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Hawkins SJ, Gärtner Y, Offner T, Weiss L, Maiello G, Hassenklöver T, Manzini I. The olfactory network of larval Xenopus laevis regenerates accurately after olfactory nerve transection. Eur J Neurosci 2024; 60:3719-3741. [PMID: 38758670 DOI: 10.1111/ejn.16375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2023] [Revised: 04/10/2024] [Accepted: 04/14/2024] [Indexed: 05/19/2024]
Abstract
Across vertebrate species, the olfactory epithelium (OE) exhibits the uncommon feature of lifelong neuronal turnover. Epithelial stem cells give rise to new neurons that can adequately replace dying olfactory receptor neurons (ORNs) during developmental and adult phases and after lesions. To relay olfactory information from the environment to the brain, the axons of the renewed ORNs must reconnect with the olfactory bulb (OB). In Xenopus laevis larvae, we have previously shown that this process occurs between 3 and 7 weeks after olfactory nerve (ON) transection. In the present study, we show that after 7 weeks of recovery from ON transection, two functionally and spatially distinct glomerular clusters are reformed in the OB, akin to those found in non-transected larvae. We also show that the same odourant response tuning profiles observed in the OB of non-transected larvae are again present after 7 weeks of recovery. Next, we show that characteristic odour-guided behaviour disappears after ON transection but recovers after 7-9 weeks of recovery. Together, our findings demonstrate that the olfactory system of larval X. laevis regenerates with high accuracy after ON transection, leading to the recovery of odour-guided behaviour.
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Affiliation(s)
- Sara J Hawkins
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus Liebig University Gießen, Gießen, Germany
- School of Biological Sciences, Faculty of Environmental and Life Sciences, University of Southampton, Southampton, UK
| | - Yvonne Gärtner
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus Liebig University Gießen, Gießen, Germany
- School of Biological Sciences, Faculty of Environmental and Life Sciences, University of Southampton, Southampton, UK
- Department of Neurology, Focus Program Translational Neuroscience (FTN) and Immunotherapy (FZI), Rhine-Main Neuroscience Network (rmn2), University Medical Center of the Johannes Gutenberg University Mainz, Mainz, Germany
| | - Thomas Offner
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus Liebig University Gießen, Gießen, Germany
| | - Lukas Weiss
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus Liebig University Gießen, Gießen, Germany
| | - Guido Maiello
- Department of Experimental Psychology, Justus Liebig University Gießen, Gießen, Germany
- School of Psychology, Faculty of Environmental and Life Sciences, University of Southampton, Southampton, UK
| | - Thomas Hassenklöver
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus Liebig University Gießen, Gießen, Germany
| | - Ivan Manzini
- Institute of Animal Physiology, Department of Animal Physiology and Molecular Biomedicine, Justus Liebig University Gießen, Gießen, Germany
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Butowt R, von Bartheld CS. Anosmia in COVID-19: Underlying Mechanisms and Assessment of an Olfactory Route to Brain Infection. Neuroscientist 2021; 27:582-603. [PMID: 32914699 PMCID: PMC7488171 DOI: 10.1177/1073858420956905] [Citation(s) in RCA: 194] [Impact Index Per Article: 64.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In recent months it has emerged that the novel coronavirus-responsible for the COVID-19 pandemic-causes reduction of smell and taste in a large fraction of patients. The chemosensory deficits are often the earliest, and sometimes the only signs in otherwise asymptomatic carriers of the SARS-CoV-2 virus. The reasons for the surprisingly early and specific chemosensory dysfunction in COVID-19 are now beginning to be elucidated. In this hypothesis review, we discuss implications of the recent finding that the prevalence of smell and taste dysfunction in COVID-19 patients differs between populations, possibly because of differences in the spike protein of different virus strains or because of differences in the host proteins that enable virus entry, thus modifying infectivity. We review recent progress in defining underlying cellular and molecular mechanisms of the virus-induced anosmia, with a focus on the emerging crucial role of sustentacular cells in the olfactory epithelium. We critically examine the current evidence whether and how the SARS-CoV-2 virus can follow a route from the olfactory epithelium in the nose to the brain to achieve brain infection, and we discuss the prospects for using the smell and taste dysfunctions seen in COVID-19 as an early and rapid diagnostic screening tool.
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Affiliation(s)
- Rafal Butowt
- Department of Molecular Cell Genetics, L. Rydygier Collegium Medicum, Nicolaus Copernicus University, Bydgoszcz, Poland
- Department of Anatomy, L. Rydygier Collegium Medicum, Nicolaus Copernicus University, Bydgoszcz, Poland
| | - Christopher S. von Bartheld
- Center of Biomedical Research Excellence in Cell Biology, Reno School of Medicine, University of Nevada, Reno, NV, USA
- Department of Physiology and Cell Biology, Reno School of Medicine, University of Nevada, Reno, NV, USA
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3
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Rodriguez S, Cao L, Rickenbacher GT, Benz EG, Magdamo C, Gomez LR, Holbrook EH, Albers AD, Gallagher R, Westover MB, Evans KE, Tatar DJ, Mukerji S, Zafonte R, Boyer EW, Yu CR, Albers MW. Innate immune signaling in the olfactory epithelium reduces odorant receptor levels: modeling transient smell loss in COVID-19 patients. MEDRXIV : THE PREPRINT SERVER FOR HEALTH SCIENCES 2020:2020.06.14.20131128. [PMID: 32587994 PMCID: PMC7310652 DOI: 10.1101/2020.06.14.20131128] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Post-infectious anosmias typically follow death of olfactory sensory neurons (OSNs) with a months-long recovery phase associated with parosmias. While profound anosmia is the leading symptom associated with COVID-19 infection, many patients regain olfactory function within days to weeks without distortions. Here, we demonstrate that sterile induction of anti-viral type I interferon signaling in the mouse olfactory epithelium is associated with diminished odor discrimination and reduced odor-evoked local field potentials. RNA levels of all class I, class II, and TAAR odorant receptors are markedly reduced in OSNs in a non-cell autonomous manner. We find that people infected with COVID-19 rate odors with lower intensities and have odor discrimination deficits relative to people that tested negative for COVID-19. Taken together, we propose that inflammatory-mediated loss of odorant receptor expression with preserved circuit integrity accounts for the profound anosmia and rapid recovery of olfactory function without parosmias caused by COVID-19.
