Temporal characterization of growth of fathead minnow (Pimephales promelas) larvae during sublethal hydrogen cyanide exposure

Growth of fathead minnow yolk sac larvae was characterized from changes in dry weight and total content and concentrations of RNA, DNA and protein in fish exposed to a sublethal level of HCN (58 micrograms/l) and in age matched controls. Cyanide toxicosis occurred within 24 hr of exposure as evidenced by significant reductions in protein and RNA content and RNA/DNA ratio of larvae. After 96 hr exposure to HCN, larvae exhibited the same growth rate and protein synthetic rate (RNA/DNA) as control fish. HCN toxicosis and recovery is rapid and at least partial tolerance to HCN develops within 96 hr of exposure in larval fathead minnows.     

Pre-exposure affects the olfactory response of Drosophila melanogaster to menthol

A modification of the trap assay (Woodard et al., 1989) was used to evaluate the response of Drosophila melanogaster (Meigen) to food media containing menthol. Dose-response curves for flies to mentholic foods were produced for flies that had been pre-exposed to menthol, during development and adult life, and flies that had not been exposed to menthol before the assay. Mentholic food media were less attractive to Drosophila than plain food medium. Rearing flies on a medium containing menthol reduced their aversion to some concentrations of menthol. The rearing effect was not simply due to lowered general activity levels resulting from developing in a medium containing menthol. There was a threshold concentration of menthol in the rearing medium below which we found no induced behavioural change.     

The stimulation of hepatic gluconeogenesis by acetoacetate precursors. A role for the monocarboxylate translocator

The regulation of the gluconeogenic pathway from the 3-carbon precursors pyruvate, lactate, and alanine was investigated in the isolated perfused rat liver. Using pyruvate (less than 1 mM), lactate, or alanine as the gluconeogenic precursor, infusion of the acetoacetate precursors oleate, acetate, or beta-hydroxybutyrate stimulated the rate of glucose production and, in the case of pyruvate (less than 1 mM), the rate of pyruvate decarboxylation. alpha-Cyanocinnamate, an inhibitor of the monocarboxylate transporter, prevented the stimulation of pyruvate decarboxylation and glucose production due to acetate infusion. With lactate as the gluconeogenic precursor, acetate infusion in the presence of L-carnitine stimulated the rate of gluconeogenesis (100%) and ketogenesis (60%) without altering the tissue acetyl-CoA level usually considered a requisite for the stimulation of gluconeogenesis by fatty acids. Hence, our studies suggest that gluconeogenesis from pyruvate or other substrates which are converted to pyruvate prior to glucose synthesis may be limited or controlled by the rate of entry of pyruvate into the mitochondrial compartment on the monocarboxylate translocator.     

Increased efficiency of substrate utilization by exposure of the thermotolerant yeast strain,Kluyveromyces marxianus IMB3 to electric-field stimulation

Summary In order to enhance cellobiose utilization and conversion of substrate to ethanol by the thermotolerant yeast strain, Kluyveromyces marxianus IMB3, the organism was exposed to short, intense electric pulses. When cells were treated with pulses measuring 0.25kV for 10mS, in the presence of cellobiose, ethanol production was found to increase by almost 40% above that found in fermentations containing non-treated cells. When the extracellular culture filtrate was assayed for -glucosidase activity no significant difference in levels was detected between treated and control systems. Increasing the voltage of the pulses resulted in a decrease in ethanol production.     

Microtubules,dendritic spines and spine apparatuses

Summary Using techniques for enhanced microtubular preservation, including albumin pretreatment (Gray, 1975), occipital cortex of rats was studied electron microscopically at various ages of development. A close structural relationship was seen between microtubules, sacs of SER and the postsynaptic thickening in primordial spines and with the dense plate material of spine apparatuses. Stereoscopic preparations in addition show a more complicated substructure than previously described for the plate. Microtubules may contribute to the formation of the plate of the spine apparatus which in turn is associated with the postsynaptic thickening of the mature spine. Possible functional correlates are discussed.Dr. L.E. Westrum is an affiliate of the CDMRC at the University of Washington and a recipient of a Burroughs-Wellcome (USA) — Wellcome Trust (U.K.) Research Travel Grant. The research was also supported in part by NIH Grants NS 09678, NS 04053 (NINCDS) and DE 04942 (NIDR), DHHS     

