Effect Of Propofol On Spontaneous EEG Activities And The Release Of Neurotransmitters Of Cortical And Subcortical Structures

Despite decades of research into the molecular mechanism of anesthetic action, the mechanism by which propofol produce its different anesthetic endpoints,such as amnesia,hypnotic and loss of consciousness,immobility,analgesia,remains unclear.This study aimed to investigate the effects of propofol which produced different anesthetic endpoints on behavioral response,spontaneous electroencephalogram(EEG) activities and the efflux of major excitatory and inhibitory neurotransmitters of central nervous system in rats.Elucidation of the propofol-induced changes in multiple views and leveles with behavioral, neuroelectrophysiologic and neurobiochemical ways would help understanding the complicated mechanism of anesthetic actions of propofol.Part one Effects of propofol on spontaneous EEG activities of cerebral cortex and subcortical structures and on cortical-subcortial functional interactions in ratsExperiment 1 Effects of propofol on spontaneous EEG activities of parietal, frontal and occipital cortices and on interhemispheric functional interactionsObjective To investigate the effects of propofol on spontaneous electroencephalogram(EEG) activities of parietal,frontal and occipital cortices and interhemispheric cortical intraction by approximate entropy(ApEn) / correlation dimension(D2) and interhemispheric EEG cross-approximate entropy (C-ApEn) in rats.Method Thirty six male Wistar rats were divided into 3 groups randomly(n= 12),whose EEGs were recorded bipolarly with pairs of epidural electrodes in the left and fight parietal cortices,frontal cortices andoccipital cortices respectively.After recording 20min EEGs of awake state as baseline,anesthetic dose of propofol(10g/L) was started at 400μg/(kg·min) for 20mins and then increased to 600μg/(kg·min) for 20 mins and then to 800μg/(kg·min) for 20 mins while the rats were breathing spontaneously.Calculated and compared interhemispheric EEGs ApEn/D2 of different cortical regions and interhemispheric C-ApEn at different anesthetic dose level.In order to test the anesthetic effects of different dose of propofol used in this experiment,vibrissal and body touch respons,loss of righting reflex and loss of tail-clamped reflex respectively as criteria of anesthetic endpoints of sedation,unconsciousness and immobility were tested before all rats were subjected to be placed the epidural electrodes,.Results Most of the rats were in sedative state after propofol were infused at 400μg/(kg·min) for 20mins,and were in unconscious state(lost of righting reflex) after 600μg/(kg·min) propofol for 20mins and were in immobility state(lost of tail-clamped reflex) after 800μg/(kg·min) propofol for 20mins. ApEn and D2 of parietal,frontal and occipital cortices dose-dependently decreased as dose ofpropofol increased(p＜0.05).And the interhemispheric C-ApEn of parietal,frontal and occipital cortices dose-dependently decreased by propofol too(p＜0.05).Conclusion Propofol dose-dependently inhibited the spontaneous EEG activities of parietal,frontal,occipital cortices and the interhemispheric functional interaction,which may be involved in anesthetic actions of propofol Experiment 2 Effects of propofol on spontaneous EEG activities of subcortical structures and on cortical-subcortical functional interactionObjective To investigate the effects of propofol on spontaneous EEG activities of subcortical structures including ventral posteromedial thalamic nucleus(VPM),reticular thalamic nucleus(RTN) and pontine reticular nucleus oral part(PnO),and the effects of propofol on the cortical-subcortical and subcortical-subcortical functional interactions in rats.Method Forty eight male Wistar rats were divided into 4 groups randomly(n=12),whose spontaneous EEGs were recorded bipolarly with two pairs of epidural or deep electrodes in the left and right frontal cortices+VPMs,frontal cortices+RTNs,VPMs+RTNs and RTNs+PnOs respectively.After recording 20min EEGs of awake state as baseline, anesthetic dose of propofol(10g/L) was started at 400μg/(kg·min) for 20mins and then increased to 600μg/(kg·min) for 20 mins and then to 800μg/(kg·min) for 20 mins while the rats were breathing spontaneously.Calculated and compared ApEn/D2 of bilateral VPMs,RTNs and PnOs,and the C-ApEn of homolateral frontal cortex-VPM,frontal cortex-RTN,VPM-RTN and RTN-PnO