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Affiliation(s)
- Steven Rodriguez
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | - Luxiang Cao
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | | | - Eric G. Benz
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | - Colin Magdamo
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | | | - Eric H. Holbrook
- Dept. of Otolaryngology—Head and Neck Surgery, Mass. Eye and Ear, Boston, MA 02114
| | - Alefiya D. Albers
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
- Dept. of Psychology, Endicott College, Beverly, MA 01915
| | - Rose Gallagher
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | | | - Kyle E. Evans
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | | | - Shibani Mukerji
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
| | - Ross Zafonte
- Dept. of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital, Boston, MA 02129
| | - Edward W Boyer
- Dept. of Emergency Medicine, Brigham and Women’s Hospital, Boston, MA 02115
| | - C. Ron Yu
- Stowers Institute of Medical Research, Kansas City, MO 64110
| | - Mark W. Albers
- Dept. of Neurology, Massachusetts General Hospital, Boston, MA 02129
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4
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Increased Retinoic Acid Catabolism in Olfactory Sensory Neurons Activates Dormant Tissue-Specific Stem Cells and Accelerates Age-Related Metaplasia. J Neurosci 2020; 40:4116-4129. [PMID: 32385093 DOI: 10.1523/jneurosci.2468-19.2020] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2019] [Revised: 04/03/2020] [Accepted: 04/25/2020] [Indexed: 12/28/2022] Open
Abstract
The cellular and molecular basis of metaplasia and declining neurogenesis in the aging olfactory epithelium (OE) remains unknown. The horizontal basal cell (HBC) is a dormant tissue-specific stem cell presumed to only be forced into self-renewal and differentiation by injury. Here we analyze male and female mice and show that HBCs also are activated with increasing age as well as non-cell-autonomously by increased expression of the retinoic acid-degrading enzyme CYP26B1. Activating stimuli induce HBCs throughout OE to acquire a rounded morphology and express IP3R3, which is an inositol-1,4,5-trisphosphate receptor constitutively expressed in stem cells of the adjacent respiratory epithelium. Odor/air stimulates CYP26B1 expression in olfactory sensory neurons mainly located in the dorsomedial OE, which is spatially inverse to ventrolateral constitutive expression of the retinoic acid-synthesizing enzyme (RALDH1) in supporting cells. In ventrolateral OE, HBCs express low p63 levels and preferentially differentiate instead of self-renewing when activated. When activated by chronic CYP26B1 expression, repeated injury, or old age, ventrolateral HBCs diminish in number and generate a novel type of metaplastic respiratory cell that is RALDH- and secretes a mucin-like mucus barrier protein (FcγBP). Conversely, in the dorsomedial OE, CYP26B1 inhibits injury-induced and age-related replacement of RALDH- supporting cells with RALDH1+ ciliated respiratory cells. Collectively, these results support the concept that inositol-1,4,5-trisphosphate type 3 receptor signaling in HBCs, together with altered retinoic acid metabolism within the niche, promote HBC lineage commitment toward two types of respiratory cells that will maintain epithelial barrier function once the capacity to regenerate OE cells ceases.SIGNIFICANCE STATEMENT Little is known about signals that activate dormant stem cells to self-renew and regenerate odor-detecting neurons and other olfactory cell types after loss due to injury, infection, or toxin exposure in the nose. It is also unknown why the stem cells do not prevent age-dependent decline of odor-detecting neurons. We show that (1) stem cells are kept inactive by the vitamin A derivative retinoic acid, which is synthesized and degraded locally by olfactory cells; (2) old age as well as repeated injuries activate the stem cells and exhaust their potential to produce olfactory cells; and (3) exhausted stem cells alter the local retinoic acid metabolism and maintain the epithelial tissue barrier by generating airway cells instead of olfactory cells.
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5
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Affiliation(s)
- David M Coppola
- Department of Biology, Randolph-Macon College, Ashland, VA, USA
| | - Burton Slotnick
- Department of Psychology, American University, Washington, DC, USA
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6
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Laska M. Olfactory Discrimination Learning in an Outbred and an Inbred Strain of Mice. Chem Senses 2015; 40:489-96. [DOI: 10.1093/chemse/bjv032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
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Yoder WM, Gaynor L, Windham E, Lyman M, Munizza O, Setlow B, Bizon JL, Smith DW. Characterizing olfactory binary mixture interactions in Fischer 344 rats using behavioral reaction times. Chem Senses 2015; 40:325-34. [PMID: 25877697 DOI: 10.1093/chemse/bjv014] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Response times provide essential subthreshold perceptual data that extend beyond accuracy alone. Behavioral reaction times (RTs) were used to characterize rats' ability to detect individual odorants in a series of complimentary binary odorant mixture ratios. We employed an automated, liquid-dilution olfactometer to train Fischer 344 rats (N = 8) on an odor identification task using nonreinforced probe trials. Binary mixture ratios composed of aliphatic odorants (citral and octanol) were arranged such that relative contributions of the 2 components varied systematically by a factor of 1% (v/v). Odorant concentrations for the target (S+), control (S-), and mixture (S+:S-) odorants were presented relative to threshold for each rat. Rats were initially trained to respond by licking at a spout to obtain liquid reward for either citral or octanol as the reinforced target (S+) odorant. After achieving 100% accuracy, rats were transferred to variable ratio (VR 2) reinforcement for correct responding. Nonreinforced probe trials (2 per block of 22 trials) were tested for each mixture ratio and recorded as either S+ (rats lick-responded in the presence of the mixture) or S- (rats refrained from licking), thereby indicating detection of the trained, S+ odorant. To determine the perceived salience for each ratio, RTs (latency from odorant onset to lick response) were recorded for each trial. Consistent with previous studies, RTs for both odorants were shortest (~150-200ms) when the probe trials consisted of a single, monomolecular component. Binary mixtures that contained as little as 1% of the S-, nontarget odorant, however, were sufficiently different perceptually to increase behavioral RTs (i.e., rats hesitated longer before responding); RTs changed systematically as a function of the binary ratio. Interestingly, the rate of RT change was dependent on which odorant served as the S+, suggesting an asymmetric interaction between the 2 odorants. The data demonstrate the value of behavioral RT as a sensitive measure of suprathreshold perceptual responding.
