Sniff Rhythm-paced Fast and Slow Gamma Oscillations in the Olfactory Bulb: Relation to 1 Tufted and Mitral Cells and Behavioral States 2 3

19 20 Odor signals are conveyed from the olfactory bulb (OB) to the olfactory cortex by two 21 types of projection neurons, tufted cells and mitral cells, which differ in signal timing 22 and firing frequency in response to odor inhalation. Whereas tufted cells respond with 23 early-onset high frequency burst discharges starting at the middle of the inhalation 24 phase of sniff, mitral cells show odor responses with later-onset lower frequency burst 25 discharges. Since odor inhalation induces prominent gamma oscillations of local field 26 potentials (LFPs) in the OB during the transition period from inhalation to exhalation 27 that accompany synchronized spike discharges of tufted cells and mitral cells, we 28 addressed the question of whether the odor-induced gamma oscillations encompass two 29 distinct gamma oscillatory sources, tufted celland mitral cell-subsystems, by 30 simultaneously recording the sniff rhythms and local field potentials in the OB of freely 31 behaving rats. We observed that individual sniffs induced nested gamma oscillations 32 with two distinct parts during the inhalation-exhalation transition period: early-onset 33 fast gamma oscillations followed by later-onset slow gamma oscillations. These results 34 suggest that tufted cells carry odor signals with early-onset fast gamma 35 synchronization at the early phase of sniff, whereas mitral cells send them with 36 later-onset slow gamma synchronization. We also observed that each sniff typically 37 induced both fast and slow gamma oscillations during awake whereas respiration 38 during slow-wave sleep and REM sleep failed to induce these oscillations. These results 39 suggest that behavioral states regulate the generation of sniff rhythm-paced fast and 40 slow gamma oscillations in the OB. 41 42 43