Layer-Specific fMRI Responses to Excitatory and Inhibitory Neuronal Activities in the Olfactory Bulb

High-resolution functional magnetic resonance imaging (fMRI) detects localized neuronal activity via the hemodynamic response, but it is unclear whether it accurately identifies neuronal activity specific to individual layers. To address this issue, we preferentially evoked neuronal activity in superficial, middle, and deep layers of the rat olfactory bulb: the glomerular layer by odor (5% amyl acetate), the external plexiform layer by electrical stimulation of the lateral olfactory tract (LOT), and the granule cell layer by electrical stimulation of the anterior commissure (AC), respectively. Electrophysiology, laser-Doppler flowmetry of cerebral blood flow (CBF), and blood oxygenation level-dependent (BOLD) and cerebral blood volume-weighted (CBV) fMRI at 9.4 T were performed independently. We found that excitation of inhibitory granule cells by stimulating LOT and AC decreased the spontaneous multi-unit activities of excitatory mitral cells and subsequently increased CBF, CBV, and BOLD signals. Odor stimulation also increased the hemodynamic responses. Furthermore, the greatest CBV fMRI responses were discretely separated into the same layers as the evoked neuronal activities for all three stimuli, whereas BOLD was poorly localized with some exception to the poststimulus undershoot. In addition, the temporal dynamics of the fMRI responses varied depending on the stimulation pathway, even within the same layer. These results indicate that the vasculature is regulated within individual layers and CBV fMRI has a higher fidelity to the evoked neuronal activity compared with BOLD. Our findings are significant for understanding the neuronal origin and spatial specificity of hemodynamic responses, especially for the interpretation of laminar-resolution fMRI. SIGNIFICANCE STATEMENT Functional magnetic resonance imaging (fMRI) is a noninvasive, in vivo technique widely used to map function of the entire brain, including deep structures, in animals and humans. However, it measures neuronal activity indirectly by way of the vascular response. It is currently unclear how finely the hemodynamic response is regulated within single cortical layers and whether increased inhibitory neuronal activities affect fMRI signal changes. Both laminar specificity and the neural origins of fMRI are important to interpret functional maps properly, which we investigated by activating discrete rat olfactory bulb circuits.

[1]  Nathaniel N. Urban,et al.  There and Back Again: The Corticobulbar Loop , 2012, Neuron.

[2]  B. MacVicar,et al.  Calcium transients in astrocyte endfeet cause cerebrovascular constrictions , 2004, Nature.

[3]  Fahmeed Hyder,et al.  Odor maps of aldehydes and esters revealed by functional MRI in the glomerular layer of the mouse olfactory bulb , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[4]  J. Rossier,et al.  Cortical GABA Interneurons in Neurovascular Coupling: Relays for Subcortical Vasoactive Pathways , 2004, The Journal of Neuroscience.

[5]  Gang Chen,et al.  Layer-specific BOLD activation in awake monkey V1 revealed by ultra-high spatial resolution functional magnetic resonance imaging , 2013, NeuroImage.

[6]  G. Shepherd,et al.  Analysis of Relations between NMDA Receptors and GABA Release at Olfactory Bulb Reciprocal Synapses , 2000, Neuron.

[7]  Matthew Ennis,et al.  Complementary postsynaptic activity patterns elicited in olfactory bulb by stimulation of mitral/tufted and centrifugal fiber inputs to granule cells. , 2007, Journal of neurophysiology.

[8]  J. Pekar,et al.  Physiological origin for the BOLD poststimulus undershoot in human brain: Vascular compliance versus oxygen metabolism , 2011, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[9]  D. Attwell,et al.  Glial and neuronal control of brain blood flow , 2022 .

[10]  G. Westbrook,et al.  Detecting Activity in Olfactory Bulb Glomeruli with Astrocyte Recording , 2005, The Journal of Neuroscience.

[11]  F. Helmchen,et al.  Simultaneous BOLD fMRI and fiber-optic calcium recording in rat neocortex , 2012, Nature Methods.

[12]  Seong-Gi Kim,et al.  Layer-dependent BOLD and CBV-weighted fMRI responses in the rat olfactory bulb , 2014, NeuroImage.