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Affiliation(s)
- Wendy M Yoder
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida, Gainesville, FL 32611, USA
| | - Leslie Gaynor
- Interdisciplinary Studies Major in Neurobiological Sciences, University of Florida, Gainesville, FL 32611, USA
| | - Ethan Windham
- Health Science Program, University of Florida, Gainesville, FL 32611, USA
| | - Michelle Lyman
- Interdisciplinary Studies Major in Neurobiological Sciences, University of Florida, Gainesville, FL 32611, USA
| | - Olivia Munizza
- Interdisciplinary Studies Major in Neurobiological Sciences, University of Florida, Gainesville, FL 32611, USA
| | - Barry Setlow
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida, Gainesville, FL 32611, USA, Department of Psychiatry, University of Florida, Gainesville, FL 32611, USA, Department of Neuroscience, University of Florida, Gainesville, FL 32611, USA and
| | | | - David W Smith
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida, Gainesville, FL 32611, USA, Center for Smell and Taste, University of Florida, Gainesville, FL 32611, USA
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8
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Yoder WM, Munizza O, Lyman M, Smith DW. A technique for characterizing the time course of odor adaptation in mice. Chem Senses 2014; 39:631-40. [PMID: 25082871 DOI: 10.1093/chemse/bju036] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Although numerous studies have analyzed the temporal characteristics underlying olfactory adaptation at the level of the olfactory receptor neuron, to date, there have been no comparable behavioral measures in an animal model. In this study, odor adaptation was estimated in a group of mice employing a psychophysical technique recently developed for use in humans. The premise of this technique is that extended presentation of an odorant will produce odor adaptation, decreasing the sensitivity of the receptors and increasing thresholds for a brief, simultaneous target odorant presented at different time points on the adaptation contour; adaptation is estimated as the increase in threshold for a target odorant presented simultaneously with an adapting odorant, across varying adapting-to-target odorant onset delays. Previous research from our laboratory suggests that this method provides a reliable estimate of the onset time course of rapid adaptation in human subjects. Consistent with physiological and behavioral data from human subjects, the present findings demonstrate that measurable olfactory adaptive effects can be observed for odorant exposures as brief as 50-100ms, with asymptotic levels evident 400-600ms following adapting odorant onset. When compared with the adaptation contour in humans using the same odorant and stimulus paradigm, some differences in the onset characteristics are evident and may be related to sniffing behavior and to relative differences in thresholds. These data show that this psychophysical paradigm can be adapted for use in animal models, where experimental and genetic manipulations can be used to characterize the different mechanisms underlying odor adaptation.
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Affiliation(s)
- Wendy M Yoder
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida, 945 Center Drive PO Box 112250, Gainesville, FL 32611, USA
| | - Olivia Munizza
- CLAS Interdisciplinary Studies Major in Neurobiological Sciences, University of Florida, 945 Center Drive PO Box 112250, Gainesville, FL 32611, USA and
| | - Michelle Lyman
- CLAS Interdisciplinary Studies Major in Neurobiological Sciences, University of Florida, 945 Center Drive PO Box 112250, Gainesville, FL 32611, USA and
| | - David W Smith
- Program in Behavioral and Cognitive Neuroscience, Department of Psychology, University of Florida, 945 Center Drive PO Box 112250, Gainesville, FL 32611, USA, Center for Smell and Taste, University of Florida, 945 Center Drive PO Box 112250, Gainesville, FL 32611, USA
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9
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Holbrook EH, Iwema CL, Peluso CE, Schwob JE. The regeneration of P2 olfactory sensory neurons is selectively impaired following methyl bromide lesion. Chem Senses 2014; 39:601-16. [PMID: 25056730 DOI: 10.1093/chemse/bju033] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The capacity of the peripheral olfactory system to recover after injury has not been thoroughly explored. P2-IRES-tauLacZ mice were exposed to methyl bromide, which causes epithelial damage and kills 90% of the P2 neurons. With subsequent neuronal regeneration, P2 neurons recover within their usual territory to equal control numbers by 1 month but then decline sharply to roughly 40% of control by 3 months. At this time, the P2 projection onto the olfactory bulb is erroneous in several respects. Instead of converging onto 1 or 2 glomeruli per surface, small collections of P2 axons innervate multiple glomeruli at roughly the same position in the bulb as in controls. Within these glomeruli, the P2 axons are aggregated near the edge, whereas the remainder of the glomerulus contains olfactory marker protein (+), non-P2 axons, violating the one receptor-one glomerulus rule normally observed. The aggregates are denser than found in control P2-innervated glomeruli, suggesting that the P2 axons may not be synaptically connected. Based on published literature and other data, we hypothesize that P2 neurons lose out in an activity-based competition for synaptic territory within the glomeruli and are not maintained at control numbers due to a lack of trophic support from the bulb.
