Diverse dynamics of glutamatergic input from sensory neurons underlie heterogeneous response patterns of olfactory bulb outputs in vivo

Mitral/tufted (MT) cells of the olfactory bulb (OB) show diverse temporal responses to odorant stimulation that are thought to encode odor information. To understand the role of sensory input dynamics versus OB circuit mechanisms in generating this diversity, we imaged glutamate signaling onto MT cell dendrites in anesthetized and awake mice. We found surprising diversity in the dynamics of these signals, including excitatory, suppressive, and biphasic responses as well as nonlinear changes in glutamate signaling across inhalations. Simultaneous imaging of glutamate and calcium signals from MT cell dendrites revealed highly correlated responses for both signals. Glutamate responses were only weakly impacted by blockade of postsynaptic activity, implicating sensory neurons as a primary source of glutamate signaling onto MT cells. Thus, the dynamics of sensory input alone, rather than emergent features of OB circuits, may account for much of the diversity in MT cell responses that underlies OB odor representations.