Deletion Of MGluR5 In Excitatory Neurons Of The Forebrain Altered Learning And Memory In Conditional Knockout Mice

Objective:mGluR5 is an important metabolic glutamate receptor,which is widely found in presynaptic and postsynaptic neurons of central nervous system and peripheral nervous svstem.It is involved in physiological processes such as neural excitatory network regulation,synaptic plasticity,learning and memory.In this study,by constructing CamK ?-cre;mGluR5f/f mice,mGluR5 was specifically knocked out in the forebrain,which include cortex,hippocampus,amygdala and other regions,so as to more accurately study the influence of mGluR5 on synaptic function and learning and memory process.Method:CamK ?-cre;mGluR5f/f mice,the research object,were constructed by using the Cre-Loxp system.mGluR5 protein was knock out in the excitatory neurons in the forebrain.Electrophysiological technique was used to study the cKO mice including input/output(I/O)function,miniature excitatory postsynaptic current(mEPSC),miniature inhibitory postsynaptic current(mIPSC),NMDAR-EPSC,long-term potentiation(LTP)and long-term depression(LTD).Behavioral experiments include:open field,T maze and Morris water maze test and cued and contextual fear conditioning.We examined the NMDA-EPSC and expression of synapse related proteins to investigate the mechanismResults:In this study,the I/O function in the hippocampal CA1 region of mice was determined.The experimental results showed that there was no difference in the basic synaptic transmission between cKO mice and control mice.In the experiments of LTP and LTD which induced in the Schaffer collateral pathway at CA3-CA1 region,cKO mice showed weakened LTP and LTD compared with control mice.mEPSC and mIPSC of neurons in the hippocampal CA1 area were recorded.The frequency of mEPSC in cKO mice showed an increasing trend,while the frequency and amplitude of mIPSC did not change.In behavior experiments,cKO mice showed no difference compared with the control mice in the total movement distance and the exploration time in the central region of the open field.There showed significant differences in the T maze and the Morris water maze between cKO mice and control mice.In cued test of fear conditioning experiment,freezing percentage of cKO group was obviously lower than control.Through the electrophysiological experiments of NMDA-EPSC and western blot,we found that the expression of NMDA receptor and other synapse related proteins was reduced.Conclusion:CamK ?-cre;mGluR5f/f mice were successfully constructed with mGluR5 specific knockout in the excitatory neurons of cortex,hippocampus and amygdala.Electrophysiological records showed that specific knockout of mGluR5 did not affect basic synaptic transmission but weakened LTP and LTD and enhanced the frequency of miniature excitatory postsynaptic currents.It indicates the alteration of neurotransmission and synaptic plasticity.In behavioral experiments,it was found that conditioned mGluR5 knockout had no effect on mice's self-exploration and behavioral tension in the new environment,but short-term working memory,spatial memory and amygdala-related fear memory were impaired.Through the electrophysiological experiments of NMDA-EPSC and western blot,we found that the expression of NMDA receptor and other synapse related proteins was reduced.It suggests that mGluR5 may interact with related proteins and affect corresponding physiological functions.