Place Field Formation Of Hippocampal Place Cell

Hippocampal place cell is a kind of complex spiking neuron which encoding the information about the animal’s environmental location. Place cell in hippocampus CA1, CA2 is Pyramidal cell, but in DG is Granulosa cells. Since 1971 John O’keefe found place cells, researchers have made depth and extensive research on this field, But how hippocampal place cells react when animals just entering a new environment, and how it is changing when animals enter the environment back and forth? It remains many questions.We recorded a total number of 126 place cells in six effective rat hippocampal CA1 region. Chose 88 cells which meet the condition:firing rate>4Hz from the 126 recorded place cell as analysis subjects. We can put them into four types according to their place field number and linear direction in experimental orbital environment: unidirectional neuron with single place field, unidirectional neuron with multiple place fields, bidirectional neuron with double place fields and bidirectional neuron with multiple place fields. The statistic shows bidirectional neuron with double place fields is the largest one in numbers (48.9%). Unidirectional neuron with single place field is the second one (27.3%) and the least one is unidirectional neuron with multiple place fields (4.5%).To further investigate the place field variation and formation of hippocampal place cell in rats, we put rats into curved track environment four time (section),30min per time and also 30min per interval in homecage. The result shows that in different section even the same place cell fires in various firing rate. For instance unidirectional neuron with single place field in 1-4 section, their average peak firing rate in place field is S1:15.96±6.62Hz、S2:16.69±6.06 Hz、S3:21.01±6.93 Hz and S4:25.72 ±8.59 Hz. In each corresponding section their liner length of place field never give the same value and show decreasing tendency with in time increasing in place field. Indicate that with the new environment gradually transformed into the familiar environment, firing property of rat hippocampal place cells become more stable (Peak firing rate increases) and precise (place field length reduced) gradually.Meanwhile, one part of place cell their peak firing position are very stable across 4 sections, but the other part shows variation such as some kinds of place cell place field form in S2,S3 even in S4. There also exist some place cell which disappeared gradually with the time of rat enter the experimental environment.Furthermore, we investigated the phase precession occurred between theta oscillation and recorded place cell firing sequences. When the place field appears, the phenomenon of theta phase precession followed at once, but not stabile and significant enough. With the familiar with the environment, the place cell firing and phase precession tend to stabile. While place field disappear, the number of action potentials drastically decreased, but phase precession still exist, after disappearance of place field, the phase precession follow its step immediately.In summary, when rat running into two-dimensional linear track different hippocampal CA1 place cells exhibit different direction-dependent and place field properties. With the new environment becomes to the familiar environment, rat hippocampal place cell show some regular pattern of its variation which means the place field firing rate become more higher and the length of place field location is more centralized. Place field forming and disappearing accompanied by significant phase procession. This study for further insight into the formation and properties of hippocampal place cells have a certain promoting.