Effects Of Dorsalstriatal αCaMKII Down-expression On Learning And Synaptic Plasticity In Mice

Brain science is one of the most challenging and active international leading basic disciplines of21st century. Learning and memory, as high function of brain, are critical to mammalian, especially for human survival. Calcium/calmodulin-dependent protein kinase II (CaMKII) is an important multifunctional serine/threonine protein kinase. As a subtype of CaMKII, alpha CaMKII (aCaMKII) has been highly studied about its crucial role in hippocampal learning and memory. Striatum is one of the important region in brain and rich of aCaMKII. It receives glutamatergic innervation from nearly all areas of cerebral cortex, and participates in the modulation of motor skill learning and stimulus-response learning. Dysfunction of the striatum is associated with various pathological disorders, exemplified as Parkinson’s disease and Huntington’s disease. So far, however, the synaptic mechanism underlying the regulation of striatal aCaMKII in related learning and memory remains unseen yet.Our study used in vivo injection of small RNA fragments interference techniques to specifically down-regulate the expression of striatal aCaMKII. Behavioral tasks and electrophysiological techniques were used to study the effects of down-expression of striatal aCaMKII on striatum-related learning abilities, cortico-striatal excitatory postsynaptic potential (EPSP) and N-methyl-D-aspatate (NMDA) dependent long-term potentiation (LTP).The main five conclusions are as follows:1. The down expression of striatal aCaMKII in the aCaMKⅡ-shRNA miceBy using the western blotting techniques, we identified that the expression of striatal aCaMKII in aCaMKII-shRNA mice was significantly lower than the WT-GFP control mice, which laid the foundation for our follow-up experiments.2. Impaired striatum related learning ability in aCaMKⅡ-shRNA miceNumerous studies have indicated the close relationship between striatum and several behavioral tasks.We combined genetic and pharmacological methods to investigate the effects of down-regulation of striatal aCaMKII on related learning abilities. The results suggested that the aCaMKII-shRNA mice showed significant impairments both in motor skill learning and stimulus-response learning abilities. By conducting the open field, pole test, stepping test and wire suspension, we measured the locomotor ability in both groups. These results indicated that the impaired ability in rotarod and water cross maze was not due to its declined basal motor function. 3. Normal basal electrophysiological properties and impaired synaptic plasticity in aCaMKII-shRNA miceThe down regulation of aCaMKII did not influence the basal electrophysiological properties of striatal MSNs, including resting membrane potential (RP), input resistance, action potentials (APs) and current voltage curve (I-V Curve). We used the brain slice field potential recording technique to investigate the effect of striatal down expression of aCaMKII on cortico-striatum synaptic plasticity. Compared to the WT-GFP mice, the cortico-striatal NMDAR-dependent LTP of aCaMKII-shRNA mice was significantly decreased.4. Impaired postsynaptic glutamatergic receptors function in aCaMKII-shRNA miceNumerous studies have indicated the essential role of AMPAR and NMDAR in learning and memory. The western blotting results showed that the expression of AMPAR had no obvious change in aCaMKII-shRNA mice. However, the phosphorylation level of AMPAR and expression level of NMDAR both decreased significantly in aCaMKII-shRNA mice. By using the in vitro patch clamp, we found that the AMPAR and NMDAR mediated EPSC in the aCaMKII-shRNA mice were significantly decreased compared to the controls.5. Impaired dopamine concentration in aCaMKII-shRNA miceBy using the LC-MS method, we found that DA in aCaMKII-shRNA mice striatum showed a remarkable reduction compared with the WT-GFP mice.The results indicate that the decrease of aCaMKII imparies the striatum related leanring abilities and corticostriatal plasticity. These impairments may be due to the functional declines of NMDAR and AMPAR caused by aCaMKII down regulation.