[13]  W. Nickell,et al.  Evidence for presynaptic inhibition of the olfactory commissural pathway by cholinergic agonists and stimulation of the nucleus of the diagonal band , 1993, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[14]  B. Strowbridge,et al.  Opposing inward and outward conductances regulate rebound discharges in olfactory mitral cells. , 2007, Journal of neurophysiology.

[15]  G. Westbrook,et al.  Dendrodendritic Inhibition in the Olfactory Bulb Is Driven by NMDA Receptors , 1998, The Journal of Neuroscience.

[16]  J. Duyn,et al.  Functional MRI impulse response for BOLD and CBV contrast in rat somatosensory cortex , 2007, Magnetic resonance in medicine.

[17]  V. Murthy,et al.  Coupling of Neural Activity to Blood Flow in Olfactory Glomeruli Is Mediated by Astrocytic Pathways , 2008, Neuron.

[18]  S. Laughlin,et al.  An Energy Budget for Signaling in the Grey Matter of the Brain , 2001, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[19]  Steen Moeller,et al.  Combined imaging–histological study of cortical laminar specificity of fMRI signals , 2006, NeuroImage.

[20]  Vishnu B. Sridhar,et al.  In vivo Stimulus-Induced Vasodilation Occurs without IP3 Receptor Activation and May Precede Astrocytic Calcium Increase , 2013, The Journal of Neuroscience.

[21]  Ping Wang,et al.  Cortical layer-dependent BOLD and CBV responses measured by spin-echo and gradient-echo fMRI: Insights into hemodynamic regulation , 2006, NeuroImage.

[22]  S. Ogawa,et al.  Biophysical and Physiological Origins of Blood Oxygenation Level-Dependent fMRI Signals , 2012, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[23]  W. Nickell,et al.  Neurophysiology of magnocellular forebrain inputs to the olfactory bulb in the rat: frequency potentiation of field potentials and inhibition of output neurons , 1988, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[24]  Lawrence L. Wald,et al.  Laminar analysis of 7T BOLD using an imposed spatial activation pattern in human V1 , 2010, NeuroImage.

[25]  J. Mayhew,et al.  Fine detail of neurovascular coupling revealed by spatiotemporal analysis of the hemodynamic response to single whisker stimulation in rat barrel cortex. , 2008, Journal of neurophysiology.

[26]  K. Uğurbil,et al.  Layer-Specific fMRI Reflects Different Neuronal Computations at Different Depths in Human V1 , 2012, PloS one.

[27]  Junjie Liu,et al.  Laminar profiles of functional activity in the human brain , 2007, NeuroImage.

[28]  K. Mori,et al.  Centrifugal influence on olfactory bulb activity in the rabbit , 1978, Brain Research.

[29]  Jeffry S. Isaacson,et al.  Cortical Feedback Control of Olfactory Bulb Circuits , 2012, Neuron.

[30]  Hong-wei Dong,et al.  Activation of Group I Metabotropic Glutamate Receptors on Main Olfactory Bulb Granule Cells and Periglomerular Cells Enhances Synaptic Inhibition of Mitral Cells , 2007, The Journal of Neuroscience.

[31]  R G Shulman,et al.  Assessment and discrimination of odor stimuli in rat olfactory bulb by dynamic functional MRI. , 2000, Proceedings of the National Academy of Sciences of the United States of America.

[32]  Naoshige Uchida,et al.  Sensory-Evoked Intrinsic Optical Signals in the Olfactory Bulb Are Coupled to Glutamate Release and Uptake , 2006, Neuron.

[33]  D. Korol,et al.  Unilateral naris closure and vascular development in the rat olfactory bulb , 1992, Neuroscience.

[34]  M. C. Angulo,et al.  Neuron-to-astrocyte signaling is central to the dynamic control of brain microcirculation , 2003, Nature Neuroscience.

[35]  D. Attwell,et al.  Bidirectional control of CNS capillary diameter by pericytes , 2006, Nature.

[36]  Ji-Kyung Choi,et al.  Exogenous contrast agent improves sensitivity of gradient‐echo functional magnetic resonance imaging at 9.4 T , 2004, Magnetic resonance in medicine.