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Affiliation(s)
- Eric H Holbrook
- Department of Otology and Laryngology, Harvard Medical School and Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114, USA, Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA
| | - Carrie L Iwema
- Department of Cell and Developmental Biology and Program in Neuroscience, SUNY Upstate Medical University, 766 Irving Avenue, Syracuse, NY 13210, USA and
| | - Carolyn E Peluso
- Program in Cell, Molecular, and Developmental Biology, Sackler School of Graduate Biomedical Sciences, Tufts University, 136 Harrison Avenue, Boston, MA 02111, USA
| | - James E Schwob
- Department of Developmental, Molecular and Chemical Biology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA, Department of Cell and Developmental Biology and Program in Neuroscience, SUNY Upstate Medical University, 766 Irving Avenue, Syracuse, NY 13210, USA and
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10
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Franceschini V, Bettini S, Pifferi S, Menini A, Siciliano G, Ognio E, Brini AT, Di Oto E, Revoltella RP. Transplanted human adipose tissue-derived stem cells engraft and induce regeneration in mice olfactory neuroepithelium in response to dichlobenil subministration. Chem Senses 2014; 39:617-29. [PMID: 25056732 DOI: 10.1093/chemse/bju035] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
We used immunodeficient mice, whose dorsomedial olfactory region was permanently damaged by dichlobenil inoculation, to test the neuroregenerative properties of transplanted human adipose tissue-derived stem cells after 30 and 60 days. Analysis of polymerase chain reaction bands revealed that stem cells preferentially engrafted in the lesioned olfactory epithelium compared with undamaged mucosa of untreated transplanted mice. Although basal cell proliferation in untransplanted lesioned mice did not give rise to neuronal cells in the olfactory mucosa, we observed clusters of differentiating olfactory cells in transplanted mice. After 30 days, and even more at 60 days, epithelial thickness was partially recovered to normal values, as also the immunohistochemical properties. Functional reactivity to odorant stimulation was also confirmed through electro-olfactogram recording in the dorsomedial epithelium. Furthermore, we demonstrated that engrafted stem cells fused with mouse cells in the olfactory organ, even if heterokaryons detected were too rare to hypothesize they directly repopulated the lesioned epithelium. The data reported prove that the migrating transplanted stem cells were able to induce a neuroregenerative process in a specific lesioned sensory area, enforcing the perspective that they could become an available tool for stem cell therapy.
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Affiliation(s)
- Valeria Franceschini
- Department of Biological, Geological and Environmental Sciences, University of Bologna, and Foundation Onlus Stem Cells and Life, Via Selmi 3, 40126 Bologna, Italy,
| | - Simone Bettini
- Department of Biological, Geological and Environmental Sciences, University of Bologna, and Foundation Onlus Stem Cells and Life, Via Selmi 3, 40126 Bologna, Italy
| | - Simone Pifferi
- International School for Advanced Studies, SISSA, Via Bonomea 265, 34136 Trieste, Italy
| | - Anna Menini
- International School for Advanced Studies, SISSA, Via Bonomea 265, 34136 Trieste, Italy
| | - Gabriele Siciliano
- Department of Clinical and Experimental Medicine, University of Pisa, Via Roma 67, 56126 Pisa, Italy
| | - Emanuela Ognio
- IRCCS San Martino, National Institute for Cancer Research (IST), Largo Rosanna Benzi 10, 16132 Genua, Italy
| | - Anna Teresa Brini
- Department of Biomedical, Surgical and Odontoiatric Sciences, University of Milan, Via Vanvitelli 32, 2019 Milan, Italy
| | - Enrico Di Oto
- Department of Hematology and Oncology "L. and A. Seragnoli," Section of Anatomic Pathology at Bellaria Hospital, University of Bologna, Via Altura 3, 40139 Bologna, Italy and
| | - Roberto P Revoltella
- Institute for Chemical, Physical Processes, C.N.R. and Foundation Onlus Stem Cells and Life, Via L.L. Zamenhof 8, 56127 Pisa, Italy
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11
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Cheung MC, Jang W, Schwob JE, Wachowiak M. Functional recovery of odor representations in regenerated sensory inputs to the olfactory bulb. Front Neural Circuits 2014; 7:207. [PMID: 24431990 PMCID: PMC3882662 DOI: 10.3389/fncir.2013.00207] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Accepted: 12/20/2013] [Indexed: 12/20/2022] Open
Abstract
The olfactory system has a unique capacity for recovery from peripheral damage. After injury to the olfactory epithelium (OE), olfactory sensory neurons (OSNs) regenerate and re-converge on target glomeruli of the olfactory bulb (OB). Thus far, this process has been described anatomically for only a few defined populations of OSNs. Here we characterize this regeneration at a functional level by assessing how odor representations carried by OSN inputs to the OB recover after massive loss and regeneration of the sensory neuron population. We used chronic imaging of mice expressing synaptopHluorin in OSNs to monitor odor representations in the dorsal OB before lesion by the olfactotoxin methyl bromide and after a 12 week recovery period. Methyl bromide eliminated functional inputs to the OB, and these inputs recovered to near-normal levels of response magnitude within 12 weeks. We also found that the functional topography of odor representations recovered after lesion, with odorants evoking OSN input to glomerular foci within the same functional domains as before lesion. At a finer spatial scale, however, we found evidence for mistargeting of regenerated OSN axons onto OB targets, with odorants evoking synaptopHluorin signals in small foci that did not conform to a typical glomerular structure but whose distribution was nonetheless odorant-specific. These results indicate that OSNs have a robust ability to reestablish functional inputs to the OB and that the mechanisms underlying the topography of bulbar reinnervation during development persist in the adult and allow primary sensory representations to be largely restored after massive sensory neuron loss.
