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Abstract
An important contributing factor for the high sensitivity of sensory systems is the exquisite sensitivity of the sensory receptor cells. We report here the signaling threshold of the olfactory receptor neuron (ORN). We first obtained a best estimate of the size of the physiological electrical response successfully triggered by a single odorant-binding event on a frog ORN, which was ∼0.034 pA and had an associated transduction domain spanning only a tiny fraction of the length of an ORN cilium. We also estimated the receptor-current threshold for an ORN to fire action potentials in response to an odorant pulse, which was ∼1.2 pA. Thus, it takes about 35 odorant-binding events successfully triggering transduction during a brief odorant pulse in order for an ORN to signal to the brain.
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52
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Liu Q, Ye W, Hu N, Cai H, Yu H, Wang P. Olfactory receptor cells respond to odors in a tissue and semiconductor hybrid neuron chip. Biosens Bioelectron 2010; 26:1672-8. [PMID: 20943368 DOI: 10.1016/j.bios.2010.09.019] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 09/02/2010] [Accepted: 09/06/2010] [Indexed: 11/30/2022]
Abstract
Olfactory systems of human beings and animals have the abilities to sense and distinguish varieties of odors. In this study, a bioelectronic nose was constructed by fixing biological tissues onto the surface of light-addressable potentiometric sensor (LAPS) to mimic human olfaction and realize odor differentiation. The odorant induced potentials on tissue-semiconductor interface was analyzed by sensory transduction theory and sheet conductor model. The extracellular potentials of the receptor cells in the olfactory epithelium were detected by LAPS. Being stimulated by different odorants, such as acetic acid and butanedione, olfactory epithelium activities were analyzed on basis of local field potentials and presented different firing modes. The signals fired in different odorants could be distinguished into different clusters by principal component analysis (PCA). Therefore, with cellular populations well preserved, the epithelium tissue and LAPS hybrid system will be a promising neuron chip of olfactory biosensors for odor detecting.
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Affiliation(s)
- Qingjun Liu
- Biosensor National Special Laboratory, Department of Biomedical Engineering, Zhejiang University, Hangzhou 310027, PR China
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53
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Sagheddu C, Boccaccio A, Dibattista M, Montani G, Tirindelli R, Menini A. Calcium concentration jumps reveal dynamic ion selectivity of calcium-activated chloride currents in mouse olfactory sensory neurons and TMEM16b-transfected HEK 293T cells. J Physiol 2010; 588:4189-204. [PMID: 20837642 DOI: 10.1113/jphysiol.2010.194407] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Ca(2+)-activated Cl(-) channels play relevant roles in several physiological processes, including olfactory transduction, but their molecular identity is still unclear. Recent evidence suggests that members of the transmembrane 16 (TMEM16, also named anoctamin) family form Ca(2+)-activated Cl(-) channels in several cell types. In vertebrate olfactory transduction, TMEM16b/anoctamin2 has been proposed as the major molecular component of Ca(2+)-activated Cl(-) channels. However, a comparison of the functional properties in the whole-cell configuration between the native and the candidate channel has not yet been performed. In this study, we have used the whole-cell voltage-clamp technique to measure functional properties of the native channel in mouse isolated olfactory sensory neurons and compare them with those of mouse TMEM16b/anoctamin2 expressed in HEK 293T cells. We directly activated channels by rapid and reproducible intracellular Ca(2+) concentration jumps obtained from photorelease of caged Ca(2+) and determined extracellular blocking properties and anion selectivity of the channels. We found that the Cl(-) channel blockers niflumic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB) and DIDS applied at the extracellular side of the membrane caused a similar inhibition of the two currents. Anion selectivity measured exchanging external ions and revealed that, in both types of currents, the reversal potential for some anions was time dependent. Furthermore, we confirmed by immunohistochemistry that TMEM16b/anoctamin2 largely co-localized with adenylyl cyclase III at the surface of the olfactory epithelium. Therefore, we conclude that the measured electrophysiological properties in the whole-cell configuration are largely similar, and further indicate that TMEM16b/anoctamin2 is likely to be a major subunit of the native olfactory Ca(2+)-activated Cl(-) current.
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Affiliation(s)
- Claudia Sagheddu
- International School for Advanced Studies, Scuola Internazionale Superiore di Studi Avanzati, SISSA, Trieste, Italy
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54
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Frank ME, Goyert HF, Hettinger TP. Time and intensity factors in identification of components of odor mixtures. Chem Senses 2010; 35:777-87. [PMID: 20720093 DOI: 10.1093/chemse/bjq078] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Identification of odors of compounds introduced into changeable olfactory environments is the essence of olfactory coding, which focuses perception on the latest stimulus with the greatest salience. Effects of stimulus intensity and adapting time on mixture component identification after adapting with one component were each studied in 10 human subjects. Odors of 1 and 5 mM vanillin (vanilla) and phenethyl alcohol (rose) were identified, with adapting time varied by sniffing naturally once or twice, or sniffing 5 times, once every 2 s. Odors of water-adapted single compounds were identified nearly perfectly (94%), self-adapted to 51% but did not cross-adapt (94%), showing the 2 compounds had quickly adapting independent odors. Identifications of the vanilla and rose odors in water-adapted mixtures were reduced to 59% and 79%, respectively. Following single-component adaptation, the average 33% identification of odors of adapted (ambient) mixture components contrasted with the greater average 86% identification of new unadapted (extra) mixture components. Identifications were lower for 1 than 5 mM components when concentrations were not matched, and ambient component identifications were lower after 10-s adaptation than after 1 or 2 sniffs. Rapid selective adaptation and mixture component suppression manipulate effective intensity to promote emergence of characteristic odor qualities in dynamic natural settings.
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Affiliation(s)
- Marion E Frank
- Department of Oral Health and Diagnostic Sciences, Division of Periodontology, Center for Chemosensory Sciences, School of Dental Medicine, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030-1715, USA.
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55
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Antolin S, Reisert J, Matthews HR. Olfactory response termination involves Ca2+-ATPase in vertebrate olfactory receptor neuron cilia. ACTA ACUST UNITED AC 2010; 135:367-78. [PMID: 20351061 PMCID: PMC2847921 DOI: 10.1085/jgp.200910337] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In vertebrate olfactory receptor neurons (ORNs), odorant-induced activation of the transduction cascade culminates in production of cyclic AMP, which opens cyclic nucleotide–gated channels in the ciliary membrane enabling Ca2+ influx. The ensuing elevation of the intraciliary Ca2+ concentration opens Ca2+-activated Cl− channels, which mediate an excitatory Cl− efflux from the cilia. In order for the response to terminate, the Cl− channel must close, which requires that the intraciliary Ca2+ concentration return to basal levels. Hitherto, the extrusion of Ca2+ from the cilia has been thought to depend principally on a Na+–Ca2+ exchanger. In this study, we show using simultaneous suction pipette recording and Ca2+-sensitive dye fluorescence measurements that in fire salamander ORNs, withdrawal of external Na+ from the solution bathing the cilia, which incapacitates Na+–Ca2+exchange, has only a modest effect on the recovery of the electrical response and the accompanying decay of intraciliary Ca2+ concentration. In contrast, exposure of the cilia to vanadate or carboxyeosin, a manipulation designed to block Ca2+-ATPase, has a substantial effect on response recovery kinetics. Therefore, we conclude that Ca2+-ATPase contributes to Ca2+ extrusion in ORNs, and that Na+–Ca2+exchange makes only a modest contribution to Ca2+ homeostasis in this species.
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Affiliation(s)
- Salome Antolin
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, England, UK
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56
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Ma W, Trusina A, El-Samad H, Lim WA, Tang C. Defining network topologies that can achieve biochemical adaptation. Cell 2009; 138:760-73. [PMID: 19703401 DOI: 10.1016/j.cell.2009.06.013] [Citation(s) in RCA: 563] [Impact Index Per Article: 37.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 03/29/2009] [Accepted: 06/03/2009] [Indexed: 11/19/2022]
Abstract
Many signaling systems show adaptation-the ability to reset themselves after responding to a stimulus. We computationally searched all possible three-node enzyme network topologies to identify those that could perform adaptation. Only two major core topologies emerge as robust solutions: a negative feedback loop with a buffering node and an incoherent feedforward loop with a proportioner node. Minimal circuits containing these topologies are, within proper regions of parameter space, sufficient to achieve adaptation. More complex circuits that robustly perform adaptation all contain at least one of these topologies at their core. This analysis yields a design table highlighting a finite set of adaptive circuits. Despite the diversity of possible biochemical networks, it may be common to find that only a finite set of core topologies can execute a particular function. These design rules provide a framework for functionally classifying complex natural networks and a manual for engineering networks. For a video summary of this article, see the PaperFlick file with the Supplemental Data available online.
