Department of Neurology, Zhongshan Hospital, Fudan University, 180 Fenglin Road, Shanghai, 200032, China.
Department of The State Key Laboratory of Medical Neurobiology, The Institutes of Brain Science and the Collaborative Innovation Center for Brain Science, Fudan University, Shanghai, China.
Mol Neurobiol. 2021 Jan;58(1):156-169. doi: 10.1007/s12035-020-02086-y. Epub 2020 Sep 10.
Focal cortical dysplasia (FCD) is a major cause for drug-resistant epilepsies. The molecular and cellular mechanisms of epileptogenesis in FCD are still poorly understood. Some studies have suggested that deficiencies of γ-aminobutyric acid (GABA) system may play an important role in type II FCD, but it remains controversial. In order to examine whether and how GABAergic interneurons and synaptic function are affected, we generated a somatic mTOR hyperactivation-based mouse model of type II FCD by in utero electroporation, quantified densities of interneurons in the malformed cortices, and recorded miniature inhibitory postsynaptic currents in dysmorphic neurons. We detected 20-25% reduction of GABAergic interneurons within malformed cortices, independent of cortical regions and cell subtypes but proportionate to the decrease of global neuron counts. GABAergic synaptic transmission from interneurons to mTOR hyperactivated dysmorphic neurons was dramatically disrupted, outweighing the decrease of interneuron counts. Postnatal mTOR inhibition partially rescued these alterations of GABAergic system. We also quantified the expression of GABA receptor, GABA transporter, and chloridion transporter encoding genes and found that their expression was relatively intact within the malformed cortices. Taken together, these results confirmed that GABAergic interneuron and synapse transmission are disturbed profoundly in an mTOR-dependent manner in type II FCD. Our study suggests that postsynaptic mechanisms independent of interneuron reduction or altered expression of GABA synapse genes might be accountable for the impaired GABAergic neurotransmission in type II FCD as well as other mTOR-related epilepsies.
局灶性皮质发育不良（FCD）是耐药性癫痫的主要原因。FCD 中致痫的分子和细胞机制仍知之甚少。一些研究表明，γ-氨基丁酸（GABA）系统的缺陷可能在 II 型 FCD 中起重要作用，但仍存在争议。为了研究 GABA 能中间神经元和突触功能是否受到影响以及如何受到影响，我们通过宫内电穿孔生成了一种基于体细胞 mTOR 过度激活的 II 型 FCD 小鼠模型，定量了畸形皮质中的中间神经元密度，并在畸形神经元中记录了微小抑制性突触后电流。我们检测到畸形皮质内 GABA 能中间神经元减少了 20-25%，与皮质区域和细胞亚型无关，但与神经元总数的减少成比例。来自中间神经元的 GABA 能突触传递到 mTOR 过度激活的畸形神经元的功能严重受损，超过了中间神经元数量的减少。产后 mTOR 抑制部分挽救了这些 GABA 能系统的改变。我们还定量了 GABA 受体、GABA 转运体和氯离子转运体编码基因的表达，发现它们在畸形皮质内的表达相对完整。综上所述，这些结果证实了 GABA 能中间神经元和突触传递在 II 型 FCD 中以 mTOR 依赖的方式受到严重干扰。我们的研究表明，在 II 型 FCD 以及其他 mTOR 相关癫痫中，突触后机制独立于中间神经元减少或 GABA 突触基因表达的改变可能导致 GABA 能神经传递受损。
