Figure 8. Type 2.2 periglomerular (PG) cells are inhibited by the basal forebrain (BF) GABAergic input.

(A) 10 superimposed loose cell-attached (LCA) traces and the corresponding peri stimulus time histogram (PSTH) for 44 consecutive trials (bin 20 ms) in a cell from a dlx5/6 mouse. Photostimulation of the BF fibers (blue arrow) transiently blocked spiking. Bottom: average firing frequency per bin (20 ms) and per episode for 28 cells that were inhibited by the BF input, without evidence of parallel cholinergic excitation (Figure 8—figure supplement 1). (B) BF-induced spiking inhibition persisted in the presence of 6-nitro-7-sulfamoylbenzo[f]quinoxaline-2,3-dione (NBQX), D-2-amino-5-phosphonopentanoic acid (D-AP5), and mecamylamine but was blocked by gabazine (GBZ). The two PSTHs are from the same cell as in (A) (bin 20 ms). Bottom: average firing rate per bin (20 ms) and per episode for seven cells in control conditions (gray line, six cells in the presence of blockers, one cell in artificial cerebrospinal fluid [ACSF]) and when GBZ (5 µM) was added (blue). (C) Duration of the post-stimulus spiking inhibition in cells with a BF-induced inhibitory response (blue) vs. in cells with a biphasic inhibition-muscarinic excitation response (gray). See also Figure 8—figure supplement 2 for caveats in these measurements. (D) Whole-cell characterization of a cell with an inhibitory response. Top: BF impact on firing (cell-attached recording, 38 episodes are superimposed) and BF-evoked IPSCs (whole-cell recording, 15 superimposed episodes). The histogram compares the decay time constants of photo-evoked GABAergic IPSCs in seven PG cells that were only inhibited (blue bars) vs. in cells with a mixed GABA/ACh response (gray bars). Bottom left: olfactory nerve (ON)-evoked EPSCs (left, four superimposed traces). Onset latencies > 2 ms (inset) are consistent with a plurisynaptic response. Bottom right: current-clamp voltage responses to current steps.

Figure 8—figure supplement 1. Absence of cholinergic excitation in periglomerular (PG) cells showing a transient inhibition of spiking.

(A) Low-frequency photostimulation of the basal forebrain (BF) axons (one flash per 2-s-long episode, starting at episode 41). (B) Single photostimulation (blue arrow). Each gray line is a cell, the black line is the ensemble average.

Figure 8—figure supplement 2. Caveats for the measurements of spiking inhibition duration.

(A) Raster plots from three example cells with various spiking activities that were inhibited by the basal forebrain (BF) input. The duration of the BF-induced inhibition was measured as the average time between the flash (blue bar) and the first spike after the flash (red tick). Histograms show the distribution of the first spike timing in each case and the calculated average duration. (B) Average first spike timing in all the cells used for Figure 8A as a function of their baseline firing frequency.