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. 2005 Oct 19;25(42):9782–9793. doi: 10.1523/JNEUROSCI.3269-05.2005

Figure 6.

Figure 6.

CCK-expressing interneurons exhibit distinct firing patterns during theta and ripple oscillations. A, During theta oscillations, CCK-expressing interneurons (color traces of individual cells) fire with highest probability at the ascending phase of the theta wave recorded extracellularly in stratum pyramidale. For each cell, 1352 ± 1121 (range, 42-3693) theta cycles were recorded. For clarity, two theta cycles are shown. Top, Schematic theta wave; 0, 360, and 720° mark the troughs. The averaged firing probability of the CCK-expressing interneurons and, for comparison, of eight PV-expressing basket cells [5 published by Klausberger et al. (2003)] is shown in gray columns. Note that CCK-expressing cells fire out of phase with PV-expressing basket cells. Because the somata of pyramidal cells receive input from PV- and CCK-expressing basket cells at a probable ratio of 2:1 (Nyiri et al., 2001), the average firing probability of the PV-expressing basket cells was multiplied by 0.66 and added to the average firing probability of the three identified CCK-expressing basket cells multiplied by 0.33. The weighted sum of the firing probabilities of CCK- and PV-expressing basket cells still provides a theta-modulated GABAergic input to the soma of pyramidal cells. B, During ripple episodes, the average firing probability of the CCK-expressing interneurons showed no change (gray columns) relative to the preripple and postripple time. In contrast, the PV-expressing basket cells strongly increased their firing. Individual CCK-expressing interneurons (color traces) exhibited variable firing patterns ranging from slightly excited at the beginning and end of the ripple episodes to weakly inhibited. For each cell, 55 ± 36 (range, 18-113) ripple episodes were recorded. The start, maximum amplitude, and end (bottom) of the normalized ripple episodes are marked as -1, 0, and 1, respectively. C, Comparison of ripple episodes with and without the firing of basket cell T64c. The peri-ripple periods preceding or after ripples with (bottom) or without (middle) basket-cell firing show similar firing rates, indicating that the instantaneous firing frequency of the cell did not influence whether it would fire during a certain ripple episode.