title: Comparison of glomerular activity patterns by fMRI and wide-field calcium imaging: Implications for principles underlying odor mapping.
abstract: Functional imaging signals arise from distinct metabolic and hemodynamic events at the neuropil, but how these processes are influenced by pre- and post-synaptic activities need to be understood for quantitative interpretation of stimulus-evoked mapping data. The olfactory bulb (OB) glomeruli, spherical neuropil regions with well-defined neuronal circuitry, can provide insights into this issue. Optical calcium-sensitive fluorescent dye imaging (OICa(2+)) reflects dynamics of pre-synaptic input to glomeruli, whereas high-resolution functional magnetic resonance imaging (fMRI) using deoxyhemoglobin contrast reveals neuropil function within the glomerular layer where both pre- and post-synaptic activities contribute. We imaged odor-specific activity patterns of the dorsal OB in the same anesthetized rats with fMRI and OICa(2+) and then co-registered the respective maps to compare patterns in the same space. Maps by each modality were very reproducible as trial-to-trial patterns for a given odor, overlapping by ~80%. Maps evoked by ethyl butyrate and methyl valerate for a given modality overlapped by ~80%, suggesting activation of similar dorsal glomerular networks by these odors. Comparison of maps generated by both methods for a given odor showed ~70% overlap, indicating similar odor-specific maps by each method. These results suggest that odor-specific glomerular patterns by high-resolution fMRI primarily tracks pre-synaptic input to the OB. Thus combining OICa(2+) and fMRI lays the framework for studies of OB processing over a range of spatiotemporal scales, where OICa(2+) can feature the fast dynamics of dorsal glomerular clusters and fMRI can map the entire glomerular sheet in the OB.
authors.affiliation: Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA. Electronic address: basavaraju.ganganna@yale.edu.
authors.forename: Basavaraju G
authors.initials: BG
authors.lastname: Sanganahalli
authors.affiliation: Department of Neurobiology, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT, USA.
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Rebello
authors.affiliation: Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Herman
authors.affiliation: Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
authors.forename: Xenophon
authors.initials: X
authors.lastname: Papademetris
authors.affiliation: Department of Neurobiology, Yale University, New Haven, CT, USA.
authors.forename: Gordon M
authors.initials: GM
authors.lastname: Shepherd
authors.affiliation: Department of Neurobiology, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT, USA. Electronic address: jverhagen@jbpierce.org.
authors.forename: Justus V
authors.initials: JV
authors.lastname: Verhagen
authors.affiliation: Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Department of Biomedical Engineering, Yale University, New Haven, CT, USA. Electronic address: fahmeed.hyder@yale.edu.
authors.forename: Fahmeed
authors.initials: F
authors.lastname: Hyder
mesh_terms: D000818:Animals; D001931:Brain Mapping / Q000379:methods*; D002118:Calcium; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009812:Odorants; D009830:Olfactory Bulb / Q000502:physiology*; D061848:Optical Imaging / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012903:Smell / Q000502:physiology*
chemical_list: D002118:Calcium
keywords: BOLD signal; Energetics; Functional hyperemia; Glutamate; Intrinsic signal; Olfaction