51
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Rojas-Líbano D, Wimmer Del Solar J, Aguilar-Rivera M, Montefusco-Siegmund R, Maldonado PE. Local cortical activity of distant brain areas can phase-lock to the olfactory bulb's respiratory rhythm in the freely behaving rat. J Neurophysiol 2018; 120:960-972. [PMID: 29766764 DOI: 10.1152/jn.00088.2018] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
An important unresolved question about neural processing is the mechanism by which distant brain areas coordinate their activities and relate their local processing to global neural events. A potential candidate for the local-global integration are slow rhythms such as respiration. In this study, we asked if there are modulations of local cortical processing that are phase-locked to (peripheral) sensory-motor exploratory rhythms. We studied rats on an elevated platform where they would spontaneously display exploratory and rest behaviors. Concurrent with behavior, we monitored whisking through electromyography and the respiratory rhythm from the olfactory bulb (OB) local field potential (LFP). We also recorded LFPs from dorsal hippocampus, primary motor cortex, primary somatosensory cortex, and primary visual cortex. We defined exploration as simultaneous whisking and sniffing above 5 Hz and found that this activity peaked at ~8 Hz. We considered rest as the absence of whisking and sniffing, and in this case, respiration occurred at ~3 Hz. We found a consistent shift across all areas toward these rhythm peaks accompanying behavioral changes. We also found, across areas, that LFP gamma (70-100 Hz) amplitude could phase-lock to the animal's OB respiratory rhythm, a finding indicative of respiration-locked changes in local processing. In a subset of animals, we also recorded the hippocampal theta activity and found that occurred at frequencies overlapped with respiration but was not spectrally coherent with it, suggesting a different oscillator. Our results are consistent with the notion of respiration as a binder or integrator of activity between brain regions.
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Affiliation(s)
- Daniel Rojas-Líbano
- Laboratorio de Neurociencia Cognitiva y Social, Facultad de Psicología, Universidad Diego Portales , Santiago , Chile
| | - Jonathan Wimmer Del Solar
- Unidad de Investigación y Desarrollo, Hospital El Carmen de Maipú , Santiago , Chile.,Programa de Neurología, Facultad de Ciencias Médicas, Universidad de Santiago de Chile , Santiago , Chile
| | | | - Rodrigo Montefusco-Siegmund
- Escuela de Kinesiología, Facultad de Medicina, Universidad Austral de Chile , Valdivia , Chile.,Department of Neuroscience and Biomedical Neuroscience Institute, Universidad de Chile , Santiago , Chile
| | - Pedro E Maldonado
- Department of Neuroscience and Biomedical Neuroscience Institute, Universidad de Chile , Santiago , Chile
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52
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Behavioral readout of spatio-temporal codes in olfaction. Curr Opin Neurobiol 2018; 52:18-24. [PMID: 29694923 DOI: 10.1016/j.conb.2018.04.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Revised: 03/10/2018] [Accepted: 04/07/2018] [Indexed: 11/21/2022]
Abstract
Neural recordings performed at an increasing scale and resolution have revealed complex, spatio-temporally precise patterns of activity in the olfactory system. Multiple models may explain the functional consequences of the spatio-temporal olfactory code, but the link to behavior remains unclear. Recent evidence in the field suggests a behavioral sensitivity to both fine spatial and temporal features in the code. How these features and combinations of features give rise to olfactory behavior is the subject of active research in the field. Modern genetic and optogenetic methods show great promise in testing the link between olfactory codes and behavior.
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53
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Stimulus dependent diversity and stereotypy in the output of an olfactory functional unit. Nat Commun 2018; 9:1347. [PMID: 29632302 PMCID: PMC5890244 DOI: 10.1038/s41467-018-03837-1] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 03/14/2018] [Indexed: 11/24/2022] Open
Abstract
Olfactory inputs are organized in an array of functional units (glomeruli), each relaying information from sensory neurons expressing a given odorant receptor to a small population of output neurons, mitral/tufted (MT) cells. MT cells respond heterogeneously to odorants, and how the responses encode stimulus features is unknown. We recorded in awake mice responses from “sister” MT cells that receive input from a functionally characterized, genetically identified glomerulus, corresponding to a specific receptor (M72). Despite receiving similar inputs, sister MT cells exhibit temporally diverse, concentration-dependent, excitatory and inhibitory responses to most M72 ligands. In contrast, the strongest known ligand for M72 elicits temporally stereotyped, early excitatory responses in sister MT cells, consistent across a range of concentrations. Our data suggest that information about ligand affinity is encoded in the collective stereotypy or diversity of activity among sister MT cells within a glomerular functional unit in a concentration-tolerant manner. Mitral/tufted (MT) cells connect to a single glomerulus and receive inputs from sensory neurons expressing the same odorant receptor. Here the authors report that sister MT cells connected to the M72 glomerulus exhibit variable responses to most M72 ligands but respond in a reproducible and stereotyped way to a high-affinity M72 ligand.
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54
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Thompson GJ, Sanganahalli BG, Baker KL, Herman P, Shepherd GM, Verhagen JV, Hyder F. Spontaneous activity forms a foundation for odor-evoked activation maps in the rat olfactory bulb. Neuroimage 2018; 172:586-596. [PMID: 29374582 DOI: 10.1016/j.neuroimage.2018.01.051] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 01/16/2018] [Accepted: 01/20/2018] [Indexed: 12/12/2022] Open
Abstract
Fluctuations in spontaneous activity have been observed by many neuroimaging techniques, but because these resting-state changes are not evoked by stimuli, it is difficult to determine how they relate to task-evoked activations. We conducted multi-modal neuroimaging scans of the rat olfactory bulb, both with and without odor, to examine interaction between spontaneous and evoked activities. Independent component analysis of spontaneous fluctuations revealed resting-state networks, and odor-evoked changes revealed activation maps. We constructed simulated activation maps using resting-state networks that were highly correlated to evoked activation maps. Simulated activation maps derived by intrinsic optical signal (IOS), which covers the dorsal portion of the glomerular sheet, significantly differentiated one odor's evoked activation map from the other two. To test the hypothesis that spontaneous activity of the entire glomerular sheet is relevant for representing odor-evoked activations, we used functional magnetic resonance imaging (fMRI) to map the entire glomerular sheet. In contrast to the IOS results, the fMRI-derived simulated activation maps significantly differentiated all three odors' evoked activation maps. Importantly, no evoked activation maps could be significantly differentiated using simulated activation maps produced using phase-randomized resting-state networks. Given that some highly organized resting-state networks did not correlate with any odors' evoked activation maps, we posit that these resting-state networks may characterize evoked activation maps associated with odors not studied. These results emphasize that fluctuations in spontaneous activity form a foundation for active processing, signifying the relevance of resting-state mapping to functional neuroimaging.
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Affiliation(s)
- Garth J Thompson
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Basavaraju G Sanganahalli
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA
| | - Keeley L Baker
- Department of Neuroscience, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT USA
| | - Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA
| | | | - Justus V Verhagen
- Department of Neuroscience, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT USA
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
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55
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Iwata R, Kiyonari H, Imai T. Mechanosensory-Based Phase Coding of Odor Identity in the Olfactory Bulb. Neuron 2017; 96:1139-1152.e7. [PMID: 29216451 DOI: 10.1016/j.neuron.2017.11.008] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 10/13/2017] [Accepted: 11/06/2017] [Indexed: 11/17/2022]
Abstract
Mitral and tufted (M/T) cells in the olfactory bulb produce rich temporal patterns of activity in response to different odors. However, it remains unknown how these temporal patterns are generated and how they are utilized in olfaction. Here we show that temporal patterning effectively discriminates between the two sensory modalities detected by olfactory sensory neurons (OSNs): odor and airflow-driven mechanical signals. Sniff-induced mechanosensation generates glomerulus-specific oscillatory activity in M/T cells, whose phase was invariant across airflow speed. In contrast, odor stimulation caused phase shifts (phase coding). We also found that odor-evoked phase shifts are concentration invariant and stable across multiple sniff cycles, contrary to the labile nature of rate coding. The loss of oscillatory mechanosensation impaired the precision and stability of phase coding, demonstrating its role in olfaction. We propose that phase, not rate, coding is a robust encoding strategy of odor identity and is ensured by airflow-induced mechanosensation in OSNs.
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Affiliation(s)
- Ryo Iwata
- Laboratory for Sensory Circuit Formation, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan
| | - Hiroshi Kiyonari
- Animal Resource Development Unit and Genetic Engineering Team, RIKEN Center for Life Science Technologies, Kobe 650-0047, Japan
| | - Takeshi Imai
- Laboratory for Sensory Circuit Formation, RIKEN Center for Developmental Biology, Kobe 650-0047, Japan; PRESTO, Japan Science and Technology Agency (JST), Saitama 332-0012, Japan; Graduate School of Biostudies, Kyoto University, Kyoto 606-8501, Japan; Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
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56
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Jacob V, Monsempès C, Rospars JP, Masson JB, Lucas P. Olfactory coding in the turbulent realm. PLoS Comput Biol 2017; 13:e1005870. [PMID: 29194457 PMCID: PMC5736211 DOI: 10.1371/journal.pcbi.1005870] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2017] [Revised: 12/19/2017] [Accepted: 11/01/2017] [Indexed: 01/10/2023] Open
Abstract
Long-distance olfactory search behaviors depend on odor detection dynamics. Due to turbulence, olfactory signals travel as bursts of variable concentration and spacing and are characterized by long-tail distributions of odor/no-odor events, challenging the computing capacities of olfactory systems. How animals encode complex olfactory scenes to track the plume far from the source remains unclear. Here we focus on the coding of the plume temporal dynamics in moths. We compare responses of olfactory receptor neurons (ORNs) and antennal lobe projection neurons (PNs) to sequences of pheromone stimuli either with white-noise patterns or with realistic turbulent temporal structures simulating a large range of distances (8 to 64 m) from the odor source. For the first time, we analyze what information is extracted by the olfactory system at large distances from the source. Neuronal responses are analyzed using linear-nonlinear models fitted with white-noise stimuli and used for predicting responses to turbulent stimuli. We found that neuronal firing rate is less correlated with the dynamic odor time course when distance to the source increases because of improper coding during long odor and no-odor events that characterize large distances. Rapid adaptation during long puffs does not preclude however the detection of puff transitions in PNs. Individual PNs but not individual ORNs encode the onset and offset of odor puffs for any temporal structure of stimuli. A higher spontaneous firing rate coupled to an inhibition phase at the end of PN responses contributes to this coding property. This allows PNs to decode the temporal structure of the odor plume at any distance to the source, an essential piece of information moths can use in their tracking behavior.
