The Role Of GABA_A Receptor In The Thalamic Reticular Nucleus Under Propofol And Isoflurane Anesthesia

Background and objective: Recent studies show that the thalamus plays an important role in anesthesia and sleep,especially thalamic reticular nucleus(TRN),which is a pivotal nucleus of inhibitory thalamocortical system.TRN has been shown to participate in NREM sleep.However,whether TRN is also involved in the process of general anesthesia is not clear.Therefore,our experiment utilizes the methods of microinjection and electrophysiological techniques to observe the effect of TRN on loss of righting reflex(LORR)and resumption of righting reflex(RORR)with continuous propofol or isoflurane anesthesia.Subsequently,we observe the changes of TRN local field potentials(LFPs)and cortical electroencephalogram(EEG)by activating or inhibiting the GABAA receptors of TRN.The experiment is done to investigate the role of TRN in the process of propofol anesthesia or isoflurane anesthesia,as well as to provide a new target for the study of general anesthesia.Methods:This experiment includes three parts.Part 1:behavioral observation :TRN microinjection models of rats were established and all model rats were randomly divided into two groups: Propofol anesthesia group(Pro group)and Isoflurane anesthesia group(Iso group).Each group contained 15 rats.We do the microinjection experiments every 3 days.In this before and after self-control study,the rats were microinjected with saline,GABAAR agonists(muscimol,0.5 g/ul)and GABAAR antagonist(Gabazine 0.5 g/ul)for 1ul respectively before anesthesia.In every group,rats were injected with saline(1?l/side)and 1 ?l muscimol or gabazine(3 days later)vehicle into the TRN and then anesthetized with propofol or isoflurane.Later,LORR time and RORR time were recorded under continuous propofol or isoflurane anesthesia.Subsequently,TRN microinjection models were reestablished and the effect of activation or inhibition of TRN's GABAAreceptors on the sensitivity of anesthetic drugs were observed.Finally,histological methods were carried out to verify the location of the microinjection cannula.Part 2: LFPs of TRN recording: TRN microinjection models were established.Then the rats in either Pro group or Iso group were randomly divided into three small groups:saline group,muscimol group and Gabazine group,each group contained 8 rats.LFPs ofTRN were recorded for 600 s before and after TRN microinjection.At last,we made the comparison of the changes of TRN's LFPs in the same frequency band before and after TRN microinjection with the same depth of anesthesia.Part 3: EEG recording of motor cortex.The method of establishing microinjection models and grouping was almost the same with part 2.We recorded the EEG of motor cortex for 600 s before and after TRN microinjection with the same depth of anesthesia and made the comparison.Results:(1)Compared with saline microinjection,GABAAR agonists shortened the LORR time and significantly prolonged RORR time(P ? 0.05)in continuous propofol or isoflurane anesthesia.(P ? 0.05).Compared with saline microinjection,GABAAR antagonist had no effect on the induction but the RORR time was significantly shortened in continuous propofol or isoflurane anesthesia(P?0.05).(2)Compared with saline microinjection,Propofol and isoflurane concentration curve was obvious shift left microinjecting muscimol;But there are not affecting with microinjecting Gabazine.(3)Under propofol anesthesia,TRN microinjection of GABAAR agonist increased?ratio,decreased ? and ? ratio in local field potentials of TRN(P?0.05).Microinjecting GABAAR antagonist was the opposite effect on ? ratio,but increased?and ?(12-25Hz)ratio in local field potentials of TRN(P?0.05).TRN microinjection of muscimol increased?(1-4 Hz)and ?(4-8 Hz)ratio and decreased ?(8-12 Hz)and ?(25-60 Hz)ratio in motor cortex(P?0.05).Microinjecting Gabazine was just the opposite effect in motor cortex(P?0.05).(4)Under isoflurane anesthesia,TRN microinjection of GABAAR agonist increased?ratio,decreased ? ratio in local field potentials of TRN(P ? 0.05).Microinjecting GABAAR antagonist was the opposite effect in local field potentials of TRN(P ?0.05).TRN microinjection of muscimol augmented ? ratio and reduced ? ratio in motor cortex,without affecting other power(P?0.05).Microinjecting Gabazine just added ?ratio and cut down the ratio of ? ?? and ?(P?0.05).Conclusion:(1)TRN was involved in induction and emergence of propofol and isoflurane anesthesia.(2)The GABAA receptor of TRN is involved in the regulation of propofol and isoflurane efficacy.