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Affiliation(s)
- Wenzhe Ma
- Center for Theoretical Biology, Peking University, Beijing 100871, China
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57
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A novel cyclic nucleotide-gated ion channel enriched in synaptic terminals of isotocin neurons in zebrafish brain and pituitary. Neuroscience 2009; 165:79-89. [PMID: 19778592 DOI: 10.1016/j.neuroscience.2009.09.040] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2008] [Revised: 09/14/2009] [Accepted: 09/16/2009] [Indexed: 11/23/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels are nonselective cation channels opened by binding of intracellular cyclic GMP or cyclic AMP. CNG channels mediate sensory transduction in the rods and cones of the retina and in olfactory sensory neurons, but in addition, CNG channels are also expressed elsewhere in the CNS, where their physiological roles have not yet been well defined. Besides the CNG channel subtypes that mediate vision and olfaction, zebrafish has an additional subtype, CNGA5, which is expressed almost exclusively in the brain. We have generated CNGA5-specific monoclonal antibodies, which we use here to show that immunoreactivity for CNGA5 channels is highly enriched in synaptic terminals of a discrete set of neurons that project to a subregion of the pituitary, as well as diffusely in the brain and spinal cord. Double labeling with a variety of antibodies against pituitary hormones revealed that CNGA5 is located in the terminals of neuroendocrine cells that secrete the nonapeptide hormone/transmitter isotocin in the neurohypophysis, brain, and spinal cord. Furthermore, we show that CNGA5 channels expressed in Xenopus oocytes are highly permeable to Ca(2+), which suggests that the channels are capable of modulating isotocin release in the zebrafish brain and pituitary. Isotocin is the teleost homolog of the mammalian hormone oxytocin, and like oxytocin, it regulates reproductive and social behavior. Therefore, the high calcium permeability of CNGA5 channels and their strategic location in isotocin-secreting synaptic terminals suggest that activation of CNGA5 channels in response to cyclic nucleotide signaling may have wide-ranging neuroendocrine and behavioral effects.
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58
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Pifferi S, Dibattista M, Sagheddu C, Boccaccio A, Al Qteishat A, Ghirardi F, Tirindelli R, Menini A. Calcium-activated chloride currents in olfactory sensory neurons from mice lacking bestrophin-2. J Physiol 2009; 587:4265-79. [PMID: 19622610 DOI: 10.1113/jphysiol.2009.176131] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Olfactory sensory neurons use a chloride-based signal amplification mechanism to detect odorants. The binding of odorants to receptors in the cilia of olfactory sensory neurons activates a transduction cascade that involves the opening of cyclic nucleotide-gated channels and the entry of Ca(2+) into the cilia. Ca(2+) activates a Cl(-) current that produces an efflux of Cl(-) ions and amplifies the depolarization. The molecular identity of Ca(2+)-activated Cl(-) channels is still elusive, although some bestrophins have been shown to function as Ca(2+)-activated Cl(-) channels when expressed in heterologous systems. In the olfactory epithelium, bestrophin-2 (Best2) has been indicated as a candidate for being a molecular component of the olfactory Ca(2+)-activated Cl(-) channel. In this study, we have analysed mice lacking Best2. We compared the electrophysiological responses of the olfactory epithelium to odorant stimulation, as well as the properties of Ca(2+)-activated Cl(-) currents in wild-type (WT) and knockout (KO) mice for Best2. Our results confirm that Best2 is expressed in the cilia of olfactory sensory neurons, while odorant responses and Ca(2+)-activated Cl(-) currents were not significantly different between WT and KO mice. Thus, Best2 does not appear to be the main molecular component of the olfactory channel. Further studies are required to determine the function of Best2 in the cilia of olfactory sensory neurons.
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Affiliation(s)
- Simone Pifferi
- International School for Advanced Studies, Scuola Internazionale Superiore di Studi Avanzati, SISSA, and Italian Institute of Technology, SISSA Unit, Trieste, Italy
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59
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Abstract
In recent years, considerable progress has been achieved in the comprehension of the profound effects of pheromones on reproductive physiology and behavior. Pheromones have been classified as molecules released by individuals and responsible for the elicitation of specific behavioral expressions in members of the same species. These signaling molecules, often chemically unrelated, are contained in body fluids like urine, sweat, specialized exocrine glands, and mucous secretions of genitals. The standard view of pheromone sensing was based on the assumption that most mammals have two separated olfactory systems with different functional roles: the main olfactory system for recognizing conventional odorant molecules and the vomeronasal system specifically dedicated to the detection of pheromones. However, recent studies have reexamined this traditional interpretation showing that both the main olfactory and the vomeronasal systems are actively involved in pheromonal communication. The current knowledge on the behavioral, physiological, and molecular aspects of pheromone detection in mammals is discussed in this review.
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60
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Modelling and sensitivity analysis of the reactions involving receptor, G-protein and effector in vertebrate olfactory receptor neurons. J Comput Neurosci 2009; 27:471-91. [PMID: 19533315 DOI: 10.1007/s10827-009-0162-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 04/08/2009] [Accepted: 04/23/2009] [Indexed: 10/20/2022]
Abstract
A biochemical model of the receptor, G-protein and effector (RGE) interactions during transduction in the cilia of vertebrate olfactory receptor neurons (ORNs) was developed and calibrated to experimental recordings of cAMP levels and the receptor current (RC). The model describes the steps from odorant binding to activation of the effector enzyme which catalyzes the conversion of ATP to cAMP, and shows how odorant stimulation is amplified and delayed by the RGE transduction cascade. A time-dependent sensitivity analysis was performed on the model. The model output-the cAMP production rate-is particularly sensitive to a few, dominant parameters. During odorant stimulation it depends mainly on the initial density of G-proteins and the catalytic constant for cAMP production.
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61
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Takeuchi H, Ishida H, Hikichi S, Kurahashi T. Mechanism of olfactory masking in the sensory cilia. J Gen Physiol 2009; 133:583-601. [PMID: 19433623 PMCID: PMC2713142 DOI: 10.1085/jgp.200810085] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 04/22/2009] [Indexed: 12/02/2022] Open
Abstract
Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide-gated (CNG) and Ca2+-activated Cl- (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.
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Affiliation(s)
- Hiroko Takeuchi
- Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan
| | - Hirohiko Ishida
- Perfumery Development Research Laboratories, Kao Corporation, Tokyo, 131-8501, Japan
| | - Satoshi Hikichi
- Perfumery Development Research Laboratories, Kao Corporation, Tokyo, 131-8501, Japan
| | - Takashi Kurahashi
- Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan
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62
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Rock JR, O'Neal WK, Gabriel SE, Randell SH, Harfe BD, Boucher RC, Grubb BR. Transmembrane protein 16A (TMEM16A) is a Ca2+-regulated Cl- secretory channel in mouse airways. J Biol Chem 2009; 284:14875-80. [PMID: 19363029 DOI: 10.1074/jbc.c109.000869] [Citation(s) in RCA: 209] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
For almost two decades, it has been postulated that calcium-activated Cl(-) channels (CaCCs) play a role in airway epithelial Cl(-) secretion, but until recently, the molecular identity of the airway CaCC(s) was unknown. Recent studies have unequivocally identified TMEM16A as a glandular epithelial CaCC. We have studied the airway bioelectrics of neonatal mice homozygous for a null allele of Tmem16a (Tmem16a(-/-)) to investigate the role of this channel in Cl(-) secretion in airway surface epithelium. When compared with wild-type tracheas, the Tmem16a(-/-) tracheas exhibited a >60% reduction in purinoceptor (UTP)-regulated CaCC activity. Other members of the Tmem16 gene family, including Tmem16f and Tmem16k, were also detected by reverse transcription-PCR in neonatal tracheal epithelium, suggesting that other family members could be considered as contributing to the small residual UTP response. TMEM16A, however, appeared to contribute little to unstimulated Cl(-) secretion, whereas studies with cystic fibrosis transmembrane conductance regulator (CFTR)-deficient mice and wild-type littermates revealed that unstimulated Cl(-) secretion reflected approximately 50% CFTR activity and approximately 50% non-Tmem16a activity. Interestingly, the tracheas of both the Tmem16a(-/-) and the CFTR(-/-) mice exhibited similar congenital cartilaginous defects that may reflect a common Cl(-) secretory defect mediated by the molecularly distinct Cl(-) channels. Importantly, the residual CaCC activity in Tmem16a(-/-) mice appeared inadequate for normal airway hydration because Tmem16a(-/-) tracheas exhibited significant, neonatal, lumenal mucus accumulation. Our data suggest that TMEM16A CaCC-mediated Cl(-) secretion appears to be necessary for normal airway surface liquid homeostasis.
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Affiliation(s)
- Jason R Rock
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27708, USA
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63
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Abstract
Adaptation is a general property of sensory receptor neurons and has been extensively studied in isolated cell preparation of olfactory receptor neurons. In contrast, little is known about the conditions under which peripheral adaptation occurs in the CNS during odorant stimulation. Here, we used two-photon laser-scanning microscopy and targeted extracellular recording in freely breathing anesthetized rats to investigate the correlate of peripheral adaptation at the first synapse of the olfactory pathway in olfactory bulb glomeruli. We find that during sustained stimulation at high concentration, odorants can evoke local field potential (LFP) postsynaptic responses that rapidly adapt with time, some within two inhalations. Simultaneous measurements of LFP and calcium influx at olfactory receptor neuron terminals reveal that postsynaptic adaptation is associated with a decrease in odorant-evoked calcium response, suggesting that it results from a decrease in glutamate release. This glomerular adaptation was concentration-dependent and did not change the glomerular input-output curve. In addition, in situ application of antagonists of either ionotropic glutamate receptors or metabotropic GABA(B) receptors did not affect this adaptation, thus discarding the involvement of local presynaptic inhibition. Glomerular adaptation, therefore, reflects the response decline of olfactory receptor neurons to sustained odorant. We postulate that peripheral fast adaptation is a means by which glomerular output codes for high concentration of odor.
