Similarities And Differences Between Firing Patterns And Place Field Characteristics Of Two Types Of Pyramidal Neurons In Hippocampal CA1 Area

Neurons in the CA1 area of the hippocampus can be classified as excitatory pyramidal neurons and inhibitory interneurons.It has long believed that the morphology and function of pyramidal neurons are homogeneous,but recent studies have shown that pyramidal neurons of the hippocampus CA1 area are heterogeneous.In the CA1 area of the dorsal hippocampus,there are morphological and functional differences between the two pyramidal cell subpopulations defined by the calciumbinding protein Calretinin.We combined multi-channel in vivo recording technique and optogenetics technique to record the firing activity of two types of pyramidal neurons in different behavioral states in conscious,free-moving mice,and explore the differences of firing profiles,local field potential(LFP)phase-locked relationships,and place cell characteristics between the two types of cells.Pyramidal neurons were classified as Calretinin-positive neurons and Calretininnegative neurons by opto-tagging.After analyzing mean firing rate and burst index of the two types of pyramidal neurons,the results showed that the mean firing rate of Calretinin-negative pyramidal neurons is significantly higher than Calretinin-positive pyramidal neurons in different behavioral states.During slow wave sleep(SWS)period,Calretinin-positive pyramidal neurons have a higher burst index than Calretininnegative.LFP phase-locked analysis was performed on two types of pyramidal neurons.The results showed that the two types of pyramidal cells tend to phase-locked at theta oscillation troughs during rapid eye movement sleep(REM)period and awake running(RUN)period.We compared the changes of prefer phase between RUN and REM periods,there were no significant differences between the two types of pyramidal neuron.We observed their preferred phase of ripple rhythm,both of them tend to fire at troughs of ripple oscillations.Further,we compared the differences in the place cell firing characteristics of two types of cells.The results showed that Calretinin-negative pyramidal neurons have a higher mean firing rate than Calretinin-positive pyramidal neurons in the place field.However,there was no significant difference was found in peak firing rate,radios of place cell,spatial information,place cell size,positions of peak firing rate and phase precession coefficient.Our study found that the two type pyramidal neurons are significantly different at firing rate,but no significant difference in phase-locked,place cell characteristics.