Glomerulus-specific synchronization of mitral cells in the olfactory bulb.

Odor elicits a well-organized pattern of glomerular activation in the olfactory bulb. However, the mechanisms by which this spatial map is transformed into an odor code remain unclear. We examined this question in rat olfactory bulb slices in recordings from output mitral cells. Electrical stimulation of incoming afferents elicited slow ( approximately 2 Hz) oscillations that originated in glomeruli and were highly synchronized for mitral cells projecting to the same glomerulus. Cyclical depolarizations were generated by glutamate activation of dendritic autoreceptors, while the slow frequency was determined primarily by the duration of regenerative glutamate release. Patterned stimuli elicited stimulus-entrained oscillations that amplified weak and variable inputs. We suggest that these oscillations maintain the fidelity of the spatial map by ensuring that all mitral cells within a glomerulus-specific network respond to odor as a functional unit.