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64
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Imai T, Sakano H. Odorant receptor-mediated signaling in the mouse. Curr Opin Neurobiol 2009; 18:251-60. [PMID: 18721880 DOI: 10.1016/j.conb.2008.07.009] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 07/16/2008] [Indexed: 11/17/2022]
Abstract
In the mouse olfactory system, there are approximately 1000 types of odorant receptors (ORs), which perform multiple functions in olfactory sensory neurons (OSNs). In addition to detecting odors, the functional OR protein ensures the singular gene choice of the OR by negative-feedback regulation. ORs also direct the axonal projection of OSNs both globally and locally by modulating the transcriptional levels of axon-guidance and axon-sorting molecules. In these latter processes, the second messenger, cAMP, plays differential roles in the fasciculation and targeting of axons. In this review, we will discuss how ORs differentially regulate intracellular signals for distinct functions.
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Affiliation(s)
- Takeshi Imai
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0032, Japan.
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65
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Briscoe J. Making a grade: Sonic Hedgehog signalling and the control of neural cell fate. EMBO J 2009; 28:457-65. [PMID: 19197245 PMCID: PMC2647768 DOI: 10.1038/emboj.2009.12] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2009] [Accepted: 01/09/2009] [Indexed: 01/14/2023] Open
Affiliation(s)
- James Briscoe
- Developmental Neurobiology, National Institute for Medical Research, London, UK.
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66
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Kwon HJ, Koo JH, Zufall F, Leinders-Zufall T, Margolis FL. Ca extrusion by NCX is compromised in olfactory sensory neurons of OMP mice. PLoS One 2009; 4:e4260. [PMID: 19165324 PMCID: PMC2621343 DOI: 10.1371/journal.pone.0004260] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2008] [Accepted: 12/09/2008] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The role of olfactory marker protein (OMP), a hallmark of mature olfactory sensory neurons (OSNs), has been poorly understood since its discovery. The electrophysiological and behavioral phenotypes of OMP knockout mice indicated that OMP influences olfactory signal transduction. However, the mechanism by which this occurs remained unknown. PRINCIPAL FINDINGS We used intact olfactory epithelium obtained from WT and OMP(-/-) mice to monitor the Ca(2+) dynamics induced by the activation of cyclic nucleotide-gated channels, voltage-operated Ca(2+) channels, or Ca(2+) stores in single dendritic knobs of OSNs. Our data suggested that OMP could act to modulate the Ca(2+)-homeostasis in these neurons by influencing the activity of the plasma membrane Na(+)/Ca(2+)-exchanger (NCX). Immunohistochemistry verifies colocalization of NCX1 and OMP in the cilia and knobs of OSNs. To test the role of NCX activity, we compared the kinetics of Ca(2+) elevation by stimulating the reverse mode of NCX in both WT and OMP(-/-) mice. The resulting Ca(2+) responses indicate that OMP facilitates NCX activity and allows rapid Ca(2+) extrusion from OSN knobs. To address the mechanism by which OMP influences NCX activity in OSNs we studied protein-peptide interactions in real-time using surface plasmon resonance technology. We demonstrate the direct interaction of the XIP regulatory-peptide of NCX with calmodulin (CaM). CONCLUSIONS Since CaM also binds to the Bex protein, an interacting protein partner of OMP, these observations strongly suggest that OMP can influence CaM efficacy and thus alters NCX activity by a series of protein-protein interactions.
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Affiliation(s)
- Hyun J. Kwon
- Department of Anatomy and Neurobiology, School of Medicine, University of Maryland, Baltimore, Maryland, United States of America
- Department of Engineering and Computer Science, Andrews University, Berrien Springs, Michigan, United States of America
| | - Jae Hyung Koo
- Department of Anatomy and Neurobiology, School of Medicine, University of Maryland, Baltimore, Maryland, United States of America
| | - Frank Zufall
- Department of Physiology, University of Saarland, Homburg, Germany
| | | | - Frank L. Margolis
- Department of Anatomy and Neurobiology, School of Medicine, University of Maryland, Baltimore, Maryland, United States of America
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67
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Abstract
Cyclic nucleotide-gated (CNG) channels are ion channels which are activated by the binding of cGMP or cAMP. The channels are important cellular switches which transduce changes in intracellular concentrations of cyclic nucleotides into changes of the membrane potential and the Ca2+ concentration. CNG channels play a central role in the signal transduction pathways of vision and olfaction. Structurally, the channels belong to the superfamily of pore-loop cation channels. They share a common domain structure with hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and Eag-like K+ channels. In this chapter, we give an overview on the molecular properties of CNG channels and describe the signal transduction pathways these channels are involved in. We will also summarize recent insights into the physiological and pathophysiological role of CNG channel proteins that have emerged from the analysis of CNG channel-deficient mouse models and human channelopathies.
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Affiliation(s)
- Martin Biel
- Center for Integrated Protein Science CIPS-M and Zentrum für Pharmaforschung-Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, München, 81377, Germany.
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68
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Hartzell HC, Yu K, Xiao Q, Chien LT, Qu Z. Anoctamin/TMEM16 family members are Ca2+-activated Cl- channels. J Physiol 2008; 587:2127-39. [PMID: 19015192 DOI: 10.1113/jphysiol.2008.163709] [Citation(s) in RCA: 202] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Ca(2+)-activated Cl- channels (CaCCs) perform many important functions in cell physiology including secretion of fluids from acinar cells of secretory glands, amplification of olfactory transduction, regulation of cardiac and neuronal excitability, mediation of the fast block to polyspermy in amphibian oocytes, and regulation of vascular tone. Although a number of proteins have been proposed to be responsible for CaCC currents, the anoctamin family (ANO, also known as TMEM16) exhibits characteristics most similar to those expected for the classical CaCC. Interestingly, this family of proteins has previously attracted the interest of both developmental and cancer biologists. Some members of this family are up-regulated in a number of tumours and functional deficiency in others is linked to developmental defects.
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Affiliation(s)
- H Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, 615 Michael Street, 535 Whitehead Bldg, Atlanta, GA 30322, USA.
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69
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Kleene SJ. The electrochemical basis of odor transduction in vertebrate olfactory cilia. Chem Senses 2008; 33:839-59. [PMID: 18703537 DOI: 10.1093/chemse/bjn048] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Most vertebrate olfactory receptor neurons share a common G-protein-coupled pathway for transducing the binding of odorant into depolarization. The depolarization involves 2 currents: an influx of cations (including Ca2+) through cyclic nucleotide-gated channels and a secondary efflux of Cl- through Ca2+-gated Cl- channels. The relation between stimulus strength and receptor current shows positive cooperativity that is attributed to the channel properties. This cooperativity amplifies the responses to sufficiently strong stimuli but reduces sensitivity and dynamic range. The odor response is transient, and prolonged or repeated stimulation causes adaptation and desensitization. At least 10 mechanisms may contribute to termination of the response; several of these result from an increase in intraciliary Ca2+. It is not known to what extent regulation of ionic concentrations in the cilium depends on the dendrite and soma. Although many of the major mechanisms have been identified, odor transduction is not well understood at a quantitative level.
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Affiliation(s)
- Steven J Kleene
- Department of Cancer and Cell Biology, University of Cincinnati, PO Box 670667, 231 Albert Sabin Way, Cincinnati, OH 45267-0667, USA.
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70
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Abstract
Retinal rods and cones, which are the front-end light detectors in the eye, achieve wonders together by being able to signal single-photon absorption and yet also able to adjust their function to brightness changes spanning 10(9)-fold. How these cells detect light is now quite well understood. Not surprising for almost any biological process, the intial step of seeing reveals a rich complexity as the probing goes deeper. The odyssey continues, but the knowledge gained so far is already nothing short of remarkable in qualitative and quantitative detail. It has also indirectly opened up the mystery of odorant sensing. Basic science aside, clinical ophthalmology has benefited tremendously from this endeavor as well. This article begins by recapitulating the key developments in this understanding from the mid-1960s to the late 1980s, during which period the advances were particularly rapid and fit for an intricate detective story. It then highlights some details discovered more recently, followed by a comparison between rods and cones.
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Affiliation(s)
- Dong-Gen Luo
- *Solomon H. Snyder Department of Neuroscience and
- Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Tian Xue
- *Solomon H. Snyder Department of Neuroscience and
- Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - King-Wai Yau
- *Solomon H. Snyder Department of Neuroscience and
- Department of Ophthalmology and
- Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, MD 21205
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71
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Dolzer J, Krannich S, Stengl M. Pharmacological investigation of protein kinase C- and cGMP-dependent ion channels in cultured olfactory receptor neurons of the hawkmoth Manduca sexta. Chem Senses 2008; 33:803-13. [PMID: 18635555 PMCID: PMC2580732 DOI: 10.1093/chemse/bjn043] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In the hawkmoth Manduca sexta, pheromone stimuli of different strength and duration rise the intracellular Ca2+ concentration in olfactory receptor neurons (ORNs). While second-long pheromone stimuli activate protein kinase C (PKC), which apparently underlies processes of short-term adaptation, minute-long pheromone stimuli elevate cyclic guanosine monophosphate (cGMP) concentrations, which correlates with time courses of long-term adaptation. To identify ion channels involved in the sliding adjustment of olfactory sensitivity, inside-out patch clamp recordings on cultured ORNs of M. sexta were performed to characterize Ca2+-, PKC-, and cGMP-dependent ion channels. Stepping to positive holding potentials in high intracellular Ca2+ elicits different Ca2+-dependent ion channels, namely small-conductance channels (2–20 ps), medium-conductance channels (20–100 ps), and large-conductance channels (>100 ps). Ion channels of 40, 60, and 70 ps opened after PKC activation, whereas 10- and >100-ps channels were observed less frequently. Application of 8-bromo cyclic guanosine monophosphate opened 55- and 70-ps channels and increased the open probability of >100-ps channels, whereas even in the presence of phorbol ester 40-ps channels were inhibited. Thus, cGMP elevations activate a different set of ion channels as compared with PKC and suppress at least one PKC-dependent ion channel.
