Neural Coding Mechanisms For Working Memory Of Rats Affected By Propofol

ObjectivePropofol is one of most common anethestic agent in clinical operations. Whether it brings negative effects in recognition ability or not after operations to patients is a widely forcused clinical problem. In the study, rats as research object, were infused with propofol according to0.9mg/Kg.min which was a interested dosage in clinic, and working memory behaviors of the rats in different post-operation periods were collected and analysed. we can get two different mode neural signals in the prefrontal cortex related to working momery:local field potential and action potentials of neurals group. We can get the effect on working momery through behavior characteristic、the coding mode of LFPs and the coding mode of action potentials of neurals group.Methods1. Laboratory animalsMale SD rats, weights300-350g, are trained in the Y type maze in order to grasp working momery task.2. Separate10rats into two group. One is propofol group(5); the other is contrast group(5). The propofol groups are injected propofol as0.9mg/kg-min for two hours.3. Implant multichannel micro-arrays in the prefrontal cortex of two group rats.4. After the operations, the two group rats are tested working momery in the Y type maze. At the same time, records the16-channels neural signals in the prefrontal cortex of the rats, using the Cerebus-128, until the correct rate is much than90%.5. Separate the LFPs and action potentials from the original signals.16-channel LFPs were acquired through lowpass filtering the original data (0-500Hz).16-channel highpass signals were acquired through hrghpass filtering the original data (=500Hz). Spikes, or multi-unit, were recognized above-65μV thresholds and3.0SNR. Neuron action potential time-space series were got through sorting the16-channel valid spikes by Offline Sorter software (Plexon, USA). 6. The differents of the two group rats’LFPs coding working momery(1) Local linear regression based on the weighted least square method was used to remove the baseline drift and power-line interference on LFPs.(2) The phase synchronization pattern of16-channel LFPs Instantaneous phase extraction of16-channel LFPs:The method of instantaneous phase extraction was the commonly used Hilbert transform; Selecting a reference channel:The reference channel is of the fastest average firing rate in all channels; Sliding window and step parameter:The length of sliding widow is50ms and step is12.5ms; The synchronous phase activity of16-channel LFPs were obtained by calculating cross-correlation measure between the reference channel and other channels.(3) The complex pattern of16-channel LFPs Select windows wide as200ms, using Lem-ziv complex method, calculates the average value of very window. Sliding step is50ms.7. The coding pattern of neural ensemble’s action potentials The rate code method of neuronal ensemble were scored in a selected window (200ms) with a moving step (50ms). The neuronal ensemble was performed by counting spikes in the window from the initial point to the end of the spatiotemporal sequences of neuronal firing.8. Research the results from the behavior character、LFPs coding pattern and neural ensemble’s rate code; summarize the effects on the rats’working momery affected by0.9mg/kg-min propofol.Results:1The effect on rats’behavior character(1)At the first three days, the propofol groups’correct rate is55±5%、60±5%、70±4.6%in respectively, saller than the contrast groups’89±5%、92±4.7%90±5%(P＜0.01)。 At the fourth day the propofol group is88±5%, the same as the contrast group,93±4%(P＞0.05)。(2) At the first two days, the propofol group is the same, from the second day,the correct rate is much than proxima luce (P＜0.05)。2The effect on LFPs phase synchronization pattern (1) At the first three days, mean of LFPs phase synchronization of the propofol group befor reference point are0.3149±0.0828,0.2894±0.0924,0.3470±0.0753in respectively, the same as the mean of LFPs phase synchronization of the propofol group after reference point0.2993±0.0627,0.3203±0.1024,0.3383±0.086(P>0.05)。 At the fourth day, mean of LFPs phase synchronization of the propofol group befor reference point is0.1892±0.0429, saller than the mean of LFPs phase synchronization of the propofol group after reference point (0.4270±0.0692)(p＜0.01)。(2) In the contrast group the mean of LFPs phase synchronization after reference point is much larger than the mean befer the reference point, after reference point0.4791±0.0964、0.4801±0.083、0.4853±0.0719、0.4361±0.0768, befer the reference point0.1687±0.0546、0.1661±0.0379、0.1663±0.0382、0.1739±0.0296,(p＜0.01)。3The complex pattern of16-channel LFPs(1) At the first three days, mean of LFPs complex of the propofol group befor reference point are0.2419±0.0864,0.2316±0.0817,0.2348±0.0941, the same as the mean after reference point0.2261±0.0314,0.2625±0.0843,0.2759±0.0847,(P＞0.05)。 At the fourth day, mean of LFPs complex of the propofol group after reference point is0.3917±0.0785, much larger than the mean of LFPs complex of the propofol group befor reference point0.2284±0.0634,(p＜0.05)。(2) In the contrast mean of LFPs complex after reference point are0.4437±0.0757、0.4562±0.0639、0.4692±0.072、0.4823±0.0869, much larger than mean of LFPs complex befor reference point0.2019±0.0362、0.2548±0.0537、0.2219±0.0569、0.2465±0.0529,(p＜0.05)。4The coding pattern of neural ensemble’s action potentials At the first three days, the propofol group dose not form the neural ensemble, at the fourth day, it dose. The contrast group forms the neural ensemble every day.ConclusionsThis paper aimed at the propofol effect on working momey among behavior character,16-channel LFPs, neuron action potentials and the conclusions as follows:1The effect on the behavior character At the first three days,0.9mg/kg-min propofol decrease the rats’working momery. It can recovery at the fourth day.2The effect on LFPs coding pattern(1) At the first three days,0.9mg/kg-min propofol affect the rats’LFPs phase synchronization pattern. It can recovery at the fourth day.(2) At the first three days,0.9mg/kg-min propofol affect the rats’LFPs complex pattern. It can recovery at the fourth day.3The coding pattern of neural ensemble’s action potentialsAt the first three days, the propofol group dose not form the neural ensemble, It can recovery at the fourth day.