Figure 3.

Perisomatic inhibitory currents are essential for the generation of the SWR LFP in stratum pyramidale. To examine the contribution of perisomatically evoked inhibitory currents to the SWR LFP, gabazine was locally puffed next to a recording electrode in stratum pyramidale (experimental setup is shown at the top). A, There were no changes in global network activity as measured by the nearby (∼100–150 μm) control electrode (top). On the electrode (marked “puffing channel”) located close to the gabazine puff (n = 8; 10 μm gabazine), robust changes were detected. B, Averages (n = 20) of SWR LFPs (top), traces filtered for ripple frequency (middle), and MUs (bottom) triggered by the SWR peak during baseline activity (left) and after the puff (right). At the bottom, a raster plot of spikes is shown from consecutive SWRs. C, After the gabazine puff, the amplitude of the SWR envelope [5.17 mV (4.21; 6.71) in control and 2.81 mV (2.06; 4) after the application of gabazine] and the amplitude of ripple oscillations decreased strongly (ripple negative peaks were below the detection limit after gabazine puffs). D, The ripple phase-locked MUs vanished after the gabazine puff, and their frequency also decreased [5.17 (4.21; 6.71) vs 2.81 (2.06; 4) MUs/SWR in control and after application of gabazine, respectively; p < 0.001].