Kegg Pathway: Olfactory transduction

Environ Sci Technol. 2009 Nov 1; 43(21): 8393-8399
Kolmakov NN, Hubbard PC, Lopes O, Canario AV

Exposure of Olfactory epithelium to environmentally relevant concentrations of copper disrupts olfaction in fish. To examine the dynamics of recovery at both functional and morphological levels after acute copper exposure, unilateral exposure of goldfish Olfactory epithelia to 100 muM CuSO(4) (10 min) was followed by electro-olfactogram (EOG) recording and scanning electron microscopy. Sensitivity to amino acids (l-arginine and l-serine), generally considered food-related odorants, recovered most rapidly (three days), followed by that to catecholamines (3-O-methoxytyramine), bile acids (taurolithocholic acid) and the steroid pheromone, 17,20beta-dihydroxy-4-pregnen-3-one 20-sulfate, which took 28 days to reach full recovery. Sensitivity to the postovulatory pheromone prostaglandin F(2alpha) had not fully recovered even at 28 days. These changes in sensitivity were correlated with changes in the recovery of ciliated and microvillous receptor cell types. Microvillous cells appeared largely unaffected by CuSO(4) treatment. Cilia in ciliated receptor neurones, however, appeared damaged one day post-treatment and were virtually absent after three days but had begun to recover after 14 days. Together, these results support the hypothesis that microvillous receptor neurones detect amino acids whereas ciliated receptor neurones were not functional and are responsible for detection of social stimuli (bile acids and pheromones). Furthermore, differences in sensitivity to copper may be due to different transduction pathways in the different cell types.

Fly (Austin). 2009 Oct 6; 3(4):
Rattner BP

As has become tradition, this year's Southern California Drosophila Conference was hosted by the Developmental Biology Center (http://dbc.bio.uci.edu/) at the University of California, Irvine. On September 11, 2009, speakers from institutions in Los Angeles, Orange, Riverside, and San Diego Counties presented their latest results in an informal and friendly atmosphere and had the opportunity to learn about new resources and facilities, establish collaborations, and network about job openings and training opportunities. The talks presented covered the use of flies to study a variety of topics including the mechanisms of action of human pathogens, human diseases, and aging and lifespan extension. In addition, attendees heard about aspects of Drosophila neuronal development, Olfactory behavior, transcriptional regulation, and signal transduction. Some of the highlights of the meeting are summarized in this brief report.

Mol Cell Biochem. 2009 Nov 15;
Jankowska A, Warchol JB

To date, the calcium-regulated membrane guanylate cyclase Rod Outer Segment Guanylate Cyclase type 1 (ROS-GC1) transduction system in addition to photoreceptors is known to be expressed in three other types of neuronal cells: in the pinealocytes, mitral cells of the Olfactory bulb and the gustatory epithelium of tongue. Very recent studies from our laboratory show that expression of ROS-GC1 is not restricted to the neuronal cells; the male gonads and the spermatozoa also express ROS-GC1. In this presentation, the authors review the existing information on the localization and function of guanylate cyclase with special emphasis on Ca(2+)-modulated membrane guanylate cyclase, ROS-GC1, in the testes. The role of ROS-GC1 and its Ca(2+)-sensing modulators in the processes of spermatogenesis and fertilization are discussed.

Front Cell Neurosci. 2009; 3: 11
Fenech C, Patrikainen L, Kerr DS, Grall S, Liu Z, Laugerette F, Malnic B, Montmayeur JP

Taste receptors for sweet, bitter and umami tastants are G-protein-coupled receptors (GPCRs). While much effort has been devoted to understanding G-protein-receptor interactions and identifying the components of the signalling cascade downstream of these receptors, at the level of the G-protein the modulation of receptor signal transduction remains relatively unexplored. In this regard a taste-specific regulator of G-protein signaling (RGS), RGS21, has recently been identified. To study whether guanine nucleotide exchange factors (GEFs) are involved in the transduction of the signal downstream of the taste GPCRs we investigated the expression of Ric-8A and Ric-8B in mouse taste cells and their interaction with G-protein subunits found in taste buds. Mammalian Ric-8 proteins were initially identified as potent GEFs for a range of Galpha subunits and Ric-8B has recently been shown to amplify Olfactory signal transduction. We find that both Ric-8A and Ric-8B are expressed in a large portion of taste bud cells and that most of these cells contain IP3R-3 a marker for sweet, umami and bitter taste receptor cells. Ric-8A interacts with Galpha-gustducin and Galphai2 through which it amplifies the signal transduction of hTas2R16, a receptor for bitter compounds. Overall, these findings are consistent with a role for Ric-8 in mammalian taste signal transduction.