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Affiliation(s)
- Vincent Jacob
- Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France
- Peuplements végétaux et bioagresseurs en milieu végétal, CIRAD, Université de la Réunion, Saint Pierre, Ile de la Réunion, France
| | - Christelle Monsempès
- Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France
| | - Jean-Pierre Rospars
- Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France
| | - Jean-Baptiste Masson
- Decision and Bayesian Computation, Pasteur Institute, CNRS UMR 3571, 25-28 rue du Dr Roux, 75015 Paris, France
- Bioinformatics and Biostatistics Hub, C3BI, Pasteur Institute, CNRS USR 3756, 25-28 rue du Dr Roux, 75015 Paris, France
| | - Philippe Lucas
- Institute of Ecology and Environmental Sciences, INRA, route de St Cyr, Versailles, France
- * E-mail:
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57
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Activity Patterns Elicited by Airflow in the Olfactory Bulb and Their Possible Functions. J Neurosci 2017; 37:10700-10711. [PMID: 28972124 DOI: 10.1523/jneurosci.2210-17.2017] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Revised: 09/23/2017] [Accepted: 09/28/2017] [Indexed: 12/29/2022] Open
Abstract
Olfactory sensory neurons (OSNs) can sense both odorants and airflows. In the olfactory bulb (OB), the coding of odor information has been well studied, but the coding of mechanical stimulation is rarely investigated. Unlike odor-sensing functions of OSNs, the airflow-sensing functions of OSNs are also largely unknown. Here, the activity patterns elicited by mechanical airflow in male rat OBs were mapped using fMRI and correlated with local field potential recordings. In an attempt to reveal possible functions of airflow sensing, the relationship between airflow patterns and physiological parameters was also examined. We found the following: (1) the activity pattern in the OB evoked by airflow in the nasal cavity was more broadly distributed than patterns evoked by odors; (2) the pattern intensity increases with total airflow, while the pattern topography with total airflow remains almost unchanged; and (3) the heart rate, spontaneous respiratory rate, and electroencephalograph power in the β band decreased with regular mechanical airflow in the nasal cavity. The mapping results provide evidence that the signals elicited by mechanical airflow in OSNs are transmitted to the OB, and that the OB has the potential to code and process mechanical information. Our functional data indicate that airflow rhythm in the olfactory system can regulate the physiological and brain states, providing an explanation for the effects of breath control in meditation, yoga, and Taoism practices.SIGNIFICANCE STATEMENT Presentation of odor information in the olfactory bulb has been well studied, but studies about breathing features are rare. Here, using blood oxygen level-dependent functional MRI for the first time in such an investigation, we explored the global activity patterns in the rat olfactory bulb elicited by airflow in the nasal cavity. We found that the activity pattern elicited by airflow is broadly distributed, with increasing pattern intensity and similar topography under increasing total airflow. Further, heart rate, spontaneous respiratory rate in the lung, and electroencephalograph power in the β band decreased with regular airflow in the nasal cavity. Our study provides further understanding of the airflow map in the olfactory bulb in vivo, and evidence for the possible mechanosensitivity functions of olfactory sensory neurons.
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58
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Grillet M, Campagner D, Petersen R, McCrohan C, Cobb M. The peripheral olfactory code in Drosophila larvae contains temporal information and is robust over multiple timescales. Proc Biol Sci 2017; 283:rspb.2016.0665. [PMID: 27194701 PMCID: PMC4892805 DOI: 10.1098/rspb.2016.0665] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Accepted: 04/20/2016] [Indexed: 11/29/2022] Open
Abstract
We studied the electrophysiological activity of two classes of Drosophila melanogaster larval olfactory sensory neurons (OSNs), Or24a and Or74a, in response to 1 s stimulation with butanol, octanol, 2-heptanone, and propyl acetate. Each odour/OSN combination produced unique responses in terms of spike count and temporal profile. We used a classifier algorithm to explore the information content of OSN activity, and showed that as well as spike count, the activity of these OSNs included temporal information that enabled the classifier to accurately identify odours. The responses of OSNs during continuous odour exposure (5 and 20 min) showed that both types of neuron continued to respond, with no complete adaptation, and with no change to their ability to encode temporal information. Finally, we exposed larvae to octanol for 3 days and found only minor quantitative changes in OSN response to odours, indicating that the larval peripheral code is robust when faced with long-term exposure to odours, such as would be found in a natural context.
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Affiliation(s)
- Micheline Grillet
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
| | - Dario Campagner
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
| | - Rasmus Petersen
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
| | - Catherine McCrohan
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
| | - Matthew Cobb
- Faculty of Life Sciences, University of Manchester, Manchester M13 9PT, UK
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59
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Cell-Type-Specific Modulation of Sensory Responses in Olfactory Bulb Circuits by Serotonergic Projections from the Raphe Nuclei. J Neurosci 2017; 36:6820-35. [PMID: 27335411 DOI: 10.1523/jneurosci.3667-15.2016] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Accepted: 05/17/2016] [Indexed: 12/15/2022] Open
Abstract
UNLABELLED Serotonergic neurons in the brainstem raphe nuclei densely innervate the olfactory bulb (OB), where they can modulate the initial representation and processing of olfactory information. Serotonergic modulation of sensory responses among defined OB cell types is poorly characterized in vivo Here, we used cell-type-specific expression of optical reporters to visualize how raphe stimulation alters sensory responses in two classes of GABAergic neurons of the mouse OB glomerular layer, periglomerular (PG) and short axon (SA) cells, as well as mitral/tufted (MT) cells carrying OB output to piriform cortex. In PG and SA cells, brief (1-4 s) raphe stimulation elicited a large increase in the magnitude of responses linked to inhalation of ambient air, as well as modest increases in the magnitude of odorant-evoked responses. Near-identical effects were observed when the optical reporter of glutamatergic transmission iGluSnFR was expressed in PG and SA cells, suggesting enhanced excitatory input to these neurons. In contrast, in MT cells imaged from the dorsal OB, raphe stimulation elicited a strong increase in resting GCaMP fluorescence with only a slight enhancement of inhalation-linked responses to odorant. Finally, optogenetically stimulating raphe serotonergic afferents in the OB had heterogeneous effects on presumptive MT cells recorded extracellularly, with an overall modest increase in resting and odorant-evoked responses during serotonergic afferent stimulation. These results suggest that serotonergic afferents from raphe dynamically modulate olfactory processing through distinct effects on multiple OB targets, and may alter the degree to which OB output is shaped by inhibition during behavior. SIGNIFICANCE STATEMENT Modulation of the circuits that process sensory information can profoundly impact how information about the external world is represented and perceived. This study investigates how the serotonergic system modulates the initial processing of olfactory information by the olfactory bulb, an obligatory relay between sensory neurons and cortex. We find that serotonergic projections from the raphe nuclei to the olfactory bulb dramatically enhance the responses of two classes of inhibitory interneurons to sensory input, that this effect is mediated by increased glutamatergic drive onto these neurons, and that serotonergic afferent activation alters the responses of olfactory bulb output neurons in vivo These results elucidate pathways by which neuromodulatory systems can dynamically regulate brain circuits during behavior.
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60
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Short SM, Morse TM, McTavish TS, Shepherd GM, Verhagen JV. Respiration Gates Sensory Input Responses in the Mitral Cell Layer of the Olfactory Bulb. PLoS One 2016; 11:e0168356. [PMID: 28005923 PMCID: PMC5179112 DOI: 10.1371/journal.pone.0168356] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 11/30/2016] [Indexed: 12/23/2022] Open
Abstract
Respiration plays an essential role in odor processing. Even in the absence of odors, oscillating excitatory and inhibitory activity in the olfactory bulb synchronizes with respiration, commonly resulting in a burst of action potentials in mammalian mitral/tufted cells (MTCs) during the transition from inhalation to exhalation. This excitation is followed by inhibition that quiets MTC activity in both the glomerular and granule cell layers. Odor processing is hypothesized to be modulated by and may even rely on respiration-mediated activity, yet exactly how respiration influences sensory processing by MTCs is still not well understood. By using optogenetics to stimulate discrete sensory inputs in vivo, it was possible to temporally vary the stimulus to occur at unique phases of each respiration. Single unit recordings obtained from the mitral cell layer were used to map spatiotemporal patterns of glomerular evoked responses that were unique to stimulations occurring during periods of inhalation or exhalation. Sensory evoked activity in MTCs was gated to periods outside phasic respiratory mediated firing, causing net shifts in MTC activity across the cycle. In contrast, odor evoked inhibitory responses appear to be permitted throughout the respiratory cycle. Computational models were used to further explore mechanisms of inhibition that can be activated by respiratory activity and influence MTC responses. In silico results indicate that both periglomerular and granule cell inhibition can be activated by respiration to internally gate sensory responses in the olfactory bulb. Both the respiration rate and strength of lateral connectivity influenced inhibitory mechanisms that gate sensory evoked responses.
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Affiliation(s)
- Shaina M. Short
- Yale School of Medicine, Dept. Neuroscience, New Haven, CT, United States of America
- The John B. Pierce Laboratory, New Haven, CT, United States of America
- * E-mail:
| | - Thomas M. Morse
- Yale School of Medicine, Dept. Neuroscience, New Haven, CT, United States of America
| | - Thomas S. McTavish
- Yale School of Medicine, Dept. Neuroscience, New Haven, CT, United States of America
| | - Gordon M. Shepherd
- Yale School of Medicine, Dept. Neuroscience, New Haven, CT, United States of America
| | - Justus V. Verhagen
- Yale School of Medicine, Dept. Neuroscience, New Haven, CT, United States of America
- The John B. Pierce Laboratory, New Haven, CT, United States of America
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61
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Weiss T, Shushan S, Ravia A, Hahamy A, Secundo L, Weissbrod A, Ben-Yakov A, Holtzman Y, Cohen-Atsmoni S, Roth Y, Sobel N. From Nose to Brain: Un-Sensed Electrical Currents Applied in the Nose Alter Activity in Deep Brain Structures. Cereb Cortex 2016; 26:4180-4191. [PMID: 27591145 PMCID: PMC5066827 DOI: 10.1093/cercor/bhw222] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Revised: 05/16/2016] [Accepted: 06/27/2016] [Indexed: 01/02/2023] Open
Abstract
Rules linking patterns of olfactory receptor neuron activation in the nose to activity patterns in the brain and ensuing odor perception remain poorly understood. Artificially stimulating olfactory neurons with electrical currents and measuring ensuing perception may uncover these rules. We therefore inserted an electrode into the nose of 50 human volunteers and applied various currents for about an hour in each case. This induced assorted non-olfactory sensations but never once the perception of odor. To validate contact with the olfactory path, we used functional magnetic resonance imaging to measure resting-state brain activity in 18 subjects before and after un-sensed stimulation. We observed stimulation-induced neural decorrelation specifically in primary olfactory cortex, implying contact with the olfactory path. These results suggest that indiscriminate olfactory activation does not equate with odor perception. Moreover, this effort serendipitously uncovered a novel path for minimally invasive brain stimulation through the nose.
