Electrophysiological And Morphological Characterizations Of Dysmorphic Neurons In Focal Cortical Dysplasia

Background:Epilepsy is a common chronic disease in neurology caused by the abnormal synchronous discharge of neurons in the brain.In most cases,antiepileptic drugs can effectively control epilepsy,but about 30%of epilepsy cases are drug-resistant and can only be treated by surgical resection of the epilepstic focus.Focal cortical dysplasia(FCD)is the major cause of both pediatric and adult intractable epilepsy,and it is generally characterized by the dysmorphic neurons and cortical dyslamination in pathological examinations.However,the functional properties and epileptogenic mechanism of the dysmorphic neurons are remain unclear.Objective:In this study,brain tissue biopsies were obtained from the epilepsy cases caused by focal cortical dysplasia or other etiologies.We used a variety of experimental techniques to explore the electrophysiological and morphological characteristics of dysmorphic neurons and the possible mechanism of epileptogenesis in focal cortical dysplasia.Methods:Firstly,the electrophysiological properties of neurons in human brain epilepsy tissues were evaluated by whole-cell patch clamp technology.The electrophysiological characteristics of dysmorphic neurons were quantified.Subsequently,the morphology of record neurons were reconstructed through intracellularly filling of biocytin and immunofluorescence experiment.The morphological features of dysmorphic neurons were quantified.Through integrating electrophysiological and morphological analysis,key electrophysiological and morphological features of dysmorphic neurons were identified.In addition,we evaluated the glutamatergic and GABAergic synaptic inputs in dysmorphic neurons and the possible epileptogenic mechanism of dysmorphic neurons.Results:(1)The dysmorphic neurons in focal cortical dysplasia demonstrated similar electrophysiological properties with cortical pyramidal neurons,but not interneurons or fast-spiking neurons.(2)Through the unsupervised clustering algorithm,neurons could be divided into five morphological subclusters and three electrophysiological subclusters.Dysmorphic neurons were mostly in morphological cluster M1 and M2 subclusters,characterized by increased cell body size and complex dendritic structures.The dysmorphic neurons were more concentrated in E1 subclusters,characterized by higher rheobase,increased membrane capacitance and decreased input resistance.(3)The integrated analysis revealed distinct electrophysiological and morphological characterisitcs in the upper layer dysmorphic neurons.In the meantime,compared with upper layer pyramidal neurons,upper layer dysmorphic neurons received more GABAergic synaptic inputs,but fewer glutamatergic synaptic inputs.(4)The expression of Na+-K+-2C1-cotransporter 1(NKCC1)is upregulated in dysmorphic neurons in FCD,comparing with the autoptic brain tissues with no history of epilepsy.Conclusions:Dysmorphic neurons demonstrated similar electrophysiological properties with pyramidal neurons,but they have larger cell body size and more complex dendritic structures.The dysmorphic neurons were enriched in the upper layer cortex of FCD,and received enhanced GABAergic synaptic inputs but reduced glutamatergic inputs.In addition,NKCC1 was upregulated in dysmorphic neurons,suggesting that GABA may exert a depolarizing effect in dysmorphic neurons.The imbalance of synaptic exciation and inhibtion of dysmorphic neurons may lead to epilepsy in FCD.