Rhinology. 2009 Sep; 47(3): 242-7
Ahmed MK, Takumida M, Ishibashi T, Hamamoto T, Hirakawa K

We investigated the expression of transient receptor potential vanilloid (TRPV)-1-4 in the mouse Olfactory epithelium (OE) in comparison to its expression in respiratory epithelium. CBA/J mice were used. The localization of TRPV-1, -2, -3 and -4 in the nasal mucosa was investigated using immunohistochemistry and a double staining study for TRPV-1 and -2 and SP was also carried out. TRPV-1-4, were expressed variably in the OE with a diffuse pattern in lamina propria, and were expressed in respiratory epithelium with strong positive expression in glandular cells of lamina propria. The double-staining study revealed coexpression of TRPV-1 and -2 and substance P (SP) in the trigeminal nerve fibers of the OE. Coexpression of TRPV-1 and SP was marked around the blood vessels and seromucinous gland of respiratory epithelium while TRPV-2 showed no co-localization. TRPV-1-4 were found to be localized in the mouse OE and respiratory epithelium. Our results suggest that TRPVs may play multiple roles in the OE, contributing to Olfactory adaptation, Olfactory/trigeminal interactions in nasal chemoreception and OE homeostasis; they may also be involved in Olfactory transduction as well as Olfactory dysfunction secondary to sinonasal inflammatory disease. TRPVs in respiratory mucosa may play a significant role in nasal nociception, ciliary movement and the regulation of mucous secretion.

J Neurosci. 2009 Oct 14; 29(41): 12802-6
Singer JH, Glowatzki E, Moser T, Strowbridge BW, Bhandawat V, Sampath AP

Sensory receptors transduce physical stimuli in the environment into neural signals that are interpreted by the brain. Although considerable attention has been given to how the sensitivity and dynamic range of sensory receptors is established, peripheral synaptic interactions improve the fidelity with which receptor output is transferred to the brain. For instance, synapses in the retina, cochlea, and primary Olfactory system use mechanisms that fine-tune the responsiveness of postsynaptic neurons and the dynamics of exocytosis; these permit microcircuit interactions to encode efficiently the output of sensory receptors with the fidelity and dynamic range necessary to extract the salient features of the physical stimuli. The continuous matching of presynaptic and postsynaptic responsiveness highlight how the primary sensory organs have been optimized and can be modulated to resolve sparse sensory signals and to encode the entire range of receptor output.

J Comp Neurol. 2009 Dec 10; 517(5): 683-94
Gribaudo S, Bovetti S, Garzotto D, Fasolo A, De Marchis S

Neurogranin (Ng) is a brain-specific postsynaptic protein involved in activity-dependent synaptic plasticity through modulation of Ca(2+)/calmodulin (CaM)-dependent signal transduction in neurons. In this study, using biochemical and immunohistochemical approaches, we demonstrate Ng expression in the adult mouse Olfactory bulb (OB), the first relay station in odor information processing. We show that Ng is principally associated with the granule cell layer (GCL), which is composed of granule cell inhibitory interneurons. This cell type is continuously renewed during adult life and plays a key role in OB circuits, integrating and modulating the activity of mitral/tufted cells. Our results indicate that Ng localizes in the soma and dendrites of a defined subpopulation of mature GABAergic granule cells, enriched in the deep portion of the GCL. Ng-immunopositive cells largely coexpress the Ca(+)/CaM-dependent kinase IV (CaMKIV), a downstream protein of CaM signaling cascade, whereas no colocalization was observed between Ng and the calcium-binding protein calretinin. Finally, we demonstrate that adult neurogenesis contributes to the Ng-expressing population, with more newly generated Ng-positive cells integrated in the deep GCL. Together, these results provide a new specific neurochemical marker to identify a subpopulation of Olfactory granule cells and suggest possible functional implications for Ng in OB plasticity mechanisms.

