Hippocampal Neural Activity In NR2B Transgenic Rats

A mass of research indicate that NMDA receptor have been involved in the process of synaptic plasticity. We speculate that the improvement of learning and memory may owe to the overexpression of NR2B in prefrontal cortex which results in increasing attenuation constant of NMDA receptor and prolonging opening time of NMDA receptor. Compare to mouse, the rat has bigger brain volume which is more convenient for doing research in the method of Electrophysiology and ethology. As for this, we designed the microdrive array of sixteen independently moveable electrodes for rat here according to the mouse driver. We use this device for multi-channel recording in CA1 area of rat. It allows us to study the in vivo neurons activities of NR2B transgenic rat.First of all,we observed wave shape of extracellular action potential of NR2B transgenic rat in CA1 area and compare it to wild type rats'. We found that the average half-wave width and the average wave length of pyramidal cell is 0.16±0.01ms 0.50±0.07ms in NR2B transgenic rat respectively. There is no significant difference(p>0.05) compared to wild type rat (average half-wave width: 0.18±0.03 ms; the average wave length:0.51±0.06 ms). Besides, the average half-wave width and the average wave length of interneuron is 0.15±0.03 ms and 0.26±0.05 ms, there is also not much difference(p>0.05) compared to wild type rat(average half-wave width:0.13±0.02 ms; average wave length:0.21±0.04 ms).Our data shows that the features of extracellular action potential about NR2B transgenic rat haven't changed in CA1 area.We have further investigation in the firing frequency of hippocampus CA1 neurons in wild type and NR2B transgenic rat. The average firing frequency of pyramidal cells in wild type rat is 0.71±0.56Hz, while it is 0.62±0.49Hz in NR2B transgenic rat. The average firing frequency of interneurons in wild type rat is 15.95±3.41Hz, whereas it is 14.24±7.79Hz in NR2B transgenic rat. There is no significant difference(p>0.05) about average firing frequency of pyramidal cells and interneurons in two rat type. Recorded during exploration, rat has shown a clear theta rhythm in hippocampal CA1 area. We analyzed the real-time spectrum of LFP(local field potential) in CA1 area and compare the peak value of spectrum densities of wild type rat and NR2B transgenic rat. The mean peak value of NR2B rat is 46.24±6.31 and the mean peak value of wild type is 44.47±3.18.It is reported that there are many place cells in hippocampus CA1 area. They can code the information about space location in environment and their firing show strong spatial selectivity. In order to observe the coding of space information about hippocampus neuron in NR2B rat, we designed a rectangle track which has a automatic feed water control system so that the rat can shuttle between the two ends of the track to get water rewards. We recorded some place cells which have direction selectivity in both wild type rat and NR2B transgenic rat. Most of the place cells only have one place field when the rat move to specific direction(clockwise or anticlockwise).Some other place cells have place field whenever the rat run clockwise or anticlockwise. Further study shows that the average firing rate of place cells in NR2B transgenic rat is obviously higher than the wild type rat's.The in-field firing rate of place cells about wild type rat is 13.9±3.41Hz, and it is 18.14±3.51Hz in NR2B transgenic rat.(p<0.01)Our research reveals that there are no significant differences about average half-wave width, average wave length, mean firing rate of pyramidal cells or interneurons, and theta LFP in wild type rat and NR2B transgenic rat. But the firing rate of place cells in NR2B transgenic rat is observably higher than the firing rate in wild type rat. We speculate this phenomenon shows the NR2B transgenic rat has stronger ability in space learning and memory may have relation with the changed firing rate of place cells in hippocampus.