely dissociated or in hippocampal slices, revealed that AMPAR function was enhanced up to 50% during flurazepam (FZP) withdrawal, without changes in whole-cell channel kinetic properties. Agonist-elicited AMPA currents showed a negative shift in rectification in the presence of spermine, suggesting augmented membrane incorporation of glutamate receptor (GluR) 2-lacking AMPARs. As GluR1-containing AMPARs are critical for activity-dependent alterations in excitatory strength, we sought to determine whether changes in GluR1 subunit distribution in CA1 neurons occurred during benzodiazepine withdrawal. Confocal image analysis revealed that FZP withdrawal promoted GluR1 subunit incorporation into somatic and proximal dendritic membranes of CA1 neurons without GluR2 subunit alterations. Findings of immunoblot studies were consistent with immunofluorescent studies indicating increased GluR1, but not GluR2, subunit protein levels in cytosolic, crude membrane and postsynaptic density-enriched fractions from CA1 minislices. As with long-term potentiation (LTP), the FZP-withdrawal-induced GluR1 incorporation into CA1 neuron membranes may require the GluR1-trafficking protein, synapse-associated protein 97, which was also elevated in membrane-associated fractions. Together, our findings provide evidence that during FZP withdrawal, increased membrane incorporation of GluR1-containing AMPARs and associated up-regulation of AMPAR functions in hippocampal CA1 pyramidal neurons share fundamental similarities with the mechanisms underlying LTP. This implies that glutamatergic neuronal remodeling observed in LTP also subserves physiological adaptations to drug withdrawal.
谷氨酸能突触功能的改变是神经元可塑性的核心机制，它也可能介导长期药物效应，包括依赖性和成瘾性。苯二氮䓬戒断会导致谷氨酸能强度增加，但在苯二氮䓬戒断期间，α-氨基-3-羟基-5-甲基异恶唑-4-丙酸（AMPA）受体（AMPARs）在功能和结构上是否发生重塑尚不确定。对大鼠海马CA1神经元进行全细胞膜片钳记录，无论是急性分离的神经元还是海马脑片中的神经元，结果显示在氟西泮（FZP）戒断期间，AMPAR功能增强了50%，而全细胞通道动力学特性没有变化。在精胺存在的情况下，激动剂诱发的AMPA电流在整流方面出现负向偏移，这表明缺乏谷氨酸受体（GluR）2的AMPARs在膜上的整合增加。由于含GluR1的AMPARs对兴奋性强度的活动依赖性改变至关重要，我们试图确定在苯二氮䓬戒断期间，CA1神经元中GluR1亚基分布是否发生变化。共聚焦图像分析显示，FZP戒断促进了GluR1亚基整合到CA1神经元的体细胞和近端树突膜中，而GluR2亚基没有改变。免疫印迹研究结果与免疫荧光研究一致，表明来自CA1微小脑片的胞质、粗膜和富含突触后致密物的组分中，GluR1亚基蛋白水平增加，而GluR2亚基蛋白水平没有增加。与长时程增强（LTP）一样，FZP戒断诱导的GluR1整合到CA1神经元膜中可能需要GluR1转运蛋白——突触相关蛋白97，其在膜相关组分中也有所升高。总之，我们的研究结果提供了证据，表明在FZP戒断期间，含GluR1的AMPARs在海马CA1锥体神经元中的膜整合增加以及AMPAR功能的相关上调与LTP的潜在机制有基本相似之处。这意味着在LTP中观察到的谷氨酸能神经元重塑也有助于对药物戒断的生理适应。