J Gen Physiol. 2009 Nov; 134(5): 397-408
Waldeck C, Vocke K, Ungerer N, Frings S, Möhrlen F

Olfactory receptor neurons respond to odor stimulation with a receptor potential that results from the successive activation of cyclic AMP (cAMP)-gated, Ca(2+)-permeable channels and Ca(2+)-activated chloride channels. The cAMP-gated channels open at micromolar concentrations of their ligand and are subject to a Ca(2+)-dependent feedback inhibition by calmodulin. Attempts to understand the operation of these channels have been hampered by the fact that the channel protein is composed of three different subunits, CNGA2, CNGA4, and CNGB1b. Here, we explore the individual role that each subunit plays in the gating process. Using site-directed mutagenesis and patch clamp analysis, we identify three functional modules that govern channel operation: a module that opens the channel, a module that stabilizes the open state at low cAMP concentrations, and a module that mediates rapid Ca(2+)-dependent feedback inhibition. Each subunit could be assigned to one of these functions that, together, define the gating logic of the Olfactory transduction channel.

Proc Natl Acad Sci U S A. 2009 Oct 13; 106(41): 17570-5
Doengi M, Hirnet D, Coulon P, Pape HC, Deitmer JW, Lohr C

We studied GABAergic signaling in astrocytes of Olfactory bulb slices using confocal Ca(2+) imaging and two-photon Na(+) imaging. GABA evoked Ca(2+) transients in astrocytes that persisted in the presence of GABA(A) and GABA(B) receptor antagonists, but were suppressed by inhibition of GABA uptake by SNAP 5114. Withdrawal of external Ca(2+) blocked GABA-induced Ca(2+) transients, and depletion of Ca(2+) stores with cyclopiazonic acid reduced Ca(2+) transients by approximately 90%. This indicates that the Ca(2+) transients depend on external Ca(2+), but are mainly mediated by intracellular Ca(2+) release, conforming with Ca(2+)-induced Ca(2+) release. Inhibition of ryanodine receptors did not affect GABA-induced Ca(2+) transients, whereas the InsP(3) receptor blocker 2-APB inhibited the Ca(2+) transients. GABA also induced Na(+) increases in astrocytes, potentially reducing Na(+)/Ca(2+) exchange. To test whether reduction of Na(+)/Ca(2+) exchange induces Ca(2+) signaling, we inhibited Na(+)/Ca(2+) exchange with KB-R7943, which mimicked GABA-induced Ca(2+) transients. Endogenous GABA release from neurons, activated by stimulation of afferent axons or NMDA application, also triggered Ca(2+) transients in astrocytes. The significance of GABAergic Ca(2+) signaling in astrocytes for control of blood flow is demonstrated by SNAP 5114-sensitive constriction of blood vessels accompanying GABA uptake. The results suggest that GABAergic signaling is composed of GABA uptake-mediated Na(+) rises that reduce Na(+)/Ca(2+) exchange, thereby leading to a Ca(2+) increase sufficient to trigger Ca(2+)-induced Ca(2+) release via InsP(3) receptors. Hence, GABA transporters not only remove GABA from the extracellular space, but may also contribute to intracellular signaling and astrocyte function, such as control of blood flow.

BMC Evol Biol. 2009; 9: 242
Churcher AM, Taylor JS

BACKGROUND: A common feature of chemosensory systems is the involvement of G protein-coupled receptors (GPCRs) in the detection of environmental stimuli. Several lineages of GPCRs are involved in vertebrate olfaction, including trace amine-associated receptors, type 1 and 2 vomeronasal receptors and odorant receptors (ORs). Gene duplication and gene loss in different vertebrate lineages have lead to an enormous amount of variation in OR gene repertoire among species; some fish have fewer than 100 OR genes, while some mammals possess more than 1000. Fascinating features of the vertebrate Olfactory system include allelic exclusion, where each Olfactory neuron expresses only a single OR gene, and axonal guidance where neurons expressing the same receptor project axons to common glomerulae. By identifying homologous ORs in vertebrate and in non-vertebrate chordates, we hope to expose ancestral features of the chordate Olfactory system that will help us to better understand the evolution of the receptors themselves and of the cellular components of the Olfactory system. RESULTS: We have identified 50 full-length and 11 partial ORs in Branchiostoma floridae. No ORs were identified in Ciona intestinalis. Phylogenetic analysis places the B. floridae OR genes in a monophyletic clade with the vertebrate ORs. The majority of OR genes in amphioxus are intronless and many are also tandemly arrayed in the genome. By exposing conserved amino acid motifs and testing the ability of those motifs to discriminate between ORs and non-OR GPCRs, we identified three OR-specific amino acid motifs common in cephalochordate, fish and mammalian and ORs. CONCLUSION: Here, we show that amphioxus has orthologs of vertebrate ORs. This conclusion demonstrates that the receptors, and perhaps other components of vertebrate olfaction, evolved at least 550 million years ago. We have also identified highly conserved amino acid motifs that may be important for maintaining receptor conformation or regulating receptor activity. We anticipate that the identification of vertebrate OR orthologs in amphioxus will lead to an improved understanding of OR gene family evolution, OR gene function, and the mechanisms that control cell-specific expression, axonal guidance, signal transduction and signal integration.

