Effects of Elevating Brain Derived Neurotrophic Factor on Hippocampal Physiology

脑源性神经营养因子（BDNF）可引起海马脑片神经元突触递质释放的适度增加和长时程增强（LTP）的显著易化。申请人的工作表明，它对胆碱能隔-海马投射触发的节律也有深远的影响。拟议的研究将确定BDNF的上调是否再现了外源性BDNF所获得的效果。第二个目标是检验BDNF对LTP的作用依赖于属于整合素家族的粘附受体的激活的假设。AMPA型谷氨酸受体的正调节剂（ampakines）将用于增加培养的海马切片中BDNF的产生。生理测试将在AMPA受体药物被洗出并且BDNF蛋白水平大大高于对照后进行。特定目标#1测试了这样的预测：在高频刺激期间，增加的脑源性神经营养因子将伴随着成对脉冲易化的减少和对“突触疲劳”的更大抵抗力。BDNF的trkB受体的抑制剂将用于本实验和后续实验，以证实ampakine治疗的结果取决于神经营养因子。具体目标#2检查突触后功能和可塑性，包括突触反应的NMDA组分和LTP的诱导/表达。这个实验与项目二的一个组成部分密切相关。具体目标#3比较了BDNF升高切片中胆碱能诱导的β-节律与 控制系统（与项目4合作）。最近发现的自发节律将用于确定BDNF的作用是否对胆碱能调节具有选择性。具体目标#4将测试（a）由BDNF引起的增强的LTP是否被整联蛋白拮抗剂阻断和（B）BDNF是否激活整联蛋白。具体目标#5测试了BDNF蛋白含量的急性（6小时）和慢性（5天）增加将与突触生理学的不同变化相关的预测。目标5中BDNF蛋白的慢性增加将通过间隔应用ampakines来诱导（见项目一）。这些研究将：（1）提供 首次描述了伴随药理学升高的内源性BDNF水平的生理变化，2）探索了神经营养因子可以调节可塑性的新途径，和3）解决了AMPA受体调节剂临床应用的关键问题。

Brain Derived Neurotrophic Factor (BDNF) causes a modest increase in transmitter release and a marked facilitation of long-term potentiation (LTP) at glutamatergic synapses in hippocampal slices. Work by the applicants indicates that it also has a profound effect on rhythms triggered by the cholinergic septo-hippocampal projections. The proposed studies will determine if up-regulation of BDNF reproduces the effects obtained with exogenous BDNF. A second goal is to test the hypothesis that BDNF's effects on LTP depend on activation of adhesion receptors belonging to the integrin family. Positive modulators of AMPA-type glutamate receptors (ampakines) will be used to increase BDNF production in cultured hippocampal slices. Physiological tests will be carried out after AMPA receptor drugs have been washed out and BDNF protein levels are greatly elevated above control. Specific Aim #1 tests the prediction that increased BDNF will be accompanied by reduced paired pulse facilitation and greater resistance to 'synaptic fatigue' during high frequency stimulation. Inhibitors of BDNF's trkB receptor will be used in this and subsequent experiments to confirm that the consequences of ampakine treatments depend on the neurotrophin. Specific Aim #2 examines post-synaptic functioning and plasticity including the NMDA components of synaptic responses and the induction / expression of LTP. This experiment is closely related to a component of Project Two. Specific Aim #3 compares cholinergically induced beta-rhythms in BDNF elevated slices with those in yoked controls (collaboration with Project 4). Recently discovered spontaneous rhythms will be used to determine if BDNF's effects are selective to cholinergic modulation. Specific Aim #4 will test if (a) the enhanced LTP caused by BDNF is blocked by integrin antagonists and (b) BDNF activates integrins. Specific Aim #5 tests the prediction that acute (6 hrs) and chronic (5 days) increases in BDNF protein content will be associated with different changes in synaptic physiology. Chronic increases in BDNF protein in Aim #5 will be induced with spaced applications of ampakines (see Project One). Together these studies will 1) provide a first description of the physiological changes that accompany pharmacologically-elevated endogenous BDNF levels, 2) explore a novel route whereby the neurotrophin could regulate plasticity, and 3) address issues that are critical to the clinical use of AMPA receptor modulators.