Gap junctions in olfactory neurons modulate olfactory sensitivity

<p>Abstract</p> <p>Background</p> <p>One of the fundamental questions in olfaction is whether olfactory receptor neurons (ORNs) behave as independent entities within the olfactory epithelium. On the basis that mature ORNs express multiple connexins, I postulated that gap junctional communication modulates olfactory responses in the periphery and that disruption of gap junctions in ORNs reduces olfactory sensitivity. The data collected from characterizing connexin 43 (Cx43) dominant negative transgenic mice OlfDNCX, and from calcium imaging of wild type mice (WT) support my hypothesis.</p> <p>Results</p> <p>I generated OlfDNCX mice that express a dominant negative Cx43 protein, Cx43/β-gal, in mature ORNs to inactivate gap junctions and hemichannels composed of Cx43 or other structurally related connexins. Characterization of OlfDNCX revealed that Cx43/β-gal was exclusively expressed in areas where mature ORNs resided. Real time quantitative PCR indicated that cellular machineries of OlfDNCX were normal in comparison to WT. Electroolfactogram recordings showed decreased olfactory responses to octaldehyde, heptaldehyde and acetyl acetate in OlfDNCX compared to WT. Octaldehyde-elicited glomerular activity in the olfactory bulb, measured according to odor-elicited <it>c-fos </it>mRNA upregulation in juxtaglomerular cells, was confined to smaller areas of the glomerular layer in OlfDNCX compared to WT. In WT mice, octaldehyde sensitive neurons exhibited reduced response magnitudes after application of gap junction uncoupling reagents and the effects were specific to subsets of neurons.</p> <p>Conclusions</p> <p>My study has demonstrated that altered assembly of Cx43 or structurally related connexins in ORNs modulates olfactory responses and changes olfactory activation maps in the olfactory bulb. Furthermore, pharmacologically uncoupling of gap junctions reduces olfactory activity in subsets of ORNs. These data suggest that gap junctional communication or hemichannel activity plays a critical role in maintaining olfactory sensitivity and odor perception.</p

Diurnal and nocturnal distribution of stratospheric NO: from solar and stellar occultation measurements in the Arctic vortex' Comparison with models and ILAS satellite measurements

International audienceNO2 mixing ratio profiles were measured at sunset between 14 and 30 km using the Limb Profile Monitor of the Atmosphere (LPMA) experiment and during the night between 13 and 31 km using the Absorption par Minoritaires Ozone et NOx (AMON) experiment inside the Arctic vortex, both on February 26, 1997. Coinciding profiles measured by the Improved Limb Atmospheric Spectrometer (ILAS) instrument on board ADEOS have been used to check the consistency between the satellite and balloon profiles for NO2, 03, and HNO3. A box model has been used for the photochemical correction of the LPMA NO2 profiles at sunset. The resulting NO2 balloon-borne profiles of LPMA and AMON are compared to each other after accounting for the day/night photochemical variation using the box model initialized with measurements. The comparisons thus performed show an average difference less than 9% between the two measurements (considered to sample similar air masses) when the box model is initialized with little chlorine activation (i.e., when the major burden of chlorine is stored in C1ONO2) for a 1 day integration. The comparison with the Reprobus 3-D chemistry transport model (CTM) seasonal simulations clearly confirms an underestimation of NO2 by the model below 25 km, in the altitude range where aerosols lead to a complete removal of NOx in the model. Recent updates of rate coefficients for conversion of HNO3 into NO2 only slightly improve the NO2 model results in vortex conditions. These results suggest that a source of NO2 is still lacking in the CTM

Validation of five years (2003–2007) of SCIAMACHY CO total column measurements using ground-based spectrometer observations

This paper presents a validation study of SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) carbon monoxide (CO) total column measurements from the Iterative Maximum Likelihood Method (IMLM) algorithm using ground-based spectrometer observations from twenty surface stations for the five year time period of 2003–2007. Overall we find a good agreement between SCIAMACHY and ground-based observations for both mean values as well as seasonal variations. For high-latitude Northern Hemisphere stations absolute differences between SCIAMACHY and ground-based measurements are close to or fall within the SCIAMACHY CO 2σ precision of 0.2 × 1018 molecules/cm2 (~10%) indicating that SCIAMACHY can observe CO accurately at high Northern Hemisphere latitudes. For Northern Hemisphere mid-latitude stations the validation is complicated due to the vicinity of emission sources for almost all stations, leading to higher ground-based measurements compared to SCIAMACHY CO within its typical sampling area of 8° × 8°. Comparisons with Northern Hemisphere mountain stations are hampered by elevation effects. After accounting for these effects, the validation provides satisfactory results. At Southern Hemisphere mid- to high latitudes SCIAMACHY is systematically lower than the ground-based measurements for 2003 and 2004, but for 2005 and later years the differences between SCIAMACHY and ground-based measurements fall within the SCIAMACHY precision. The 2003–2004 bias is consistent with previously reported results although its origin remains under investigation. No other systematic spatial or temporal biases could be identified based on the validation presented in this paper. Validation results are robust with regard to the choices of the instrument-noise error filter, sampling area, and time averaging required for the validation of SCIAMACHY CO total column measurements. Finally, our results show that the spatial coverage of the ground-based measurements available for the validation of the 2003–2007 SCIAMACHY CO columns is sub-optimal for validation purposes, and that the recent and ongoing expansion of the ground-based network by carefully selecting new locations may be very beneficial for SCIAMACHY CO and other satellite trace gas measurements validation efforts