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Affiliation(s)
- Man C Cheung
- Department of Biology, Boston University Boston, MA, USA
| | - Woochan Jang
- Department of Anatomy and Cellular Biology, Tufts University School of Medicine Boston, MA, USA
| | - James E Schwob
- Department of Anatomy and Cellular Biology, Tufts University School of Medicine Boston, MA, USA
| | - Matt Wachowiak
- Department of Biology, Boston University Boston, MA, USA ; Brain Institute and Department of Neurobiology and Anatomy, University of Utah Salt Lake City, UT, USA
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12
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Early formation of GABAergic synapses governs the development of adult-born neurons in the olfactory bulb. J Neurosci 2012; 32:9103-15. [PMID: 22745509 DOI: 10.1523/jneurosci.0214-12.2012] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
In mammals, olfactory bulb granule cells (GCs) are generated throughout life in the subventricular zone. GABAergic inputs onto newborn neurons likely regulate their maturation, but the details of this process remain still elusive. Here, we investigated the differentiation, synaptic integration, and survival of adult-born GCs when their afferent GABAergic inputs are challenged by conditional gene targeting. Migrating GC precursors were targeted with Cre-eGFP-expressing lentiviral vectors in mice with a floxed gene encoding the GABA(A) receptor α2-subunit (i.e., Gabra2). Ablation of the α2-subunit did not affect GC survival but dramatically delayed their maturation. We found a reduction in postsynaptic α2-subunit and gephyrin clusters accompanied by a decrease in the frequency and amplitude of GABAergic postsynaptic currents beginning ∼14 d post-injection (dpi). In addition, mutant cells exhibited altered dendritic branching and spine density. Spine loss appeared with mislocation of glutamatergic synapses on dendritic shafts and a reduction of spontaneous glutamatergic postsynaptic currents, underscoring the relevance of afferent GABAergic transmission for a proper synaptic integration of newborn GCs. To test the role of GABAergic signaling during much early stages of GC maturation, we used a genetic strategy to selectively inactivate Gabra2 in precursor cells of the subventricular zone. In these mice, labeling of newborn GCs with eGFP lentiviruses revealed similar morphological alterations as seen on delayed Gabra2 inactivation in migrating neuroblasts, with reduced dendritic branching and spine density at 7 dpi. Collectively, these results emphasize the critical role of GABAergic synaptic signaling for structural maturation of adult-born GCs and formation of glutamatergic synapses.
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13
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Early activation of microglia triggers long-lasting impairment of adult neurogenesis in the olfactory bulb. J Neurosci 2012; 32:3652-64. [PMID: 22423088 DOI: 10.1523/jneurosci.6394-11.2012] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Microglia, the innate immune cells of the brain, engulf and eliminate cellular debris during brain injury and disease. Recent observations have extended their roles to the healthy brain, but the functional impact of activated microglia on neural plasticity has so far been elusive. To explore this issue, we investigated the role of microglia in the function of the adult olfactory bulb network in which both sensory afferents and local microcircuits are continuously molded by the arrival of adult-born neurons. We show here that the adult olfactory bulb hosts a large population of resident microglial cells. Deafferentation of the olfactory bulb resulted in a transient activation of microglia and a concomitant reduction of adult olfactory bulb neurogenesis. One day after sensory deafferentation, microglial cells proliferate in the olfactory bulb, and their numbers peaked at day 3, and reversed at day 7 after lesion. Similar lesions performed on immunodeficient mice demonstrate that the both innate and adaptive lymphocyte responses are dispensable for the lesion-induced microglial proliferation and activation. In contrast, when mice were treated with an antiinflammatory drug to prevent microglial activation, olfactory deafferentation did not reduce adult neurogenesis, showing that activated microglial cells per se, and not the lack of sensory experience, relates to the survival of adult-born neurons. We conclude that the status of the resident microglia in the olfactory bulb is an important factor directly regulating the survival of immature adult-born neurons.
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14
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Larsson L, Laska M. Ultra-high olfactory sensitivity for the human sperm-attractant aromatic aldehyde bourgeonal in CD-1 mice. Neurosci Res 2011; 71:355-60. [PMID: 21893110 DOI: 10.1016/j.neures.2011.08.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2011] [Revised: 07/27/2011] [Accepted: 08/16/2011] [Indexed: 11/15/2022]
Abstract
Recent studies have shown that certain aromatic aldehydes are ligands for olfactory receptors expressed in mammalian sperm cells and induce sperm chemotaxis. Using a conditioning paradigm, the olfactory sensitivity of five CD-1 mice for seven aromatic aldehydes was investigated. With all seven stimuli, the mice discriminated concentrations as low as 0.01 ppm (parts per million) from the solvent, and with bourgeonal the animals even detected concentrations as low as 0.1 ppq (parts per quadrillion) which constitutes the lowest olfactory detection threshold value reported in this species so far. The presence of a tertiary butyl group in para-position (relative to the functional aldehyde group) combined with a lack of an additional alkyl group next to the functional aldehyde group may be responsible for the extraordinary sensitivity of the mice for bourgeonal.
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Affiliation(s)
- Linda Larsson
- IFM Biology, Section of Zoology, Linköping University, 58183 Linköping, Sweden
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15
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Kim JW, Hong SL, Lee CH, Jeon EH, Choi AR. Relationship between olfactory function and olfactory neuronal population in C57BL6 mice injected intraperitoneally with 3-methylindole. Otolaryngol Head Neck Surg 2010; 143:837-42. [PMID: 21109087 DOI: 10.1016/j.otohns.2010.08.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2010] [Revised: 08/04/2010] [Accepted: 08/13/2010] [Indexed: 01/20/2023]
Abstract
OBJECTIVE It is not known how many olfactory receptor neurons should be intact to maintain olfaction in mouse models treated with 3-methylindole. The aim of this study is to investigate the relationship between a simple olfactory test outcome and the olfactory neuronal population. STUDY DESIGN Mouse model. SETTING Animal laboratory of the Seoul National University Bundang Hospital. SUBJECTS AND METHODS Olfactory dysfunction was induced by intraperitoneal injection of 3-methylindole in 38 six-week-old female C57BL6 mice. Olfactory function was evaluated by a food-finding test following 72-hour starvation. The olfactory neuronal population was quantified by olfactory marker protein (OMP) expression. RESULTS The average time for finding food was 8.1 seconds in control mice. It was 13.4, 84.4, 90.1, and 111.4 seconds for mice injected with 100, 200, 300, and 400 μg/g of 3-methylindole, respectively. Harvesting the whole olfactory neuroepithelium, densitometric analysis showed significant decrease of OMP in the 300- and 400-μg/g groups as compared with controls (18.8% and 17.5% of relative density, respectively). In the olfactory bulb, there was a significant decrease of OMP in the 200-, 300-, and 400-μg/g groups (44.5%, 37.0%, and 9.0% of relative density, respectively). The food-finding time had a significant reverse correlation with the relative density of OMP both in the olfactory bulb and in the olfactory neuroepithelium. CONCLUSION Our study showed that olfactory impairment was correlated with olfactory neuronal population in mice treated with 3-methylindole. The food-finding test would be a useful tool that could be easily performed without special training in the 3-methylindole-treated C57BL6 anosmic mouse model.
