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，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（长期增强（LTP）和长期抑制（LTD））随着发育而改变。这些过程涉及由特定的NMDA受体（NR）亚基触发的谷氨酸受体（GluR）亚基的改变。我们的行为数据表明，大鼠早期癫痫发作（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。与之前的生化研究表明GluR2是孤立下调的相反，我们的电生理数据表明突触GluR1在ELS后短暂上调，但随后被保留在内部池中。NR2A的总表达量永久降低。我们假设GluR1的短暂上调巩固了异常的发育轨迹。这一轨迹导致GluR1和NR2A的进一步异常调节，随后介导LTP和LTD的异常以及我们在ELS后观察到的学习障碍。亚突触机制的异常表达调节了GluR1和NR2A的这些改变，并造成了长期影响。目前，临床上还没有针对这种常见、使人衰弱且费用昂贵的疾病的治疗干预措施。对不成熟的兴奋性突触易受早期发作影响的原因和由此产生的持久变化的全面描述，将为这一缺陷以及发育中的突触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，我们提出了涉及大鼠体外电生理和生化研究的三个特定目的：特定目的1 (SA1)：在发育早期表达同源GluR1受体使CA1海马突触易受ELS影响。特异性Aim 2 (SA2): ELS引起GluR1和NR2A受体表达的快速、持续改变，这与正常发育相反。特异性目的3 (SA3): ELS后GluR1和NR2A受体表达的持续改变是由亚突触机制表达的改变介导的。这些目标将为未来r01资助的机制研究提供必要的证据，这些研究旨在解决药物干预问题，防止ELS对学习障碍的影响。

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.