| ObjectiveAnxiety disorders,the most common form of neurosis,is characterized by anxiety experience as an over-concern for the future.Anxiety disorders impaire the patient’s physical and mental health.Some studies have suggested that anxiety disorders related to the prefrontal cortex anomalies activity.The use of brain network analysis helps to further understand the pathogenesis of anxiety.In this study,we simultaneously recorded local filed potentials(LFPs)from the m PFC of rats during anxiety state in the elevated plus maze(EPM).The functional connectivity among LFP was measured by the directed transform function(DTF)via spectral Granger causal connectivity analysis during anxiety.We evaluated the brain network so as to understand the neural network changes of rats in anxiety state and provide help for exploring the pathogenesis of anxiety disorders.Methods1.Experimental animal:Male Sprague-Dawley rats(n=8,12-14 weeks,weighing between 300 and 350 g).All procedures relating to animal care and treatment were in accordance with the Guide for the Care and Use of Laboratory Animals and approved by the Tianjin Medical University Animal Care and Use Committee.2.Surgery and EPM experiments:The rats were implanted with 16-channel tungsten microwire electrode array targeting the m PFC.Rats were free to explore the the elevated plus maze and 16 channel LFPs were recorded in rat prefrontal cortex during anxiety-related tasks.And the camera system was used to synchronously record the free moving of rats for 10 min.The Ethovision XT 8.5 software was used to detect the position of the animal in the maze.In order to calculate changes in m PFC theta power during anxiety-related tasks,spectrograms spanning 10 seconds centered at the transitions were calculated.3.Data preprocessing:16-channel LFPs were filtered using by Butterworth low pass filter(0.3-500 Hz).Baseline fitting and a 50-Hz notch filter were used to remove the baseline drift caused by the motion noise in the 16-channel LFPs signal,as well as the power-frequency interference caused by the environment.4.Frequency Analysis: The short-time Fourier transform(Short-Time Fourier Transform,STFT)was used to perform time-frequency analysis on the anxiety state of 16-channel LFPs,and the characteristic frequency bands of the anxiety state m PFC LFPs were obtained.Each of these bands has a range of delta(1-4 Hz),theta(4-12 Hz),beta(12-30 Hz),low-gamma(30-70 Hz),and high-gamma(70-120 Hz).5.Directed transform function(DTF): Use of Directed Transfer Function(DTF)to calculate the DTF value of an anxious 16-channel LFPs.6.Granger causality analysis: The Granger causality analysis was used to calculate the DTF matrix of the rats in the closed band and open arm of the elevated plus maze.The strength of the network connection was analyzed.7.Analyze the network characteristic parameter: Built networks based on graph theory at first.Calculated the network characteristic parameter(global efficiency)of each frequency band,analyze the network characteristic of anxiety state.8.Statistical analysis:Using the statistical analysis method of independent sample t-test,the statistical analysis of the network connection strength DTFmean and network global efficiency Eglob of LFPs in different frequency bands of open arms and closed arms was carried out.The network connectivity strengths of DTFmean and Eglob in the different frequency bands of LFPs in open arms and closed arms were analyzed.Measurement data were expressed as mean ± standard error.Results1.Behavioral measurements of rats in the EPMEight rats showed normal levels in the anxiety-like behavior test.The number of times into the open arms was 19.2 ± 1.2,accounting for 36.1 ± 1.8% of the total entries.And the duration in open arm was 146.2 ± 11.5 s,accounting for 26.7 ± 1.4% of the total time.2.Time-frequency analysisThe power of LFPs was mainly concentrated in theta band during anxiety.The band energy density from high to low show that theta band was highest,followed by delta band,beta band and low-gamma band,the lowest high-gamma band.Theta band energy density was significantly different between the open arm and the closed arm.Theta power was higher in the closed arm(19.463±2.574)than in the open arm(12.812±0.738)(P<0.05).Theta power gradually diminished as the rat moves from the closed arm to the open arm.3.Construct LFP network based on DTF matrixThe connectivity in each band from high to low show that theta band was highest,followed by delta band,beta band and low-gamma band,the lowest high-gamma band.The DTF matrix of each bands had significant differences between the open arm and the closed arm.The network connection strength of the theta band in closed arm during the anxiety state was 0.0309±0.0008,the network connection strength of the theta band in the open arms was 0.0207±0.0007(P<0.001);DTF value in delta band in the closed arms was 0.0305±0.0009,DTF value in the open arms was 0.0201±0.0007(P<0.001);The network connection strength of the beta band in closed arm during the anxiety state was 0.0274±0.0008,DTF value in the open arms was 0.0202±0.0006(P<0.001);DTF value in low-gamma band in the closed arms was 0.0243±0.0009,DTF value in the open arms was 0.021±0.0008(P<0.05);DTF value in high-gamma band in the closed arms was 0.0211±0.0007,DTF value in the open arms was 0.0185±0.0006(P<0.05).4.Quantitative description of LFP networkBased on the DTF value,construct the LFP frequency band network and calculate the global efficiency of the open arm and closed arm at each frequency band.The theta band has the largest Eglob value,followed by the delta band and the beta band.There was no significant difference among the low-gamma and high-gamma between the open arm and the closed arm.Eglob value of theta band in the closed arms was 0.0398±0.0010,Eglob value in the open arms was 0.0289±0.0012(P<0.001);Eglob value of delta band in the closed arms was 0.0393±0.0011,Eglob value in the open arms was 0.0279±0.0012(P<0.001);Eglob value of beta band in the closed arms was 0.0374±0.0011,Eglob value in the open arms was 0.0298±0.0009(P<0.001);Eglob value of low-gamma band in the closed arms was 0.0345±0.0012,Eglob value in the open arms was 0.0299±0.0010(P>0.05);Eglob value of high-gamma band in the closed arms was 0.0311±0.0012,Eglob value in the open arms was 0.0278±0.0009(P>0.05).ConclusionIn this study,based on the anxiety state multi-channel neural signals of normal rats during free exploration of elevated plus-maze,we studied the functional connection of neural oscillations and neuronal information in anxiety state m PFC.The results showed that:1.The nervous oscillations of rats in anxiety state are mainly concentrated in theta band.Theta power in the closed arms was higher than in the open arms.Theta power decreased during the transitions from the closed arms to the open arms,suggesting a change in theta frequency of the m PFC related to exploratory behavior.2.The theta network of the rats in the elevated plus-maze had a stronger function connection than other networks.The causality of the theta network in the closed arm was stronger,and the m PFC causal connection in the open arm was weaker.In the process of anxiety,theta network increased and then weakened,suggesting a change in function connection in the m PFC related to anxiety-like behavior.3.The global efficiency of theta networks in rats with elevated plus-maze is higher than that of other networks.The global efficiency of theta networks is higher in the Eglob values of the closed arms and lower in the open arms.In the process of anxiety,theta global network efficiency enhanced and then decreased. |
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