Orexinergic Neuron Is Involved In The Regulation Of Sedative And Hypnotic Actions Of Dexmedetomidine

Objective: Two of the most mysterious and challenging problems in the field of neuroscience are the mechanism of sleep-wake modulation and the mechanism of general anesthesia.Anesthesia and sleep are essentially different,but there are many common neural mechanisms.Many studies have shown that sleep-wake circuits are also involved in the regulation of general anesthesia.Previous studies have shown that the orexinergic systems,which are involved in sleep-arousal regulation,also play important roles in the anesthesia-arousal process.So,are orexinegic systems involved in the anesthetic effect of dexmedetomidine,a novel adrenergic ?2 receptor agonist? In this study,cell-patch clamp technique was used to observe the effect of dexmedetomidine on the firing frequency of orexinergic neurons in the perifornical area of lateral hypothalamus in vitro;electroencephalogram(EEG)and behavior tests were combined to explore the effects of orexinergic systems on the sedative and hypnotic actions of dexmedetomidine.Methods: 1.The firing frequency of orexinergic neurons in brain slices were clamped at 0 pA under cell-attached recording mode current clamp with the application of dexmedetomidine(0.1-10 ?M).2.Loss of righting reflex(LORR)was used as the basis for judging the start of hypnotic state of mice,and the return of righting reflex(RORR)was used as the basis for judging the arousal from anesthesia of mice.The impacts of intracerebroventricular injection of orexin-A and orexin receptor type 1 antagonist SB-334867 on high dose dexmedetomidine(400 ?g/kg,i.p.)induced hypnotic effects were observed by measuring anesthesia induction time,anesthesia latency and EEG in mice.3.Locomotor activity and EEG were used to observe the effect of orexin-A and SB-334867 on low dose dexmedetomidine(12.5-100 ?g/kg,i.p.)induced sedation.Results: 1.The firing rate of orexinergic neurons were inhibited by dexmedetomidine in a dose-dependent manner.When the concentration of dexmedetomidine was 0.1 ?M,1 ?M and 10 ?M,the inhibition rate of spontaneous firing frequency was(25.11 ± 3.690)%,(41.79 ± 8.202)%,(89.93 ± 3.987)% respectively(n=4).2.Intracerebroventricular injection of orexin-A(3 pmol)did not change the induction time of dexmedetomidine significantly(n=6,P>0.05),while shortened the anesthesia latency significantly(n=6,P<0.001);all mice accepting orexin-A(3 pmol)showed decreased delta power(n=4,P<0.001).Meanwhile with the application of SB-334867(60 nmol,icv),the induction time of dexmedetomidine did not change significantly(n=6,P>0.05),but the anesthesia latency of dexmedetomidine was significantly prolonged(n=6,P<0.05 v.s.15 nmol SB,P<0.001 v.s.Vehicle),delta power was increased(n=4,P<0.01).3.Orexin-A(3 pmol,icv)could significantly weaken the sedation effects of dexmedetomidine(12.5-100 ?g/kg,i.p.),while SB-334867(60 nmol,icv)could enhance the inhibitory effect on spontaneous activity in mice.With the application of dexmedetomidine(50 ?g/kg,i.p.)orexin-A significantly decreased delta power(n=4,P<0.001),while SB-334867 enhanced delta power(n=4,P<0.01).Conclusion: The results showed that dexmedetomidine significantly inhibited the firing rate of orexinergic neurons in a dose-dependent manner.The regulation of orexinergic signal can affect the sedative and hypnotic effects of dexmedetomidine and the delta power.Orexinergic signal plays an important role in the sedative and hypnotic effects of dexmedetomidine.