When the MC was in the low firing rate regime, a clear increase in firing could be observed during light stimulation, followed by a decrease (Figure 6C). When the same MC was firing at a higher rate, excitation was less prominent (Figure 6D). We analyzed the significance of the excitatory effect by comparing our data to 100,000 randomly aligned

histograms (see Experimental Procedures for details). We found three of six cells to have a significant excitatory response (p < 0.01). Population analysis of these experiments, with the firing rate of each cell normalized to the prestimulus period, is shown in Figures 6E and 6F. With 240 pA current injection, AON input had a dual effect consisting VE-821 ic50 of a brief increase in firing probability followed by a more prolonged decrease. On average firing probability was increased

to a peak of 9.5 ± 11.3 times the baseline with a latency of 7 ± 1.7 ms (n = 6; Figure 6E). The average firing in the 10 ms periods of light stimulation was 5 ± 7.8 times the rate during the 10 ms right before stimulation (n = 6, p < 0.01, rank-sum test). In the 15 ms following light stimulation, firing was reduced to 0.4 ± 0.5 of baseline values (p < 0.05, rank-sum test) (Figure 6E). With 300 pA, Selleck Epigenetic inhibitor AON input had a smaller effect on firing probability during light stimulation, increasing it to a peak of 2.0 ± 0.5 times the baseline, and an average increase of 1.8 ± 0.7 times baseline values in the 10 ms period of light stimulation (n = 6; p < 0.01, rank-sum test). The inhibitory effect with 300 pA was manifested as a decrease of the average firing rate to 0.5 ± 0.5 of baseline Metalloexopeptidase values (p < 0.05, rank-sum test; Figure 6F).

This inhibition was followed by a rebound increase in firing rate presumably due to the intrinsic biophysical properties of MCs (Balu and Strowbridge, 2007). These results indicate that AON inputs can have multiple effects on MCs, depending on their ongoing activity, in part due to the newly discovered direct excitatory inputs. We next tested the functional significance of the AON inputs to MCs in vivo. We used tungsten electrodes to record the activity of single MCs from the dorsal OB in anesthetized rats 2–4 weeks postinjection of the virus. Breathing was continuously monitored with a piezoelectric belt that was wrapped around the rat’s torso and a light stimulus consisting of a pair of 40 ms stimuli, separated by 50 ms, was delivered every 15 s. Putative MCs/TCs were identified based on their depth and their strong breathing related firing pattern (Macrides and Chorover, 1972). Previous studies have noted that GCs are not visible to extracellular electrodes (Kay and Laurent, 1999; Rinberg et al., 2006; Doucette et al., 2011). Figure 7A shows an example of such an experiment. Single units were identified by stereotyped spike waveforms identified using cluster analysis (Figure 7A1). Figure 7A2 shows five traces aligned by the light stimulus (blue square).