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Affiliation(s)
- Tali Weiss
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Sagit Shushan
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel.,Department of Otolaryngology-Head and Neck Surgery, Edith Wolfson Medical Center, Holon 58100, Israel
| | - Aharon Ravia
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Avital Hahamy
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Lavi Secundo
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Aharon Weissbrod
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Aya Ben-Yakov
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Yael Holtzman
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
| | - Smadar Cohen-Atsmoni
- Department of Otolaryngology-Head and Neck Surgery, Edith Wolfson Medical Center, Holon 58100, Israel
| | - Yehudah Roth
- Department of Otolaryngology-Head and Neck Surgery, Edith Wolfson Medical Center, Holon 58100, Israel
| | - Noam Sobel
- Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel
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62
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Cavarretta F, Marasco A, Hines ML, Shepherd GM, Migliore M. Glomerular and Mitral-Granule Cell Microcircuits Coordinate Temporal and Spatial Information Processing in the Olfactory Bulb. Front Comput Neurosci 2016; 10:67. [PMID: 27471461 PMCID: PMC4943958 DOI: 10.3389/fncom.2016.00067] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Accepted: 06/17/2016] [Indexed: 11/20/2022] Open
Abstract
The olfactory bulb processes inputs from olfactory receptor neurons (ORNs) through two levels: the glomerular layer at the site of input, and the granule cell level at the site of output to the olfactory cortex. The sequence of action of these two levels has not yet been examined. We analyze this issue using a novel computational framework that is scaled up, in three-dimensions (3D), with realistic representations of the interactions between layers, activated by simulated natural odors, and constrained by experimental and theoretical analyses. We suggest that the postulated functions of glomerular circuits have as their primary role transforming a complex and disorganized input into a contrast-enhanced and normalized representation, but cannot provide for synchronization of the distributed glomerular outputs. By contrast, at the granule cell layer, the dendrodendritic interactions mediate temporal decorrelation, which we show is dependent on the preceding contrast enhancement by the glomerular layer. The results provide the first insights into the successive operations in the olfactory bulb, and demonstrate the significance of the modular organization around glomeruli. This layered organization is especially important for natural odor inputs, because they activate many overlapping glomeruli.
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Affiliation(s)
- Francesco Cavarretta
- Department of Neuroscience, School of Medicine, Yale UniversityNew Haven, CT, USA; Department of Mathematics "Federigo Enriques", University of MilanMilan, Italy
| | - Addolorata Marasco
- Department of Mathematics and Application "R. Cacciopoli", University of Naples Federico II Naples, Italy
| | - Michael L Hines
- Department of Neuroscience, School of Medicine, Yale University New Haven, CT, USA
| | - Gordon M Shepherd
- Department of Neuroscience, School of Medicine, Yale University New Haven, CT, USA
| | - Michele Migliore
- Department of Neuroscience, School of Medicine, Yale UniversityNew Haven, CT, USA; Institute of Biophysics, National Research CouncilPalermo, Italy
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63
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Nache V, Wongsamitkul N, Kusch J, Zimmer T, Schwede F, Benndorf K. Deciphering the function of the CNGB1b subunit in olfactory CNG channels. Sci Rep 2016; 6:29378. [PMID: 27405959 PMCID: PMC4942689 DOI: 10.1038/srep29378] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 06/15/2016] [Indexed: 11/29/2022] Open
Abstract
Olfactory cyclic nucleotide-gated (CNG) ion channels are key players in the signal transduction cascade of olfactory sensory neurons. The second messengers cAMP and cGMP directly activate these channels, generating a depolarizing receptor potential. Olfactory CNG channels are composed of two CNGA2 subunits and two modulatory subunits, CNGA4, and CNGB1b. So far the exact role of the modulatory subunits for channel activation is not fully understood. By measuring ligand binding and channel activation simultaneously, we show that in functional heterotetrameric channels not only the CNGA2 subunits and the CNGA4 subunit but also the CNGB1b subunit binds cyclic nucleotides and, moreover, also alone translates this signal to open the pore. In addition, we show that the CNGB1b subunit is the most sensitive subunit in a heterotetrameric channel to cyclic nucleotides and that it accelerates deactivation to a similar extent as does the CNGA4 subunit. In conclusion, the CNGB1b subunit participates in ligand-gated activation of olfactory CNG channels and, particularly, contributes to rapid termination of odorant signal in an olfactory sensory neuron.
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Affiliation(s)
- Vasilica Nache
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Nisa Wongsamitkul
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Jana Kusch
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Thomas Zimmer
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
| | - Frank Schwede
- BIOLOG Life Science Institute, Flughafendamm 9A, D-28199 Bremen, Germany
| | - Klaus Benndorf
- Institute of Physiology II, Jena University Hospital, Friedrich Schiller University Jena, D-07743 Jena, Germany
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64
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Significance of sniffing pattern during the acquisition of an olfactory discrimination task. Behav Brain Res 2016; 312:341-54. [PMID: 27343936 DOI: 10.1016/j.bbr.2016.06.039] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Revised: 06/16/2016] [Accepted: 06/20/2016] [Indexed: 11/24/2022]
Abstract
Active sampling of olfactory environment consists of sniffing in rodents. The importance of sniffing dynamics is well established at the neuronal and behavioral levels. Patterns of sniffing have been shown to be modulated by the physicochemical properties of odorants, particularly concentration and sorption. Sniffing is also heavily impacted by higher processing related to the behavioral context, emotion and attentional demand. However, how the pattern of sniffing evolves over the course of learning of an experimental olfactory conditioning is still poorly understood. We tested this question by monitoring sniffing activity, using a whole-body plethysmograph, on rats performing a two-alternative choice odor discrimination task. We followed sniff variations at different learning stages (naïve, well-trained, expert). We found that during the acquisition of an odor discrimination task, rats acquired a global sniffing pattern, independent of the odor pair used. This pattern consists of a longer sampling duration, a higher sniffing frequency, and a larger amplitude. In parallel, subtle differences of sniffing between the two odors of a pair were also observed. This sniffing behavior was not only associated with a better and faster acquisition of the discrimination task but was also transferred to other odor sets and refined after a long-term pause so as to reduce the sampling duration and maintain a specific sniffing frequency. Our results provide additional arguments that sniffing is a complex sensorimotor act that is strongly affected by olfactory learning.
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65
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Jercog P, Rogerson T, Schnitzer MJ. Large-Scale Fluorescence Calcium-Imaging Methods for Studies of Long-Term Memory in Behaving Mammals. Cold Spring Harb Perspect Biol 2016; 8:a021824. [PMID: 27048190 PMCID: PMC4852807 DOI: 10.1101/cshperspect.a021824] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
During long-term memory formation, cellular and molecular processes reshape how individual neurons respond to specific patterns of synaptic input. It remains poorly understood how such changes impact information processing across networks of mammalian neurons. To observe how networks encode, store, and retrieve information, neuroscientists must track the dynamics of large ensembles of individual cells in behaving animals, over timescales commensurate with long-term memory. Fluorescence Ca(2+)-imaging techniques can monitor hundreds of neurons in behaving mice, opening exciting avenues for studies of learning and memory at the network level. Genetically encoded Ca(2+) indicators allow neurons to be targeted by genetic type or connectivity. Chronic animal preparations permit repeated imaging of neural Ca(2+) dynamics over multiple weeks. Together, these capabilities should enable unprecedented analyses of how ensemble neural codes evolve throughout memory processing and provide new insights into how memories are organized in the brain.
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Affiliation(s)
- Pablo Jercog
- CNC Program, Stanford University, Stanford, California 94305
| | - Thomas Rogerson
- CNC Program, Stanford University, Stanford, California 94305
| | - Mark J Schnitzer
- CNC Program, Stanford University, Stanford, California 94305 Howard Hughes Medical Institute, Stanford University, Stanford, California 94305 James H. Clark Center for Biomedical Engineering & Sciences, Stanford University, Stanford, California 94305
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66
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Lehmann A, D'Errico A, Vogel M, Spors H. Spatio-Temporal Characteristics of Inhibition Mapped by Optical Stimulation in Mouse Olfactory Bulb. Front Neural Circuits 2016; 10:15. [PMID: 27047340 PMCID: PMC4801895 DOI: 10.3389/fncir.2016.00015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2016] [Accepted: 03/04/2016] [Indexed: 12/04/2022] Open
Abstract
Mitral and tufted cells (MTCs) of the mammalian olfactory bulb are connected via dendrodendritic synapses with inhibitory interneurons in the external plexiform layer. The range, spatial layout, and temporal properties of inhibitory interactions between MTCs mediated by inhibitory interneurons remain unclear. Therefore, we tested for inhibitory interactions using an optogenetic approach. We optically stimulated MTCs expressing channelrhodopsin-2 in transgenic mice, while recording from individual MTCs in juxtacellular or whole-cell configuration in vivo. We used a spatial noise stimulus for mapping interactions between MTCs belonging to different glomeruli in the dorsal bulb. Analyzing firing responses of MTCs to the stimulus, we did not find robust lateral inhibitory effects that were spatially specific. However, analysis of sub-threshold changes in the membrane potential revealed evidence for inhibitory interactions between MTCs that belong to different glomerular units. These lateral inhibitory effects were short-lived and spatially specific. MTC response maps showed hyperpolarizing effects radially extending over more than five glomerular diameters. The inhibitory maps exhibited non-symmetrical yet distance-dependent characteristics.
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Affiliation(s)
| | - Anna D'Errico
- Max Planck Institute of Biophysics Frankfurt am Main, Germany
| | - Martin Vogel
- Max Planck Institute of Biophysics Frankfurt am Main, Germany
| | - Hartwig Spors
- Max Planck Institute of BiophysicsFrankfurt am Main, Germany; Department of Neuropediatrics, Justus-Liebig-UniversityGiessen, Germany
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67
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Genovese F, Thews M, Möhrlen F, Frings S. Properties of an optogenetic model for olfactory stimulation. J Physiol 2016; 594:3501-16. [PMID: 26857095 DOI: 10.1113/jp271853] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2015] [Accepted: 01/22/2016] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS In olfactory research it is difficult to deliver stimuli with defined intensity and duration to olfactory sensory neurons. Expression of channelrhodopsin 2 (ChR2) in olfactory sensory neurons provides a means to activate these neurons with light flashes. Appropriate mouse models are available. The present study explores the suitability of an established olfactory marker protein (OMP)/ChR2-yellow fluorescent protein (YFP) mouse model for ex vivo experimentation. Expression of ChR2 in sensory neurons of the main olfactory epithelium, the septal organ and vomeronasal organ is characterized. Expression pattern of ChR2 in olfactory receptor neurons and the properties of light responses indicate that light stimulation does not impact on signal transduction in the chemosensory cilia. Light-induced electro-olfactograms are characterized with light flashes of different intensities, durations and frequencies. The impact of light-induced afferent stimulation on the olfactory bulb is examined with respect to response amplitude, polarity and low-pass filtering. ABSTRACT For the examination of sensory processing, it is helpful to deliver stimuli in precisely defined temporal and spatial patterns with accurate control of stimulus intensity. This is challenging in experiments with the mammalian olfactory system because airborne odorants have to be transported into the intricate sensory structures of the nose and must dissolve in mucus to be detected by sensory neurons. Defined and reproducible activity can be generated in olfactory sensory neurons that express the light-gated ion channel channelrhodopsin 2 (ChR2). The neurons can be stimulated by light flashes in a controlled fashion by this optogenetic approach. Here we examined the application of an olfactory marker protein (OMP)/ChR2-yellow fluorescent protein (YFP) model for ex vivo exploration of the olfactory epithelium and the olfactory bulb of the mouse. We studied the expression patterns of ChR2 in the main olfactory system, the vomeronasal system, and the septal organ, and we found that ChR2 is absent from the sensory cilia of olfactory sensory neurons. In the olfactory epithelium, we characterized light-induced electro-olfactograms with respect to peripheral encoding of stimulus intensity, stimulus duration and stimulus frequency. In acute slices of the olfactory bulb, we identified specific aspects of the ChR2-induced input signal, concerning its dynamic range, its low-pass filter property and its response to prolonged stimulation. Our study describes the performance of the OMP/ChR2-YFP model for ex vivo experimentation on the peripheral olfactory system and documents its versatility and its limitations for olfactory research.
