Impact of early life seizures on glutamate receptors and synaptic function

描述(由申请人提供)：临床证据表明，婴儿和儿童癫痫发作会导致长期学习障碍。然而，在实验室研究中，对此提出的机制是不一致的，部分原因是不同的实验范式。调节学习和记忆的突触特性(长时程增强(LTP)和长时程抑制(LTD))随着发育而改变。这些过程涉及谷氨酸受体(GluR)亚单位的改变，而谷氨酸受体(GluR)亚单位由特定的NMDA受体(NR)亚单位触发。我们的行为数据表明，大鼠早期癫痫(ELS)的一次发作会导致后来的学习障碍。这在不改变神经元形态和连接的情况下发生。体外研究表明，海马LTP和LTD的改变与谷氨酸受体的异常调节一致。与先前的生化研究表明GluR2单独下调相反，我们的电生理数据表明突触GluR1在ELS后不久短暂上调，但后来在内部池中保持。NR2a的总表达永久减少。我们假设，GluR1的短暂上调巩固了一种异常的发育轨迹。这一轨迹导致了GluR1和NR2a的进一步异常调节，从而介导了LTP和LTD的异常以及我们在ELS后观察到的学习障碍。突触亚机制的异常表达调节了GluR1和NR2a的这些变化，并硬连接了长期影响。目前，对于这种常见的、使人虚弱和昂贵的疾病，临床上还没有可用的治疗干预措施。彻底描述是什么使未成熟的兴奋性突触容易受到早期癫痫发作的影响，以及由此导致的长期持久的变化，将为了解这一缺陷以及突触发育的神经生物学提供有价值的见解。为了验证我们的假设并解决相反的观察结果，我们提出了三个涉及大鼠体外电生理和生化研究的特定目标：特定目标1(SA1)：在发育早期同源GluR1受体的表达使CA1海马突触对ELs易感。特异性目标2(SA2)：ELS导致GluR1和NR2A受体表达的快速、持续变化，这与正常发育相反。特异性靶点3(SA3)：ELS后GluR1和NR2a受体表达的持续变化是通过突触下层机制的表达变化介导的。这些目的将为支持未来由R01资助的机械学研究提供必要的证据，这些研究旨在解决可以防止ELS对学习障碍的影响的药物干预。

DESCRIPTION (provided by applicant): Clinical evidence demonstrates that seizures in infants and children cause long-term learning disabilities. However in laboratory studies, the proposed mechanisms for this are inconsistent, partly due to different experimental paradigms. Synaptic properties mediating learning and memory (long-term potentiation (LTP) and long-term depression (LTD)) change with development. These processes involve alterations in glutamate receptor (GluR) subunits that are triggered by specific NMDA receptor (NR) subunits. Our behavioral data demonstrate that a single episode of early-life seizures (ELS) in rats causes later learning disability. This occurs without alteration of neuronal morphology and connections. In vitro studies show alterations in hippocampal LTP and LTD that are consistent with abnormal regulation of glutamate receptors. Contrary to prior biochemical studies suggesting isolated down-regulation of GluR2, our electrophysiological data suggests synaptic GluR1 is transiently up-regulated shortly after ELS but later held in internal pools. Total expression of NR2A becomes permanently decreased. We hypothesize that the transient up-regulation of GluR1 consolidates an abnormal developmental trajectory. This trajectory leads to further abnormal regulation of GluR1 and NR2A that subsequently mediates the abnormal LTP and LTD and the learning disability that we observe following ELS. Abnormal expression of sub-synaptic machinery regulates these alterations in GluR1 and NR2A and hard-wires the long term effects. Currently, there are no therapeutic interventions clinically available for this common, debilitating and costly condition. Thorough characterization of both what makes immature excitatory synapses vulnerable to early-life seizures and the resulting long lasting changes will provide valuable insight into this deficiency as well as the neurobiology of developing synapses. To test our hypothesis and resolve contrary observations we propose three Specific Aims involving in vitro electrophysiological and biochemical studies in rats: Specific Aim 1 (SA1): Expression of homomeric GluR1 receptors early in development makes CA1 hippocampal synapses vulnerable to ELS. Specifc Aim 2 (SA2): ELS causes a rapid, persistent alteration of expression of GluR1 and NR2A receptors that is contrary to normal development. Specific Aim 3 (SA3): The persistent alteration of expression of GluR1 and NR2A receptors following ELS is mediated by altered expression of sub-synaptic machinery. These Aims will provide the evidence necessary to support future R01-funded mechanistic studies that address pharmacological interventions that could prevent the effects of ELS on learning impairment.