Fentanyl Attenuates Air Stimulus-evoked Field Potential Response In Cerebellar Molecular Layer In Vivo In Mice

[Objective]The mu-opioid receptor(MOR)is widely distributed in the central nervous system.Activation of MOR can produce pharmacological effects such as sedation,analgesia,and euphoria,as well as the behaviors related to rewards and motivation.Persistent heavy use of opioids can also cause addiction and tolerance.As we know,the physiological functions of the cerebellum are not only involved in sensory perception,motor coordination,motor learning and precise control of autonomous movement,but also participate in the mood regulation,cognition,learning and memory.Studies have shown that functional MOR is widely distributed in the cerebellum,and the role of MOR activation in cerebellum has not been reported.Therefore,we used electrophysiology and pharmacology methods to investigate the effect of fentanyl on tactile stimulus-evoked field potential response in cerebellar molecular layer,and to explore the role of activating MOR on sensory information transmission in cerebellar molecular layer in vivo in mice.[Methods]1.KM adult male mice were selected.Mice were anesthetized with urethane(1.3 g/kg body weight,intraperitoneal injection),and the whiskers of mice were cut after it had no blink reflex.To avoid respiratory obstruction the mice were tracheotomized.Then the maxilla of mice was fixed with a custom-made stereotaxic frame to ensure that the brain of mice was in a stable state during craniotomy.The muscle tissue on the head surface was removed to expose the skull,and a watertight chamber was made above the skull.The skull and the dura mater in cerebellar Crus Ⅱ were removed to perfuse the brain surface with artificial cerebrospinal fluid(ACSF)containing oxygen.The rectal temperature of the animal was maintained at 37 ± 0.2 ℃ in the course of the experiment.2.The extracellular field potential recordings from molecular layer were performed with an Axopatch-200B amplifier.The potentials were acquired through a Digidata 1440 series analog-to-digital interface on a personal computer using Clampfit 10.4 software.3.Electrophysiological data were analyzed using Clampfit 10.4 software(Molecular Devices,Foster City,California,USA).All data are expressed as the mean± SEM.The differences were evaluated using Student’s paired t-test or one-way ANOVA of variance on SPSS software(Chicago,Illinois,USA).P values below 0.05 were considered to indicate a statistically significant difference between experimental groups.[Results]1.Application of 5 μM fentanyl on the cerebellar surface perfusion can significantly reduce the amplitude,AUC,half-width,decay time and increases the rise time of facial stimulus-evoked field potential responses in the cerebellar molecular layer P1,but no significant change in the amplitude of facial stimulus-evoked field potential responses in the cerebellar molecular layer N1.2.The fentanyl-induced decrease in the amplitude of facial stimulation-evoked field potential responses in the cerebellar molecular layer P1 was concentration-dependence.The 50%of inhibiting concentration was 5.53 μM.3.CTOP,an antagonist of MOR,blocked the fentanyl-induced inhibition of facial stimulation-evoked field potential responses in the cerebellar molecular layer P1.4.Application of fentanyl inhibited the spontaneous and tactile-evoked spike firing of MLIs.5.Application of either PKA inhibitor or an adenylate cyclase(AC)agonist,blocked fentanyl-induced inhibition of facial stimulation-evoked field potential responses P1 in the cerebellar molecular layer.[Conclusion]1.Fentanyl can attenuate the sensory information transmission in the cerebellar molecular layer of mice,by inhibiting the discharge activity of MLIs.2.The inhibition of fentanyl on sensory information transmission in cerebellar molecular layer via activation of MOR is related to the AC-cAMP-PKA signaling pathway.