The Study Of The Role Of ?CaMK? In Dentate Gyrus Related Cognitive Functions And Synaptic Plasticity

Ca2+/calmodulin-dependent protein kinase ?,CaMK?(CaMK?)consists of a and? isoforms in hippocampus.aCaMK?,but not ?CaMKII have been studied extensively for its role in hippocampal learning and synaptic plasticity.Furthermore,it is totally unclear whether and how PCaMK? plays role in dentate gyrus(DG)related pattern separation,behavioral flexibility and long-term depression(LTD).In this study,using ?CaMK?-F90G transgenic(TG)mice generated by chemical-genetic approaches,in which exogenous ?CaMK?-F90G of DG was regulated specifically,temporally and reversibly,we investigated the effects of ?CaMK?overexpression in DG on cognitive functions and synaptic plasticity systematically.The main results are as follows:1.Impaired behavioral flexibility in ?CaMK?-F90G transgenic mice.Behavioral flexibility of TG mice was impaired in the reversal learning phases of both radial arm maze task and water cross maze task,and NM-PP1,the specific inhibitor of exogenous ?CaMK?-F90G,reversed these deficits.TG mice,however,exhibited normal emotion,novel objective recognition,spatial reference memory and pattern separation.2.Impaired DG MPP NMDAR-LTD in ?CaMK?-F90G transgenic mice.In vitro electrophysiological experiments showed that NMDAR-LTD in DG medial perforant path(MPP)induced by different forms of stimulation was significantly impaired in TG mice,which could be reversed by NM-PP1.On the other hand,TG mice exhibited normal basic electrophysiological properties and basal synaptic transmission of GCs,while NMDAR-independent LTD at DG MPP and NMDAR-LTD at Schaffer pathway were also unaffected.3.Excessive CaMK? activity,impaired PP1/2A activity,overexpressedsynaptosomal stargazin and defective ?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor(AMPAR)internalisation and dephosphorylation in ?CaMK?-F90G transgenic mice.Western blotting and activity Assay Kit showed excessive CaMK? activity during NMDAR-LTD in DG of TG mice,which might lead to impaired PP1/PP2A activity and overexpression of synaptosomal stargazin,thereby resulting in defective AMPAR internalization and dephosphorylation of GluA1-Ser831 and GluAl-Ser845.These changes might cause NMDAR-LTD deficit and could be reversed by NM-PP1.4.Abnormal activity of Akt-GSK3? pathway in ?CaMKII-F90G transgenic mice.Western blotting analysis showed an excessive Akt activity in TG mice during NMDAR-LTD,which impaired GSK3? activity,and NM-PP1 reversed the abnormal Akt-GSK3? activity.Suppression of excessive Akt activity could restore GSK3?activity during NMDAR-LTD,and partly reversed the defective AMPAR internalization and dephosphorylation,NMDAR-LTD and behavioral flexibility in TG mice,suggesting that abnormal activity of this pathway might be one of the mechanisms underlying deficits in NMDAR-LTD and behavioral flexibility.Collectively,?CaMK? overexpression of DG impaired behavioral flexibility and NMDAR-LTD,which indicated that NMDAR-LTD might be the cellular mechanism of behavioral flexibility.Further investigation revealed that PCaMK? overexpression impaired AMPAR internalization and dephosphorylation of GluA1-Ser831 and GluA1-Ser845 during NMDAR-LTD,which might be caused by inhibited PP1/2A activity,overexpressed synaptosomal stargazin and abnormal activity of Akt-GSK3? pathway,due to excessive CaMK? activity.Our study for the first time reveals the pivotal role of ?CaMK? in behavioral flexibility and forebrain LTD,and provides useful data for completely understanding the contribution of CaMK? holoenzyme to cognitive functions and synaptic plasticity.