Efferent controls in crustacean mechanoreceptors

International audienceSince the 1960s it has been known that central neural networks can elaborate motor patterns in the absence of any sensory feedback. However, sensory and neuromodulatory inputs allow the animal to adapt the motor command to the actual mechanical configuration or changing needs. Many studies in invertebrates, particularly in crustacea, have described several mechanisms of sensory-motor integration and have shown that part of this integration was supported by the efferent control of the mechanosensory neurons themselves. In this article, we review the findings that support such an efferent control of mechanosensory neurons in crustacea. Various types of crustacean proprioceptors feeding information about joint movements and strains to central neural networks are considered, together with evidence of efferent controls exerted on their sensory neurons. These efferent controls comprise (1) the neurohormonal modulation of the coding properties of sensory neurons by bioamines and peptides; (2) the presynaptic inhibition of sensory neurons by GABA, glutamate and histamine; and (3) the long-term potentiation of sensory-motor synapses by glutamate. Several of these mechanisms can coexist on the same sensory neuron, and the functional significance of such multiple modulations is discussed

Measurement of Atmospheric Volatile Organic Compounds from Urban, Industrial and Biogenic Sources by Proton-­Transfer Ion Trap Mass Spectrometry

Volatile organic compounds (VOCs) are released into the atmosphere through a variety of processes. An understanding of the chemistry of VOCs is critical because of their role in air pollution and climate, but their diversity challenges even modern analytical methods. In this work, I present VOC measurements made by Proton-Transfer-Reaction Ion Trap Mass Spectrometry (PIT-MS) in air impacted by different emission sources: biogenic, urban, industrial and biomass burning. The main goal of these studies was to use the PIT-MS instrument\u27s high time resolution, full mass scan capability and capacity for collision-induced dissociation (CID) to quantify complex VOC mixtures. CID was successfully used to identify VOCs and to separate isomeric and isobaric VOCs in biogenic emissions and biomass burning plumes. Comparison of PIT-MS results with other VOC measurement methods, the use of gas chromatography with PIT-MS and CID were all used to characterize the specificity of methods that use proton transfer by H3O+ ions in all four field environments. The results revealed many limitations to common PTR signal attributions. Results from these studies demonstrate the usefulness of the PIT-MS instrument to characterize complex VOC mixtures. In Mexico City, three major sources of VOC emissions were identified: vehicular traffic, liquid propane gas (LPG) usage and chemical formation. VOC emissions relative to carbon monoxide (CO) are about a factor of 2 larger in Mexico City than in the United States. In Houston, TX, PIT-MS measurements were used to evaluate an industrial emissions inventory. The complexity of measured VOCs in industrial plumes is significantly larger than described in the inventory and for many VOCs, emission fluxes inferred from the measurements are significantly higher than those listed in the inventory. Results from these campaigns could inform future inventories and help inform policy decisions. Taken together, PIT-MS instrument is shown to be useful in providing routine, online VOC measurements with clear scientific merit. At the same time, the PIT-MS is successfully used to probe and extend the analytical abilities of proton-transfer-reaction based instruments for atmospheric measurements

Modulation of Phenol Oxidation in Cofacial Dyads

The presentation of two phenols on a xanthene backbone is akin to the tyrosine dyad (Y[subscript 730] and Y[subscript 731]) of ribonucleotide reductase. X-ray crystallography reveals that the two phenol moieties are cofacially disposed at 4.35 Å. Cyclic voltammetry reveals that phenol oxidation is modulated within the dyad, which exhibits a splitting of one-electron waves with the second oxidation of the phenol dyad occurring at larger positive potential than that of a typical phenol. In contrast, a single phenol appended to a xanthene exhibits a two-electron process, consistent with reported oxidation pathways of phenols in acetonitrile. The perturbation of the phenol potential by stacking is reminiscent of a similar effect for guanines stacked within DNA base pairs.National Institutes of Health (U.S.) (GM5R01

Condições e Obstáculos ao Empreendedorismo no Brasil: Conditions and Barriers to Entrepreneurship in Brazil

