The Effect Study Of Dopamine On CA1 And CA3 Gamma Oscillations In Rat Hippocampus

BackgroundThe hippocampal gamma oscillation is a rhythm that reflects the synchronous discharge of a large number of neurons in the brain.It is believed that the oscillation mainly originates from CA3 and the entorhinal cortex.The CA1 region relies on the CA3 region to generate oscillations for information output.Recently,it has been found that the neural oscillation can be spontaneously generated by CA1.The central neurotransmitter dopamine?Dopamine,DA?participates in the oscillation of the hippocampal neuronal network and regulates the learning and memory function of the hippocampus through dopamine receptors.In some mental illnesses,gamma oscillations are found to be reduced,which may be related to impaired dopaminergic nerves.The current mechanism of dopamine regulation of isolated hippocampal gamma oscillations is not clear.This study intends to establish a separate model of CA1 and CA3 to explore the effects and mechanisms of dopamine on gamma oscillations in CA1 and CA3 regions.ObjectiveTo study the characteristics of gamma oscillations in hippocampal CA1 and CA3regions,and to explore the regulatory effect of dopamine on gamma oscillations in CA1 and CA3 regions.Methods1.Preparation of hippocampal sections:4⁶ weeks old Wistar male rats were used for cardiac perfusion after successful anaesthesia.2.Separate hippocampal CA1 and CA3 independent model brain slices:under horizontal binocular microscope,the CA1 and CA3 regions of the slices were cut and divided into appropriate sizes,which were quickly transferred to the recording tank and incubator.3.Recording gamma oscillations:after incubation for 1 hour,the frequency spectra of gamma oscillations were recorded by extracellular microelectrode and Spike2 software.On the basis of establishing an independent model of CA1 and CA3,gamma?20⁸0 Hz?oscillations were induced by 10?M carbachol.After reaching a stable state,different concentrations of dopamine?200?M,100?M,50?M?,were added and 0?M dopamine was used as the control group.After 5 min,20 min,the effects of different concentrations of dopamine on gamma oscillations induced by carbachol were observed.Statistical method:SPSS18.0 software was used to perform statistical tests.The statistical results were expressed by mean±standard deviation?x±s?.The effects of 5 min and 20 min on the same drug concentration were observed was used for paired t-test.If P<0.05,it was considered to be statistically significant.The independent sample t test was used for inter-group statistical test,If P<0.05,it was considered to be statistically significant.Results1.The isolated model of CA1 and CA3 was successfully established in rat hippocampus in vitro.High-frequency oscillations of about 45 Hz were generated in CA1region,and low-frequency oscillations of about 30 Hz were generated in CA3 region.2.After adding three concentrations of dopamine for 5 min,the main frequency of?oscillation in hippocampal CA1 region decrease(P₁₀₀=0.008,P₂₀₀=0.002).The power of100?M and 200?M groups decreased(P₁₀₀=0.021,P₂₀₀=0.002),and the high-low frequency ratio of 100?M group also decreased(P₁₀₀=0.001,P₂₀₀=0.013).After adding dopamine for 20 min,compared with that at 5 min,the power,main frequency and high/low frequency ratio of the other groups increased slightly,except that the power of?oscillation at 200?M was further decreased.ompared with the control group,the main frequency,high/low frequency ratio of 100?M group was still lower,and the power and high/low frequency ratio of 200?M group was also lower.3.After adding three concentrations of dopamine for 5 minutes,the main frequency of gamma oscillation in hippocampal CA3 region decreased(P₁₀₀=0.019,P₂₀₀=0.038),and the power of 100?M and 200?M groups decreased(P₁₀₀=0.019,P₂₀₀=0.016).The high/low frequency ratio of 200?M group also decreased(P₂₀₀=0.773).After adding dopamine for 20 minutes,compared with that at 5 minutes,the power,main frequency and high/low frequency ratio of all the other groups were increased,except that the power and main frequency of 100?M?oscillation were further decreased.Compared with the control group,the power and main frequency of 100?M and 200?M groups were still lower,and the high/low frequency ratios of 100?M and 200?M groups were higher than those of the control group.ConclusionDifferent concentrations of dopamine had different effects on the regulation of?-network oscillation in the CA1 and CA3 regions of the independent hippocampus.High concentration of dopamine reduced the power of?-oscillation in the CA1 and CA3 regions,decreased the dominant frequency,increased the high-low frequency ratio in the CA3 region,and decreased the high-low frequency ratio in the CA1 area.High concentration of dopamine can inhibit the oscillation of hippocampal network,which can be used as a reference for further study of dopamine and hippocampal network oscillation.