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

癫痫网络中癫痫发作产生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中减少，以及在颞叶癫痫（TLE）患者中。相反，体周抑制保持不变甚至增加。然而，体周抑制由两种类型的GABA能中间神经元提供，它们表达小清蛋白（PV）或胆囊收缩素（CCK）。PV篮状细胞（BC）显示快速尖峰放电，并介导快速的，“阶段性”的抑制形式，这有助于精确的时间放电和振荡同步在皮层网络。相比之下，CCK BC显示出较低频率、规则的放电，并介导较慢的（“强直性”）、行为状态依赖性抑制和调节神经元兴奋性。 我们建议，这两种BC类型的差异影响癫痫发作的出现和疾病的进展作出贡献：抑制CCK BCs变得减少，因此神经元兴奋性增加，癫痫发作的阈值变得降低。相反，PV BC的抑制作用得以维持甚至增加。然而，PV BC介导的抑制不能抵消更高的兴奋性，而是促进同步化和高频振荡，导致改变的节律发生。这种机制可能会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防止癫痫发作在一些patients.To测试这些假设，我们将采用一种结合神经解剖学，电生理学和计算的方法，专注于慢性小鼠模型TLE。我们将使用体视学方法描述控制和癫痫海马中PV和CCK BCs的数量、细胞分布和突触连接的变化。我们将研究内在和突触特性的变化，特别是代谢型受体（如GABAB受体）对GABA能输出和突触后兴奋性的调节。这些生理调查将补充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BCs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 BCs介导的体周抑制中涉及的细胞和突触机制的分歧。以及它们在TLE中的不同作用。此外，我们将获得重要的见解，改变节律和癫痫发作的产生机制，在TLE，可以帮助我们更好地了解耐药性，并确定新的治疗途径

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