Bilateral detection thresholds in dextrals and sinistrals reflect the more sensitive side of the nose, which is not lateralized [published erratum appears in Chem Senses 1998 Dec;23(6):761]

Several fundamental questions remain enigmatic concerning human olfactory sensitivity, including (i) whether detection threshold differences exist between the two sides of the nose (and, if so, whether such differences are influenced by handedness) and (ii) whether bilateral (i.e. binasal) stimulation leads to lower thresholds than unilateral stimulation (and, if so, whether the degree of facilitation is inversely related to general olfactory ability). In this study, and well-validated single staircase procedure was used to establish bilateral and unilateral detection thresholds for the cranial nerve I stimulant phenyl ethyl alcohol in 130 right- and 33 left-handed subjects. No differences in sensitivity between the left and right sides of the nose were observed in either group. Bilateral thresholds were lower, on average, than unilateral thresholds when the latter were categorized in terms of left and right nares. However, the bilateral thresholds did not differ significantly from those of the side of the nose with the lower threshold. Overall smell ability, as measured by the University of Pennsylvania Smell Identification Test, did not interact with any of the test measures. These data imply that (i) the left and right sides of the nose do not systematically differ in detection threshold sensitivity for either dextrals or sinistrals and (ii) if central integration of left:right olfactory threshold sensitivity occurs, its effects do not exceed the function of the better side of the nose.      

Morphogenic Regulation of Pathotoxin Synthesis in Cochliobolus carbonum

The fungus Cochliobolus carbonum causes leaf spot disease of maize. Highly virulent isolates of the pathogen produce a host-selective, peptide toxin that is active against susceptible genotypes of maize. Prior to infection, spores must germinate and differentiate appressoria, structures specialized for leaf penetration. Analysis of spore germination fluids by plasma desorption mass spectrometry, which allowed detection of as little as 0.5 ng toxin, revealed that spores induced to form appressoria in vitro synthesized and released the toxin at a time coincident with maturation of appressoria. Spores incubated under conditions that did not induce appressorium formation failed to produce toxin. These observations indicate that synthesis of the host-selective toxin, which is essential for successful pathogenesis of maize by C. carbonum, is regulated by infection-related morphogenesis.     

Evidence supporting the microbiota–gut–brain axis in a songbird

Recent research in mammals supports a link between cognitive ability and the gut microbiome, but little is known about this relationship in other taxa. In a captive population of 38 zebra finches (Taeniopygia guttata), we quantified performance on cognitive tasks measuring learning and memory. We sampled the gut microbiome via cloacal swab and quantified bacterial alpha and beta diversity. Performance on cognitive tasks related to beta diversity but not alpha diversity. We then identified differentially abundant genera influential in the beta diversity differences among cognitive performance categories. Though correlational, this study provides some of the first evidence of an avian microbiota–gut–brain axis, building foundations for future microbiome research in wild populations and during host development.     

Chemical biology: Paper alert

A selection of interesting papers that were published in the two months before our press date in major journals most likely to report significant results in chemical biology.     

Trends in lizard translocations in New Zealand between 1988 and 2013

There is growing concern about mitigation-driven translocations that move animals from anthropogenic threats at donor sites because of their failure rate and lack of application of scientific principles and best practice. We reviewed all known lizard translocations in New Zealand between 1988 and 2013 and identified 85 translocations of 30 lizard taxa to 46 release sites. Most translocations (62%) were motivated by conservation goals for the species or the release site, and one-third were mitigation-driven translocations, typically motivated by habitat loss due to development. Mitigation-driven translocations began in 2003, and since that time have equalled the number of conservation-motivated translocations. Conservation-motivated translocations usually released lizards on islands without mammalian predators, whereas mitigation-driven translocations usually relocated lizards to mainland sites with introduced predators. Long-term monitoring has been sparse and often rudimentary. Eight lizard translocations have recorded population growth, including one mitigation-driven translocation that was into a fenced reserve. Research on commonly used management techniques to mitigate human-related impacts is recommended to establish whether these techniques benefit lizards in the long term.     

Functional analysis of the Rubisco large subunit ÂN-methyltransferase promoter from tobacco and its regulation by light in soybean hairy roots

The ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) large subunit (LS) ^ɛ N-methyltransferase (Rubisco LSMT) catalyzes post-translational methylation of the ɛ-amino group of lysine-14 in the LS of Rubisco. The entire nucleotide sequence for the tobacco (Nicotiana tabacum) Rubisco LSMT (rbcMT-T) gene including the putative promoter region was recently reported, and sequence analysis of the promoter region revealed seven GT-1 motifs. The ability of several truncated rbcMT-T promoter fragments to confer light responsiveness to reporter gene expression in transgenic soybean (Glycine max) hairy roots was examined. Chimeric constructs consisting of the rbcMT-T promoter fused to a bacterial β-glucuronidase (GUS) reporter gene and transferred to soybean via Agrobacterium rhizogenes were evaluated. The rbcMT-T promoter fragments conferred expression of the reporter gene in transgenic hairy roots, callus, and cell suspension cultures based on histochemical and fluorometric GUS analyses. The results suggest a quantitative role for the number of GT-1 motifs in determining differential expression between light and dark conditions. Received: 7 January 1998 / Revision received: 23 March 1998 / Accepted: 13 April 1998     

End-expiratory and tidal volumes measured in conscious mice using single projection x-ray images.

The evaluation of airway resistance (R(aw)) in conscious mice requires both end-expiratory (V(e)) and tidal volumes (V(t)) (Lai-Fook SJ and Lai YL. J Appl Physiol 98: 2204-2218, 2005). In anesthetized BALB/c mice we measured lung area (A(L)) from ventral-to-dorsal x-ray images taken at FRC (V(e)) and after air inflation with 0.25 and 0.50 ml (DeltaV(L)). Total lung volume (V(L)) described by equation: V(L) = DeltaV(L) + V(FRC) = KA(L)(1.5) assumed uniform (isotropic) inflation. Total V(FRC) averaged 0.55 ml, consisting of 0.10 ml tissue, 0.21 ml blood and 0.24 ml air. K averaged 1.84. In conscious mice in a sealed box, we measured the peak-to-peak box pressure excursions (DeltaP(b)) and x-rays during several cycles. K was used to convert measured A(L)(1.5) to V(L) values. We calculated V(e) and V(t) from the plot of V(L) vs. cos(alpha - phi). Phase angle alpha was the minimum point of the P(b) cycle to the x-ray exposure. Phase difference between the P(b) and V(L) cycles (phi) was measured from DeltaP(b) values using both room- and body-temperature humidified box air. A similar analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that phi depended also on increased R(aw). In conscious mice, V(e) (0.24 ml) doubled after Mch (50-125 mg/ml) aerosol exposure with constant V(t), frequency (f), DeltaP(b), and R(aw). In anesthetized mice, in addition to an increased V(e), repeated 100 mg/ml Mch exposures increased both DeltaP(b) and R(aw) and decreased f to apnea in 10 min. Thus conscious mice adapted to Mch by limiting R(aw), while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.