A fluorescence-based high-throughput assay for antimicrotubule drugs

With the advent of combinatorial chemistry and the extensive libraries of potential drugs produced from it, there is a growing need for rapid sensitive, high-throughput screening for drug potency. Microtubules are important targets for anticancer agents, and new antimicrotubule compounds are of continued interest in drug development. The in vitro potency of antimicrotubule drugs may be evaluated by measuring the extent of tubulin assembly. The extent of polymerization is proportional to the turbidity of the solution, which usually has been measured as apparent absorption. The turbidity method has inherent problems that hinder its adaptation to a high-throughput format, such as a requirement for high protein concentrations and a high coefficient of variation. We present here a high-throughput assay for antimicrotubule activity in which fluorescence is used to monitor microtubule assembly. Both assembly-inhibiting and assembly-promoting compounds can be evaluated. The assay is rapid and easy to perform, and the data are reliable, with good accuracy and reproducibility.     

Raman optical activity and circular dichroism reveal dramatic differences in the influence of divalent copper and manganese ions on prion protein folding

The binding of divalent copper ions to the full-length recombinant murine prion protein PrP23-231 at neutral pH was studied using vibrational Raman optical activity (ROA) and ultraviolet circular dichroism (UV CD). The effect of the Cu2+ ions on PrP structure depends on whether they are added after refolding of the protein in water or are present during the refolding process. In the first case ROA reveals that the hydrated alpha-helix is lost, with UV CD revealing a drop from approximately 25% to approximately 18% in the total alpha-helix content. The lost alpha-helix could be that comprising residues 145-156, located within the region associated with scrapie PrP formation. In the second case, ROA reveals the protein's structure to be almost completely disordered/irregular, with UV CD revealing a drop in total alpha-helix content to approximately 5%. Hence, although Cu2+ binding takes place exclusively within the unfolded/disordered N-terminal region, it can profoundly affect the structure of the folded/alpha-helical C-terminal region. This is supported by the finding that refolding in the presence of Cu2+ of a mutant in which the first six histidines associated with copper binding to the N-terminal region are replaced by alanine has a similar alpha-helix content to the metal-free protein. In contrast, when the protein is refolded in the presence of divalent manganese ions, ROA indicates the alpha-helix is reinforced, with UV CD revealing an increase in total alpha-helix content to approximately 30%. The very different influence of Cu2+ and Mn2+ ions on prion protein structure may originate in the different stability constants and geometries of their complexes.     

The Value of Artificial Stimuli in Behavioral Research: Making the Case for Egg Rejection Studies in Avian Brood Parasitism

Experimentation is at the heart of classical and modern behavioral ecology research. The manipulation of natural cues allows us to establish causation between aspects of the environment, both internal and external to organisms, and their effects on animals' behaviors. In recognition systems research, including the quest to understand the coevolution of sensory cues and decision rules underlying the rejection of foreign eggs by hosts of avian brood parasites, artificial stimuli have been used extensively, but not without controversy. In response to repeated criticism about the value of artificial stimuli, we describe four potential benefits of using them in egg recognition research, two each at the proximate and ultimate levels of analysis: (1) the standardization of stimuli for developmental studies and (2) the disassociation of correlated traits of egg phenotypes used for sensory discrimination, as well as (3) the estimation of the strength of selection on parasitic egg mimicry and (4) the establishment of the evolved limits of sensory and cognitive plasticity. We also highlight constraints of the artificial stimulus approach and provide a specific test of whether responses to artificial cues can accurately predict responses to natural cues. Artificial stimuli have a general value in ethological research beyond research in brood parasitism and may be especially critical in field studies involving the manipulation of a single parameter, where other, confounding variables are difficult or impossible to control experimentally or statistically.