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Affiliation(s)
- Jan Dolzer
- Department of Biology, Animal Physiology, Philipps-University of Marburg, Karl-von-Frisch-Strasse 8, Marburg D-35032, Germany
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72
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Single-photon absorptions evoke synaptic depression in the retina to extend the operational range of rod vision. Neuron 2008; 57:894-904. [PMID: 18367090 PMCID: PMC2423001 DOI: 10.1016/j.neuron.2008.01.031] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Revised: 12/28/2007] [Accepted: 01/23/2008] [Indexed: 11/21/2022]
Abstract
Adaptation or gain control allows sensory neurons to encode diverse stimuli using a limited range of output signals. Rod vision exemplifies a general challenge facing adaptational mechanisms-balancing the benefits of averaging to create a reliable signal for adaptation with the need to adapt rapidly and locally. The synapse between rod bipolar and AII amacrine cells dominates adaptation at low light levels. We find that adaptation occurs independently at each synapse and completes in <500 ms. This limited spatial and temporal integration suggests that the absorption of a single photon modulates gain. Indeed, responses to pairs of brief dim flashes showed directly that synaptic gain was depressed for 100-200 ms following transmission of a single-photon response. Presynaptic mechanisms mediated this synaptic depression. Thus, the division of light into discrete photons controls adaptation at this synapse, and gain varies with the irreducible statistical fluctuations in photon arrival.
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73
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Abstract
Most animals have evolved multiple olfactory systems to detect general odors as well as social cues. The sophistication and interaction of these systems permit precise detection of food, danger, and mates, all crucial elements for survival. In most mammals, the nose contains two well described chemosensory apparatuses (the main olfactory epithelium and the vomeronasal organ), each of which comprises several subtypes of sensory neurons expressing distinct receptors and signal transduction machineries. In many species (e.g., rodents), the nasal cavity also includes two spatially segregated clusters of neurons forming the septal organ of Masera and the Grueneberg ganglion. Results of recent studies suggest that these chemosensory systems perceive diverse but overlapping olfactory cues and that some neurons may even detect the pressure changes carried by the airflow. This review provides an update on how chemosensory neurons transduce chemical (and possibly mechanical) stimuli into electrical signals, and what information each system brings into the brain. Future investigation will focus on the specific ligands that each system detects with a behavioral context and the processing networks that each system involves in the brain. Such studies will lead to a better understanding of how the multiple olfactory systems, acting in concert, offer a complete representation of the chemical world.
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Affiliation(s)
- Minghong Ma
- Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
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74
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Function and dysfunction of CNG channels: insights from channelopathies and mouse models. Mol Neurobiol 2008; 35:266-77. [PMID: 17917115 DOI: 10.1007/s12035-007-0025-y] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2006] [Revised: 11/30/1999] [Accepted: 01/05/2007] [Indexed: 10/22/2022]
Abstract
Channels directly gated by cyclic nucleotides (CNG channels) are important cellular switches that mediate influx of Na+ and Ca2+ in response to increases in the intracellular concentration of cAMP and cGMP. In photoreceptors and olfactory receptor neurons, these channels serve as final targets for cGMP and cAMP signaling pathways that are initiated by the absorption of photons and the binding of odorants, respectively. CNG channels have been also found in other types of neurons and in non-excitable cells. However, in most of these cells, the physiological role of CNG channels has yet to be determined. CNG channels have a complex heteromeric structure. The properties of individual subunits that assemble in specific stoichiometries to the native channels have been extensively investigated in heterologous expression systems. Recently, mutations in human CNG channel genes leading to inherited diseases (so-called channelopathies) have been functionally characterized. Moreover, mouse knockout models were generated to define the role of CNG channel proteins in vivo. In this review, we will summarize recent insights into the physiological and pathophysiological role of CNG channel proteins that have emerged from genetic studies in mice and humans.
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75
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Dessaud E, Yang LL, Hill K, Cox B, Ulloa F, Ribeiro A, Mynett A, Novitch BG, Briscoe J. Interpretation of the sonic hedgehog morphogen gradient by a temporal adaptation mechanism. Nature 2008; 450:717-20. [PMID: 18046410 DOI: 10.1038/nature06347] [Citation(s) in RCA: 401] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2007] [Accepted: 10/03/2007] [Indexed: 01/04/2023]
Abstract
Morphogens act in developing tissues to control the spatial arrangement of cellular differentiation. The activity of a morphogen has generally been viewed as a concentration-dependent response to a diffusible signal, but the duration of morphogen signalling can also affect cellular responses. One such example is the morphogen sonic hedgehog (SHH). In the vertebrate central nervous system and limbs, the pattern of cellular differentiation is controlled by both the amount and the time of SHH exposure. How these two parameters are interpreted at a cellular level has been unclear. Here we provide evidence that changing the concentration or duration of SHH has an equivalent effect on intracellular signalling. Chick neural cells convert different concentrations of SHH into time-limited periods of signal transduction, such that signal duration is proportional to SHH concentration. This depends on the gradual desensitization of cells to ongoing SHH exposure, mediated by the SHH-dependent upregulation of patched 1 (PTC1), a ligand-binding inhibitor of SHH signalling. Thus, in addition to its role in shaping the SHH gradient, PTC1 participates cell autonomously in gradient sensing. Together, the data reveal a novel strategy for morphogen interpretation, in which the temporal adaptation of cells to a morphogen integrates the concentration and duration of a signal to control differential gene expression.
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Affiliation(s)
- Eric Dessaud
- Developmental Neurobiology, National Institute for Medical Research Mill Hill, London NW7 1AA, UK
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76
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Klimmeck D, Mayer U, Ungerer N, Warnken U, Schnölzer M, Frings S, Möhrlen F. Calcium-signaling networks in olfactory receptor neurons. Neuroscience 2007; 151:901-12. [PMID: 18155848 DOI: 10.1016/j.neuroscience.2007.11.023] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Revised: 10/31/2007] [Accepted: 11/16/2007] [Indexed: 01/03/2023]
Abstract
The olfactory neuroepithelium represents a unique interface between the brain and the external environment. Olfactory function comprises a distinct set of molecular tasks: sensory signal transduction, cytoprotection and adult neurogenesis. A multitude of biochemical studies has revealed the central role of Ca(2+) signaling in the function of olfactory receptor neurons (ORNs). We set out to establish Ca(2+)-dependent signaling networks in ORN cilia by proteomic analysis. We subjected a ciliary membrane preparation to Ca(2+)/calmodulin-affinity chromatography using mild detergent conditions in order to maintain functional protein complexes involved in olfactory Ca(2+) signaling. Thus, calmodulin serves as a valuable tool to gain access to novel Ca(2+)-regulated protein complexes. Tandem mass spectrometry (nanoscale liquid-chromatography-electrospray injection) identified 123 distinct proteins. Ninety-seven proteins (79%) could be assigned to specific olfactory functions, including 32 to sensory signal transduction and 40 to cytoprotection. We point out novel perspectives for research on the Ca(2+)-signaling networks in the olfactory system of the rat.
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Affiliation(s)
- D Klimmeck
- Department of Molecular Physiology, Institute of Zoology, University of Heidelberg, Im Neuenheimer Feld 230, 69120 Heidelberg, Germany
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77
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Olfactory clearance: what time is needed in clinical practice? The Journal of Laryngology & Otology 2007; 122:912-7. [DOI: 10.1017/s0022215107000977] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
AbstractObjective:To determine olfactory adaptation and clearance times for healthy individuals, and to assess the effect of common variables upon these parameters.Study design and setting:Fourteen healthy volunteers were recruited for a series of tests. Their initial olfactory threshold levels for phenethyl alcohol were determined. After olfactory exposure to a saturated solution of phenethyl alcohol (i.e. olfactory adaptation), the time taken for subjects to return to their initial olfactory threshold was then recorded (i.e. olfactory clearance). Visual analogue scale scores for subjective variables were also recorded.Results:The 14 subjects performed 120 tests in total. Despite consistent linear trends within individuals, olfactory clearance times varied widely within and between individuals. The mean olfactory clearance time for phenethyl alcohol was 170 seconds (range 81–750). Univariate analysis showed a relationship between olfactory clearance times and age (p = 0.031), symptoms (p = 0.029) and mood (p = 0.048).Conclusions:When testing a person's sense of smell in a clinical setting, recent exposure to similar smells should be noted, and a period of 15 minutes needs to be allowed before retesting if using phenethyl alcohol. Other variables need not be controlled, but greater clearance time may be needed for older patients.