O presente artigo versa sobre os fatores estruturais, sócio- políticos, culturais, organizacionais e institucionais que suportam as atividades empreendedoras no campo empresarial. Em nosso estudo apresentamos de forma resumida os resultados do estudo Global Entrepreneurship Monitor (GEM), no qual focaremos os resultados obtidos em relação ao Brasil. Deste modo, visamos verificar as condições que afetam o empreendedorismo nacional deste país. Iniciamos nossa reflexão pela apresentação da origem e do significado do ato de empreender, tal qual concebido originalmente pela ciência econômica. Em um segundo momento, expomos alguns dados atuais acerca das características do empreendedorismo brasileiro, para finalmente apresentar o resultado comentado do estudo do GEM-Brasil. Concluímos que embora o Brasil seja um país que tem evoluído em termos de um maior empreendedorismo de oportunidade, como uma conseqüência da expansão econômica que viveu o país nos anos recentes, onde o empreendedorismo de necessidade começa a dar lugar a uma classe empresarial mais bem preparada e escolarizada; este setor ainda carece de maiores aportes em termos de educação e capacitação, bem como maiores investimentos em P&D, o que significaria a alavancagem necessária a empreendimentos inovadores com grande potencial de internacionalização, haja vista as novas redes de relações internacionais estabelecidas nas últimas décadas, na qual se inclui a CPLP

High-resolution near-IR Spectral mapping with H2_{2} and [Fe II] lines of Multiple Outflows around LkHα\alpha 234

We present a high-resolution, near-IR spectroscopic study of multiple outflows in the LkH$\alpha$ 234 star formation region using the Immersion GRating INfrared Spectrometer (IGRINS). Spectral mapping over the blueshifted emission of HH 167 allowed us to distinguish at least three separate, spatially overlapped, outflows in H${_2}$ and [Fe II] emission. We show that the H${_2}$ emission represents not a single jet, but complex multiple outflows driven by three known embedded sources: MM1, VLA 2, and VLA 3. There is a redshifted H${_2}$ outflow at a low velocity, \VLSR $<$ $+$50 {\kms}, with respect to the systemic velocity of \VLSR $=$ $-$11.5 {\kms}, that coincides with the H${_2}$O masers seen in earlier radio observations two arcseconds southwest of VLA 2. We found that the previously detected [Fe II] jet with $|$\VLSR$|$ $>$ 100 {\kms} driven by VLA 3B is also detected in H${_2}$ emission, and confirm that this jet has a position angle about 240$\degree$. Spectra of the redshifted knots at 14\arcsec$-$65\arcsec northeast of LkH$\alpha$ 234 are presented for the first time. These spectra also provide clues to the existence of multiple outflows. We detected high-velocity (50$-$120 {\kms}) H${_2}$ gas in the multiple outflows around LkH$\alpha$ 234. Since these gases move at speeds well over the dissociation velocity ($>$ 40 {\kms}), the emission must originate from the jet itself rather than H${_2}$ gas in the ambient medium. Also, position-velocity diagrams and excitation diagram indicate that emission from knot C in HH 167 come from two different phenomena, shocks and photodissociation.Comment: 32 pages, 12 figures, 2 tables, Accepted for publication in the Astrophysical Journa

ASSESSMENT OF STREAM FISH MORTALITY FROM SHORT-TERM EXPOSURE TO ILLITE CLAYS USED AS AN IN SITU METHOD FOR REMEDIATING 137CS CONTAMINATED WETLANDS

Due to their physical properties, illite clays can sorb cesium-137 almost irreversibly, and therefore sequester contamination from the environment. However, applying large amounts of clay to natural aquatic habitats for in situ remediation purposes may create conditions of high turbidity and sedimentation. To evaluate potential effects of turbidity from illite application on survivorship of stream fish, yellowfin shiners (Notropis lutipinnis) and tessellated darters (Etheostoma olmstedi) were subjected to treatment with two different types of clay in flow-through simulated stream raceways. Turbidity and fish mortality were subsequently monitored for seven days. At 2-m downstream from the application point, mean turbidity peaked during clay application at 525 and 72 nephelometric turbidity units (NTU) in the air-floated illite and semi-dry illite treatments, respectively. Turbidity returned to levels similar to that of the controls (4-6 NTU) after four hours in the air-floated illite raceways and one hour in the semi-dry illite raceways. Although the majority of the suspended clay was quickly flushed from the system and the remaining settled to the bottom, turbidity did continue to fluctuate because of fish movements and sediment resuspension. Fish mortality did not significantly differ among control and illite treated raceways