Glycine Channels and Hippocampal Excitability

士的宁敏感甘氨酸门控氯通道（GlyRs）在大脑中的抑制作用在很大程度上被忽视了，尽管已知这些受体在整个中枢神经系统中都有表达。有趣的是，在一些癫痫动物模型中，脑脊液（CSF）中甘氨酸水平的增加抑制了海马和皮层中重复的神经元放电，暗示了甘氨酸受体在调节神经元兴奋性方面的重要功能。GlyRs在海马体中表达，海马体是一个高度依赖有效神经元抑制来维持正常功能的大脑区域，然而，这些受体的生理作用尚不清楚。该提议的主要假设是，在海马中，GlyRs的激活提供了一种未被描述的基本抑制机制，通过直接激活突触后受体来抑制兴奋性锥体细胞和抑制性中间神经元的活动，此外，GlyR的激活通过抑制突触传递来限制神经元网络的活动。本研究的长期目标是建立GlyR在海马中的新作用，并了解介导GlyR激活对神经元活动影响的细胞机制。大鼠海马切片中锥体细胞的细胞外突起记录以及锥体细胞和中间神经元的全细胞和穿孔斑块记录将与药理学工具相结合，以检查整个发育过程中海马突触后GlyRs的功能表达，并确定这些受体的激活如何影响突触网络。我们将仔细解决以下具体目标：1)验证GlyR在锥体细胞和中间神经元的功能性表达在整个发育过程中持续的假设，以及这两种细胞类型表达的GlyR的生理和药理学性质是相同的；2)验证GlyR激活通过突触后介导的传导抑制，在基础和过度兴奋条件下限制突触网络活动的假设。在本研究中使用海马切片制备的优点是允许在一个特征良好的系统中检查甘氨酸对单个神经元和突触回路的直接作用，其中记录的神经元保持在其原生突触环境中。我们的方法有望产生新的信息，这将为研究GlyRs的抑制作用开辟新的领域。此外，预计本研究的结果将为预防癫痫发作活动的新治疗策略的设计提供见解。

An inhibitory role of strychnine-sensitive glycine-gated chloride channels (GlyRs) in the brain has largely been ignored, despite the known expression of these receptors throughout the CNS. Interestingly, in some animal models of epilepsy, increasing the glycine levels in cerebral spinal fluid (CSF) depresses repetitive neuronal firing in hippocampus and cortex, implicated an important function of GlyRs in modulating neuronal excitability. GlyRs are expressed in hippocampus, a brain region highly dependent upon effective neuronal inhibition for normal function, however, the physiological role of these receptors is simply not known. The major hypothesis of this proposal is that in hippocampus, activation of GlyRs provides an undescribed, fundamental inhibitory mechanism that depresses the activity of excitatory pyramidal cells and inhibitory interneurons via direct activation of post-synaptic receptors and furthermore, that GlyR activation limits the of the neuronal network by depressing synaptic transmission. The long-term goal of this proposal is to establish a new role for GlyRs in hippocampus and to understand the cellular mechanisms mediating the effects of GlyR activation on neuronal activity. Extracellular popspike recordings of pyramidal cells and whole-cell and perforated patch recordings of pyramidal cells and interneurons in rat hippocampal slices will be combined with pharmacological tools to examined the functional expression of post- synaptic GlyRs in hippocampus throughout development and determine how activation of these receptors affects the synaptic network. We will carefully address the following Specific Aims: 1) To test the hypothesis that functional GlyR expression by pyramidal cells and interneurons continues throughout development and that the physiological and pharmacological properties of GlyRs expressed by these two cell types are the same and 2) To test the hypothesis that GlyR activation limits the activity of the synaptic network under basal and hyperexcitable conditions through a post-synaptically-mediated depression of transmission. The use of the hippocampal slice preparation in this study has the advantage of allowing direct glycine effects on individual neurons and synaptic circuits to be examined in a well-characterized system, where recorded neurons remain in their native synaptic environment. Our approach is anticipated to yield novel information that will pave the way for a new area of investigation into the inhibitory role of GlyRs. Furthermore, it is expected that the results from this study will provide insight into the design of novel therapeutic strategies for the prevention of seizure activity.