at different anesthetic dose level.In order to test the anesthetic effects of different dose of propofol used in this experiment,vibrissal and body touch respons,loss of righting reflex and loss of tail-clamped reflex respectively as criteria of anesthetic endpoints of sedation,unconsciousness and immobility were tested before all rats were subjected to be placed the electrodes.Results ApEn and D2 of bilateral VPMs,RTNs and PnOs and C-ApEn of homolateral frontal cortex-VPM, frontal cortex-RTN,VPM-RTN and RTN-PnO all decreased as dose of propofol increased(p＜0.05).But the decreasing amplitudes(extents) of C-ApEn of frontal cortex-VPM and frontal cortex-RTN are greater than that of VPM-RTN and RTN-PnO.Conclusion Propofol dose-dependently inhibited the spontaneous EEG activities of some subcortical structures including thalamus and reticular formation of brain stem.Moreover,propofol attenuated the functional interactions of cortex-thalamus and thalamus- reticular formation of brain stem too,which may be involved in anesthetic actions of propofol.Part Two Effect of propofol on release of excitatory and inhibitory amino acids in cortex,subcortical structures and dorsal horn of spinal cord in ratsObjective To investigate effect of propofol on the release of excitatory and inhibitory amino acids in frontal cortex,ventral posteromedial thalamic nucleus (VPM),reticular thalamic nucleus(RTN) and dorsal horn of spinal cord in rats to provide a theoretical basis for different anesthctic endpoints of propofol.Method Thirty two male Wistar rats were divided into 4 groups randomly(n=8),which is cortex group,VPM group,RTN group and spinal cord group.The efflux of glutamate(Glu),γ-aminobutyric acid(GABA) and glycine(Gly) in the primary somatosensory cortex,VPM,RTN and dorsal horn of spinal cord of rats in each group was detected using intracerebral microdialysis probe and LM liner microdialysis probes respectively under an awake condition and three dose level propofol anesthesia.Anesthetic dose of propofol(10g/L) was started at 400μg/(kg·min) for 20mins and then increased to 600μg/(kg·min) for 20 mins and then to 800μg/(kg·min) for 20 mins while the rats were breathing spontaneously. The amino acids in the microdialysate samples were tested using high performance liquid chromatography(HPLC).In order to test the anesthetic effects of different dose of propofol used in this experiment,vibrissal and body touch respons,loss of righting reflex and loss of tail-clamped reflex respectively as criteria of anesthetic endpoints of sedation,unconsciousness and immobility were tested before all rats were subjected to be placed the guide cannula for the microdialysis.Results Efflux of Glu,GABA and Gly in frontal cortex and RTN decreased under propofol anesthesia at 400μg/(kg·min) for 20mins and 600 μg/(kg·min) for 20 mins,and then increased under bigger dose of propofol(600μg/(kg·min) for 20 mins) anesthesia.But GABA increased faster and greater than Glu and Gly in frontal cortex while Glu increased more significant than GABA and Gly in RTN.GABA in frontal cortex and Glu in RTN under propofol(800μg/(kg·min) for 20 mins) producing immobility were all higher than baseline (p＜0.05).Propofol dose-dependently decreased Glu release in VPM,but a transient and slight decrease at 600μg/(kg·min) propofol for 20 mins and increase at 800μg/(kg·min) propofol for 20 mins in GABA and Gly efflux was observed in VPM.Efflux of Glu,GABA and Gly in spinal dorsal horn decreased under propofol anesthesia at all three dose leves.But propofol dose-dependently inhibited the release of Glu in dorsal horn,while efflux of GABA and Gly decreased less than 20%under low dose propofol anesthesia(400μg/(kg·min) for 20 mins) and then kept stable when dose of propofol increased enough to produce unconciousness and immobility.Conclusion Propofol had different effect on efflux of excitatory and inhibitory amino acids in different cortical and subcortical regions.The predominant inhibitory effect induced by propofol at cortex and VPM may be involved in the anesthetic actions of propofol,while the excitatory effect of propofol on RTN which is GABAergic nuclue may be important too and need futher research.Propofol inhibited both excitatory and inhibitory amino acids effux in dorsal horn of spinal cord in rats.But the predominant inhibitory action on excitatory amino acids effux may contribute to the anesthetic actions of propofol.