Effects of Elevating Brain Derived Neurotrophic Factor on Hippocampal Physiology

脑源性神经营养因子(BDNF)引起海马脑片谷氨酸能突触的递质释放和长时程增强(LTP)明显增加。申请者的工作表明，它也对由胆碱能隔-海马区投射触发的节律有深远的影响。拟议的研究将确定上调BDNF是否能重现外源性BDNF的效果。第二个目标是验证BDNF对LTP的影响依赖于整合素家族中黏附受体的激活这一假设。AMPA型谷氨酸受体(Ampakines)的正调节剂将用于增加培养的海马片中BDNF的产量。在AMPA受体药物被淘汰，BDNF蛋白水平大大高于对照组后，将进行生理测试。特定目标#1验证了这样的预测：在高频刺激过程中，BDNF的增加将伴随着成对脉冲促进作用的减少和对‘突触疲劳’的更大抵抗。BDNF的TrkB受体的抑制剂将在这次和后续的实验中使用，以证实Ampakine治疗的结果取决于神经营养素。特殊目的#2研究突触后的功能和可塑性，包括突触反应的NMDA成分和LTP的诱导/表达。这项实验与项目二的一个组成部分密切相关。具体目的#3比较胆碱能诱导的脑源性神经营养因子升高脑片的β节律与 枷锁控制(与项目4协作)。最近发现的自发节律将被用来确定BDNF的作用是否对胆碱能调制具有选择性。具体目标#4将测试(A)BDNF引起的LTP增强是否被整合素拮抗剂阻断，以及(B)BDNF是否激活整合素。具体目的#5测试BDNF蛋白含量急性(6小时)和慢性(5天)增加将与突触生理的不同变化有关的预测。间歇性应用Ampakines将导致AIM#5中BDNF蛋白的慢性增加(见项目一)。这些研究将1)共同提供一个 首先描述伴随药物升高的内源性BDNF水平的生理变化，2)探索神经营养因子调节可塑性的新途径，以及3)解决AMPA受体调节剂临床使用的关键问题。

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.