Regulation Of Dopamine Receptor 4 Agonists And Inhibitors On Synaptic Plasticity In Aged Mice

BackgroundLong term potenitation(LTP),an important form of synaptic plasticity,has been widely accepted and applied as a model for learning and memory functions at the synaptic level.Dopamine(Dopamine,DA)is the main catecholamine neurotransmitter in the brain that regulate a variety of brain function,and aging,AD and cognitive defects related diseases such as schizophrenia,as the most abundant sample D2 receptor expression in hippocampus,D4 R enhanced are closely associated with learning and memory function of the hippocampus gamma oscillation activity enhancement,but for age-related learning memory function of regulating mechanism is unclear.ObjectiveTo investigate the effect of D4R agonist PD168077 on aging learning and memory and its possible mechanism.MethodField potential recording technique was used to record the LTP induced by high frequency and the changes of LTP activated by drugs in the brain slices of young and aging mice.Western Blot and behavioral experiments were used to test the related proteins and behavioral changes.(1)Induction and recording of LTP: C57BL/J6 mice of different weeks of age were taken.After decapitation,intact brain tissue was stripped off,and the brain tissue was horizontally sectioned with Campden Instruments 5100 MZ slicer,the thickness of the brain slice was 350?m.Pulses with a pulse width of 0.1ms were sent every 20 seconds,and pulses were given at different stimulus intensities to establish the relationship between stimulus intensities and response.The downward PSP slope is calculated between 10% and 50% of the PSP maximum amplitude.The standard stimulus intensity was set to 40% of the maximum PSP amplitude induced.After establishing a stable baseline(15-30min),a single HFS(100 Hz,1s,standard intensity)was used to induce LTP,and the slope change of the PSP was recorded for 40-60 min.(2)Behavioral experiment: Water maze,Y maze and open field experiment were used to measure and evaluate the learning and memory ability of mice of different ages.(3)Western blot: the protein in mouse hippocampus was extracted,the concentration was determined,then Western Blot experiment was conducted,and the quantitative analysis was carried out with Image J.(4)Statistical analysis: Analysis of variance(ANOVA)was used for multi-group and repeated measurements.The comparison between the two sets of data was performed using the t test.Sigma Stata and SPSS22.0 were used for statistical analysis,P<0.05 was considered as statistically significant,and Graph Pad Prism8 was used for plotting.Result1.Aged mice showed decreased learning and memory function,corresponding to decreased expression of TARP?8 and impaired LTP in aged mice;2.Dopamine-4 agonist PD-168077(200n Mol/L)enhanced LTP in aged mice;3.CaMK?? inhibitor KN93(10?Mol/L)blocked the LTP enhancement of PD-168077 in aged mice,while PKA inhibitor H-89(10?Mol/L)had no effect on the LTP enhance-ment of PD-168077 in aged mice;4.Dopamine-4 agonist PD-168077 up-regulated the level of p-CaMKI? and the expression of TARP?8ConclusionD4R activation was increased by p-CaMK??,which up-regulated the expression of TARP?8 protein,and increased impaired LTP in aged mice.