SPLTRAK Abstract Submission
Diversity in Glutamatergic Input Dynamics Drives Heterogeneous Response Patterns in Olfactory Bulb Mitral and Tufted Cells in Vivo
Andrew K. Moran, Tom P. Eiting, Matt Wachowiak
University of Utah, Salt Lake City, UT, United States

In vertebrates, olfactory sensory neuron (OSN) activation drives glutamatergic excitation of mitral/tufted (MT) cells and juxtaglomerular interneurons in the olfactory bulb (OB). MT cells show diverse temporal response patterns to odorant stimulation, which are thought to arise largely from processing by inhibitory OB circuits. However, this diversity could reflect differences in the temporal dynamics of OSN inputs to MT cells. Here, we imaged odorant-evoked glutamate transients onto MT cell dendrites in the OB of anesthetized and awake mice using the glutamate sensors iGluSnFR and SF-iGluSnFR, allowing us to visualize excitatory synaptic inputs onto MT cells and compare with patterns of postsynaptic activation. We found a surprising diversity in the temporal dynamics of glutamatergic inputs to MT cells, both within and across successive odorant inhalations. First, we observed variable dynamics in the glutamate transients elicited by each inhalation, with latencies, rise-times, and durations varying across glomeruli and odorants. Second, odorants could elicit both adaptation and facilitation of glutamate transients across successive inhalations. Third, we occasionally observed suppression of glutamatergic inputs onto MT cells. To compare glutamatergic inputs and postsynaptic responses we co-expressed SF-iGluSnFR and the red-shifted calcium reporter (jRGECO1a) in the same MT cells and performed dual-color imaging. While suppression in the MT calcium signal sometimes occurred without a corresponding decrease in glutamatergic input, overall we found a strong correspondence between glutamatergic input and postsynaptic response patterns. These results suggest that diversity in glutamatergic inputs onto MT cells plays a large role in shaping the temporal patterning of activity among OB output neurons.