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Affiliation(s)
- Jeong-Whun Kim
- Department of Otorhinolaryngology, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
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16
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Laska M, Persson O, Hernandez Salazar LT. Olfactory sensitivity for alkylpyrazines-a comparative study in CD-1 mice and spider monkeys. ACTA ACUST UNITED AC 2009; 311:278-88. [PMID: 19204998 DOI: 10.1002/jez.527] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Using a conditioning paradigm, the olfactory sensitivity of four CD-1 mice for six alkylpyrazines was investigated. With all six stimuli, the animals discriminated concentrations <or=0.1 ppm (parts per million) from the odorless solvent, and with three of the six stimuli the animals were even able to detect concentrations <or=0.1 ppb (parts per billion). Four spider monkeys tested in parallel were found to detect five of the same six stimuli at concentrations <1 ppm and with one stimulus they were able to discriminate concentrations <1 ppb from the solvent. The results showed CD-1 mice to be more sensitive than spider monkeys with five of the six alkylpyrazines tested. There was a significant positive correlation between sensitivity and the number of alkyl groups attached to the pyrazine (Pyr) ring in both species. A comparison of the detection thresholds obtained here to those obtained in human subjects suggests that neither the number of functional olfactory receptor genes nor the absolute or the relative size of the olfactory bulbs reliably predict a species' olfactory sensitivity. These threshold data may provide useful information for the choice of adequate stimulus concentrations in electrophysiological or imaging studies of the olfactory system or investigations of the discriminative abilities of mice and spider monkeys.
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Vedin V, Molander M, Bohm S, Berghard A. Regional differences in olfactory epithelial homeostasis in the adult mouse. J Comp Neurol 2009; 513:375-84. [PMID: 19177519 DOI: 10.1002/cne.21973] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The olfactory sensory neurons in the nasal cavity of the adult mouse are organized into a few regions that differ in their molecular properties, as several classes of genes show regional expression. Most renowned is the fact that expression of each of hundreds of different odorant receptor genes is limited to one such region, or zone, of the olfactory neuroepithelial sheet. Zone differences are in place at birth, as exemplified here by the expression of neuronal progenitor marker Foxg1. We herein describe that an adult pattern showing regional differences in neurogenesis develops during the first few weeks of postnatal life which, e.g., is reflected in the temporal and regional regulation of the neuronal progenitor marker Ascl1. The most dorsomedial zone shows significantly fewer cells in S-phase in the adult but not in newborn mice by two different measures. Moreover, we show that there are regional differences in the relative differentiation, cell survival, and thickness of the olfactory epithelium. These findings are compatible with the view that zones are inherently distinct and that such differences contribute to generate regional differences in cellular homeostasis that in turn may modulate the capacity of a region to adjust to extrinsic influence.
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Affiliation(s)
- Viktoria Vedin
- Department of Molecular Biology, Umeå University, Sweden
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18
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Distribution and severity of spontaneous lesions in the neuroepithelium and Bowman's glands in mouse olfactory mucosa: age-related progression. Cell Tissue Res 2009; 335:489-503. [PMID: 19142664 DOI: 10.1007/s00441-008-0739-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2008] [Accepted: 11/27/2008] [Indexed: 10/21/2022]
Abstract
Age-related changes were examined in the distribution and severity of spontaneous lesions in the neuroepithelium and Bowman's glands in mouse olfactory mucosa. The olfactory mucosa of female ICR mice at postnatal ages from 10 days to 16 months were investigated histologically by hematoxylin and eosin staining, high-iron diamine-Alcian blue (HID-AB) staining, and immunohistochemistry for olfactory marker protein (OMP), betaIII tubulin (betaIIIT), and Ki67. The lesions in the neuroepithelium and Bowman's glands were quantitatively assessed by morphometric analyses of sections stained with anti-OMP antibody or HID-AB. The first appearance of neuroepithelial abnormality was observed in the dorsomedial portion of the olfactory mucosa in 5-month-old mice. The distribution and severity of lesions progressed with increasing age. In mildly affected epithelium in which OMP-positive olfactory receptor neurons (ORNs) were present but in smaller amounts, the numbers of betaIIIT-positive and Ki67-positive neuroepithelial cells tended to be increased, indicating that neurogenesis was upregulated in these areas. In contrast, severely affected epithelium in which OMP-positive ORNs were virtually absent showed high variability in the numbers of betaIIIT- and Ki67-positive cells among the areas examined, probably reflecting differences in the capacity of the basal cells remaining in the affected area to generate new neuronal cells. Histological analysis with HID-AB revealed that spontaneous lesions in Bowman's glands also occurred in aged mouse olfactory mucosa. Lesions in the neuroepithelium and underlying Bowman's glands tended to be spatially co-localized, suggesting a close association between pathogeneses in these two structures. Moreover, lesions in Bowman's glands were associated with changes in the biochemical composition of mucus on the olfactory mucosa. This information should prove useful in improving the understanding of the pathogenetic mechanisms underlying age-related changes in the peripheral olfactory system.
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Turning astrocytes from the rostral migratory stream into neurons: a role for the olfactory sensory organ. J Neurosci 2008; 28:11089-102. [PMID: 18945916 DOI: 10.1523/jneurosci.3713-08.2008] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Neurogenesis persists within a few restricted areas of the adult mammalian brain, giving rise to neurons that functionally integrate into preexisting circuits. One of these areas, the subventricular zone (SVZ), was believed, until recently, to be the unique source providing the adult olfactory bulb (OB) with newborn neurons. Because of the fact that neuroblasts derived in the SVZ migrate through the rostral migratory stream (RMS) en route to the OB, the existence of candidate neural stem cells within the RMS was long overlooked. Here, we confirm and considerably extend recent evidence for the existence of adult neural stem cells within the RMS, and go on to investigate their proliferative regulation. Specifically targeting RMS-astrocytes with lentiviral vectors encoding GFP, we demonstrate that glial cells in the RMS differentiate into both OB granule and periglomerular interneurons. In addition, ultrastructural analysis unambiguously reveals the astrocytic nature of stem cells in the adult RMS, and patch-clamp recordings demonstrate the functional integration of RMS-derived interneurons into OB circuitry. Proliferative regulation was investigated via two contrasting manipulations: exposure to an odor-enriched environment that enhances candidate stem cell proliferation in both the RMS and SVZ, and chemical lesion of the main olfactory epithelium that increases cell proliferation in the RMS only. New neurons in the adult OB can therefore arise from different neurogenic areas that can be separately regulated.
