OBJECTIVETo analyze the electrical activity property changes in nucleus accumbens (NAc) of heroin-induced conditioned place preference (CPP) rats during different stages of heroin dependence and to explore NAc's roles in the formation of drug dependence.

METHODSRecording electrodes were bilaterally embedded into the NAcs of rats with the aid of stereotaxic apparatus, followed by establishment of heroin-dependent rat model. The NAc electrical activity during 3 different stages of heroin dependence, including heroin pre-exposure, immediate post-exposure and heroin withdrawal, were respectively recorded using EEG wireless telemetry techniques. The frequency distribution (ranging from 0.5 to 30 Hz) and the amplitude of NAc electrical activity were analyzed and measured.

RESULTSHeroin-dependent rat models were successfully established and their withdrawal symptoms were evident. All rats showed a conditioned place preference (CPP) for the white box after 5-10 days of heroin-exposure, and displayed a maximum withdrawal symptoms on 2d after heroin- withdrawal. During all statges of heroin-dependence, the NAc electrical activity contained the highest proportion of delta rhythm and the lowest proportion of alpha2 rhythm. The discharge frequence band was similar across different stages. There was a significantly increased ratio of low-frequency discharges (delta rhythm) and decreased ratio of high-frequency discharges (beta rhythm) in NAc of rats during the immediate post- heroin exposure stage when compared with that during pre-exposure and heroin withdrawal stages. During the withdrawal stage, the ratio of at rhythm was significantly lower than during pre- and post-heroin exposure stages (P < 0.01). Further, the mean discharge amplitude in NAcs during immediate post-exposure and withdrawal stages was significantly increased relative to pre-exposure stage. However, the mean discharge amplitude during heroin withdrawal stage was significantly lower than during immediate post-exposure stage.

CONCLUSIONThe electrical activity properties in rat NAcs showed a significant change during different stages of heroin-dependence, which suggested that neuronal activities in NAcs might contribute to the modulation of drug-dependence.

Animals ; Conditioning, Operant ; Heroin ; pharmacology ; Heroin Dependence ; physiopathology ; Male ; Nucleus Accumbens ; physiopathology ; Rats ; Rats, Sprague-Dawley ; Telemetry

OBJECTIVETo study the correlation between EEG characteristics of medial prefrontal cortex (mPFC) and drug-seeking behavior of rats with morphine dependent place preference under shuttling condition.

METHODSForty rats were randomly divided into four groups (n = 10): morphine PL group, NS PL group, morphine IL group and NS IL group. After embeding the electrode in prelimbic (PL) or infralimbic (IL) cortex of each group by brain stereotaxic operation, the model of morphine dependent conditioned place preference (CPP) in rats was established. The differences of EEG wave percentage in mPFC were telemetered and analyzed when rats shuttled before and after the model.

RESULTSAfter the model, the withdrawal symptoms were evident in morphine PL and IL group, and the activity time and distance in white box were increased obviously. Compared with control group, after the model, the EEG in morphine PL group showed that: when the rats shuttled to white box, 8 wave decreased obviously, P wave increased obviously. When the rats shuttled to black box, brain waves showed opposite changes. The EEG in morphine IL group showed that: when the rats shuttled to white box, a wave increased obviously, P and a wave decreased obviously. When the rats shuttled to black box, the brain wave had no significant differences compared with control group.

CONCLUSIONThe EEG changes are different in PL and IL cortex of morphine CPP rats under shuttling condition, and the EEG changes are also different when rats shuttling to white or black box. There is possibly different mechanism, when different drug-seeking environmental cues caused EEG changes in different regions of mPFC.

Animals ; Conditioning (Psychology) ; Cues ; Drug-Seeking Behavior ; Electroencephalography ; Morphine Dependence ; physiopathology ; Prefrontal Cortex ; physiopathology ; Rats ; Telemetry