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78
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Reisert J, Yau KW, Margolis FL. Olfactory marker protein modulates the cAMP kinetics of the odour-induced response in cilia of mouse olfactory receptor neurons. J Physiol 2007; 585:731-40. [PMID: 17932148 DOI: 10.1113/jphysiol.2007.142471] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Olfactory marker protein (OMP), a phylogenetically conserved protein, is highly, and almost exclusively, expressed in vertebrate olfactory receptor neurons (ORNs). Although OMP is widely used as a marker for ORNs, its function has remained largely elusive. Here we used suction-pipette recordings from isolated ORNs of OMP(-/-) mice to investigate its role in olfactory transduction. Vertebrate olfactory transduction is initiated when odourants bind to receptor proteins to activate an adenylyl cyclase via a G protein-coupled signalling pathway. This leads to an increase in cAMP and the opening of a cyclic nucleotide-gated (CNG), non-selective cation channel which depolarizes the cells. Ca(2+) influx through the CNG channel in turn activates a Ca(2+)-activated Cl(-) channel, causing a Cl(-) efflux and further depolarization. In the absence of OMP, the time-to-transient-peak of the response, the latency to first spike, and the response termination were slowed 2- to 8-fold, indicating its role in regulating olfactory response kinetics and termination. This phenotype persisted in OMP(-/-) ORNs even in low external Ca(2+) solution chosen to prevent Cl(-) channel activation, suggesting OMP acts upstream of Cl(-) channel activation. Furthermore, the response kinetics in cilia are virtually indistinguishable between OMP(-/-) and wild-type ORNs when intracellular cAMP level was elevated by the phospho-diesterase inhibitor, IBMX, suggesting OMP acts upstream of cAMP production. Together, our results suggest a role for OMP in regulating the kinetics and termination of olfactory responses, implicating a novel mechanism for fast and robust response termination to ensure the temporal resolution of the odour stimulus. These observations also help explain the deficits in odour detection threshold and odour quality discrimination seen in the OMP(-/-) mice.
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Affiliation(s)
- Johannes Reisert
- Department of Neuroscience, Johns Hopkins University School of Medicine, 725 N. Wolfe Street, Baltimore, MD 21205, USA.
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79
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Elsaesser R, Paysan J. The sense of smell, its signalling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells. BMC Neurosci 2007; 8 Suppl 3:S1. [PMID: 17903277 PMCID: PMC1995455 DOI: 10.1186/1471-2202-8-s3-s1] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existence of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use.
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Affiliation(s)
- Rebecca Elsaesser
- Johns Hopkins University School of Medicine, 725 N. Wolfe St., 408 WBSB, Baltimore, MD 21205, USA
| | - Jacques Paysan
- Technical University of Darmstadt, Institute of Zoology, Schnittspahnstrasse 3, D-64287 Darmstadt, Germany
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80
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Strassmaier T, Karpen JW. Novel N7- and N1-substituted cGMP derivatives are potent activators of cyclic nucleotide-gated channels. J Med Chem 2007; 50:4186-94. [PMID: 17665892 PMCID: PMC2597524 DOI: 10.1021/jm0702581] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels, key players in olfactory and visual signal transduction, generate electrical responses to odorant- and light-induced changes in cyclic nucleotide concentration. Previous work suggests that substitutions are tolerated solely at the C8 position on the purine ring of cGMP. Our studies with C8, 2'-OH, and 2-NH2-modified cGMP derivatives support this assertion. To gain further insight into determinants important for CNG channel binding and activation, we targeted previously unexplored positions. Modifications at N7 of 8-SH-cGMP (6) are well tolerated by olfactory and retinal rod CNG channels. Toleration of a very large substituent, a 3400 molecular weight PEG, at either N7 or C8 argues for broad accommodation at these positions in the binding site. Modification at N1 of cGMP reduces the apparent affinity for the channel; however, when combined with 8-parachlorophenylthio derivatization, the resulting cGMP analogue is more potent than cGMP itself. These studies establish the N7 and N1 positions of cGMP as targets for modification in the design of novel CNG channel agonists.
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Affiliation(s)
| | - Jeffrey W. Karpen
- Corresponding author: Jeffrey W. Karpen, Phone 503-494-7463. E-mail:
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81
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Assisi C, Stopfer M, Laurent G, Bazhenov M. Adaptive regulation of sparseness by feedforward inhibition. Nat Neurosci 2007; 10:1176-84. [PMID: 17660812 PMCID: PMC4061731 DOI: 10.1038/nn1947] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Accepted: 06/26/2007] [Indexed: 11/10/2022]
Abstract
In the mushroom body of insects, odors are represented by very few spikes in a small number of neurons, a highly efficient strategy known as sparse coding. Physiological studies of these neurons have shown that sparseness is maintained across thousand-fold changes in odor concentration. Using a realistic computational model, we propose that sparseness in the olfactory system is regulated by adaptive feedforward inhibition. When odor concentration changes, feedforward inhibition modulates the duration of the temporal window over which the mushroom body neurons may integrate excitatory presynaptic input. This simple adaptive mechanism could maintain the sparseness of sensory representations across wide ranges of stimulus conditions.
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Affiliation(s)
- Collins Assisi
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, California 92037, USA
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82
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Boccaccio A, Menini A. Temporal development of cyclic nucleotide-gated and Ca2+ -activated Cl- currents in isolated mouse olfactory sensory neurons. J Neurophysiol 2007; 98:153-60. [PMID: 17460108 DOI: 10.1152/jn.00270.2007] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A Ca(2+)-activated Cl(-) current constitutes a large part of the transduction current in olfactory sensory neurons. The binding of odorants to olfactory receptors in the cilia produces an increase in cAMP concentration; Ca(2+) enters into the cilia through CNG channels and activates a Cl(-) current. In intact mouse olfactory sensory neurons little is known about the kinetics of the Ca(2+)-activated Cl(-) current. Here, we directly activated CNG channels by flash photolysis of caged cAMP or 8-Br-cAMP and measured the current response with the whole cell voltage-clamp technique in mouse neurons. We measured multiphasic currents in the rising phase of the response at -50 mV. The current rising phase became monophasic in the absence of extracellular Ca(2+), at +50 mV, or when most of the intracellular Cl(-) was replaced by gluconate to shift the equilibrium potential for Cl(-) to -50 mV. These results show that the second phase of the current in mouse intact neurons is attributed to a Cl(-) current activated by Ca(2+), similarly to previous results on isolated frog cilia. The percentage of the total saturating current carried by Cl(-) was estimated in two ways: 1) by measuring the maximum secondary current and 2) by blocking the Cl(-) channel with niflumic acid. We estimated that in the presence of 1 mM extracellular Ca(2+) and in symmetrical Cl(-) concentrations the Cl(-) component can constitute up to 90% of the total current response. These data show how to unravel the CNG and Ca(2+)-activated Cl(-) component of the current rising phase.
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Affiliation(s)
- Anna Boccaccio
- International School for Advanced Studies, SISSA, Sector of Neurobiology, Basovizza, Trieste, Italy.
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83
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Antolin S, Matthews HR. The effect of external sodium concentration on sodium-calcium exchange in frog olfactory receptor cells. J Physiol 2007; 581:495-503. [PMID: 17379630 PMCID: PMC2075203 DOI: 10.1113/jphysiol.2007.131094] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
During the response of vertebrate olfactory receptor cells to stimulation, Ca(2+) enters the cilia via cyclic nucleotide-gated channels and is extruded by Na(+)-Ca(2+) exchange. The rise in Ca(2+) concentration opens a Ca(2+)-activated Cl(-) conductance which carries most of the inward receptor current. The dependence of Ca(2+) extrusion upon external Na(+) concentration was studied by using the falling phase of the Ca(2+)-activated Cl(-) current following a brief exposure to the phosphodiesterase inhibitor IBMX to monitor indirectly the decay in intraciliary Ca(2+) concentration. External Na(+) concentration was reduced by partial substitution with guanidinium, an ion which permeates the cyclic nucleotide-gated channel but does not support Na(+)-Ca(2+) exchange. The time constant describing the decay in current following IBMX stimulation was surprisingly little affected by substitution of external Na(+), being substantially retarded only when its concentration was reduced to a third or less of its normal value in Ringer solution. When the cilia were returned to Ringer solution after a period in reduced-Na(+) solution, the time constant for the final decay of current was similar to that seen when returning immediately to IBMX-free Ringer solution. This observation suggests that Ca(2+) extrusion via Na(+)-Ca(2+) exchange dominates the falling phase of the response to IBMX, which can therefore be used to assess exchanger activity. Rate constants derived from the time constants for current decay at different external Na(+) concentrations could be fitted by the Hill equation with a K(d) of 54 +/- 4 mm and Hill coefficient of 3.7 +/- 0.4. The cooperativity of the dependence upon external Na(+) concentration indicates that at least three Na(+) ions enter for each exchanger cycle, while the high affinity for external Na(+) contrasts with the photoreceptor and cardiac exchangers. The functional importance of this observation is that the relative insensitivity of the Na(+)-Ca(2+) exchanger to external Na(+) concentration allows normal response termination even following partial dilution or concentration of the olfactory mucus.
