Odorant modulation of neuronal activity and local field potential in sensory-deprived olfactory bulb.

Neuronal discharge and local field potential (LFP) oscillations in the olfactory bulb (OB) are modulated by odorant stimulation. The LFP oscillations have been proposed as the mechanism that facilitates synchronization of OB output neurons and the representation of similar odorants. Gamma LFP oscillations depend on the OB inhibitory network and early sensory deprivation modifies this inhibitory network. However, little is known about the LFP oscillations and neuronal discharge in the deprived OB. We examined the mitral/tufted (MT) cells' oscillatory activity and LFP oscillations in both sensory-deprived and normal OBs in urethane anesthetized rats. We found that MT cells in deprived and normal OBs have similar basal mean firing rate; 44% of the recorded cells in deprived OB and only 8% of the cells in normal OB showed firing rate modulation by odorants, both exhibiting a similar ratio of excitatory to inhibitory responses. A fraction of MT cells exhibited oscillatory discharge centered on gamma (60-70 Hz) and beta (20 Hz) frequencies, although this feature was not consistently dependent on odorant stimulation. Odorants decreased the LFP oscillatory power in the gamma band (35-90 Hz) and increased the power in the beta band (12-30 Hz). The modulation of LFP oscillations by odorants was also predominant in the deprived (53%) compared to the normal OB (17%). In contrast, a higher fraction of MT cells' discharge was locked to the gamma LFP cycle in the normal OB. These results suggest that early unilateral olfactory deprivation increases the OB sensitivity to odorants and reduce the temporal synchrony between unitary activity and gamma LFP oscillations without altering the basal neuronal discharge.