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Affiliation(s)
- Federica Genovese
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Marion Thews
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Frank Möhrlen
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Stephan Frings
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
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68
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Silva Teixeira CS, Cerqueira NMFSA, Silva Ferreira AC. Unravelling the Olfactory Sense: From the Gene to Odor Perception. Chem Senses 2015; 41:105-21. [PMID: 26688501 DOI: 10.1093/chemse/bjv075] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Although neglected by science for a long time, the olfactory sense is now the focus of a panoply of studies that bring new insights and raises interesting questions regarding its functioning. The importance in the clarification of this process is of interest for science, but also motivated by the food and perfume industries boosted by a consumer society with increasingly demands for higher quality standards. In this review, a general overview of the state of art of science regarding the olfactory sense is presented with the main focus on the peripheral olfactory system. Special emphasis will be given to the deorphanization of the olfactory receptors (ORs), a critical issue because the specificity and functional properties of about 90% of human ORs remain unknown mainly due to the difficulties associated with the functional expression of ORs in high yields.
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Affiliation(s)
- Carla S Silva Teixeira
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Arquiteto Lobão Vital, Apartado 2511, 4202-401 Porto, Portugal
| | - Nuno M F S A Cerqueira
- UCIBIO@Requimte/Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4169-007 Porto, Portugal and
| | - António C Silva Ferreira
- Escola Superior de Biotecnologia, Universidade Católica Portuguesa, Rua Arquiteto Lobão Vital, Apartado 2511, 4202-401 Porto, Portugal, Department of Viticulture and Oenology, Institute for Wine Biotechnology, University of Stellenbosch, Private Bag XI, Matieland 7602, South Africa
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69
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Competing Mechanisms of Gamma and Beta Oscillations in the Olfactory Bulb Based on Multimodal Inhibition of Mitral Cells Over a Respiratory Cycle. eNeuro 2015; 2:eN-TNC-0018-15. [PMID: 26665163 PMCID: PMC4672204 DOI: 10.1523/eneuro.0018-15.2015] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 10/28/2015] [Accepted: 10/29/2015] [Indexed: 11/21/2022] Open
Abstract
Gamma (∼40-90 Hz) and beta (∼15-40 Hz) oscillations and their associated neuronal assemblies are key features of neuronal sensory processing. However, the mechanisms involved in either their interaction and/or the switch between these different regimes in most sensory systems remain misunderstood. Based on in vivo recordings and biophysical modeling of the mammalian olfactory bulb (OB), we propose a general scheme where OB internal dynamics can sustain two distinct dynamic states, each dominated by either a gamma or a beta regime. The occurrence of each regime depends on the excitability level of granule cells, the main OB interneurons. Using this model framework, we demonstrate how the balance between sensory and centrifugal input can control the switch between the two oscillatory dynamic states. In parallel, we experimentally observed that sensory and centrifugal inputs to the rat OB could both be modulated by the respiration of the animal (2-12 Hz) and each one phase shifted with the other. Implementing this phase shift in our model resulted in the appearance of the alternation between gamma and beta rhythms within a single respiratory cycle, as in our experimental results under urethane anesthesia. Our theoretical framework can also account for the oscillatory frequency response, depending on the odor intensity, the odor valence, and the animal sniffing strategy observed under various conditions including animal freely-moving. Importantly, the results of the present model can form a basis to understand how fast rhythms could be controlled by the slower sensory and centrifugal modulations linked to the respiration. Visual Abstract: See Abstract.
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70
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Huston SJ, Stopfer M, Cassenaer S, Aldworth ZN, Laurent G. Neural Encoding of Odors during Active Sampling and in Turbulent Plumes. Neuron 2015; 88:403-18. [PMID: 26456047 DOI: 10.1016/j.neuron.2015.09.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Revised: 05/11/2015] [Accepted: 08/31/2015] [Indexed: 12/19/2022]
Abstract
Sensory inputs are often fluctuating and intermittent, yet animals reliably utilize them to direct behavior. Here we ask how natural stimulus fluctuations influence the dynamic neural encoding of odors. Using the locust olfactory system, we isolated two main causes of odor intermittency: chaotic odor plumes and active sampling behaviors. Despite their irregularity, chaotic odor plumes still drove dynamic neural response features including the synchronization, temporal patterning, and short-term plasticity of spiking in projection neurons, enabling classifier-based stimulus identification and activating downstream decoders (Kenyon cells). Locusts can also impose odor intermittency through active sampling movements with their unrestrained antennae. Odors triggered immediate, spatially targeted antennal scanning that, paradoxically, weakened individual neural responses. However, these frequent but weaker responses were highly informative about stimulus location. Thus, not only are odor-elicited dynamic neural responses compatible with natural stimulus fluctuations and important for stimulus identification, but locusts actively increase intermittency, possibly to improve stimulus localization.
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Affiliation(s)
- Stephen J Huston
- Howard Hughes Medical Institute, Janelia Research Campus, Ashburn, VA 20147, USA
| | - Mark Stopfer
- National Institutes of Health, NICHD, 35 Lincoln Drive, MSC 3715, Bethesda, MD 20892, USA
| | - Stijn Cassenaer
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Zane N Aldworth
- National Institutes of Health, NICHD, 35 Lincoln Drive, MSC 3715, Bethesda, MD 20892, USA
| | - Gilles Laurent
- Max Planck Institute for Brain Research, Max-von-Laue-Strasse 4, 60438 Frankfurt am Main, Germany.
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71
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Hamel EJO, Grewe BF, Parker JG, Schnitzer MJ. Cellular level brain imaging in behaving mammals: an engineering approach. Neuron 2015; 86:140-59. [PMID: 25856491 PMCID: PMC5758309 DOI: 10.1016/j.neuron.2015.03.055] [Citation(s) in RCA: 101] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Fluorescence imaging offers expanding capabilities for recording neural dynamics in behaving mammals, including the means to monitor hundreds of cells targeted by genetic type or connectivity, track cells over weeks, densely sample neurons within local microcircuits, study cells too inactive to isolate in extracellular electrical recordings, and visualize activity in dendrites, axons, or dendritic spines. We discuss recent progress and future directions for imaging in behaving mammals from a systems engineering perspective, which seeks holistic consideration of fluorescent indicators, optical instrumentation, and computational analyses. Today, genetically encoded indicators of neural Ca(2+) dynamics are widely used, and those of trans-membrane voltage are rapidly improving. Two complementary imaging paradigms involve conventional microscopes for studying head-restrained animals and head-mounted miniature microscopes for imaging in freely behaving animals. Overall, the field has attained sufficient sophistication that increased cooperation between those designing new indicators, light sources, microscopes, and computational analyses would greatly benefit future progress.
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Affiliation(s)
| | | | - Jones G Parker
- CNC Program, Stanford University, Stanford, CA 94305, USA; Pfizer Neuroscience Research Unit, Cambridge, MA 02139, USA
| | - Mark J Schnitzer
- CNC Program, Stanford University, Stanford, CA 94305, USA; Howard Hughes Medical Institute, Stanford University, Stanford, CA 94305, USA.
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72
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Gilra A, Bhalla US. Bulbar microcircuit model predicts connectivity and roles of interneurons in odor coding. PLoS One 2015; 10:e0098045. [PMID: 25942312 PMCID: PMC4420273 DOI: 10.1371/journal.pone.0098045] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 04/23/2014] [Indexed: 01/13/2023] Open
Abstract
Stimulus encoding by primary sensory brain areas provides a data-rich context for understanding their circuit mechanisms. The vertebrate olfactory bulb is an input area having unusual two-layer dendro-dendritic connections whose roles in odor coding are unclear. To clarify these roles, we built a detailed compartmental model of the rat olfactory bulb that synthesizes a much wider range of experimental observations on bulbar physiology and response dynamics than has hitherto been modeled. We predict that superficial-layer inhibitory interneurons (periglomerular cells) linearize the input-output transformation of the principal neurons (mitral cells), unlike previous models of contrast enhancement. The linearization is required to replicate observed linear summation of mitral odor responses. Further, in our model, action-potentials back-propagate along lateral dendrites of mitral cells and activate deep-layer inhibitory interneurons (granule cells). Using this, we propose sparse, long-range inhibition between mitral cells, mediated by granule cells, to explain how the respiratory phases of odor responses of sister mitral cells can be sometimes decorrelated as observed, despite receiving similar receptor input. We also rule out some alternative mechanisms. In our mechanism, we predict that a few distant mitral cells receiving input from different receptors, inhibit sister mitral cells differentially, by activating disjoint subsets of granule cells. This differential inhibition is strong enough to decorrelate their firing rate phases, and not merely modulate their spike timing. Thus our well-constrained model suggests novel computational roles for the two most numerous classes of interneurons in the bulb.
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Affiliation(s)
- Aditya Gilra
- National Centre for Biological Sciences (NCBS), Tata Institute of Fundamental Research (TIFR), Bangalore, 560065, India
| | - Upinder S. Bhalla
- National Centre for Biological Sciences (NCBS), Tata Institute of Fundamental Research (TIFR), Bangalore, 560065, India
- * E-mail:
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73
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Nunez-Parra A, Li A, Restrepo D. Coding odor identity and odor value in awake rodents. PROGRESS IN BRAIN RESEARCH 2015; 208:205-22. [PMID: 24767484 DOI: 10.1016/b978-0-444-63350-7.00008-5] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/25/2023]
Abstract
In the last decade, drastic changes in the understanding of the role of the olfactory bulb and piriform cortex in odor detection have taken place through awake behaving recording in rodents. It is clear that odor responses in mitral and granule cells are strikingly different in the olfactory bulb of anesthetized versus awake animals. In addition, sniff recording has evidenced that mitral cell responses to odors during the sniff can convey information on the odor identity and sniff phase. Moreover, we review studies that show that the mitral cell conveys information on not only odor identity but also whether the odor is rewarded or not (odor value). Finally, we discuss how the substantial increase in awake behaving recording raises questions for future studies.