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Affiliation(s)
- Salome Antolin
- Physiological Laboratory, Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK
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84
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Pelz D, Roeske T, Syed Z, de Bruyne M, Galizia CG. The molecular receptive range of an olfactory receptor in vivo (Drosophila melanogaster Or22a). ACTA ACUST UNITED AC 2007; 66:1544-63. [PMID: 17103386 DOI: 10.1002/neu.20333] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Understanding how odors are coded within an olfactory system requires knowledge about its input. This is constituted by the molecular receptive ranges (MRR) of olfactory sensory neurons that converge in the glomeruli of the olfactory bulb (vertebrates) or the antennal lobe (AL, insects). Aiming at a comprehensive characterization of MRRs in Drosophila melanogaster we measured odor-evoked calcium responses in olfactory sensory neurons that express the olfactory receptor Or22a. We used an automated stimulus application system to screen [Ca(2+)] responses to 104 odors both in the antenna (sensory transduction) and in the AL (neuronal transmission). At 10(-2) (vol/vol) dilution, 39 odors elicited at least a half-maximal response. For these odorants we established dose-response relationships over their entire dynamic range. We tested 15 additional chemicals that are structurally related to the most efficient odors. Ethyl hexanoate and methyl hexanoate were the best stimuli, eliciting consistent responses at dilutions as low as 10(-9). Two substances led to calcium decrease, suggesting that Or22a might be constitutively active, and that these substances might act as inverse agonists, reminiscent of G-protein coupled receptors. There was no difference between the antennal and the AL MRR. Furthermore we show that Or22a has a broad yet selective MRR, and must be functionally described both as a specialist and a generalist. Both these descriptions are ecologically relevant. Given that adult Drosophila use approximately 43 ORs, a complete description of all MRRs appears now in reach.
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Affiliation(s)
- Daniela Pelz
- Institut für Neurobiologie, Freie Universität Berlin, D-14195 Berlin, Germany
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85
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Pézier A, Acquistapace A, Renou M, Rospars JP, Lucas P. Ca2+ stabilizes the membrane potential of moth olfactory receptor neurons at rest and is essential for their fast repolarization. Chem Senses 2007; 32:305-17. [PMID: 17267420 DOI: 10.1093/chemse/bjl059] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The role of Ca(2+) in insect olfactory transduction was studied in the moth Spodoptera littoralis. Single sensillum recordings were made to investigate in vivo the role of sensillar Ca(2+) on the electrophysiological properties of sex pheromone responsive olfactory receptor neurons (ORNs). Lowering the sensillar Ca(2+) concentration to 2 x 10(-8) M increased ORN spontaneous firing activity and induced long bursts of action potentials (APs) superimposed on spontaneous negative deflections of the transepithelial potential. We inferred that Ca(2+) stabilizes the membrane potential of ORNs, keeping the spontaneous firing activity at a low and regular level. Neither the amplitude and kinetics of the rising phase of sensillar potentials (SPs) recorded in response to pheromone stimuli nor the AP generation during stimulation depended on the extracellular Ca(2+) concentration. Thus, extracellular Ca(2+) is not absolutely necessary for ORN response. Partial inhibition of responses with a calmodulin antagonist, W-7, also indicates that intracellular Ca(2+) contributes to the ORN response and suggests that Ca(2+) release from internal stores is involved. In 2 x 10(-8) M Ca(2+), the repolarization of the SP was delayed when compared with higher Ca(2+) concentrations. Therefore, in contrast to depolarization, ORN repolarization depends on extracellular Ca(2+). Ca(2+)-gated K(+) channels identified from cultured ORNs with whole-cell recordings are good candidates to mediate ORN repolarization.
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Affiliation(s)
- Adeline Pézier
- UMR1272 Physiologie de l'Insecte: Signalisation et Communication, INRA, Route de St Cyr, 78026 Versailles Cedex, France
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86
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Chen TY, Takeuchi H, Kurahashi T. Odorant inhibition of the olfactory cyclic nucleotide-gated channel with a native molecular assembly. ACTA ACUST UNITED AC 2006; 128:365-71. [PMID: 16940558 PMCID: PMC2151561 DOI: 10.1085/jgp.200609577] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Human olfaction comprises the opposing actions of excitation and inhibition triggered by odorant molecules. In olfactory receptor neurons, odorant molecules not only trigger a G-protein–coupled signaling cascade but also generate various mechanisms to fine tune the odorant-induced current, including a low-selective odorant inhibition of the olfactory signal. This wide-range olfactory inhibition has been suggested to be at the level of ion channels, but definitive evidence is not available. Here, we report that the cyclic nucleotide-gated (CNG) cation channel, which is a key element that converts odorant stimuli into electrical signals, is inhibited by structurally unrelated odorants, consistent with the expression of wide-range olfactory inhibition. Interestingly, the inhibitory effect was small in the homo-oligomeric CNG channel composed only of the principal channel subunit, CNGA2, but became larger in channels consisting of multiple types of subunits. However, even in the channel containing all native subunits, the potency of the suppression on the cloned CNG channel appeared to be smaller than that previously shown in native olfactory neurons. Nonetheless, our results further showed that odorant suppressions are small in native neurons if the subsequent molecular steps mediated by Ca2+ are removed. Thus, the present work also suggests that CNG channels switch on and off the olfactory signaling pathway, and that the on and off signals may both be amplified by the subsequent olfactory signaling steps.
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Affiliation(s)
- Tsung-Yu Chen
- Center for Neuroscience and Department of Neurology, University of California, Davis, CA 95616, USA.
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87
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Gautam SH, Otsuguro KI, Ito S, Saito T, Habara Y. T-type Ca2+ channels mediate propagation of odor-induced Ca2+ transients in rat olfactory receptor neurons. Neuroscience 2006; 144:702-13. [PMID: 17110049 DOI: 10.1016/j.neuroscience.2006.10.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2006] [Revised: 10/07/2006] [Accepted: 10/09/2006] [Indexed: 11/26/2022]
Abstract
Propagation of odor-induced Ca(2+) transients from the cilia/knob to the soma in mammalian olfactory receptor neurons (ORNs) is thought to be mediated exclusively by high-voltage-activated Ca(2+) channels. However, using confocal Ca(2+) imaging and immunocytochemistry we identified functional T-type Ca(2+) channels in rat ORNs. Here we show that T-type Ca(2+) channels in ORNs also mediate propagation of odor-induced Ca(2+) transients from the knob to the soma. In the presence of the selective inhibitor of T-type Ca(2+) channels mibefradil (10-15 microM) or Ni(2+) (100 microM), odor- and forskolin/3-isobutyl-1-methyl-xanthine (IBMX)-induced Ca(2+) transients in the soma and dendrite were either strongly inhibited or abolished. The percentage of inhibition of the Ca(2+) transients in the knob, however, was 40-50% less than that in the soma. Ca(2+) transients induced by 30 mM K(+) were partially inhibited by mibefradil, but without a significant difference in the extent of inhibition between the knob and soma. Furthermore, an increase of as little as 2.5 mM in the extracellular K(+) concentration (7.5 mM K(+)) was found to induce Ca(2+) transients in ORNs, and such responses were completely inhibited by mibefradil or Ni(2+). Total replacement of extracellular Na(+) with N-methyl-d-glutamate inhibited none of the odor-, forskolin/IBMX- or 7.5 mM K(+)-induced Ca(2+) transients. Positive immunoreactivity to the Ca(v)3.1, Ca(v)3.2 and Ca(v)3.3 subunits of the T-type Ca(2+) channel was observed throughout the soma, dendrite and knob. These data suggest that involvement of T-type Ca(2+) channels in the propagation of odor-induced Ca(2+) transients in ORNs may contribute to signal transduction and odor sensitivity.
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Affiliation(s)
- S H Gautam
- Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan
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88
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Gautam SH, Otsuguro KI, Ito S, Saito T, Habara Y. T-type Ca2+ channels contribute to IBMX/forskolin- and K(+)-induced Ca(2+) transients in porcine olfactory receptor neurons. Neurosci Res 2006; 57:129-39. [PMID: 17074407 DOI: 10.1016/j.neures.2006.09.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2006] [Revised: 09/15/2006] [Accepted: 09/25/2006] [Indexed: 01/08/2023]
Abstract
T-type Ca(2+) channels are low-voltage-activated Ca(2+) channels that control Ca(2+) entry in excitable cells during small depolarization above resting potentials. Using Ca(2+) imaging with a laser scanning confocal microscope we investigated the involvement of T-type Ca(2+) channels in IBMX/forskolin- and sparingly elevated extracellular K(+)-induced Ca(2+) transients in freshly isolated porcine olfactory receptor neurons (ORNs). In the presence of mibefradil (10microM) or Ni(2+) (100microM), the selective T-type Ca(2+) channel inhibitors, IBMX/forskolin-induced Ca(2+) transients in the soma were either strongly (>60%) inhibited or abolished completely. However, the Ca(2+) transients in the knob were only partially (<60%) inhibited. Ca(2+) transients induced by 30mM K(+) were also partially ( approximately 60%) inhibited at both the knob and soma. Furthermore, ORNs responded to as little as a 2.5mM increase in the extracellular K(+) concentration (7.5mM K(+)), and such responses were completely inhibited by mibefradil or Ni(2+). These results reveal functional expression of T-type Ca(2+) channels in porcine ORNs, and suggest a role for these channels in the spread Ca(2+) transients from the knob to the soma during activation of the cAMP cascade following odorant binding to G-protein-coupled receptors on the cilia/knob of ORNs.