Genes Brain Behav. 2009 Oct; 8(7): 639-49
Hasen NS, Gammie SC

The Trpc2 gene codes for an ion channel found in the vomeronasal organ (VNO). Studies using the Trpc2(-/-) (KO) mouse have exploited the gene's role in signal transduction to explore the VNO's role in pheromonally mediated behaviors. To date, no study has evaluated the impact of the Trpc2 gene on activity within the brain. In this study, we examine the gene's effect on brain regions governing maternal aggression. We intruder-tested lactating dams and then quantified Fos immunoreactivity (Fos-IR) in the vomeronasal amygdala, hypothalamus, Olfactory regions and accessory Olfactory bulb (AOB). Our data confirm previous reports that loss of the Trpc2 gene severely diminishes maternal aggression. We also show that deletion of the gene results in differential hypotrophy of the glomerular layer (GlA) of the AOB, with the anterior portion the GlA resembling that of wild-type mice, and the posterior portion reduced or absent. This anatomy is suggestive of residual functioning in the apical VNO of these animals. Our Fos study describes an impact of the deletion on a network of 21 brain regions involved in emotion, aggression and olfaction, suggesting that signals from the VNO mediate activity throughout the brain. Home-cage observations of KO dams show specific deficits in nest-building, suggesting a role for pup pheromones in inducing and maintaining pup-directed maternal behaviors as well as maternal aggression.

J Neurosci Methods. 2009 Dec 15; 185(1): 89-98
Audisio C, Raimondo S, Nicolino S, Gambarotta G, Di Scipio F, Macrì L, Montarolo F, Giacobini-Robecchi MG, Porporato P, Filigheddu N, Graziani A, Geuna S, Perroteau I

Cell transplantation therapy has raised a great interest in the perspective of its employment for nerve tissue repair. Among the various cell populations proposed, Olfactory ensheathing glial cells have raised great interest over recent years, especially in the perspective of their employment for neural repair because of their homing capacity in both central and peripheral nervous system. This paper is aimed to provide an in vitro characterization of the NOBEC (neonatal Olfactory bulb ensheathing cell) line that was obtained from primary cells dissociated from rat neonatal Olfactory bulb (OB) and immortalized by retroviral transduction of SV40 large T antigen. Light and electron microscopy investigation showed that NOBECs are a homogeneous cell population both at structural and ultrastructural level. RT-PCR, Western blotting and immunocytochemistry showed that NOBECs express the glial markers S100, GFAP (Glial Fibrillar Acid Protein) and p75NGFR as well as NRG1 (neuregulin-1) and ErbB1-2-3 receptors; while they are negative for ErbB4. Yet, NOBECs exhibit a high proliferation and migration basal activity and can be transducted with vectors carrying GFP (green fluorescent protein) and NRG1 cDNA. Functional stimulation by means of NRG1-III-beta3 overexpression through viral transduction induced a significant increase in cell proliferation rate while it had no effect on cell migration. Altogether, these results show that NOBEC cell line retain glial features both morphologically and functionally, responding to the NRG1/ErbB-mediated gliotrophic stimulus, and represents thus a good tool for in vitro assays of glial cell manipulation and for in vivo experimental studies of glial cell transplantation in the central and peripheral nervous system.

