Effects Of NR2A Overexpression On Dendritic Spines Of Pyramidal Neurons And Synaptic Plasticity In Lateral Amygdala

So many studies have indicated that NMDAR-dependent synaptic plasticity is the mechanism of learning and memory. Abundant NMDARs, composed of two NRl and two NR2 subunits, are expressed in Amygdala. Constituent NR2 subunits, which are mainly NR2A and NR2B subunits, control the pharmacological and kinetic characteristics of NMDA receptors. However, little has been reported that studies on whether the overexpression of NR2A subunits in amygdala will affect the synaptic plasticity of lateral amygdala. Thus, we explored the effects of NR2A subunits overexpression in amygdala to density of dendritic spines on pyramidal neurons, to basic electrophysiological properties of pyramidal neurons, to basic synaptic transmission in lateral amygdala and to NMDAR-dependent chemical LTD on thalamus-lateral amygdala pathway. Our results as follows:1. NR2A subunits increased in amygdala of NR2A transgenic miceOur results of Western blot indicated that NR2A subunits in amygdala of NR2A transgenic mice is 2.31 ± 0.33 times of that in their littermate controls on total protein level and there was significant difference between two groups (Paired t-test, P= 0.001 < 0.01). With the similar results, NR2A subunits in amygdala of NR2A transgenic mice expressed 1.50 ± 0.36 times of that in their littermate controls on membrane protein level (Paired t-test, P= 0.0402< 0.05), while the NR2B (Paired t-test, P= 0.6977> 0.05) and NRl (Paired t-test, P= 0.6462> 0.05) subunits unchanged. Therefore, the NR2A transgenic mice should be an excellent model for exploring the NMDAR-dependent chemical LTD on thalamus-lateral amygdala pathway.2. The density of dendritic spines on pyramidal neurons in lateral amygdala of NR2A transgenic mice was unchanged.Our Golgi Staining results suggested that the density of dendritic spines in NR2A transgenic mice is 1.28 ± 0.05 per micrometer, while the littermate control is 1.17 ± 0.05 per micrometer. There is no difference between NR2A transgenic mice and their littermate controls (Unpaired t-test, P= 0.7739> 0.05).3. The basic electrophysiological properties of pyramidal neurons and basic synaptic transmission in lateral amygdala both displayed normalOur results of patch clamp recording in vitro indicated that NR2A transgenic mice displayed normal resting potential, input resistance and firing rate of pyramidal neurons. The frequency and amplitude of miniature excitatory postsynaptic currents (mEPSC) unchanged as well. Our western blot results, matched to the unchanged frequency and amplitude of mEPSC very well, showed that the Synaptophysin (SYP) unchanged in total protein of Amygdala and that the expression level of GluRl, GluR2 subunits composing AMPA receptors were normal in membrane protein of Amygdala. In brief, the NR2A overexpression did not affect the basic electrophysiological properties of pyramidal neurons in lateral amygdala, did not influent the basic synaptic transmission, either.4. The NMDAR-dependent chemical LTD on Thalamus-Lateral Amygdala pathway of NR2A transgenic mice was impairedOur field potential recording results showed that the NMDAR-dependent chemical LTD on thalamus-lateral amygdala pathway of NR2A transgenic mice impaired. The same with the impaired chemical LTD results, We found that the GluRl and GluR2 subunits expression in NR2A transgenic mice significantly higher than their littermate controls on membrane protein level after inducing chemical LTD with NMD A. The results above suggested that the increased NR2A subunits in amygdala may impaired NMDAR-dependent chemical LTD on thalamus-lateral amygdala pathway through interfering the AMPA receptors’ internalization mediated by GluR2 subunits.According to all the results above, NR2A overexpression in amygdala did not affect the density of dendritic spines, basic electrophysiological properties of pyramidal neurons and basic synaptic transmission of lateral amygdala, but impaired the NMDAR-dependent chemical LTD on thalamus-lateral amygdala pathway. Our further studies suggested that the increased NR2 A subunits in amygdala may impaired NMDAR-dependent chemical LTD on thalamus-lateral amygdala pathway through interfering the AMPARs’ internalization mediated by GluR2 subunits.