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Affiliation(s)
- Shree Hari Gautam
- Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
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89
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Boccaccio A, Lagostena L, Hagen V, Menini A. Fast adaptation in mouse olfactory sensory neurons does not require the activity of phosphodiesterase. ACTA ACUST UNITED AC 2006; 128:171-84. [PMID: 16880265 PMCID: PMC2151529 DOI: 10.1085/jgp.200609555] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Vertebrate olfactory sensory neurons rapidly adapt to repetitive odorant stimuli. Previous studies have shown that the principal molecular mechanisms for odorant adaptation take place after the odorant-induced production of cAMP, and that one important mechanism is the negative feedback modulation by Ca2+-calmodulin (Ca2+-CaM) of the cyclic nucleotide-gated (CNG) channel. However, the physiological role of the Ca2+-dependent activity of phosphodiesterase (PDE) in adaptation has not been investigated yet. We used the whole-cell voltage-clamp technique to record currents in mouse olfactory sensory neurons elicited by photorelease of 8-Br-cAMP, an analogue of cAMP commonly used as a hydrolysis-resistant compound and known to be a potent agonist of the olfactory CNG channel. We measured currents in response to repetitive photoreleases of cAMP or of 8-Br-cAMP and we observed similar adaptation in response to the second stimulus. Control experiments were conducted in the presence of the PDE inhibitor IBMX, confirming that an increase in PDE activity was not involved in the response decrease. Since the total current activated by 8-Br-cAMP, as well as that physiologically induced by odorants, is composed not only of current carried by Na+ and Ca2+ through CNG channels, but also by a Ca2+-activated Cl− current, we performed control experiments in which the reversal potential of Cl− was set, by ion substitution, at the same value of the holding potential, −50 mV. Adaptation was measured also in these conditions of diminished Ca2+-activated Cl− current. Furthermore, by producing repetitive increases of ciliary's Ca2+ with flash photolysis of caged Ca2+, we showed that Ca2+-activated Cl− channels do not adapt and that there is no Cl− depletion in the cilia. All together, these results indicate that the activity of ciliary PDE is not required for fast adaptation to repetitive stimuli in mouse olfactory sensory neurons.
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Affiliation(s)
- Anna Boccaccio
- International School for Advanced Studies, S.I.S.S.A., Sector of Neurobiology, 34014 Trieste, Italy.
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90
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Zimmerman AL. The sweet smell of success: Conclusive evidence that cyclic AMP hydrolysis does not trigger fast adaptation in olfactory receptor cells. ACTA ACUST UNITED AC 2006; 128:149-51. [PMID: 16880264 PMCID: PMC2151528 DOI: 10.1085/jgp.200609626] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Affiliation(s)
- Anita L Zimmerman
- Department of Molecular Pharmacology and Physiology, Brown University Medical School, Providence, RI 02912, USA.
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91
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Michalakis S, Reisert J, Geiger H, Wetzel C, Zong X, Bradley J, Spehr M, Hüttl S, Gerstner A, Pfeifer A, Hatt H, Yau KW, Biel M. Loss of CNGB1 protein leads to olfactory dysfunction and subciliary cyclic nucleotide-gated channel trapping. J Biol Chem 2006; 281:35156-66. [PMID: 16980309 PMCID: PMC2885922 DOI: 10.1074/jbc.m606409200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Olfactory receptor neurons (ORNs) employ a cyclic nucleotide-gated (CNG) channel to generate a receptor current in response to an odorant-induced rise in cAMP. This channel contains three types of subunits, the principal CNGA2 subunit and two modulatory subunits (CNGA4 and CNGB1b). Here, we have analyzed the functional relevance of CNGB1 for olfaction by gene targeting in mice. Electro-olfactogram responses of CNGB1-deficient (CNGB1-/-) mice displayed a reduced maximal amplitude and decelerated onset and recovery kinetics compared with wild-type mice. In a behavioral test, CNGB1-/- mice exhibited a profoundly decreased olfactory performance. Electrophysiological recordings revealed that ORNs of CNGB1-/- mice weakly expressed a CNG current with decreased cAMP sensitivity, very rapid flicker-gating behavior and no fast modulation by Ca2+-calmodulin. Co-immunoprecipitation confirmed the presence of a CNGA2/CNGA4 channel in the olfactory epithelium of CNGB1-/- mice. This CNGA2/CNGA4 channel was targeted to the plasma membrane of olfactory knobs, but failed to be trafficked into olfactory cilia. Interestingly, we observed a similar trafficking defect in mice deficient for the CNGA4 subunit. In conclusion, these results demonstrate that CNGB1 has a dual function in vivo. First, it endows the olfactory CNG channel with a variety of biophysical properties tailored to the specific requirements of olfactory transduction. Second, together with the CNGA4 subunit, CNGB1 is needed for ciliary targeting of the olfactory CNG channel.
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Affiliation(s)
- Stylianos Michalakis
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
| | - Johannes Reisert
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Heidi Geiger
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
| | - Christian Wetzel
- Lehrstuhl für Zellphysiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - Xiangang Zong
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
| | - Jonathan Bradley
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Marc Spehr
- Lehrstuhl für Zellphysiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - Sabine Hüttl
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
| | - Andrea Gerstner
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
| | - Alexander Pfeifer
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
| | - Hanns Hatt
- Lehrstuhl für Zellphysiologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
| | - King-Wai Yau
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Martin Biel
- Department Pharmazie, Zentrum für Pharmaforschung, Ludwig-Maximilians Universität München, D-81377 München, Germany
- To whom correspondence should be addressed: Dept. Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 7, D-81377 München, Germany. Tel.: 49-89-2180-77327; Fax: 49-89-2180-77326;
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92
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Pifferi S, Pascarella G, Boccaccio A, Mazzatenta A, Gustincich S, Menini A, Zucchelli S. Bestrophin-2 is a candidate calcium-activated chloride channel involved in olfactory transduction. Proc Natl Acad Sci U S A 2006; 103:12929-34. [PMID: 16912113 PMCID: PMC1568948 DOI: 10.1073/pnas.0604505103] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Ca-activated Cl channels are an important component of olfactory transduction. Odor binding to olfactory receptors in the cilia of olfactory sensory neurons (OSNs) leads to an increase of intraciliary Ca concentration by Ca entry through cyclic nucleotide-gated (CNG) channels. Ca activates a Cl channel that leads to an efflux of Cl from the cilia, contributing to the amplification of the OSN depolarization. The molecular identity of this Cl channel remains elusive. Recent evidence has indicated that bestrophins are able to form Ca-activated Cl channels in heterologous systems. Here we have analyzed the expression of bestrophins in the mouse olfactory epithelium and demonstrated that only mouse bestrophin-2 (mBest2) was expressed. Single-cell RT-PCR showed that mBest2 was expressed in OSNs but not in supporting cells. Immunohistochemistry revealed that mBest2 was expressed on the cilia of OSNs, the site of olfactory transduction, and colocalized with the main CNGA2 channel subunit. Electrophysiological properties of Ca-activated Cl currents from native channels in dendritic knob/cilia of mouse OSNs were compared with those induced by the expression of mBest2 in HEK-293 cells. We found the same anion permeability sequence, small estimated single-channel conductances, a Ca sensitivity difference of one order of magnitude, and the same side-specific blockage of the two Cl channel blockers commonly used to inhibit the odorant-induced Ca-activated Cl current in OSNs, niflumic acid, and 4-acetamido-4'-isothiocyanato-stilben-2,2'-disulfonate (SITS). Therefore, our data suggest that mBest2 is a good candidate for being a molecular component of the olfactory Ca-activated Cl channel.
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Affiliation(s)
- Simone Pifferi
- *Sector of Neurobiology, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy; and
| | - Giovanni Pascarella
- Giovanni Armenise–Harvard Foundation Laboratory, Sector of Neurobiology, International School for Advanced Studies (SISSA), AREA Science Park, S.S. 14, Km 163.5, Basovizza, 34012 Trieste, Italy
| | - Anna Boccaccio
- *Sector of Neurobiology, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy; and
| | - Andrea Mazzatenta
- *Sector of Neurobiology, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy; and
| | - Stefano Gustincich
- Giovanni Armenise–Harvard Foundation Laboratory, Sector of Neurobiology, International School for Advanced Studies (SISSA), AREA Science Park, S.S. 14, Km 163.5, Basovizza, 34012 Trieste, Italy
| | - Anna Menini
- *Sector of Neurobiology, International School for Advanced Studies (SISSA), Via Beirut 2-4, 34014 Trieste, Italy; and
- To whom correspondence should be addressed. E-mail:
| | - Silvia Zucchelli
- Giovanni Armenise–Harvard Foundation Laboratory, Sector of Neurobiology, International School for Advanced Studies (SISSA), AREA Science Park, S.S. 14, Km 163.5, Basovizza, 34012 Trieste, Italy
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93
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Gautam SH, Otsuguro KI, Ito S, Saito T, Habara Y. Intensity of odorant stimulation affects mode of Ca2+ dynamics in rat olfactory receptor neurons. Neurosci Res 2006; 55:410-20. [PMID: 16730825 DOI: 10.1016/j.neures.2006.04.012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2006] [Revised: 04/18/2006] [Accepted: 04/19/2006] [Indexed: 10/24/2022]
Abstract
We investigated the relation between the intensity of odorant stimulation and the mode of spatiotemporal Ca(2+) dynamics in Fluo-4-loaded rat olfactory receptor neurons (ORNs) using a confocal laser scanning microscope. We found that relatively smaller Ca(2+) transients remained confined to the knob while larger ones spread to the soma with latency. Prolonged odor exposure ensured the spread of Ca(2+) transients from the knob to the soma. Upon exposing ORNs to progressively increasing concentrations of odor, the Ca(2+) transients that were confined to the knob at lower concentrations extended to the soma at higher concentrations. Stimulation with progressively increasing concentrations of forskolin plus IBMX yielded identical results. Partial inhibition of adenylyl cyclase by MDL12330A changed the odor response extending to the soma to a response confined to the knob. Blocking of L-type Ca(2+) channels by nifedipine reduced the magnitude of the response extending to the soma but had no effect on the response confined to the knob. It is thus suggested that Ca(2+) transients confined to the knob represent weak stimulation, and, speculatively, such responses either constitute inhibitory responses or indicate weak excitatory responses that fail to outstand the spontaneous electrical noise of ORNs.