Cell Signal. 2010 Jan; 22(1): 150-7
Klasen K, Corey EA, Kuck F, Wetzel CH, Hatt H, Ache BW

Recent evidence has revived interest in the idea that phosphoinositides (PIs) may play a role in signal transduction in mammalian Olfactory receptor neurons (ORNs). To provide direct evidence that odorants indeed activate PI signaling in ORNs, we used adenoviral vectors carrying two different fluorescently tagged probes, the pleckstrin homology (PH) domains of phospholipase C delta 1 (PLC delta 1) and the general receptor of phosphoinositides (GRP1), to monitor PI activity in the dendritic knobs of ORNs in vivo. Odorants mobilized PI(4,5)P(2)/IP(3) and PI(3,4,5)P(3), the substrates and products of PLC and PI3K. We then measured odorant activation of PLC and PI3K in Olfactory ciliary-enriched membranes in vitro using a phospholipid overlay assay and ELISAs. Odorants activated both PLC and PI3K in the Olfactory cilia within 2s of odorant stimulation. Odorant-dependent activation of PLC and PI3K in the Olfactory epithelium could be blocked by enzyme-specific inhibitors. Odorants activated PLC and PI3K with partially overlapping specificity. These results provide direct evidence that odorants indeed activate PI signaling in mammalian ORNs in a manner that is consistent with the idea that PI signaling plays a role in Olfactory transduction.

Neuroscience. 2009 Sep 22;
Khan S, Perry C, Tetreault ML, Henry D, Trimmer JS, Zimmerman AL, Matthews G

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.

Oncology. 2009; 77(3-4): 231-43
Mao L, Xia YP, Zhou YN, Dai RL, Yang X, Wang YJ, Duan SJ, Qiao X, Mei YW, Hu B

OBJECTIVES: Sonic hedgehog (Shh) signaling pathway is associated with tumor development; however, the role of Shh signaling in the development of Olfactory neuroblastoma (ONB) is unknown. This study aimed to investigate the relationship between the regulation of Shh signaling and the pathogenesis of ONB. METHODS: The expression of Shh signaling components was characterized by immunohistochemistry in human non-tumor Olfactory epithelium and ONB specimens, and by RT-PCR and immunoblotting in human ONB cell lines. The impact of the treatment with cyclopamine (a selective inhibitor of the Shh pathway) and/or exogenous Shh on ONB cell proliferation, cycle and apoptosis was examined by MTT, soft agar colony formation and flow cytometry assays, respectively. The influence of Shh signaling on the expression of Shh signaling components and cell cycle-related regulators was determined by immunoblotting and quantitative RT-PCR, respectively. RESULTS: The expression of Pacthed1, Gli1 and Gli2 was detected in 70, 70, and 65% of human ONB specimens, respectively, and in proportion of ONB cell lines, but not in non-tumor Olfactory epithelium. Treatment with cyclopamine inhibited the proliferation and colony formation of ONB cells, induced ONB cell cycle arrest and apoptosis, and down-regulated the expression of Pacthed1, Gli1 and cyclin D1, but up-regulated p21 expression in vitro. These regulatory effects of cyclopamine were partially or completely erased by exogenous Shh. CONCLUSION: These data suggest that the Shh signaling pathway is crucial for the growth of ONB.

Eur Arch Otorhinolaryngol. 2009 Aug 29;
Gudziol V, Pietsch J, Witt M, Hummel T

Options for the treatment of hyposmia are limited; available therapies do not provide a long-lasting effect. A recent study suggests that an unspecific phosphodiesterase inhibitor (PDE-I) increases Olfactory sensitivity due to interaction with the signal transduction in the Olfactory epithelium. The aim of the present study was to investigate whether theophylline, an unspecific PDE-I, evokes changes in the electro-olfactogram (EOG) which would support the hypothesis of a drug-related impact on signal transduction. In addition, the uptake of topically administered theophylline in the Olfactory epithelium should be investigated. EOG was obtained in 29 samples of supravital mouse Olfactory epithelia. Olfactory stimulation (phenylethyl alcohol, PEA and hydrogen sulfide, H(2)S) was performed using an air-dilution olfactometer. Theophylline concentration in the Olfactory epithelium of five samples was measured by means of high pressure liquid chromatography. Administration of theophylline resulted in a tendency towards smaller EOG amplitudes (p = 0.055), being reduced by 13 and 25% in response to stimulation with PEA or H(2)S, respectively. In comparison to the application of Ringer's solution, theophylline resulted in a significant (p = 0.031) decrease of the EOG amplitude. Latency was not significantly (p = 0.10) influenced by drug administration. The theophylline concentration in the Olfactory epithelium ranged from 0.21 to 1.53 mug/mg. Theophylline seems to be taken up into the Olfactory epithelium of supravital mice and to interact with the Olfactory signal transduction.