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Affiliation(s)
- Alexia Nunez-Parra
- Department of Cell and Developmental Biology, Rocky Mountain Taste and Smell Center and Neuroscience Program, University of Colorado Medical School, Aurora, CO, USA
| | - Anan Li
- Department of Cell and Developmental Biology, Rocky Mountain Taste and Smell Center and Neuroscience Program, University of Colorado Medical School, Aurora, CO, USA; State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, The Chinese Academy of Sciences, Wuhan, China
| | - Diego Restrepo
- Department of Cell and Developmental Biology, Rocky Mountain Taste and Smell Center and Neuroscience Program, University of Colorado Medical School, Aurora, CO, USA.
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74
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Carey RM, Sherwood WE, Shipley MT, Borisyuk A, Wachowiak M. Role of intraglomerular circuits in shaping temporally structured responses to naturalistic inhalation-driven sensory input to the olfactory bulb. J Neurophysiol 2015; 113:3112-29. [PMID: 25717156 DOI: 10.1152/jn.00394.2014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Accepted: 02/20/2015] [Indexed: 11/22/2022] Open
Abstract
Olfaction in mammals is a dynamic process driven by the inhalation of air through the nasal cavity. Inhalation determines the temporal structure of sensory neuron responses and shapes the neural dynamics underlying central olfactory processing. Inhalation-linked bursts of activity among olfactory bulb (OB) output neurons [mitral/tufted cells (MCs)] are temporally transformed relative to those of sensory neurons. We investigated how OB circuits shape inhalation-driven dynamics in MCs using a modeling approach that was highly constrained by experimental results. First, we constructed models of canonical OB circuits that included mono- and disynaptic feedforward excitation, recurrent inhibition and feedforward inhibition of the MC. We then used experimental data to drive inputs to the models and to tune parameters; inputs were derived from sensory neuron responses during natural odorant sampling (sniffing) in awake rats, and model output was compared with recordings of MC responses to odorants sampled with the same sniff waveforms. This approach allowed us to identify OB circuit features underlying the temporal transformation of sensory inputs into inhalation-linked patterns of MC spike output. We found that realistic input-output transformations can be achieved independently by multiple circuits, including feedforward inhibition with slow onset and decay kinetics and parallel feedforward MC excitation mediated by external tufted cells. We also found that recurrent and feedforward inhibition had differential impacts on MC firing rates and on inhalation-linked response dynamics. These results highlight the importance of investigating neural circuits in a naturalistic context and provide a framework for further explorations of signal processing by OB networks.
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Affiliation(s)
- Ryan M Carey
- Department of Biomedical Engineering, Boston University, Boston, Massachusetts
| | | | - Michael T Shipley
- Department of Anatomy and Neurobiology, Program in Neuroscience, University of Maryland School of Medicine, Baltimore, Maryland; and
| | - Alla Borisyuk
- Department of Mathematics, University of Utah, Salt Lake City, Utah
| | - Matt Wachowiak
- Department of Neurobiology and Anatomy and Brain Institute, University of Utah, Salt Lake City, Utah
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75
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Rebello MR, Kandukuru P, Verhagen JV. Direct behavioral and neurophysiological evidence for retronasal olfaction in mice. PLoS One 2015; 10:e0117218. [PMID: 25675095 PMCID: PMC4326425 DOI: 10.1371/journal.pone.0117218] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2014] [Accepted: 12/18/2014] [Indexed: 11/26/2022] Open
Abstract
The neuroscience of flavor perception is hence becoming increasingly important to understand food flavor perception that guides food selection, ingestion and appreciation. We recently provided evidence that rats can use the retronasal mode of olfaction, an essential element of human flavor perception. We showed that in rats, like humans, odors can acquire a taste. We and others also defined how the input of the olfactory bulb (OB) -not functionally imageable in humans- codes retronasal smell in anesthetized rat. The powerful awake transgenic mouse, however, would be a valuable additional model in the study of flavor neuroscience. We used a go/no-go behavioral task to test the mouse's ability to detect and discriminate the retronasal odor amyl acetate. In this paradigm a tasteless aqueous odor solution was licked by water-restricted head-fixed mice from a lick spout. Orthonasal contamination was avoided. The retronasal odor was successfully discriminated by mice against pure distilled water in a concentration-dependent manner. Bulbectomy removed the mice's ability to discriminate the retronasal odor but not tastants. The OB showed robust optical calcium responses to retronasal odorants in these awake mice. These results suggest that mice, like rats, are capable of smelling retronasally. This direct neuro-behavioral evidence establishes the mouse as a useful additional animal model for flavor research.
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Affiliation(s)
- Michelle R. Rebello
- The John B. Pierce Laboratory and Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Padma Kandukuru
- The John B. Pierce Laboratory and Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Justus V. Verhagen
- The John B. Pierce Laboratory and Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- * E-mail:
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76
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G protein-coupled odorant receptors underlie mechanosensitivity in mammalian olfactory sensory neurons. Proc Natl Acad Sci U S A 2014; 112:590-5. [PMID: 25550517 DOI: 10.1073/pnas.1418515112] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mechanosensitive cells are essential for organisms to sense the external and internal environments, and a variety of molecules have been implicated as mechanical sensors. Here we report that odorant receptors (ORs), a large family of G protein-coupled receptors, underlie the responses to both chemical and mechanical stimuli in mouse olfactory sensory neurons (OSNs). Genetic ablation of key signaling proteins in odor transduction or disruption of OR-G protein coupling eliminates mechanical responses. Curiously, OSNs expressing different OR types display significantly different responses to mechanical stimuli. Genetic swap of putatively mechanosensitive ORs abolishes or reduces mechanical responses of OSNs. Furthermore, ectopic expression of an OR restores mechanosensitivity in loss-of-function OSNs. Lastly, heterologous expression of an OR confers mechanosensitivity to its host cells. These results indicate that certain ORs are both necessary and sufficient to cause mechanical responses, revealing a previously unidentified mechanism for mechanotransduction.
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77
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Rebello MR, McTavish TS, Willhite DC, Short SM, Shepherd GM, Verhagen JV. Perception of odors linked to precise timing in the olfactory system. PLoS Biol 2014; 12:e1002021. [PMID: 25514030 PMCID: PMC4267717 DOI: 10.1371/journal.pbio.1002021] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2014] [Accepted: 10/30/2014] [Indexed: 11/19/2022] Open
Abstract
The temporal dynamics of glomeruli activity can be behaviorally discerned by mice down to 13 milliseconds. While the timing of neuronal activity in the olfactory bulb (OB) relative to sniffing has been the object of many studies, the behavioral relevance of timing information generated by patterned activation within the bulbar response has not been explored. Here we show, using sniff-triggered, dynamic, 2-D, optogenetic stimulation of mitral/tufted cells, that virtual odors that differ by as little as 13 ms are distinguishable by mice. Further, mice are capable of discriminating a virtual odor movie based on an optically imaged OB odor response versus the same virtual odor devoid of temporal dynamics—independently of the sniff-phase. Together with studies showing the behavioral relevance of graded glomerular responses and the response timing relative to odor sampling, these results imply that the mammalian olfactory system is capable of very high transient information transmission rates. Olfactory receptor neurons respond to odors in the olfactory epithelium located in the nasal cavity in mammals. Each olfactory receptor neuron expresses only one olfactory receptor, out of several hundred encoded in the mammalian genome. Olfactory receptor neurons expressing the same olfactory receptor are scattered throughout the olfactory epithelium; however, their axons converge in one of thousands of glomeruli in the olfactory bulb. The glomeruli are the first neural relay station in the olfactory system, where olfactory receptor neurons transmit olfactory information to mitral cells. It is well established that different odors evoke different spatial patterns across the glomeruli. It is believed that the more similar the patterns, the more similar the evoked odor perceptions. Glomeruli also are activated in odor-specific sequences in time. These dynamics could increase the amount of information about odors by immense amounts. We used transgenic mice, whose mitral cells were made responsive to light, and asked how well they could discriminate the temporal dynamics of simple spatial patterns of light presented to the olfactory bulb after each sniff. Mice could detect the presence of temporal dynamics down to 13 ms, which provides ample resolution for them to be able to detect the dynamics in response to actual odors. Mice could also discern whether virtual odors, based on actual olfactory bulb activity, were dynamic or static and did so without reference to exact sniff-time. We conclude that both the spatial glomerular activity patterns and the temporal dynamics thereof are used in the mammalian olfactory system to encode odors.
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Affiliation(s)
- Michelle R. Rebello
- The John B. Pierce Laboratory, New Haven, Connecticut, United States of America
- Yale School of Medicine, Dept. Neurobiology, New Haven, Connecticut, United States of America
| | - Thomas S. McTavish
- Yale School of Medicine, Dept. Neurobiology, New Haven, Connecticut, United States of America
| | - David C. Willhite
- The John B. Pierce Laboratory, New Haven, Connecticut, United States of America
- Yale School of Medicine, Dept. Neurobiology, New Haven, Connecticut, United States of America
| | - Shaina M. Short
- The John B. Pierce Laboratory, New Haven, Connecticut, United States of America
- Yale School of Medicine, Dept. Neurobiology, New Haven, Connecticut, United States of America
| | - Gordon M. Shepherd
- Yale School of Medicine, Dept. Neurobiology, New Haven, Connecticut, United States of America
| | - Justus V. Verhagen
- The John B. Pierce Laboratory, New Haven, Connecticut, United States of America
- Yale School of Medicine, Dept. Neurobiology, New Haven, Connecticut, United States of America
- * E-mail:
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78
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Gautam SH, Short SM, Verhagen JV. Retronasal odor concentration coding in glomeruli of the rat olfactory bulb. Front Integr Neurosci 2014; 8:81. [PMID: 25386123 PMCID: PMC4208450 DOI: 10.3389/fnint.2014.00081] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Accepted: 09/26/2014] [Indexed: 11/22/2022] Open
Abstract
The mammalian olfactory system processes odorants presented orthonasally (inhalation through the nose) and also retronasally (exhalation), enabling identification of both external as well as internal objects during food consumption. There are distinct differences between ortho- and retronasal air flow patterns, psychophysics, multimodal integration, and glomerular responses. Recent work indicates that rats can also detect odors retronasally, that rats can associate retronasal odors with tastes, and that their olfactory bulbs (OBs) can respond to retronasal odorants but differently than to orthonasal odors. To further characterize retronasal OB input activity patterns, experiments here focus on determining the effects of odor concentration on glomerular activity by monitoring calcium activity in the dorsal OB of rats using a dextran-conjugated calcium-sensitive dye in vivo. Results showed reliable concentration-response curves that differed between odorants, and recruitment of additional glomeruli, as odor concentration increased. We found evidence of different concentration-response functions between glomeruli, that in turn depended on odor. Further, the relation between dynamics and concentration differed remarkably among retronasal odorants. These dynamics are suggested to reduce the odor map ambiguity based on response amplitude. Elucidating the coding of retronasal odor intensity is fundamental to the understanding of feeding behavior and the neural basis of flavor. These data further establish and refine the rodent model of flavor neuroscience.
