Structure and function of the hippocampal CA2 region in temporal lobe epilepsy

人类颞叶癫痫(TLE)的特点是难治性癫痫发作，主要起源于海马区，同时伴有海马区结构的改变。后者包括部分AMMONS角(CA3、CA1)和门区的主细胞和中间神经元的丢失，反应性胶质增生和颗粒细胞层的分散。相反，CA2区的神经元对TLE引起的病变大多具有抵抗力。尽管有这一显著特征，但由于缺乏合适的方法来准确区分CA2主细胞与邻近的CA3和CA1区，迄今几乎没有人研究CA2区在TLE中的作用。最近，新的方法(如病毒示踪、CA2特异性抗体和转基因小鼠品系)被开发出来，从而可以对CA2进行有针对性的研究，并对其结构、连接性和健康大脑的功能产生新的见解。我们计划使用这些方法，在TLE小鼠模型和癫痫手术中获得的人类海马区组织中，研究CA2在癫痫海马区网络中的突触整合中的作用。我们的项目旨在确定保留的CA2区在癫痫发作和传播中可能发挥的关键作用，因为由于CA3和CA1区的神经元丢失，这些区域的功能高度受损。因此，我们将使用小鼠的海马内海人藻酸盐模型和来自癫痫手术的人海马区组织，我们直接从国防部获得。神经外科医生。利用组织学方法(免疫细胞化学、原位杂交)，我们将量化动物模型和患者组织中CA2区域的保存程度，并将其与临床参数(例如癫痫发作频率、癫痫持续时间、癫痫发作年龄)相关联。我们将使用在齿状颗粒细胞及其轴突中表达绿色荧光蛋白的转基因小鼠品系，用共聚焦和电子显微镜来表征CA2区苔藓纤维的投射。特定的病毒示踪剂将使我们能够检测CA2区的突触输入和输出，并表征其与病理性海马网络的整合。此外，我们将在体内进行局部场电位和单细胞活动的电生理记录，以研究CA2在癫痫活动中的功能作用。此外，我们将在人类海马组织和癫痫小鼠的急性切片上进行膜片钳记录，以测量CA2锥体细胞的生理特性和癫痫可能的变化。我们项目的广泛方法，将动物模型的易获得性和灵活性与人类TLE的临床情况相结合，为CA2的作用提供了新的见解，这可能是新的治疗方法的奠基。

Human temporal lobe epilepsy (TLE) is characterized by refractory epileptic seizures mainly of hippocampal origin together with structural changes in the hippocampus. The latter include the loss of principal cells and interneurons in parts of the Ammons horn (CA3, CA1) and hilus, reactive gliosis and the dispersion of the granule cell layer. In contrast, the neurons of the CA2 region are mostly resistant to the pathological changes induced by TLE. Despite this conspicuous feature the role of the CA2 region in TLE has hardly been investigated up to now due to a lack of suitable methods to precisely distinguish CA2 principal cells from the neighboring regions CA3 and CA1. Recently, novel methods (e.g., viral tracing, CA2-specific antibodies and transgenic mouse lines) have been developed allowing for targeted investigation of CA2 and yield new insights into its structure, connectivity and function in the healthy brain. We are planning to use these methods, both, in a well-established mouse model for TLE and in human hippocampal tissue obtained from epilepsy surgery to investigate the role of CA2 with respect to its synaptic integration in the epileptic hippocampal network. Our project aims at determining a critical role that the preserved CA2 region might play in seizure onset and propagation since CA3 and CA1 are functionally highly impaired due to neuronal loss in these regions.We will therefore use the intrahippocampal kainate model in mice and human hippocampal tissue from epilepsy surgery, which we obtain directly from the Dept. of Neurosurgery. Using histological methods (immunocytochemistry, in situ hybridization) we will quantify the degree of preservation of the CA2 region in the animal model and patient tissue and correlate it with clinical parameters (e.g., frequency of seizures, duration of epilepsy, age at epilepsy onset). We will characterize the mossy fiber projection in the CA2 region with confocal and electron microscopy using a transgenic mouse line that expresses green-fluorescent protein in dentate granule cells and their axons. Specific viral tracers will allow us to detect the synaptic in- and outputs of the CA2 region and to characterize its integration in to the pathological hippocampal network. Furthermore, we will perform electrophysiological in vivo recordings of local field potentials and single cell activity to investigate the functional role of CA2 in epileptic activity. In addition, we will perform patch-clamp recordings in acute slices from human hippocampal tissue and epileptic mice to measure the physiological properties of CA2 pyramidal cells and possible alterations in epilepsy. The broad approach of our project, which combines the easy accessibility and flexibility of the animal model with the clinical condition of human TLE promises new insights into the role of CA2, which might be seminal for new therapeutic approaches.