It has been proposed that synchronized reciprocal interactions between M/T and GCs underlie

the generation of OB γ oscillations (Rall and Shepherd, 1968). Our results indicate that γ frequency Cilengitide molecular weight cortical activity propagates to the OB and is sufficient to drive local γ oscillations, presumably by synchronizing GC activity. As in cortex, odors elicited both β and γ oscillations in the LFP under control conditions (A trials, p < 0.05, Holm test, n = 10; Figures 8B1 and 8B3). While odor-evoked γ oscillations are thought to arise from reciprocal interactions between M/T cells and GCs, lesion studies suggest that β oscillations additionally require a feedback loop involving cortical projections (Gray and Skinner, 1988; Martin et al., 2006; Neville and Haberly, 2003). Consistent with these studies, photostimulation that briefly disrupted odor-evoked β oscillations in the cortex also acutely suppressed β oscillations in the OB (B trials, p < 0.05, Holm test, n = 10; Figures 8B2 and 8B3). Surprisingly, multi-unit recordings in the mitral cell layer revealed that cortical photostimulation had differential effects on spontaneous and odor-evoked M/T cell activity. Although spontaneous firing was not significantly

affected by cortical activation FRAX597 research buy (p > 0.05), odor-evoked firing was consistently reduced (p < 0.001, Wilcoxon signed-rank test, n = 15 odor-recording site pairs; Figures 8C1 and 8C2). These results demonstrate that, under our conditions, cortical photoactivation preferentially reduces M/T cell population activity during the processing of sensory stimuli implying a synergistic Carnitine dehydrogenase effect between sensory

input and cortical activity. Because multi-unit activity is dominated by neurons with high firing frequencies, we determined the effect of cortical photostimulation on isolated single units whose average firing rates varied over a large range. At the single unit level, M/T cell odor-evoked responses varied from clear excitation (Figure 8D1) to pure decreases in firing due to lateral inhibition (Figure 8D2). Cortical photoactivation both reduced odor-evoked increases in firing (Figure 8D1) and augmented odor-evoked inhibitory responses (Figure 8D2) in individual cells. The simplest interpretation of these effects is that cortical activation enhances recurrent and/or lateral inhibition. Across the population of M/T cell single units (n = 40 odor-unit pairs, seven mice), cortical photostimulation could both increase and decrease spontaneous firing rate (Figures 8E1 and S2). In contrast, cortical activation consistently led to decreases in firing rates in the presence of odor stimuli (p > 0.05 and p < 0.001 for spontaneous and odor-evoked activity respectively, Wilcoxon signed-rank test; Figure 8E2).