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20
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Abstract
Odors often produce different sensations when presented in front of the nose or intraorally, when eaten. It is a long-standing question whether these differences in sensations are due, for example, to the additional mechanical sensations elicited by the food in the mouth or additional odor release during mastication. To study this phenomenon in detail, a stimulation technique has been developed that allows controlled ortho- or retronasal presentation of odorous stimuli. Results from psychophysical, electrophysiological, and imaging studies suggest that there are clear differences in the perception of ortho- and retronasal stimuli. This 'duality of the sense of smell' is also observed in a clinical context where some patients exhibit good retronasal olfactory function with little or no orthonasal function left, and vice versa. The differences between ortho- and retronasal perception of odors are thought to be, at least partly, due to absorption of odors to the olfactory epithelium, which appears to differ in relation to the direction of the airflow across the olfactory epithelium.
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Affiliation(s)
- Thomas Hummel
- Smell & Taste Clinic, Department of Otorhinolaryngology, University of Dresden Medical School, Fetscherstrasse 74, D-01307 Dresden.
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21
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Olfactory discrimination of aliphatic odorants at 1 ppm: too easy for CD-1 mice to show odor structure-activity relationships? J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2008; 194:971-80. [PMID: 18810459 DOI: 10.1007/s00359-008-0370-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2008] [Revised: 08/25/2008] [Accepted: 09/05/2008] [Indexed: 02/02/2023]
Abstract
Using an operant conditioning paradigm we tested the ability of CD-1 mice to discriminate between 25 odorants comprising members of five homologous series of aliphatic odorants (C4-C8) presented at a gas phase concentration of 1 ppm. We found (a) that all mice significantly discriminated between all 50 stimulus pairs that involved odorants sharing the same functional group, but differing in carbon chain length, as well as between all 50 stimulus pairs that involved odorants sharing the same carbon chain length but differing in functional group, (b) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length with the acetic esters and the 2-ketones, but not with the 1-alcohols, n-aldehydes, and n-carboxylic acids tested, and (c) that odorant pairs differing in functional group were significantly better discriminated than odorant pairs differing in carbon chain length. These findings demonstrate that CD-1 mice have excellent discrimination ability for structurally related aliphatic odorants, that correlations between discrimination performance and structural similarity of odorants are odorant class-specific rather than a general phenomenon, and that both carbon chain length and type of functional group play an important role for odor quality coding in mice.
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22
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Abstract
Systematic mapping studies involving 365 odorant chemicals have shown that glomerular responses in the rat olfactory bulb are organized spatially in patterns that are related to the chemistry of the odorant stimuli. This organization involves the spatial clustering of principal responses to numerous odorants that share key aspects of chemistry such as functional groups, hydrocarbon structural elements, and/or overall molecular properties related to water solubility. In several of the clusters, responses shift progressively in position according to odorant carbon chain length. These response domains appear to be constructed from orderly projections of sensory neurons in the olfactory epithelium and may also involve chromatography across the nasal mucosa. The spatial clustering of glomerular responses may serve to "tune" the principal responses of bulbar projection neurons by way of inhibitory interneuronal networks, allowing the projection neurons to respond to a narrower range of stimuli than their associated sensory neurons. When glomerular activity patterns are viewed relative to the overall level of glomerular activation, the patterns accurately predict the perception of odor quality, thereby supporting the notion that spatial patterns of activity are the key factors underlying that aspect of the olfactory code. A critical analysis suggests that alternative coding mechanisms for odor quality, such as those based on temporal patterns of responses, enjoy little experimental support.
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Affiliation(s)
- Brett A Johnson
- Department of Neurobiology and Behavior, University of California, Irvine, CA 92697-4550, USA.
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Youngentob SL, Johnson BA, Leon M, Sheehe PR, Kent PF. Predicting odorant quality perceptions from multidimensional scaling of olfactory bulb glomerular activity patterns. Behav Neurosci 2007; 120:1337-45. [PMID: 17201479 PMCID: PMC2222860 DOI: 10.1037/0735-7044.120.6.1337] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Odorants and their perceptions differ along multiple dimensions, requiring that a critical examination of any putative neural code directly assess the multidimensional nature of the encoding process. Previous work has examined simple, systematic odorant differences that, regardless of coding strategy, would be expected to produce simple, systematic predictions in neural and behavioral responses. In the present study, an odorant identification confusion matrix task that extracts precise quality relationships across odorants was used to determine whether spatially specific glomerular activity patterns predict perceptual quality relationships for odorants that cannot easily be classified a priori along a single chemical dimension. Multidimensional scaling (MDS) analysis of odorant pattern similarity measures derived from the comparison of [14C]-2-deoxyglucose glomerular activity pattern data yielded a two-dimensional odorant activity space that was highly significantly predictive of similarly obtained odorant perceptual spaces, uniformly across animals. These results strongly support the relevance of global spatial patterns in the olfactory bulb to the encoding of odor quality.
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Affiliation(s)
- Steven L Youngentob
- Department of Neuroscience and Physiology, State University of New York, Upstate Medical University, Syracuse, NY 13210, USA.
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24
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Affiliation(s)
- Michael Leon
- Department of Neurobiology and Behavior, University of California, Irvine, CA 92697, USA.