[37]  B. Strowbridge,et al.  Multiple Modes of Synaptic Excitation of Olfactory Bulb Granule Cells , 2007, The Journal of Neuroscience.

[38]  D. Norris,et al.  Layer‐specific BOLD activation in human V1 , 2010, Human brain mapping.

[39]  Seong-Gi Kim,et al.  Neural and hemodynamic responses elicited by forelimb- and photo-stimulation in channelrhodopsin-2 mice: insights into the hemodynamic point spread function. , 2014, Cerebral cortex.

[40]  M. Curtis,et al.  Olfactory bulb networks revealed by lateral olfactory tract stimulation in the in vitro isolated guinea-pig brain , 2006, Neuroscience.

[41]  Timothy H Murphy,et al.  Optogenetic Stimulation of GABA Neurons can Decrease Local Neuronal Activity While Increasing Cortical Blood Flow , 2015, Journal of cerebral blood flow and metabolism : official journal of the International Society of Cerebral Blood Flow and Metabolism.

[42]  P. Goadsby,et al.  A simple method, using 2-hydroxypropyl-β-cyclodextrin, of administering α-chloralose at room temperature , 1997, Journal of Neuroscience Methods.

[43]  V. Murthy,et al.  Functional Properties of Cortical Feedback Projections to the Olfactory Bulb , 2012, Neuron.

[44]  G. Bruce Pike,et al.  Origins of the BOLD post-stimulus undershoot , 2009, NeuroImage.

[45]  B. Rosen,et al.  Dynamic functional imaging of relative cerebral blood volume during rat forepaw stimulation , 1998, Magnetic resonance in medicine.

[46]  Seong-Gi Kim,et al.  Spatiotemporal characteristics and vascular sources of neural-specific and -nonspecific fMRI signals at submillimeter columnar resolution , 2013, NeuroImage.

[47]  Jong Chul Ye,et al.  Compressed sensing fMRI using gradient-recalled echo and EPI sequences , 2014, NeuroImage.

[48]  C. Yen Cortical layer-dependent hemodynamic regulation investigated by functional magnetic resonance imaging , 2011 .

[49]  Mayeul Collot,et al.  Calcium dynamics in astrocyte processes during neurovascular coupling , 2014, Nature Neuroscience.

[50]  K. Mori,et al.  An intracellular study of dendrodendritic inhibitory synapses on mitral cells in the rabbit olfactory bulb. , 1978, The Journal of physiology.

[51]  D. Attwell,et al.  Capillary pericytes regulate cerebral blood flow in health and disease , 2014, Nature.

[52]  R. C. Collins,et al.  Metabolic anatomy of brain: A comparison of regional capillary density, glucose metabolism, and enzyme activities , 1989, The Journal of comparative neurology.

[53]  Gordon M Shepherd,et al.  Odor-Evoked Oxygen Consumption by Action Potential and Synaptic Transmission in the Olfactory Bulb , 2009, The Journal of Neuroscience.

[54]  N. Logothetis,et al.  High-Resolution fMRI Reveals Laminar Differences in Neurovascular Coupling between Positive and Negative BOLD Responses , 2012, Neuron.

[55]  G. Shepherd,et al.  Theoretical reconstruction of field potentials and dendrodendritic synaptic interactions in olfactory bulb. , 1968, Journal of neurophysiology.

[56]  E. Hillman Coupling mechanism and significance of the BOLD signal: a status report. , 2014, Annual review of neuroscience.

[57]  D. Attwell,et al.  Synaptic Energy Use and Supply , 2012, Neuron.

[58]  Jaime Grutzendler,et al.  Regional Blood Flow in the Normal and Ischemic Brain Is Controlled by Arteriolar Smooth Muscle Cell Contractility and Not by Capillary Pericytes , 2015, Neuron.

[59]  J. Isaacson,et al.  Olfactory Reciprocal Synapses: Dendritic Signaling in the CNS , 1998, Neuron.

[60]  G. Shepherd Synaptic organization of the mammalian olfactory bulb. , 1972, Physiological reviews.

[61]  M. Ducros,et al.  The Relationship between Blood Flow and Neuronal Activity in the Rodent Olfactory Bulb , 2007, The Journal of Neuroscience.