The Critical Role Of Paraventricular Thalamic Nucleus On Regulating Loss Of Consciousness Induced By Propofol

Objective: General anesthesia has been increasing closely related to life and health,and there is great significance to explore its brain mechanism.Previous studies speculate d that the key area of action on the brain of general anesthetics might be located at the sleep-wake nucleus in the thalamus.Paraventricular thalamic nucleus(PVT),recently confirmed,is one of the most important arousal nuclei,and its neurons containing calreticulin have a strong rol e in promoting awaking.Therefore,whether the PVT neurons are the “on-off” or the key target of loss of consciousness(LOC)induced by general anesthesia needs to be solved.Methods: We used calcium fiber photometry combined with polysomno-graphy to explo re the changes of calcium signal level of a group of PVT neurons in the process of general anesthesia with propofol;Optogenetics method was used to explore the changes of behavior and cortical electrical activity in the mice caused by the short-term activ ation of PVT/CR neurons in the continuous,steady-state general anesthesia induced by propofol;Chemical genetic method was applied to explore the effects of specific activation of PVT/CR neurons on the sensitivity of propofol anesthesia and the induction and emergence time.Finally,the whole-cell patch-clamp technique was used to explore the effect s of propofol on the activity of PVT neurons and the molecular mechanism of the effect of propofol at clinical concentrat ion on PVT neurons.Results: In the slow induction period with propofol,the real-time calcium signal of PVT neurons group in vivo decreased gradually,and decreased more obviously in LOC period,and previous to loss of electromyographic activity of mice in terms of time sequence;while in the recovery period,the calcium signal increased rapidly and kept pace with the re emergence of electro-myographic activity,and maintained at a high level afterwards.During the period of blue light stimulation,in Ch R2 group,there were 5/8 mice righting completely,while the other 3/8 were not completely righted,but with a significant and continuous head up activity.However,in m Cherry group,there was no significant awakening activity.The difference of total score about awakening between the two groups was statistically significant(P<0.01).In addition,during 30 seconds before and in light,the total power value of ? wave(0-4Hz)and ? wave(4-10Hz)in Ch R2 group mice both decreased significantly(P<0.05).But there was no significant difference in m Cherry group.In the pharmacogenetic self-control experiment,compared with the Saline group,activation of PVT/CR neurons with CNO caused propofol anesthesia induction tim e to be prolonged(P<0.05),the emergence time to be significantly shortened(P<0.01),and the curve of propofol dose relative to LORR rate to shift to the right and ED 50 increased from 19.3 mg/kg to 27.7 mg/kg.The results of whole-cell patch-clamp showed that propofol at 5,10,20(?M)inhibited the spike frequency of PVT neurons in a concentration-dependent manner(the difference between B.S.and Drug was statistically significant(P<0.05)),and reversible(the difference between Drug and wash was statis tically significant(P<0.05)).Picrotoxin blocked the effect of propofol at 10 ?M on the discharge frequency of PVT neurons.Propofol at 10 ?M increased the amplitude of minute inhibitory postsynaptic current(m IPSC)(P<0.05)and prolonged the decay time of m IPSC(P<0.05).Conclusion: The Loss and recovery of consciousness during general anesthesia with propofol are closely related to the level of the PVT neuron activity.Activation of PVT/CR neurons can accelerate the transition from anesthesia to awakening state and reduce the anesthesia sensitivity of propofol.Propofol increasing the opening time of the postsynaptic GABAA receptor channel of the PVT neurons may be one of the molecular mechanisms responsible for LOC.