Role Of Adrenergic Receptors On Spontaneous Complex Spike Activity Of Cerebellar Purkinje Cell In Mice

[Objective]Abundant afferent fibers of locus coeruleus(LC)noradrenergic neurons project to the cerebellar cortex and deep cerebellar nuclei.Adrenergic receptors are widely distributed in the cerebellar cortex.It has been reported that application of norepinephrine(NE)to cerebellar cortex or activation of the LC induced a decrease in spontaneous simple spike(SS)firing activity of Purkinje cell(PC).Our previously results indicated that NE bidirectional modulated the spontaneous SS activity of PC via enhancing both inhibitory inputs from molecular layer interneuron(MLI)and excitatory inputs of parallel fibers,at the same time induced a decrease in spontaneous complex spike(CS)firing activity of Purkinje cell(PC).However,the effects of NE on the adrenergic receptors of spontaneous CS activity of cerebellar PC in living mouse have not yet been fully understood.In the present study,we examined the effects of exogenous NE on the adrenergic receptors of CS activity of PC in urethane-anesthetized mice by electrophysiological and pharmacological methods.[Methods]1.Mice were anesthetized with urethane(1.3 g/kg body weight,intraperitoneal injection).The mice were tracheotomized to avoid respiratory obstruction and fixed on a custom-made stereotaxic frame.After a watertight chamber was created,a 1-1.5 mm craniotomy was drilled to expose the cerebellar surface corresponding to vermis and Crus II.The dura mater was carefully removed,the brain surface was constantly superfused with oxygenated artificial cere-brospinal fluid(ACSF).Therectal temperature was monitored,and maintained at 37.0±0.2℃.2.The in vivo cell-attached recordings from PCs were performed with an Axopatch-200B amplifier.PCs were identified by the presence of both SS and CS under cell-attached recording conditions.3.All data are expressed as the mean± S.E.M.Differences between the mean values recorded under control and test conditions were evaluated with ANOVA using SPSS(Chicago,IL)software.P values below 0.05 were considered to indicate a statistically significant difference between experimental groups.[Results]1.Application of 25 micromole NE of the cerebellar surface perfusion can significantly reduce the number of spikelet numbers of spontaneous CS,the area under curve(AUC)and induced increases in the CS-evoked pause of SS firing.2.Phentolamine,an antagonist of α-adrenergic receptor,blocked the NE-induced inhibition of PC CS.3.In the presence of α1-adrenergic receptor antagonist,prazosin and agonist,phenylephrine have no effect of PC CS.However,application the antagonist of a2-adrenergic receptor,yohimibine blocked the NE-induced inhibition of PC CS.4.In the presence of α2-adrenergic receptor antagonist,yohimibine blocked the NE-induced inhibition of PC CS.Application of α2-adrenergic receptor agonist,UK14304(UK)can mimic the NE-induced effect of PC CS completely.5.Blocking β adrenergic receptors did not change the effect of NE on CS.[Conclusion]The activation of the α2-adrenergic receptor can inhibit the spontaneous CS activity of PC in the cerebellar cortex of mice,suggesting that the NE from the LC noradrenergic neurons can regulate the role of inferior olive by activating the local a2-adrenergic receptor in the cerebellum.