Place Cell Properties In CA1of Rat Hippocampus

Hippocampus is a vital part of the brain limbic system, related to the learning and memory function, especially in the episodic memory and spatial navigation. John O’Keefe found that a part of neurons in hippocampus has response to the special location of environment in1971, the neuron were called place cell, and the location were called place cell’s place field. For a certain environment, all the place cells’ place fields in hippocampus can over the whole environment. Further studies give the evidence that the place cell is the pyramidal cell in hippocampus.The response of place cell in the open field doesn’t depended on the direction of rat entering the place field obviously. In the linear track, place cell influenced by the distal cue, local cue, and the direction rat entering the place field. In this study, we use a linear rectangle track, which has the property of two dimensions, rat will go through the track to an end for a drop of water, then go back to the other end. During rat running, we record neuron activity in CA1of rat hippocampus. We found that the place cell in the linear rectangle track depend on the rat moving direction. Total84place cells,29is clockwise,32is anti-clockwise, and23appear in both directions. All the place cells show the phase precession according to the theta oscillation, when the rat run through the place fields.The firing pattern of pyramidal cell in CA1exist two types of Inter-Spike Interval(ISI), both type Ⅰ and type Ⅱ have a ISI peak at6ms, the peak value of type Ⅰ reach to200Hz; however, type Ⅱ just to60Hz, meanwhile, type Ⅱ has the second gentle peak at12ms.36type Ⅰ pyramidal cell have18place cells,136type Ⅱ pyramidal cell have66place cells. In the type Ⅰ place cells,5is clockwise,7is anti-clockwise,6appear in both directions; In the type Ⅱ place cells,24is clockwise,25is anti-clockwise,17appear in both directions;Within the place field parameters of the two type place cells, the parameters of type Ⅰ, length is19.3±6.9cm(n=24), mean rate is12.3±5.8Hz, peak rate is 26.5±11.9Hz; the parameters of type Ⅱ, length is16.9±6.7cm(n=83), mean rate is11.2±4.2Hz, peak rate is24.4±10.2Hz. There is no Statistical difference between these two type place cells in place field.In our research, the place cells in CA1of hippocampus show the directional dependance, and spike strains show the phase precession according to the theta oscillation when the Long-Evans rat run through the linear rectangle track. Meanwhile, two types ISI firing pattern appear in the recorded pyramidal cells, although these two classes ISI firing pattern place cells have not show the statistical difference in the response to place fields, it can be speculated that somewhere exit different physical function in neural coding mechanism.