Dendritic mechanisms of phase precession in hippocampal CA1 pyramidal neurons

Dual whole-cell patch clamp recordings from the soma and dendrites of CA1 pyramidal neurons located in hippocampal slices of adult rats were used to examine the potential mechanisms of phase precession. To mimic phasic synaptic input, 5-Hz sine wave current injections were simultaneously delivered both to the soma and apical dendrites (dendritic current was 180 degrees out-of-phase with soma). Increasing the amplitude of the dendritic current injection caused somatic action potential initiation to advance in time (move forward up to 180 degrees). The exact pattern of phase advancement is dependent on the dendritic location of input, with more distal input causing a more gradual temporal shift in spike initiation and a smaller increase in spike number. Patterned stimulation of Schaffer collateral/perforant path synaptic input can produce phase precession that is very similar to that observed with sine wave current injections. Finally, the exact amount of synaptic input required to produce phase advancement was found to be regulated by dendritic voltage-gated ion channels. Together, these data demonstrate that the summation of primarily proximal inhibition with an increasing amount of out-of-phase, primarily distal excitation can result in a form of phase advancement similar to that seen during theta activity in the intact hippocampus.