Objective To determine the effects of naloxone on the withdrawal symptom in heroin-induced conditioned place preference (CPP) rats and the spontaneous firing properties in nucleus accumbens (NAc).Methods The heroin-dependent rat models were established,and the recording electrodes were implanted to NAc via stereotaxic apparatus.After 4 days of natural withdrawal,rats were injected with naloxone (0.5mg· kg-1),after which the withdrawal symptoms were evaluated.The electrical activities of NAc neurons were recorded by wireless telemetry at the following stages:before modeling,immediately after heroin administration,and heroin withdrawal.The frequency distribution at 0.5 ～ 30.0 Hz of the spontaneous firing was arranged and compared with that after naloxone administration.Results The heroin-dependent rat model was effectively established through the CPP system.Rats showed significant withdrawal symptoms with dynamic characteristics,which appeared the most significant on the first two days of withdrawal (6.6 ± 1.7) point,compared with before modeling with statistical difference (P ＜0.01).After naloxone irritability,the withdrawal symptoms reached the highest level(7.2 ± 1.3) point,compared with before modeling with statistical difference(P ＜ 0.01).In each state,δ wave occupied the largest ratio in the spontaneous discharge,while β wave held the smallest proportion.However,the distribution gradient of the different electroencephalogram(EEG) in each state demonstrated similar characters.Compared with the state immediately after heroin administration ofδ wave (45.58 ± 7.80)％ and θ wave (22.67 ± 3.37)％,the ratio of δ wave (38.58 ±5.76％),θ wave (18.75 ±3.31)％ in the state of naloxone irritation with statistical difference(P ＜0.05).Compared with the state immediately after heroin administration of the ratio of β31 wave (7.50 ±2.28)％ and β2 wave (10.17 ± 3.33) ％,the ratio of β1 wave (11.00 ± 1.35) ％ and β2 wave (16.50 ± 2.15) ％ in the state of naloxone irritation with statistical difference (P ＜ 0.01).In summary,after naloxone irritability,EEG energy state showed the largest difference with the state immediately after heroin administration,and differed less with the state before heroin administration.Conclusion Naloxone can stimulate the withdrawal symptoms in heroin-dependent rats,and significantly affect the electrophysiological properties in NAc,which implies that naloxone exerts an important role in NAc energy state in drug-dependent rats.

The present study was aimed to explore the correlation between θ-γ neural oscillations phase-amplitude coupling (PAC) in hippocampal CA3 area and the changes of spatial identifying and cognitive ability before and after shock avoidance training in rats. According to the results of Y-type maze shock avoidance training, the rats were divided into two groups: the fast avoidance response group and the general avoidance response group. The local field potential (LFP) of hippocampal CA3 area was recorded by wireless telemetry before and after shock avoidance training. The variation of θ oscillation (3-7 Hz) and low-γ neural oscillation (30-60 Hz) PAC in hippocampal CA3 area was analyzed by MATLAB wavelet packet extraction technique. The results showed that, compared with the general avoidance response group, the fast avoidance response group exhibited higher θ-γ neural oscillation PAC in hippocampal CA3 area before training. θ-γ oscillation PAC in hippocampal CA3 area was increased in both groups after training. It was also noticed that θ-γ neural oscillation PAC of some frequency bands in the general avoidance response group were significantly higher than those in the fast avoidance response group. The results suggest that certain intensity of training can change the spatial identifying and cognitive ability of rats, and the mechanism may involve the increase of the synchrony of θ-γ neural oscillation, i.e., the enhancement of θ-γ phase-amplitude alternating frequency coupling in hippocampal neurons.
Animals ; Cognition ; Hippocampus ; Neurons ; Rats ; Theta Rhythm

The purpose of the present study is to explore the relationship of spatial learning ability and specific electrical activities of neural oscillations in the rat. The fast and general avoidance response groups were selected on the basis of the animals' responses to the electric shock in Y type maze, and their local field potentials (LFPs) of hippocampal CA3 area were recorded by wireless telemetry before and after shock avoidance training, respectively. The components of neural oscillations related to spatial identifying and learning ability were analyzed. The results showed that, compared with the general avoidance response group, the fast avoidance response group did not show any differences of LFPs in hippocampal CA3 area before electric shock avoidance trial, but showed significantly increased percentages of 0-10 Hz and 30-40 Hz rhythm in right hippocampal CA3 area after the shock avoidance training (P < 0.01 or P < 0.05). Fast Fourier transform showed that percentage increase of 0-10 Hz band occurred mainly in θ (3-7 Hz) frequency, and 30-40 Hz frequency change was equivalent to the γ1 band. Furthermore, compared with those before training, only the percentages of β, β2 (20-30 Hz) and γ1 rhythm increased (P < 0.01 or P < 0.05) in fast avoidance response rats after training, while the θ rhythm percentage remained unchanged. In contrast, θ rhythm percentage and the large amplitude (intensity: +2.5 - -2.5 db) θ waves in right CA3 area of general avoidance response rats were significantly reduced after training (P < 0.01). These results suggest that the increased percentages of β2 and γ1 rhythm and high-level (unchanged) percentage of θ rhythm in the right hippocampus CA3 area might be related to strong spatial cognition ability of fast avoidance response rats.
Animals ; Avoidance Learning ; Beta Rhythm ; CA3 Region, Hippocampal ; physiology ; Electroshock ; Gamma Rhythm ; Rats ; Spatial Learning ; Theta Rhythm