Timing of action potentials and input currents in perisomatic and trilaminar interneurons during kainate induced gamma oscillations in mice CA1 hippocampus

Nonaccommodating perisomatic basket cells had been suggested to structure gamma oscillations. Here we used simultaneous whole-cell patch clamp recordings within 150 microm of CA1 stratum pyramidale and extracellular population activity measurements in CA1 stratum radiatum of the mice hippocampal slices to show that though nonaccommodating perisomatic interneurons and trilaminar cells convey information through the same frequency of action potentials during the kainate micropressure ejection induced gamma oscillations, inhibitory inputs received by soma and proximal dendrites of pyramidal cells differ with pi radian in time. Perisomatic interneurons discharge action potentials (APs) at the positive peak of the field gamma waves, whereas trilaminar cells fire at the trough. Timing of excitatory currents in each type of interneurons coincides corresponding APs discharge time during the active network. Perisomatic interneurons receive gamma-modulated very high frequency EPSCs, while trilaminar cells receive only gamma frequency excitatory inputs. Inhibitory postsynaptic currents lag the action potentials in both cases with pi/2 intervals. Trilaminar cells APs discharge is firmly phase locked to the trough of the field gamma waves, while nonaccomodating perisomatic interneurons spike firing rotates "counter-clockwise" during the oscillations. Apical dendrite inhibition through trilaminar cells seem to play similarly important role as do nonaccommodating perisomatic cells in the formation of 30-80 Hz oscillations. In this study we showed the posibility of existence of different active events during the gamma oscillations in two strata of CA1 that are produced by the discharge of perisomatic inhibitory interneurons in the stratum pyramidale and trilaminar cells activity in the stratum radiatum after the time intervals.