The Role And Its Mechanism Of CK2 On The Extinction Of Remote Cued Fear Memory In Mice

Objective: To investigate the role and mechanism of CK2 in remote cued fear memory extinction.Methods: In this experiment,SPF C57BL/6 male 8-week-old mice were used as experimental objects to establish a conditioned model of cued fear in mice.This experiment was divided into three parts.In the first part,mice were randomly divided into extinction group(Ext group),non-extinction group(No Ext group),Recall group and No Recall group.After 14 days of fear conditioning,the extinction group and the recall group were subjected to the extinction training or recall,while the control group was subjected to the non-extinction or non-recall respectively.The mice in the four groups were sacrificed one hour after the end of behavioral study.We utilized Elisa and WB to detect the expression and activity of CK2 in the prefrontal and hippocampus.The mice in the second part were randomly separated into CX-4945 group and Veh group.After 12 days fear conditioning,mice in the CX-4945 group were intraperitoneally injected with 10 mg/kg CK2 inhibition CX-4945(once a day for two days)two days before the extinction training,and mice in the Veh group were injected with the same dose of vehicle.Both the CX-4945 group and the Veh group underwent the same behavioral process: the first extinction training was performed after 14 days of conditioning.The second extinction training was performed 24 hours later,and the extinction test was performed 24 hours later.On the 14 th day after the completion of extinction test,we observed the spontaneous recovery of fear memory in both groups.Part III mice were randomly divided into CX-4945 group and Veh group,and the experimental procedure was similar to part II.The mice in both groups were sacrificed one hour after the extinction test.p-ERK and p-CREB were observed in m PFC and Hip of mice in CX-4945 and Veh groups by immunohistochemistry and western blot.Observation of synaptic associated proteins in medial prefrontal lobe by western blot: Syn,PSD-95,NMDA receptors NR2 A and NR2 B,glutamate receptors Glu R1.Results:(1)CK2 kinase expression and activity of m PFC increased after the extinction training of remote fear memory(p < 0.05).(2)10 mg/kg CX-4945 had no effect on the anxiety-like emotional behavior,motor ability and sound sensitivity of mice.(3)Mice treated with the CK2 kinase inhibitor CX-4945 before extinction training showed lower freezing levels on extinction tests than mice in the vehicle group(p < 0.001);On the spontaneous recovery,the CX-4945 group had lower levels of freezing than vehicle group(p < 0.05).(4)After fear memory extinction test,CK2 kinase substrate ERK1/2of CX-4945 mice was activated in m PFC(p < 0.0001),the positive reaction of p-CREB in m PFC and Hip was higher than Veh group(Hip: p <0.01,m PFC: p < 0.01).WB results showed synaptic associated protein PSD-95(p < 0.05),NR2B(p < 0.01),Glu R1(p < 0.05)m PFC expression increased in CX-4945 group.These results suggest that the activity and expression of CK2 kinase in m PFC increased after remote fear memory extinction training,and inhibition of CK2 activity can promote the extinction of remote cued fear memory and inhibit the spontaneous recovery.Conclusion: These results suggest that CK2 kinase is involved in the extinction of remote cued fear memory in mice,which may be related to the activation of ERK1/2 and CREB in m PFC and the regulation of synaptic plasticity of mPFC.