Role Of Optogenetic Modulation Of Astrocytes In Neocortical Seizures

Neocortical epilepsy is a common type of epilepsy.It frequently becomes drug-resistant,which indicates a poor prognosis.Traditional treatment targeting at neurons is inefficient and has many side effects.It is necessary to find safer and more effective therapeutic targets.Recent studies have shown that astrocytes may play an important role in epilepsy.The disorder of neurotransmitters,ions and water in astrocytes can promote neuronal excitability and hypersynchronism.The immune response and persistent inflammation mediated by astrocytes can promote seizures.However,because astrocytes and neurons have many similar targets and have been unable to achieve specific modulation.The causal relationship between astrocytes activation and epilepsy is unclear.This study aims to explore the role of astrocytes in epilepsy and whether specific modualtion of astrocytes can safely and effectively treat neocortical seizures.First of all,in this study,we use optogenetics to achieve the purpose of specific modulation of astrocytes.We transfected a photosensitive protein ChR2 into astrocytes and stimulated it by blue light.In this experiment,we found that optogenetic modulation of astrocytes attenuated the severity of neocortical seizures induced by kainic acid,significantly prolonged the onset of seizures and the latency to GS,reduced the seizure stage and the number of GS.This anti-seizure effect was not dependent on the frequency of light.Furthermore,optogenetic modulation of astrocytes in different seizure phases(early stage and late stage)could attenuate neocortical seizures,indicationg its important role in the formation and spread of seizures.At the same time,optogenetic modulation of astrocytes attenuated the severity of neocortical seizures induced by pilocarpine,significantly prolonged the latency to GS and reduced the mortality.Furthermore,in order to resolve why modualtion of astrocytes had an anti-seizure effect,we employed in vivo single-unit recording.In this experiment,we found that optogenetic modulation of astrocytes can inhibit the firing of pyramidal neurons in a frequency dependent manner.When the firing frequency of pyramidal neurons is low,the inhibitory effect is not obvious.By contrast,when the frequency of the pyramidal neurons is higher,the inhibition effect is more obvious.In seizures,the frequency of pyramidal neurons is quite high,optogenetic modulation of astrocytes can inhibit the pyramidal neurons and exert the anti-seizure effect.By contrast,if we inhibited the pyramidal neurons by optogenetics,neurons had an anti-seizure effect across the whole stage instead of only in the early or late stage.At the same time,we found that inhibition of neocortical pyramidal neurons by optogenetics can affect the motor ability of mice.In addition,with the combination of pharmacology,chemical genetics,in vivo single-cell recording and specific virus intervention,the experiment further revealed that the anti-seizure effect of astrocytes is independent from the calcium signaling pathway in astrocytes.Instead,the activation of astrocytic Na+/K+ ATPase plays a major role in this process.Knockdown of the astrocytic Na+/K+ ATPase with virus can reverse the anti-seizure effect of pyramidal neurons with a high firing-rate.In the setting of seizures,the activation of Na+/K+ ATPase can promote Na+/K+ exchange and the influx of excessive extracellular K+,thereby reducing the excitability of the neural circuits.In conclusion,this study is the first to reveal that stimulation ChR2-expressing astrocytes by blue light can safely and effectively inhibit the neocortical seizures.This anti-seuzire effect was independent from the calcium signaling pathway in astrocytes,but related with astrocytic Na+/K+ ATPase activation,which inhibits the high-firing pyramidal neurons.Astrocytes,as a result,serve as a promising therapeutic target of neocortical epilepsy.This study provides new insights into the development of potential drugs in treating and preventing epilepsy.