The Mechanisms Of General Anesthetics Protects Against Cardiac Arrest-induced Brain Injury And Early Exposure Affects Oligodendrocytes And Myelin Development In Zebrafish

Background and Objective: Cardiac arrest(CA)is a leading cause of death and disability worldwide,determining the prognosis of patients after cardiac arrest.Although many victims are initially resuscitated,they often need medical care for serious brain injury,even leading to a “persistent vegetative state”,it imposes a heavy financial burden to social and family.Therefore,it is need to explore therapies which restore and protect brain function after cardiac arrest.In the present study,we used transgenic Tg(Hu C: GCa MP5)zebrafish,in which neuronal activity was indicated by intracellular Ca2+ dynamic change,to observe neuronal activity dynamic change during CA.Methods: CA model was established in zebrafish by pressing heart with a glass micropipette at 7 day post-fertilization(dpf).Successful CA was accepted when the heart stop beating and blood flow in trunk and brain vascular ceased.Neuronal activity was monitored during CA by in vivo time-lapse confocal imaging using Tg(Hu C:GCa MP5)transgenic zebrafish.The neurologic outcome and neuronal apoptosis of zebrafish after CA was evaluated by behavioral test and TUNEL staining,respectively.The effects of general anesthetics pretreatment on CA-induced brain injury were observed.Results: The zebrafish brain generated a burst of Ca2+ wave after CA.The Ca2+ wave was firstly initiated at hindbrain and then sequentially propagated to midbrain and telencephalon,the neuron displayed Ca2+ overload after Ca2+ wave propagation.Consistent with this,our study further demonstrated that neuronal apoptosis was increased in CA zebrafish.The CA-induced Ca2+ wave propagation can be prevented by midazolam or ketamine pretreatment.Similarly,midazolam or ketamine pretreatment dramatically decreased the neuronal apoptosis and improved the survival rate in CA zebrafish.Conclusions: These findings provide the first in vivo evidence that general anesthetics pretreatment protects against CA-induced brain injury by inhibiting calcium wave propagation in zebrafish.Background and Objective: There are millions of children receiving general anesthetics every year in the world.However,more and more studies reported that early exposure to general anaesthetics causes widespread neuronal apotosis and long-term behavioral abnormalities in young animals.Clinical studies also reported abnormal behavior and impaired learning abilities in child after receiving general anaesthesia in their early life.Therefore,the neurotoxicity of general anaesthetics to the developing brain has raised a great deal of concerns during the past decades.Oligodendrocyte form myelin sheath to wrap axons,providing salutatory conduction of action potentials and proper functions of the nervous system,it is important for maintaining the integrity and proper development and function of the brain.So it will be significant to study the effect of general anaesthetics on oligodendrocytes.Methods: Zebrafish embryos were exposed to general anaesthetics from 30 to 96 h postfertilization(hpf).We screened the effects of general anaesthetics on oligodendrocyte development by in vivo time-lapse confocal imaging.Transmission electron microscopy(TEM)was used to detect the myelin development.The conduction velocity of axon potential and extended latency of audition evoked C-start response was examined by in vivo electrophysiological recording and behavior test,respectively.Immunohistochemistry and associated underlying mechanisms was performed by genetic knockdown the gene expression with Morpholino oligos(MOs).Results: We demonstrated that midazolam exposure decreased OPC proliferation and migration,but not caused cell apoptosis.Other general anesthetics such as etomidate and ketamine did not decrease the OPC number in dorsal spinal cord.In addition,midazolam exposure caused axon hypomyelination,leading to slower conduction velocity of axon potential and extended latency of audition evoked C-start response.These defects could be relieved by knockdown translocator protein(Tspo)gene expression,and mimicked by Tspo agonist,implying that midazolam early exposure affected oligodendrocyte development by activating Tspo activity.Conclusions: These findings suggest that midazolam could affect oligodendrocyte development in developing animal,and elucidate the potential TSPO-associated underlying mechanisms.