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Affiliation(s)
- Shree Hari Gautam
- The John B. Pierce Laboratory New Haven, CT, USA ; Department of Neurobiology, Yale University School of Medicine New Haven, CT, USA
| | - Shaina M Short
- The John B. Pierce Laboratory New Haven, CT, USA ; Department of Neurobiology, Yale University School of Medicine New Haven, CT, USA
| | - Justus V Verhagen
- The John B. Pierce Laboratory New Haven, CT, USA ; Department of Neurobiology, Yale University School of Medicine New Haven, CT, USA
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79
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Rothermel M, Wachowiak M. Functional imaging of cortical feedback projections to the olfactory bulb. Front Neural Circuits 2014; 8:73. [PMID: 25071454 PMCID: PMC4080262 DOI: 10.3389/fncir.2014.00073] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Accepted: 06/12/2014] [Indexed: 11/16/2022] Open
Abstract
Processing of sensory information is substantially shaped by centrifugal, or feedback, projections from higher cortical areas, yet the functional properties of these projections are poorly characterized. Here, we used genetically-encoded calcium sensors (GCaMPs) to functionally image activation of centrifugal projections targeting the olfactory bulb (OB). The OB receives massive centrifugal input from cortical areas but there has been as yet no characterization of their activity in vivo. We focused on projections to the OB from the anterior olfactory nucleus (AON), a major source of cortical feedback to the OB. We expressed GCaMP selectively in AON projection neurons using a mouse line expressing Cre recombinase (Cre) in these neurons and Cre-dependent viral vectors injected into AON, allowing us to image GCaMP fluorescence signals from their axon terminals in the OB. Electrical stimulation of AON evoked large fluorescence signals that could be imaged from the dorsal OB surface in vivo. Surprisingly, odorants also evoked large signals that were transient and coupled to odorant inhalation both in the anesthetized and awake mouse, suggesting that feedback from AON to the OB is rapid and robust across different brain states. The strength of AON feedback signals increased during wakefulness, suggesting a state-dependent modulation of cortical feedback to the OB. Two-photon GCaMP imaging revealed that different odorants activated different subsets of centrifugal AON axons and could elicit both excitation and suppression in different axons, indicating a surprising richness in the representation of odor information by cortical feedback to the OB. Finally, we found that activating neuromodulatory centers such as basal forebrain drove AON inputs to the OB independent of odorant stimulation. Our results point to the AON as a multifunctional cortical area that provides ongoing feedback to the OB and also serves as a descending relay for other neuromodulatory systems.
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Affiliation(s)
- Markus Rothermel
- Brain Institute and Department of Neurobiology and Anatomy, University of Utah Salt Lake City, UT, USA
| | - Matt Wachowiak
- Brain Institute and Department of Neurobiology and Anatomy, University of Utah Salt Lake City, UT, USA
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80
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Rojas-Líbano D, Frederick DE, Egaña JI, Kay LM. The olfactory bulb theta rhythm follows all frequencies of diaphragmatic respiration in the freely behaving rat. Front Behav Neurosci 2014; 8:214. [PMID: 24966821 PMCID: PMC4053074 DOI: 10.3389/fnbeh.2014.00214] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2014] [Accepted: 05/27/2014] [Indexed: 11/13/2022] Open
Abstract
Sensory-motor relationships are part of the normal operation of sensory systems. Sensing occurs in the context of active sensor movement, which in turn influences sensory processing. We address such a process in the rat olfactory system. Through recordings of the diaphragm electromyogram (EMG), we monitored the motor output of the respiratory circuit involved in sniffing behavior, simultaneously with the local field potential (LFP) of the olfactory bulb (OB) in rats moving freely in a familiar environment, where they display a wide range of respiratory frequencies. We show that the OB LFP represents the sniff cycle with high reliability at every sniff frequency and can therefore be used to study the neural representation of motor drive in a sensory cortex.
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Affiliation(s)
- Daniel Rojas-Líbano
- Committee on Neurobiology, The University of Chicago Chicago, IL, USA ; Institute for Mind and Biology, The University of Chicago Chicago, IL, USA
| | - Donald E Frederick
- Institute for Mind and Biology, The University of Chicago Chicago, IL, USA ; Department of Psychology, The University of Chicago Chicago, IL, USA
| | - José I Egaña
- Departamento de Anestesiología y Reanimación, Facultad de Medicina, Universidad de Chile Santiago, Chile
| | - Leslie M Kay
- Committee on Neurobiology, The University of Chicago Chicago, IL, USA ; Institute for Mind and Biology, The University of Chicago Chicago, IL, USA ; Department of Psychology, The University of Chicago Chicago, IL, USA
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81
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Abstract
How is sensory information represented in the brain? A long-standing debate in neural coding is whether and how timing of spikes conveys information to downstream neurons. Although we know that neurons in the olfactory bulb (OB) exhibit rich temporal dynamics, the functional relevance of temporal coding remains hotly debated. Recent recording experiments in awake behaving animals have elucidated highly organized temporal structures of activity in the OB. In addition, the analysis of neural circuits in the piriform cortex (PC) demonstrated the importance of not only OB afferent inputs but also intrinsic PC neural circuits in shaping odor responses. Furthermore, new experiments involving stimulation of the OB with specific temporal patterns allowed for testing the relevance of temporal codes. Together, these studies suggest that the relative timing of neuronal activity in the OB conveys odor information and that neural circuits in the PC possess various mechanisms to decode temporal patterns of OB input.
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Affiliation(s)
- Naoshige Uchida
- Department of Molecular and Cellular Biology, Center for Brain Science, Harvard University, Cambridge, Massachusetts 02138;
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82
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Cholinergic inputs from Basal forebrain add an excitatory bias to odor coding in the olfactory bulb. J Neurosci 2014; 34:4654-64. [PMID: 24672011 DOI: 10.1523/jneurosci.5026-13.2014] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Cholinergic modulation of central circuits is associated with active sensation, attention, and learning, yet the neural circuits and temporal dynamics underlying cholinergic effects on sensory processing remain unclear. Understanding the effects of cholinergic modulation on particular circuits is complicated by the widespread projections of cholinergic neurons to telencephalic structures that themselves are highly interconnected. Here we examined how cholinergic projections from basal forebrain to the olfactory bulb (OB) modulate output from the first stage of sensory processing in the mouse olfactory system. By optogenetically activating their axons directly in the OB, we found that cholinergic projections from basal forebrain regulate OB output by increasing the spike output of presumptive mitral/tufted cells. Cholinergic stimulation increased mitral/tufted cell spiking in the absence of inhalation-driven sensory input and further increased spiking responses to inhalation of odorless air and to odorants. This modulation was rapid and transient, was dependent on local cholinergic signaling in the OB, and differed from modulation by optogenetic activation of cholinergic neurons in basal forebrain, which led to a mixture of mitral/tufted cell excitation and suppression. Finally, bulbar cholinergic enhancement of mitral/tufted cell odorant responses was robust and occurred independent of the strength or even polarity of the odorant-evoked response, indicating that cholinergic modulation adds an excitatory bias to mitral/tufted cells as opposed to increasing response gain or sharpening response spectra. These results are consistent with a role for the basal forebrain cholinergic system in dynamically regulating the sensitivity to or salience of odors during active sensing of the olfactory environment.
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83
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Segalàs C, Alonso P, Orbegozo A, Real E, Subirà M, López-Solà C, Martínez-Zalacaín I, Labad J, Harrison BJ, Pujol J, Menchón JM, Cardoner N, Soriano-Mas C. Brain structural imaging correlates of olfactory dysfunction in obsessive-compulsive disorder. Eur Arch Psychiatry Clin Neurosci 2014; 264:225-33. [PMID: 23995893 DOI: 10.1007/s00406-013-0439-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 08/17/2013] [Indexed: 12/19/2022]
Abstract
Olfactory dysfunction has been described in obsessive-compulsive disorder (OCD). Brain regions involved in smell processing partially overlap with structures included in the neurobiological models of OCD, although no previous studies have analyzed the neuroanatomical correlates of olfactory dysfunction in this disorder. The aim of our study was to examine the association between regional gray matter volume, as assessed by a voxel-based morphometry analysis of magnetic resonance images (MRI), and olfactory function, as assessed by the Sniffin' Sticks test (SST). Olfactory function was assessed in 19 OCD patients and 19 healthy volunteers. All participants were also scanned in a 1.5-T magnet to obtain T1-weighted anatomical MRIs, which were pre-processed and analyzed with SPM8. Three different correlation models were used to study the association between regional gray matter volumes and olfactory function in the domains assessed by the SST: detection threshold, discrimination, and identification. OCD patients showed a significant impairment in all the domains assessed by the SST. Voxel-based mapping revealed a positive association in healthy controls between detection threshold and the gray matter content of a left anterior cingulate cortex cluster. In OCD patients, a positive correlation was observed between identification errors and the gray matter volume of the left medial orbital gyrus. In a post hoc analysis, these two gray matter regions were shown to be enlarged in OCD patients. Our findings support the idea that olfactory dysfunction in OCD is associated with volumetric changes in brain areas typically implicated in the neurobiology of the disorder.
