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| Poster #258 Heterogeneous monotonic and non-monotonic responses to odor in mitral/tufted glomeruli of the mouse olfactory bulb. |
| David Wharton4, Narayan Subramanian1, Bhargav Karamched2,3,4, Richard Bertram2,3,4, Douglas A Storace1,2,3 1Department of Biological Science, Florida State University, Tallahassee, FL, United States 2Program in Neuroscience, Florida State University, Tallahassee, FL, United States 3Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, United States 4Department of Mathematics, Florida State University, Tallahassee, FL, United States |
Current models of olfactory sensory processing in the olfactory bulb (OB) posit that both intra- and interglomerular inhibitory circuits are involved in transforming incoming sensory input. However, the impact of these circuits on different kinds of olfactory receptor neuron (ORNs) inputs remains poorly understood. We generated a model of the OB input-output transformation in which the output of each glomerulus is a function of its ORN input, local intraglomerular inhibition and interglomerular normalization in which activity of each glomerulus is divided by the population response. The output of the model included linear and non-linear concentration-response relationships that were a complicated function of the input ORN Hill coefficient and affinity. The concentration-response relationships could be broadly categorized into those that either monotonically increased or decreased with increasing concentration, and others that decreased then increased, or increased then decreased. Increasing then decreasing glomeruli required normalization in our model, were present in glomeruli with higher affinity ORN input, and were heterogeneous in their decrease. In vivo 2-photon Ca2+ imaging from mitral/tufted (MTC) glomeruli in awake mice revealed the presence of glomeruli exhibiting similar response types. Notably, increasing levels of excitation drove higher levels of suppression in subsets of glomeruli. Glomeruli that first increased then decreased were present in nearly half of glomeruli. The sensitivity of individual glomeruli was significantly correlated with the degree to which it was non-monotonic. Our results demonstrate that nonlinear responses of MTC to changes in odor concentration are not unusual, but indeed are typical, and that they can be explained by interglomerular inhibition. |