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Affiliation(s)
- Shree Hari Gautam
- Laboratory of Physiology, Department of Biomedical Sciences, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo 060-0818, Japan
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94
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Pifferi S, Boccaccio A, Menini A. Cyclic nucleotide-gated ion channels in sensory transduction. FEBS Lett 2006; 580:2853-9. [PMID: 16631748 DOI: 10.1016/j.febslet.2006.03.086] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2006] [Accepted: 03/31/2006] [Indexed: 11/16/2022]
Abstract
Cyclic nucleotide-gated (CNG) channels, directly activated by the binding of cyclic nucleotides, were first discovered in retinal rods, cones and olfactory sensory neurons. In the visual and olfactory systems, CNG channels mediate sensory transduction by conducting cationic currents carried primarily by sodium and calcium ions. In olfactory transduction, calcium in combination with calmodulin exerts a negative feedback on CNG channels that is the main molecular mechanism responsible for fast adaptation in olfactory sensory neurons. Six mammalian CNG channel genes are known and some human visual disorders are caused by mutations in retinal rod or cone CNG genes.
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Affiliation(s)
- Simone Pifferi
- International School for Advanced Studies, S.I.S.S.A., Sector of Neurobiology, Via Beirut 2-4, 34014 Trieste, Italy
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95
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Abstract
Molecular mechanisms underlying olfactory signal amplification were investigated by monitoring cAMP dynamics in the intact sensory cilia. We saw that [cAMP]i increased superlinearly with time during odorant stimuli for >1 s. This time course was remarkably different from that obtained with the rapid quench method previously applied to the in vitro preparation, in which [cAMP]i change has been reported to be transient. The superlinear increase of [cAMP]i was attributable to a gradual increase of cAMP production rate that was consistent with the thermodynamical interaction model between elemental molecules, as has been revealed on the rod photoreceptor cell. It thus seems likely that the fundamental mechanism for molecular interactions between olfactory transduction elements is similar to that of the rod. In olfaction, however, cAMP production was extremely small (approximately 200,000 molecules/s/cell at the maximum), in contrast to the cGMP hydrolysis in the rod (250,000 molecules/photon). The observed numbers indicate that the olfactory receptor cell has lower amplification at the enzymatic cascade. Seemingly, such low amplification is a disadvantage for the signal transduction, but this unique mechanism would be essential to reduce the loss of ATP that is broadly used for the activities of cells. Apparently, transduction by a smaller number of second-messenger formations would be achieved by the fine ciliary structure that has a high surface-volume ratio. In addition, it is speculated that this low amplification at their enzymatic processes may be the reason why the olfactory receptor cell has acquired high amplification at the final stage of transduction channels, using Ca2+ as a third messenger.
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Affiliation(s)
- Hiroko Takeuchi
- Department of Frontier Biosciences, Osaka University, Toyonaka, Osaka 560-8531, Japan.
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96
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Gomez-Diaz C, Martin F, Alcorta E. The Inositol 1,4,5-triphosphate kinase1 gene affects olfactory reception in Drosophila melanogaster. Behav Genet 2006; 36:309-21. [PMID: 16463070 DOI: 10.1007/s10519-005-9031-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Accepted: 06/14/2005] [Indexed: 10/25/2022]
Abstract
The Inositol 1,4,5-triphosphate (IP3) route is one of the two main transduction cascades that mediate olfactory reception in Drosophila melanogaster. The activity of IP3 kinase1 reduces the levels of this substrate by phosphorylation into inositol 1,3,4,5-tetrakiphosphate (IP4). We show here that the gene is expressed in olfactory sensory organs as well as in the rest of the head. To evaluate in vivo the olfactory functional effects of up-regulating IP3K1, individuals with directed genetic changes at the reception level only were generated using the UAS/Gal4 method. In this report, we described the consequences in olfactory perception of overexpressing the IP3Kinase1 gene at eight different olfactory receptor-neuron subsets. Six out of the eight studied Gal-4/UAS-IP3K1 hybrids displayed abnormal behavioral responses to ethyl acetate, acetone, ethanol or propionaldehyde. Specific behavioral defects corresponded to the particular neuronal olfactory profile. These data confirm the role of the IP3kinase1 gene, and consequently the IP3 transduction cascade, in mediating olfactory information at the reception level.
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Affiliation(s)
- Carolina Gomez-Diaz
- Depto. Biologia Funcional, Genetica, Fac. Medicina, Universidad de Oviedo, C/ Julian Claveria s/n, 33.006, Oviedo, Spain
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97
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Brown RL, Strassmaier T, Brady JD, Karpen JW. The pharmacology of cyclic nucleotide-gated channels: emerging from the darkness. Curr Pharm Des 2006; 12:3597-613. [PMID: 17073662 PMCID: PMC2467446 DOI: 10.2174/138161206778522100] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cyclic nucleotide-gated (CNG) ion channels play a central role in vision and olfaction, generating the electrical responses to light in photoreceptors and to odorants in olfactory receptors. These channels have been detected in many other tissues where their functions are largely unclear. The use of gene knockouts and other methods have yielded some information, but there is a pressing need for potent and specific pharmacological agents directed at CNG channels. To date there has been very little systematic effort in this direction - most of what can be termed CNG channel pharmacology arose from testing reagents known to target protein kinases or other ion channels, or by accident when researchers were investigating other intracellular pathways that may regulate the activity of CNG channels. Predictably, these studies have not produced selective agents. However, taking advantage of emerging structural information and the increasing knowledge of the biophysical properties of these channels, some promising compounds and strategies have begun to emerge. In this review we discuss progress on two fronts, cyclic nucleotide analogs as both activators and competitive inhibitors, and inhibitors that target the pore or gating machinery of the channel. We also discuss the potential of these compounds for treating certain forms of retinal degeneration.
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Affiliation(s)
- R. Lane Brown
- Neurological Sciences Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Timothy Strassmaier
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA
| | - James D. Brady
- Neurological Sciences Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Jeffrey W. Karpen
- Department of Physiology and Pharmacology, Oregon Health & Science University, Portland, OR 97239, USA
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98
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Abstract
SUMMARY
In order to reveal aspects of olfactory coding, the effects of sensory adaptation on the olfactory responses of first-instar Drosophila melanogaster larvae were tested. Larvae were pre-stimulated with a homologous series of acetic esters (C3-C9), and their responses to each of these odours were then measured. The overall patterns suggested that methyl acetate has no specific pathway but was detected by all the sensory pathways studied here, that butyl and pentyl acetate tended to have similar effects to each other and that hexyl acetate was processed separately from the other odours. In a number of cases, cross-adaptation transformed a control attractive response into a repulsive response; in no case was an increase in attractiveness observed. This was investigated by studying changes in dose-response curves following pre-stimulation. These findings are discussed in light of the possible intra- and intercellular mechanisms of adaptation and the advantage of altered sensitivity for the larva.
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Affiliation(s)
- Jennefer Boyle
- Faculty of Life Sciences, The University of Manchester, Oxford Road, Manchester M13 9PT, UK
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99
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Norlin EM, Vedin V, Bohm S, Berghard A. Odorant-dependent, spatially restricted induction of c-fos in the olfactory epithelium of the mouse. J Neurochem 2005; 93:1594-602. [PMID: 15935076 DOI: 10.1111/j.1471-4159.2005.03159.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Volatile odorous chemicals are detected by around a thousand different G protein-coupled odorant receptors in the mouse. We demonstrated that exposure of the behaving mouse to odorant for a few minutes led to induction of the immediate early gene c-fos for several hours in a fraction of the olfactory sensory neurones in the nasal cavity. Associated with this odorant-specific induction event was activation of extracellular-regulated kinase (ERK)1/2 that preceded increased c-fos expression. The distribution of odorant-activated neurones mimicked the scattered and spatially limited distribution of neurones expressing a single odorant receptor gene. A small change in odorant chemical structure caused a zonal shift in the spatial distribution of activated neurones, suggesting that the gene expression change resulted from specific receptor interaction. Repeated exposure to odorant or use of different concentrations did not change the pattern of c-fos induction. These results indicate that odorant-induced c-fos expression can be used to visualize odorant representations in the olfactory epithelium that reflect late cellular events regulated by adequate odorant receptor stimulation.
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100
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Dougherty DP, Wright GA, Yew AC. Computational model of the cAMP-mediated sensory response and calcium-dependent adaptation in vertebrate olfactory receptor neurons. Proc Natl Acad Sci U S A 2005; 102:10415-20. [PMID: 16027364 PMCID: PMC1180786 DOI: 10.1073/pnas.0504099102] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We develop a mechanistic mathematical model of the G-protein coupled signaling pathway responsible for generating current responses in frog olfactory receptor neurons. The model incorporates descriptions of ligand-receptor interaction, intracellular transduction events involving the second messenger cAMP, effector ion-channel activity, and calcium-mediated feedback steps. We parameterized the model with respect to suction pipette current recordings from single cells stimulated with multiple odor concentrations. The proposed model accurately predicts the receptor-current response of the neuron to brief and prolonged odorant exposure and is able to produce the adaptation observed under repeated or sustained stimulation.
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Affiliation(s)
- Daniel P Dougherty
- Mathematical Biosciences Institute, Ohio State University, Columbus, OH 43210, USA
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