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Affiliation(s)
- Cinto Segalàs
- OCD Clinical and Research Unit, Department of Psychiatry, Hospital de Bellvitge, Bellvitge University Hospital, c/Feixa Llarga s/n, Hospitalet de Llobregat, 08907, Barcelona, Spain,
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84
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Abraham NM, Vincis R, Lagier S, Rodriguez I, Carleton A. Long term functional plasticity of sensory inputs mediated by olfactory learning. eLife 2014; 3:e02109. [PMID: 24642413 PMCID: PMC3953949 DOI: 10.7554/elife.02109] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Sensory inputs are remarkably organized along all sensory pathways. While sensory representations are known to undergo plasticity at the higher levels of sensory pathways following peripheral lesions or sensory experience, less is known about the functional plasticity of peripheral inputs induced by learning. We addressed this question in the adult mouse olfactory system by combining odor discrimination studies with functional imaging of sensory input activity in awake mice. Here we show that associative learning, but not passive odor exposure, potentiates the strength of sensory inputs up to several weeks after the end of training. We conclude that experience-dependent plasticity can occur in the periphery of adult mouse olfactory system, which should improve odor detection and contribute towards accurate and fast odor discriminations. DOI:http://dx.doi.org/10.7554/eLife.02109.001 The mammalian brain is not static, but instead retains a significant degree of plasticity throughout an animal’s life. It is this plasticity that enables adults to learn new things, adjust to new environments and, to some degree, regain functions they have lost as a result of brain damage. However, information about the environment must first be detected and encoded by the senses. Odors, for example, activate specific receptors in the nose, and these in turn project to structures called glomeruli in a region of the brain known as the olfactory bulb. Each odor activates a unique combination of glomeruli, and the information contained within this ‘odor fingerprint’ is relayed via olfactory bulb neurons to the olfactory cortex. Now, Abraham et al. have revealed that the earliest stages of odor processing also show plasticity in adult animals. Two groups of mice were exposed to the same two odors: however, the first group was trained to discriminate between the odors to obtain a reward, whereas the second group was passively exposed to them. When both groups of mice were subsequently re-exposed to the odors, the trained group activated more glomeruli, more strongly, than a control group that had never encountered the odors before. By contrast, the responses of mice in the passively exposed group did not differ from those of a control group. Given that the response of glomeruli correlates with the ability of mice to discriminate between odors, these results suggest that trained animals would now be able to discriminate between the odors more easily than other mice. In other words, sensory plasticity ensures that stimuli that have been associatively learned with or without reward will be easier to detect should they be encountered again in the future. DOI:http://dx.doi.org/10.7554/eLife.02109.002
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Affiliation(s)
- Nixon M Abraham
- Department of Basic Neurosciences, School of Medicine, University of Geneva, Geneva, Switzerland
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85
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Osborne JE, Dudman JT. RIVETS: a mechanical system for in vivo and in vitro electrophysiology and imaging. PLoS One 2014; 9:e89007. [PMID: 24551206 PMCID: PMC3925229 DOI: 10.1371/journal.pone.0089007] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Accepted: 01/13/2014] [Indexed: 11/18/2022] Open
Abstract
A number of recent studies have provided compelling demonstrations that both mice and rats can be trained to perform a variety of behavioral tasks while restrained by mechanical elements mounted to the skull. The independent development of this technique by a number of laboratories has led to diverse solutions. We found that these solutions often used expensive materials and impeded future development and modification in the absence of engineering support. In order to address these issues, here we report on the development of a flexible single hardware design for electrophysiology and imaging both in brain tissue in vitro. Our hardware facilitates the rapid conversion of a single preparation between physiology and imaging system and the conversion of a given system between preparations. In addition, our use of rapid prototyping machines ("3D printers") allows for the deployment of new designs within a day. Here, we present specifications for design and manufacturing as well as some data from our lab demonstrating the suitability of the design for physiology in behaving animals and imaging in vitro and in vivo.
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Affiliation(s)
- Jason E. Osborne
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia, United States of America
| | - Joshua T. Dudman
- Howard Hughes Medical Institute, Janelia Farm Research Campus, Ashburn, Virginia, United States of America
- * E-mail:
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86
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Fletcher ML, Bendahmane M. Visualizing olfactory learning functional imaging of experience-induced olfactory bulb changes. PROGRESS IN BRAIN RESEARCH 2014; 208:89-113. [PMID: 24767480 DOI: 10.1016/b978-0-444-63350-7.00004-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The anatomical organization of sensory neuron input allows odor information to be transformed into odorant-specific spatial maps of mitral/tufted cell glomerular activity. In other sensory systems, neuronal representations of sensory stimuli can be reorganized or enhanced following learning or experience. Similarly, several studies have demonstrated both structural and physiological experience-induced changes throughout the olfactory system. As experience-induced changes within this circuit likely serve as an initial site for odor memory formation, the olfactory bulb is an ideal site for optical imaging studies of olfactory learning, as they allow for the visualization of experience-induced changes in the glomerular circuit following learning and how these changes impact of odor representations with the bulb. Presently, optical imaging techniques have been used to visualize experience-induced changes in glomerular odor representations in a variety of paradigms in short-term habituation, chronic odor exposure, and olfactory associative conditioning.
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Affiliation(s)
- Max L Fletcher
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, USA.
| | - Mounir Bendahmane
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN, USA
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87
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88
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Kato HK, Gillet SN, Peters AJ, Isaacson JS, Komiyama T. Parvalbumin-expressing interneurons linearly control olfactory bulb output. Neuron 2013; 80:1218-31. [PMID: 24239124 DOI: 10.1016/j.neuron.2013.08.036] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/26/2013] [Indexed: 10/26/2022]
Abstract
In the olfactory bulb, odor representations by principal mitral cells are modulated by local inhibitory circuits. While dendrodendritic synapses between mitral and granule cells are typically thought to be a major source of this modulation, the contributions of other inhibitory neurons remain unclear. Here we demonstrate the functional properties of olfactory bulb parvalbumin-expressing interneurons (PV cells) and identify their important role in odor coding. Using paired recordings, we find that PV cells form reciprocal connections with the majority of nearby mitral cells, in contrast to the sparse connectivity between mitral and granule cells. In vivo calcium imaging in awake mice reveals that PV cells are broadly tuned to odors. Furthermore, selective PV cell inactivation enhances mitral cell responses in a linear fashion while maintaining mitral cell odor preferences. Thus, dense connections between mitral and PV cells underlie an inhibitory circuit poised to modulate the gain of olfactory bulb output.
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Affiliation(s)
- Hiroyuki K Kato
- Center for Neural Circuits and Behavior and Department of Neurosciences, University of California, San Diego, La Jolla, CA 92093, USA
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89
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Smear M, Resulaj A, Zhang J, Bozza T, Rinberg D. Multiple perceptible signals from a single olfactory glomerulus. Nat Neurosci 2013; 16:1687-91. [PMID: 24056698 DOI: 10.1038/nn.3519] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Accepted: 08/21/2013] [Indexed: 11/09/2022]
Abstract
Glomeruli are functional units in the olfactory system. The mouse olfactory bulb contains roughly 2,000 glomeruli, each receiving inputs from olfactory sensory neurons (OSNs) that express a specific odorant receptor gene. Odors typically activate many glomeruli in complex combinatorial patterns and it is unknown which features of neuronal activity in individual glomeruli contribute to odor perception. To address this, we used optogenetics to selectively activate single, genetically identified glomeruli in behaving mice. We found that mice could perceive the stimulation of a single glomerulus. Single-glomerulus stimulation was also detected on an intense odor background. In addition, different input intensities and the timing of input relative to sniffing were discriminated through one glomerulus. Our data suggest that each glomerulus can transmit odor information using identity, intensity and temporal coding cues. These multiple modes of information transmission may enable the olfactory system to efficiently identify and localize odor sources.
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Affiliation(s)
- Matthew Smear
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, USA
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90
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Optical dissection of odor information processing in vivo using GCaMPs expressed in specified cell types of the olfactory bulb. J Neurosci 2013; 33:5285-300. [PMID: 23516293 DOI: 10.1523/jneurosci.4824-12.2013] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Understanding central processing requires precise monitoring of neural activity across populations of identified neurons in the intact brain. In the present study, we used recently optimized variants of the genetically encoded calcium sensor GCaMP (GCaMP3 and GCaMPG5G) to image activity among genetically and anatomically defined neuronal populations in the olfactory bulb (OB), including two types of GABAergic interneurons (periglomerular [PG] and short axon [SA] cells) and OB output neurons (mitral/tufted [MT] cells) projecting to the piriform cortex. We first established that changes in neuronal spiking can be related accurately to GCaMP fluorescence changes via a simple quantitative relationship over a large dynamic range. We next used in vivo two-photon imaging from individual neurons and epifluorescence signals reflecting population-level activity to investigate the spatiotemporal representation of odorants across these neuron types in anesthetized and awake mice. Under anesthesia, individual PG and SA cells showed temporally simple responses and little spontaneous activity, whereas MT cells were spontaneously active and showed diverse temporal responses. At the population level, response patterns of PG, SA, and MT cells were surprisingly similar to those imaged from sensory inputs, with shared odorant-specific topography across the dorsal OB and inhalation-coupled temporal dynamics. During wakefulness, PG and SA cell responses increased in magnitude but remained temporally simple, whereas those of MT cells changed to complex spatiotemporal patterns reflecting restricted excitation and widespread inhibition. These results suggest multiple circuit elements with distinct roles in transforming odor representations in the OB and provide a framework for further study of early olfactory processing using optical and genetic tools.
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91
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Olfactory cortical neurons read out a relative time code in the olfactory bulb. Nat Neurosci 2013; 16:949-57. [PMID: 23685720 PMCID: PMC3695490 DOI: 10.1038/nn.3407] [Citation(s) in RCA: 130] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2013] [Accepted: 04/24/2013] [Indexed: 12/14/2022]
Abstract
Odor stimulation evokes complex spatiotemporal activity in the olfactory bulb, suggesting that the identity of activated neurons as well as the timing of their activity convey information about odors. However, whether and how downstream neurons decipher these temporal patterns remains debated. We addressed this question by measuring the spiking activity of downstream neurons while optogenetically stimulating two foci in the olfactory bulb with varying relative timing in mice. We found that the overall spike rates of piriform cortex neurons were sensitive to the relative timing of activation. Posterior piriform cortex neurons showed higher sensitivity to relative input times than neurons in the anterior piriform cortex. In contrast, olfactory bulb neurons rarely showed such sensitivity. Thus, the brain can transform a relative time code in the periphery into a firing-rate-based representation in central brain areas, providing evidence for the relevance of relative time-based code in the olfactory bulb.
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92
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Rospars JP, Sanda P, Lansky P, Duchamp-Viret P. Responses of single neurons and neuronal ensembles in frog first- and second-order olfactory neurons. Brain Res 2013; 1536:144-58. [PMID: 23688543 DOI: 10.1016/j.brainres.2013.05.018] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Revised: 05/06/2013] [Accepted: 05/08/2013] [Indexed: 11/17/2022]
Abstract
A major challenge in sensory neuroscience is to elucidate the coding and processing of stimulus representations in successive populations of neurons. Here we recorded the spiking activity of receptor neurons (RNs) and mitral/tufted cells (MCs) in the frog olfactory epithelium and olfactory bulb respectively, in response to four odorants applied at precisely controlled concentrations. We compared how RN responses are translated in MCs. We examined the time course of the instantaneous firing frequency before and after stimulation in neuron ensembles and the dependency on odorant concentration of the number of action potentials fired in a preselected 5-s time window (dose-response curves) in both single neurons and neuron ensembles. In RNs and MCs, the dose-response curves typically increase then decrease and are well described by alpha functions. We established the main quantitative properties of these curves, including the distributions of concentrations at threshold and maximum responses. We showed that the main transformations occurring in the transition from RNs to MCs is the lowering of the firing threshold and a large decrease in the total number of spikes fired. We also found that the number of action potentials fired by recorded neurons and hence their energy consumption is independent of odorant concentration, and that this is a consequence of their time- and concentration-dependent activities. This article is part of a Special Issue entitled Neural Coding 2012.
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Affiliation(s)
- Jean-Pierre Rospars
- UMR 1272 Physiologie de l'Insecte: Signalisation et Communication & Unité Mathématiques et Informatique Appliquées, INRA, F-78000 Versailles, France.