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25
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Scott JW, Acevedo HP, Sherrill L. Effects of concentration and sniff flow rate on the rat electroolfactogram. Chem Senses 2006; 31:581-93. [PMID: 16740644 PMCID: PMC2225541 DOI: 10.1093/chemse/bjj063] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Previous reports using the electroolfactogram (EOG) to study the spatial and temporal aspects of response in the rodent olfactory epithelium had focused on high odorant concentrations that gave large responses. This investigation has used lower concentrations to test the difference between responses in the rat dorsomedial and lateral recesses with a range of nasal flow rates and a range of chemical properties. The responses to a highly polar, more hydrophilic odorant changed more steeply with flow rate than responses to a very nonpolar, hydrophobic odorant. With low flow rates there was a response delay in the lateral recess, which is consistent with the models indicating lower flow rates in that region. We observed significant volume conduction effects in which large responses in the dorsomedial region obscured smaller initial portions of the lateral responses. These effects could be removed by destroying the dorsomedial response with a high concentration of a low molecular weight ester. We caution that investigators of EOG recordings from the intact epithelium must attend to the possible presence of volume conduction, which can be assessed by attention to the selectivity of odorant response, response waveform, and response latency.
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Affiliation(s)
- John W Scott
- Department of Cell Biology, 405 N Whitehead Biomedical Research Building, 615 Michael Street, Emory University School of Medicine, Atlanta, GA 30322-3030, USA.
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26
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Abstract
The act of sniffing increases the air velocity and changes the duration of airflow in the nose. It is not yet clear how these changes interact with the intrinsic timing within the olfactory bulb, but this is a matter of current research activity. An action of sniffing in generating a high velocity that alters the sorption of odorants onto the lining of the nasal cavity is expected from the established work on odorant properties and sorption in the frog nose. Recent work indicates that the receptor properties in the olfactory epithelium and olfactory bulb are correlated with the receptor gene expression zones. The responses in both the epithelium and the olfactory bulb are predictable to a considerable extent by the hydrophobicity of odorants. Furthermore, receptor expression in both rodent and salamander nose interacts with the shapes of the nasal cavity to place the receptor sensitivity to odorants in optimal places according to the aerodynamic properties of the nose.
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Affiliation(s)
- John W Scott
- Department of Cell Biology, Emory University, 405N Whitehead Biomedical Research Center, 615 Michael Street, Atlanta, GA 30322, USA.
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Clevenger AC, Restrepo D. Evaluation of the Validity of a Maximum Likelihood Adaptive Staircase Procedure for Measurement of Olfactory Detection Threshold in Mice. Chem Senses 2005; 31:9-26. [PMID: 16306319 DOI: 10.1093/chemse/bjj001] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Threshold is defined as the stimulus intensity necessary for a subject to reach a specified percent correct on a detection test. MLPEST (maximum likelihood parameter estimation by sequential testing) is a method that is able to determine threshold accurately and more rapidly than many other methods. Originally developed for human auditory and visual tasks, it has been adapted for human olfactory and gustatory tests. In order to utilize this technique for olfactory testing in mice, we have adapted MLPEST methodology for use with computerized olfactometry as a tool to estimate odor detection thresholds. Here we present Monte Carlo simulations and operant conditioning data that demonstrate the potential utility of this technique in mice, we explore the ramifications of altering MLPEST test parameters on performance, and we discuss the advantages and disadvantages of using MLPEST compared to other methods for the estimation of thresholds in rodents. Using MLPEST, we find that olfactory detection thresholds in mice deficient for the cyclic nucleotide-gated channel subunit A2 are similar to those of wild-type animals for odorants the knockout animals are able to detect.
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Affiliation(s)
- Amy C Clevenger
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, University of Colorado at Denver, CO 80045, USA.
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28
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Schoenfeld TA, Cleland TA. The anatomical logic of smell. Trends Neurosci 2005; 28:620-7. [PMID: 16182387 DOI: 10.1016/j.tins.2005.09.005] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2005] [Revised: 08/09/2005] [Accepted: 09/08/2005] [Indexed: 11/24/2022]
Abstract
Olfactory receptor neurons (ORNs) expressing the same odorant receptor gene share ligand-receptor affinity profiles and converge onto common glomerular targets in the brain. The activation patterns of different ORN populations, evoked by differential binding of odorant molecular moieties, constitute the primary odor representation. However, odorants possess properties other than receptor-binding sites that can contribute to odorant discrimination. Among terrestrial vertebrates, odorant sorptiveness--volatility and water solubility--imposes physicochemical constraints on migration through the nose during inspiration. The non-uniform distributions of ORN populations along the inspiratory axis enable sorptiveness to modify odor representations by affecting the number of molecules reaching different receptors during a sniff. Animals can then modify and analyze odor representation further by the dynamic regulation of sniffing.
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Affiliation(s)
- Thomas A Schoenfeld
- Department of Physiology, Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA 01655, USA.
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29
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Salcedo E, Zhang C, Kronberg E, Restrepo D. Analysis of training-induced changes in ethyl acetate odor maps using a new computational tool to map the glomerular layer of the olfactory bulb. Chem Senses 2005; 30:615-26. [PMID: 16141292 DOI: 10.1093/chemse/bji055] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Odor quality is thought to be encoded by the activation of partially overlapping subsets of glomeruli in the olfactory bulb (odor maps). Mouse genetic studies have demonstrated that olfactory sensory neurons (OSNs) expressing a particular olfactory receptor target their axons to a few individual glomeruli in the bulb. While the specific targeting of OSN axons provides a molecular underpinning for the odor maps, much remains to be understood about the relationship between the functional and molecular maps. In this article, we ask the question whether intensive training of mice in a go/no-go operant conditioning odor discrimination task affects odor maps measured by determining c-fos up-regulation in periglomerular cells. Data analysis is performed using a newly developed suite of computational tools designed to systematically map functional and molecular features of glomeruli in the adult mouse olfactory bulb. This suite provides the necessary tools to process high-resolution digital images, map labeled glomeruli, visualize odor maps, and facilitate statistical analysis of patterns of identified glomeruli in the olfactory bulb. The software generates odor maps (density plots) based on glomerular activity, density, or area. We find that training up-regulates the number of glomeruli that become c-fos positive after stimulation with ethyl acetate.
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Affiliation(s)
- Ernesto Salcedo
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Mail Stop 8108 PO Box 6511, Aurora, CO 80045, USA.
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