J Biol Chem. 2009 Oct 30; 284(44): 30547-55
Pick H, Etter S, Baud O, Schmauder R, Bordoli L, Schwede T, Vogel H

We have screened an odorant compound library and discovered molecules acting as chemical signals that specifically activate both G-protein-coupled Olfactory receptors (ORs) on the cell surface of Olfactory sensory neurons and the human nuclear estrogen receptor alpha (ER) involved in transcriptional regulation of cellular differentiation and proliferation in a wide variety of tissues. Hence, these apparent dual active odorants induce distinct signal transduction pathways at different subcellular localizations, which affect both neuronal signaling, resulting in odor perception, and the ER-dependent transcriptional control of specific genes. We demonstrate these effects using fluorescence-based in vitro and cellular assays. Among these odorants, we have identified synthetic sandalwood compounds, an important class of molecules used in the fragrance industry. For one estrogenic odorant we have also identified the cognate OR. This prompted us to compare basic molecular recognition principles of odorants on the two structurally and apparent functionally non-related receptors using computational modeling in combination with functional assays. Faced with the increasing evidence that ORs may perform chemosensory functions in a number of tissues outside of the nasal Olfactory epithelium, the unraveling of these molecular ligand-receptor interaction principles is of critical importance. In addition the evidence that certain Olfactory sensory neurons naturally co-express ORs and ERs may provide a direct functional link between the Olfactory and hormonal systems in humans. Our results are therefore useful for defining the structural and functional characteristics of ER-specific odorants and the role of odorant molecules in cellular processes other than olfaction.

Electrophoresis. 2009 Sep; 30(18): 3283-8
Lee SH, Jeong SH, Jun SB, Kim SJ, Park TH

The binding of Olfactory receptors with odorant molecules initiates Olfactory signal transduction, which leads to a cationic influx. In the present study, human embryonic kidney-293 cells were recombinantly engineered to co-express Olfactory receptors I7 and gustatory cyclic nucleotide gated channels, which increased the cationic influx. The odorant-induced change in the membrane potential was measured in the extracellular region using microelectrode arrays. A biphasic electrical current stimulation was applied to the cells in order to increase the intrinsic cellular activity. Upon odorants recognition, the electrical cellular activity was enhanced following each electrical stimulation pulse. Compared with odorant-only stimulation, the electrical stimulation induced up to a fivefold increase in the amplitude of the electrical signal, which was produced in response to the odorants. These results demonstrate that electrical stimulation can enhance cellular activity and increase the response signal for detecting ligand binding. This paradigm of electrical stimulation can be used as a novel method in the field of versatile cell-based biosensors for detection of specific odorants.

Science. 2009 Aug 28; 325(5944): 1081-2
Kinnamon SC, Reynolds SD

Eur J Neurosci. 2009 Sep; 30(5): 742-55
Hurtado-Chong A, Yusta-Boyo MJ, Vergaño-Vera E, Bulfone A, de Pablo F, Vicario-Abejón C

While insulin-like growth factor-I (IGF-I) supports neuronal and glial differentiation in the CNS, it is largely unknown whether IGF-I also influences neuronal migration and positioning. We show here that the pattern of Olfactory bulb (OB) layering is altered in Igf-I (-/-) mice. In these animals, Tbr1(+)-glutamatergic neurons are misplaced in the mitral cell layer (ML) and the external plexiform layer (EPL). In addition, there are fewer interneurons in the glomerular layer and the EPL of the Igf-I (-/-) mice, and fewer newborn neurons are incorporated into the OB from the forebrain subventricular zone (SVZ). Indeed, neuroblasts accumulate in the postnatal/adult SVZ of Igf-I (-/-) mice. Significantly, the positioning of Tbr1(+)-cells in a primitive ML is stimulated by IGF-I in cultured embryonic OB slices, an effect that is partially repressed by the phosphoinositide 3-kinase (PI3K) inhibitor. In OB cell cultures, IGF-I increases the phosphorylation of disabled1 (P-Dab1), an adaptor protein that is a target of Src family kinases (SFK) in the reelin signalling pathway, whereas reduced P-Dab1 levels were found in Igf-I (-/-) mice. Neuroblast migration from the rostral migratory stream (RMS) explants of postnatal Igf-I (-/-) was similar to that from Igf-I (+/+) explants. However, cell migration was significantly enhanced by IGF-I added to the explants, an effect that was repressed by PI3K and SFK inhibitors. These findings suggest that IGF-I promotes neuronal positioning in the OB and support a role for IGF-I in stimulating neuroblast exit from the SVZ into the RMS, thereby promoting the incorporation of newly formed neurons into the OB.