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93
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Abstract
Cell-to-cell variability in molecular, genetic, and physiological features is increasingly recognized as a critical feature of complex biological systems, including the brain. Although such variability has potential advantages in robustness and reliability, how and why biological circuits assemble heterogeneous cells into functional groups is poorly understood. Here, we develop analytic approaches toward answering how neuron-level variation in intrinsic biophysical properties of olfactory bulb mitral cells influences population coding of fluctuating stimuli. We capture the intrinsic diversity of recorded populations of neurons through a statistical approach based on generalized linear models. These models are flexible enough to predict the diverse responses of individual neurons yet provide a common reference frame for comparing one neuron to the next. We then use Bayesian stimulus decoding to ask how effectively different populations of mitral cells, varying in their diversity, encode a common stimulus. We show that a key advantage provided by physiological levels of intrinsic diversity is more efficient and more robust encoding of stimuli by the population as a whole. However, we find that the populations that best encode stimulus features are not simply the most heterogeneous, but those that balance diversity with the benefits of neural similarity.
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94
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Interglomerular lateral inhibition targeted on external tufted cells in the olfactory bulb. J Neurosci 2013; 33:1552-63. [PMID: 23345229 DOI: 10.1523/jneurosci.3410-12.2013] [Citation(s) in RCA: 72] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Lateral inhibition between neurons occurs in many different sensory systems, where it can perform such functions as contrast enhancement. In the olfactory bulb, lateral inhibition may occur between odorant receptor-specific glomeruli that are linked anatomically by GABAergic granule cells (GCs) and cells within the glomerular layer, although evidence supporting lateral inhibition at a functional level is modest. Here, we used patch-clamp, imaging, and glutamate uncaging methods in rat olfactory bulb slices to test for the presence of interglomerular lateral inhibition, as well as its underlying mechanisms. We found that a conditioning stimulus applied at one or a small group of glomeruli could suppress stimulus-evoked excitation of output mitral cells (MCs) at another glomerulus for interstimulus intervals of 20-50 ms and glomerular separations of up to 600 μm. The observed lateral inhibition was entirely dependent on circuitry within the glomerular layer, rather than GCs, and it involved GABAergic synaptic inputs that were targeted mainly onto tufted cells, which act as intermediaries in the excitation between olfactory sensory neurons and MCs. The key cell type responsible for mediating lateral interactions between glomeruli were GABAergic short-axon cells. These results suggest a functional segregation of GABAergic cells within the bulb, with one set located in the glomerular layer mediating suppression of MC spiking across glomeruli, and a second set, the GCs, synchronizing different glomeruli.
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95
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Optical dissection of odor information processing in vivo using GCaMPs expressed in specified cell types of the olfactory bulb. J Neurosci 2013. [PMID: 23516293 DOI: 10.1523/jneurosci.4824‐12.2013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Understanding central processing requires precise monitoring of neural activity across populations of identified neurons in the intact brain. In the present study, we used recently optimized variants of the genetically encoded calcium sensor GCaMP (GCaMP3 and GCaMPG5G) to image activity among genetically and anatomically defined neuronal populations in the olfactory bulb (OB), including two types of GABAergic interneurons (periglomerular [PG] and short axon [SA] cells) and OB output neurons (mitral/tufted [MT] cells) projecting to the piriform cortex. We first established that changes in neuronal spiking can be related accurately to GCaMP fluorescence changes via a simple quantitative relationship over a large dynamic range. We next used in vivo two-photon imaging from individual neurons and epifluorescence signals reflecting population-level activity to investigate the spatiotemporal representation of odorants across these neuron types in anesthetized and awake mice. Under anesthesia, individual PG and SA cells showed temporally simple responses and little spontaneous activity, whereas MT cells were spontaneously active and showed diverse temporal responses. At the population level, response patterns of PG, SA, and MT cells were surprisingly similar to those imaged from sensory inputs, with shared odorant-specific topography across the dorsal OB and inhalation-coupled temporal dynamics. During wakefulness, PG and SA cell responses increased in magnitude but remained temporally simple, whereas those of MT cells changed to complex spatiotemporal patterns reflecting restricted excitation and widespread inhibition. These results suggest multiple circuit elements with distinct roles in transforming odor representations in the OB and provide a framework for further study of early olfactory processing using optical and genetic tools.
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96
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Testing the sorption hypothesis in olfaction: a limited role for sniff strength in shaping primary odor representations during behavior. J Neurosci 2013; 33:79-92. [PMID: 23283324 DOI: 10.1523/jneurosci.4101-12.2013] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The acquisition of sensory information during behavior shapes the neural representation, central processing, and perception of external stimuli. In mammals, a sniff represents the basic unit of odor sampling, yet how sniffing shapes odor representations remains poorly understood. Perhaps the earliest hypothesis of the role of sniffing in olfaction arises from the fact that odorants with different physicochemical properties exhibit different patterns of deposition across the olfactory epithelium, and that these patterns are differentially affected by flow rate. However, whether sniff flow rates shape odor representations during natural sniffing remains untested, and whether animals make use of odorant sorption-airflow relationships as part of an active odor-sampling strategy remains unclear. We tested these ideas in the intact rat using a threefold approach. First, we asked whether sniff strength shapes odor representations in vivo by imaging from olfactory receptor neuron (ORN) terminals during controlled changes in inhalation flow in the anesthetized rat. Second, we asked whether sniff strength shapes odor representations by imaging from ORNs during natural sniffing in the awake rat. Third, we asked whether rats actively modulate sniff strength during an odor discrimination task. We found that, while artificial changes in flow rate can alter ORN responses, sniff strength has negligible effect on odor representations during natural sniffing, and behaving rats do not modulate flow rate to improve odor discrimination. These data suggest that modulating sniff strength does not shape odor representations sufficiently to be part of a strategy for active odor sensing in the behaving animal.
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97
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Homma R, Kovalchuk Y, Konnerth A, Cohen LB, Garaschuk O. In vivo functional properties of juxtaglomerular neurons in the mouse olfactory bulb. Front Neural Circuits 2013; 7:23. [PMID: 23459031 PMCID: PMC3578271 DOI: 10.3389/fncir.2013.00023] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2012] [Accepted: 02/02/2013] [Indexed: 01/05/2023] Open
Abstract
Juxtaglomerular neurons represent one of the largest cellular populations in the mammalian olfactory bulb yet their role for signal processing remains unclear. We used two-photon imaging and electrophysiological recordings to clarify the in vivo properties of these cells and their functional organization in the juxtaglomerular space. Juxtaglomerular neurons coded for many perceptual characteristics of the olfactory stimulus such as (1) identity of the odorant, (2) odorant concentration, (3) odorant onset, and (4) offset. The odor-responsive neurons clustered within a narrow area surrounding the glomerulus with the same odorant specificity, with ~80% of responding cells located ≤20 μm from the glomerular border. This stereotypic spatial pattern of activated cells persisted at different odorant concentrations and was found for neurons both activated and inhibited by the odorant. Our data identify a principal glomerulus with a narrow shell of juxtaglomerular neurons as a basic odor coding unit in the glomerular layer and underline the important role of intraglomerular circuitry.
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Affiliation(s)
- R Homma
- Department of Physiology, Yale University New Haven, CT, USA ; NeuroImaging Cluster, Marine Biological Laboratory Woods Hole, MA, USA
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98
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Fukunaga I, Berning M, Kollo M, Schmaltz A, Schaefer AT. Two distinct channels of olfactory bulb output. Neuron 2012; 75:320-9. [PMID: 22841316 DOI: 10.1016/j.neuron.2012.05.017] [Citation(s) in RCA: 185] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/01/2012] [Indexed: 11/26/2022]
Abstract
Rhythmic neural activity is a hallmark of brain function, used ubiquitously to structure neural information. In mammalian olfaction, repetitive sniffing sets the principal rhythm but little is known about its role in sensory coding. Here, we show that mitral and tufted cells, the two main classes of olfactory bulb projection neurons, tightly lock to this rhythm, but to opposing phases of the sniff cycle. This phase shift is established by local inhibition that selectively delays mitral cell activity. Furthermore, while tufted cell phase is unperturbed in response to purely excitatory odorants, mitral cell phase is advanced in a graded, stimulus-dependent manner. Thus, phase separation by inhibition forms the basis for two distinct channels of olfactory processing.
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Affiliation(s)
- Izumi Fukunaga
- Behavioural Neurophysiology, Max-Planck-Institute for Medical Research, Jahnstr. 29, 69120 Heidelberg, Germany
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99
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Lucero MT. Peripheral modulation of smell: fact or fiction? Semin Cell Dev Biol 2012; 24:58-70. [PMID: 22986099 DOI: 10.1016/j.semcdb.2012.09.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2012] [Accepted: 09/06/2012] [Indexed: 01/01/2023]
Abstract
Despite studies dating back 30 or more years showing modulation of odorant responses at the level of the olfactory epithelium, most descriptions of the olfactory system infer that odorant signals make their way from detection by cilia on olfactory sensory neurons to the olfactory bulb unaltered. Recent identification of multiple subtypes of microvillar cells and identification of neuropeptide and neurotransmitter expression in the olfactory mucosa add to the growing body of literature for peripheral modulation in the sense of smell. Complex mechanisms including perireceptor events, modulation of sniff rates, and changes in the properties of sensory neurons match the sensitivity of olfactory sensory neurons to the external odorant environment, internal nutritional status, reproductive status, and levels of arousal or stress. By furthering our understanding of the players mediating peripheral olfaction, we may open the door to novel approaches for modulating the sense of smell in both health and disease.
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Affiliation(s)
- Mary T Lucero
- Department of Physiology, School of Medicine, University of Utah, 420 Chipeta Way Ste, 1700 Salt Lake City, UT 84108, USA.
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100
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Abstract
Animals perceive their olfactory environment not only from odors originating in the external world (orthonasal route) but also from odors released in the oral cavity while eating food (retronasal route). Retronasal olfaction is crucial for the perception of food flavor in humans. However, little is known about the retronasal stimulus coding in the brain. The most basic questions are if and how route affects the odor representations at the level of the olfactory bulb (OB), where odor quality codes originate. We used optical calcium imaging of presynaptic dorsal OB responses to odorants in anesthetized rats to ask whether the rat OB could be activated retronasally, and how these responses compare to orthonasal responses under similar conditions. We further investigated the effects of specific odorant properties on orthonasal versus retronasal response patterns. We found that at a physiologically relevant flow rate, retronasal odorants can effectively reach the olfactory receptor neurons, eliciting glomerular response patterns that grossly overlap with those of orthonasal responses, but differ from the orthonasal patterns in the response amplitude and temporal dynamics. Interestingly, such differences correlated well with specific odorant properties. Less volatile odorants yielded relatively smaller responses retronasally, but volatility did not affect relative temporal profiles. More polar odorants responded with relatively longer onset latency and time to peak retronasally, but polarity did not affect relative response magnitudes. These data provide insight into the early stages of retronasal stimulus coding and establish relationships between orthonasal and retronasal odor representations in the rat OB.
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