Effects of TrkB Activation on Abnormalities in Neocortical FS Interneurons

描述（申请人提供）：创伤性脑损伤（TBI）导致大脑皮层异常，感觉和运动功能障碍，认知异常和癫痫。在最近的冲突中遭受严重脑震荡后幸存下来的大量个体可能发展为癫痫，这强调了了解潜在病理生理过程和制定预防策略的必要性（Garga和Lowenstein， 2006）。该项目的一个目标是获得关于可能改善或预防这种创伤后异常的方法的基本信息。损伤释放化学递质GABA的神经细胞是创伤性脑损伤的常见结果。这些抑制性细胞“中间神经元”的结构和功能的改善，可能会预防一些损伤的后果，包括癫痫。初步结果表明，快速尖峰（FS）抑制性中间神经元是皮层中最常见的中间神经元类型，在部分切断与周围大脑的连接（“下切”）而产生的皮质损伤区域中存在异常的神经过程和释放GABA的缺陷。由于这种缺陷和其他缺陷，下凹皮层变得过度兴奋，并经常产生类似于人类局灶性癫痫的脑电图活动的癫痫样电活动。神经营养蛋白BDNF及其受体TrkB对中间神经元的发育、生长和维持很重要，并且在损伤区域减少，导致TrkB激活可能纠正FS或其他中间神经元的异常并改善损伤皮层的功能。为了验证这一假设，将在麻醉的啮齿动物和用一种新设计的“小”分子LM22A-4治疗的动物身上进行削弱，LM22A-4进入大脑并激活TrkB受体。治疗约2周后，再次麻醉啮齿动物，并使用标准的体外切片和膜片钳技术获取药物治疗动物和生理盐水对照组损伤区域单个中间神经元和兴奋细胞的记录。单个神经细胞的活动

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) results in abnormalities in cerebral cortex and disorders of sensory and motor function, cognitive abnormalities and epilepsy. The potential development of epilepsy by the large number of individuals, who have survived severe concussive injury during recent conflicts, emphasizes the need for understanding the underlying pathophysiological processes and the development of prophylactic strategies (Garga and Lowenstein, 2006). A goal of this project is to obtain basic information on approaches that may improve or prevent such posttraumatic abnormalities. Injury to nerve cells that release the chemical transmitter GABA is a common result of TBI. Improvement in the structure and function of these inhibitory cells, "interneurons", may prevent some of the consequences of injury, including epilepsy. Preliminary results show that fast-spiking (FS) inhibitory interneurons, the most common type of interneuron in cortex, have abnormal nerve processes and defects in releasing GABA in areas of cortical injury produced by partially cutting connections with surrounding brain ("undercuts"). Undercut cortex becomes hyperexcitable due to this and other defects and often generates epileptiform electrical activity that resembles EEG activity in human focal epilepsy. A neurotrophic protein BDNF, and its receptor TrkB, are important for development, growth and maintenance of interneurons, and are reduced in the injured area, leading to the hypothesis that TrkB activation may correct abnormalities in FS or other interneurons and improve function in the injured cortex. To test this hypothesis, undercuts will be made in anesthetized rodents, and animals treated with a newly- engineered "small" molecule, LM22A-4, that enters the brain and activates the TrkB receptor. After treatment for ~2 weeks, rodents are re-anesthetized, and standard in vitro slice and patch clamp techniques used to obtain recordings from single interneurons and excitatory cells in areas of injury from drug-treated animals and saline controls. Activities of individual nerve cells and large groups of neurons ("field potentials") will be analyzed with appropriate software. Laser-activated release of the excitatory chemical transmitter, glutamate, will be used to map changes in excitatory and inhibitory connections in neural networks within individual slices, and effects of chronic LM22A-4 treatment. The structure of single cells will be measured after filling them with a marker called biocytin, staining slices with antibodies, and using computer-controlled microscopic imaging techniques, including light and confocal microscopy. The aims of these experiments are to determine whether activation of the TrkB receptor will improve the anatomical and functional abnormalities in FS interneurons, restore normal release of GABA and favorably affect nerve circuits in the injured cortex.