Cell-type specific changes in perisomatic inhibition in an animal model of temporal lobe epilepsy

癫痫网络中发生癫痫的主要机制是兴奋和抑制平衡的改变。事实上，有强有力的证据表明，树突抑制在动物模型以及人类颞叶癫痫（TLE）患者中有所减少。相反，周围抑制保持不变甚至增加。然而，细胞周围抑制是由两种表达小白蛋白（PV）或胆囊收缩素（CCK）的gaba能中间神经元提供的。PV篮状细胞（BCs）表现出快速的尖峰放电，并介导快速的“相位”形式的抑制，这有助于皮质网络中放电和振荡同步的精确定时。相比之下，CCK细胞表现出频率较低，有规律的放电，介导较慢（“强直”），行为状态依赖性抑制和调节神经元兴奋性。我们认为这两种类型的BC在癫痫中受到不同的影响，并有助于癫痫发作的出现和疾病的进展：CCK BC的抑制作用减弱，因此神经元兴奋性增加，癫痫发作的阈值降低。相反，PV - bc的抑制作用维持甚至增强。然而，PV - bc介导的抑制不能抵消高兴奋性，而是促进同步和高频振荡，导致节律发生改变。这样的机制可以增强癫痫发作的产生，至少部分地解释了为什么药物增强抑制不能预防某些患者的癫痫发作。为了验证这些假设，我们将采用神经解剖学、电生理学和计算方法相结合的方法，重点研究慢性小鼠TLE模型。我们将使用体视学方法来描述控制和癫痫海马中PV-和CCK bc的数量、细胞分布和突触连通性的变化。我们将研究内在和突触特性的变化，特别是代谢受体（如GABAB受体）对gaba能输出和突触后兴奋性的调节。这些生理研究将辅以定量免疫电镜分析的超微结构和分子变化。最后，我们将使用体外切片和计算网络模型分析细胞和突触特性的改变以及bc中GABAB受体的突触前和突触后分布如何影响微电路相互作用，并导致节律发生的改变和癫痫发作的产生。结果将有助于我们理解PV-和CCK bc介导的细胞周围抑制的细胞和突触机制的差异，以及它们在TLE中的不同作用。此外，我们将获得重要的见解，改变节律发生和癫痫发作的机制，可以帮助我们更好地了解耐药和确定新的治疗途径

A major mechanism underlying seizure generation in epileptic networks is an altered balance of excitation and inhibition. In fact, there is strong evidence that dendritic inhibition is reduced in animal models, as well as in human patients with temporal lobe epilepsy (TLE). In contrast, perisomatic inhibition remains unchanged or even increase. However, perisomatic inhibition is provided by two types of GABAergic interneuron which express either parvalbumin (PV) or cholecystokinin (CCK). PV basket cells (BCs) show fast-spiking firing and mediate a rapid, “phasic”-form of inhibition which contributes to the precise timing of discharge and oscillatory synchronization in cortical networks. In contrast, CCK BCs show lower-frequency, regular firing and mediate slower (“tonic”), behavior state-dependent inhibition and modulate neuronal excitability. We propose that the two BC types are differentially affected in epilepsy and contribute to the emergence of seizures and the progression of the disease: inhibition by CCK BCs becomes diminished, therefore neuronal excitability increases and the threshold for seizure generation becomes reduced. In contrast, inhibition by PV BCs is maintained or even increased. However, PV BC-mediated inhibition cannot counterbalance the higher excitability, but rather promotes synchronization and high frequency oscillations, leading to altered rhythmogenesis. Such a mechanism could potentiate seizure generation explaining, at least partially, why drugs enhancing inhibition cannot prevent seizures in some patients.To test these hypotheses, we will apply a combined neuroanatomical, electrophysiological and computational approach focusing on a chronic mouse model of TLE. We will characterize changes in the number, cellular distribution and synaptic connectivity of PV- and CCK BCs in control and epileptic hippocampus using stereological methods. We will investigate changes in the intrinsic and synaptic properties, in particular the regulation of the GABAergic output and postsynaptic excitability by metabotropic receptors, such as GABAB receptors. These physiological investigations will be complemented by quantitative immuno-electron microscopic analysis of ultrastructural and molecular changes. Finally we will analyze how the altered cellular and synaptic properties and the pre- and postsynaptic distribution of GABAB receptors in BCs influence microcircuit interactions and lead to altered rhythmogenesis and the generation of seizures using in vitro slice and computational network models.Results will contribute to our understanding of the divergence of cellular and synaptic mechanisms involved in perisomatic inhibition meditated by PV- and CCK BCs, as well as their differential role in TLE. Furthermore, we will obtain important insights into the mechanisms of altered rhythmogenesis and seizure generation in TLE that can help us better understand drug resistance and identify new therapeutic avenues