Gustatory Responsiveness to food-associated acids in the spider monkey (Ateles geoffroyi)

The gustatory responsiveness of four adult spider monkeys to five food-associated acids was assessed in two-bottle preference tests of brief duration (3 min). The animals were given the choice between a 30 mM sucrose solution and defined concentrations of citric acid, ascorbic acid, malic acid, acetic acid, or tannic acid dissolved in a 30 mM sucrose solution. With this procedure,Ateles geoffroyi was found to significantly discriminate concentrations as low as 5 mM ascorbic acid, citric acid, and acetic acid, 10 mM malic acid, and 0.1 mM tannic acid from the alternative stimulus. With the latter two substances, the monkeys rejected all suprathreshold concentrations tested, whereas with the former three substances, the animals showed an inverted U-shaped function of preference, i.e. they rejected high concentrations, but significantly preferred low but detectable concentrations of these acidic tastants over the alternative sweet stimulus. The results showed (1) the spider monkey to respond to the same range of acid concentrations as other nonhuman primate species; (2) thatAteles geoffroyi, is able to detect food-associated acids at concentrations well below those present in most fruits; and (3) that unlike most other primate species tested so far, spider monkeys do not generally reject acidic tastants but show a substanceand concentration-dependent change in responsiveness that may range from rejection to preference. The results support the assumptions that spider monkeys may use sourness and/or astringency of food-associated acids as a criterion for food selection, and that the gustatory responsiveness ofAteles geoffroyi to acidic tastants might reflect an evolutionary adaptation to frugivory.     

The role of oxygen availability in the embryonation of Heterakis gallinarum eggs

The importance of oxygen availability in the embryonation of the infective egg stages of the gastrointestinal nematode parasite Heterakis gallinarum was studied in the laboratory. Unembryonated H. gallinarum eggs were kept under either aerobic conditions by gassing with oxygen, or anaerobic conditions by gassing with the inert gas nitrogen, under a range of constant temperatures. Oxygenated eggs embryonated at a rate influenced by temperature. Conversely, eggs treated with nitrogen showed no embryonation although when these eggs were transferred from nitrogen to oxygen gas after 60 days of treatment, embryonation occurred. This demonstrated that oxygen is an essential requirement for H. gallinarum egg development, although undeveloped eggs remain viable, even after 60 days in low oxygen conditions. The effects of climate on the biology of free-living stages studied under constant laboratory conditions cannot be applied directly to the field where climatic factors exhibit daily cycles. The effect of fluctuating temperature on development was investigated by including an additional temperature group in which H. gallinarum eggs were kept under daily temperature cycles between 12 and 22°C. Cycles caused eggs to develop significantly earlier than those in the constant mean cycle temperature, 17°C, but significantly slower than those in constant 22°C suggesting that daily temperature cycles had an accelerating effect on H. gallinarum egg embryonation but did not accelerate to the higher temperature. These results suggest that daily fluctuations in temperature influence development of the free-living stages and so development cannot be accurately predicted on the basis of constant temperature culture.     

Ability to discriminate between related odor mixtures

The purpose of this study was to investigate (i) the abilityof human subjects to detect changes in related odor mixturesfollowing omission of components, and (ii) the possible relationshipbetween the number of substances comprising a mixture and theability to detect changes in its composition. A total of 36panelists was tested repeatedly in five separate sessions usingsniff bottles, and asked to rate the difference between pairsof stimuli using a 6-point verbal scale. Stimuli were 3-, 6-and 12-component mixtures paired with stimuli from which oneor more of the components had been omitted or had been leftunchanged. Rating behavior was highly consistent, with no significantdifferences found between sessions or panels in judging theidentical control pairs. Although asymmetrical pairs were judgedto be different significantly more often than control pairs,correct assignment was considerably poorer than expected. Correlationsbetween complexity of a stimulus and ability to discriminatechanges in its composition were weak and possibly confoundedby substance-specific, synergistic effects. While factors suchas lack of feedback or the arbitrary nature of the stimuli mayhave affected performance, it remains to be investigated whetherthe findings indeed reflect our limited capacity to discriminatebetween related odor mixtures.     

Quantal entry of diphtheria toxin to the cytosol

The rate-limiting step in diphtheria toxin (DT) intoxication of Vero cells has been determined utilizing cycloheximide as an inhibitor of the intoxication process. Cycloheximide is shown to inhibit the toxin catalyzed ADP-ribosylation of elongation factor 2 (EF-2). The inhibition is blocked by puromycin thus establishing the ribosome as the location of cycloheximide protection. Washing cells free of cycloheximide rapidly reverses the protective effect. The initial rates of protein synthesis inhibition observed after removal of cycloheximide from DT-intoxicated cells are 5 to 12-fold greater than rates observed in unprotected cells and are shown to reflect ADP-ribosylation of EF-2 by cytosolic DT. Ten to thirty minutes after cycloheximide removal, the rate of protein synthesis inhibition abruptly changes to values identical to those of unprotected cells. Both the initial rates and extent of the initial rapid inactivation are directly related to toxin concentration and time of incubation with DT in the presence of cycloheximide. We concluded that: the rate-limiting step in protein synthesis inhibition by DT is not the ADP-ribosylation of EF-2 by cytosolic toxin but rather the earlier entry step of DT into the cytosol. DT enters the cytosol as a bolus of sufficient size to rapidly inactivate all EF-2 in that cell. It is inferred from 1 and 2 that the first order inactivation rate exhibited by DT is the result of the probability of the release of a bolus of toxin to the cytosol of any cell in the population per unit time. Autoradiographic analysis of intoxicated cell populations support this two-population state model. The size of a single bolus or quantum of DT is calculated from data over the range of 10(-11) to 10(-9) M DT and is found to remain constant. We suggest that the cytosolic entry mechanism of DT results from a unique ability of the internalized toxin molecules to destabilize the vesicular membrane resulting in a random release of a bolus of toxin into the cytosol. Because the bolus size remains constant over a 50-fold change in receptor occupancy the possibility is raised that DT undergoes a post-receptor packaging process, package size remaining a constant and package number increasing with receptor occupancy.     

Damage to Pseudomonas aeruginosa PAO1 bacteriophage F116 DNA by biocides

The mechanism of action of biocides against viruses has not been widely studied, although two main targets are viral proteins (capsids, enzymes) and the viral genome. This study was undertaken in order to investigate the efficacy of several disinfectants against the nucleic acid of the Pseudomonas aeruginosa PAO bacteriophage F116. Of all the biocides tested, only peracetic acid affected significantly the phage genome. However, it is not clear whether the nucleic acid was damaged inside the phage capsid or when released into the surrounding medium.     

The acute effects of low-intensity exercise on plasma lipids in endurance-trained and untrained young adults.

The acute effects of low-intensity exercise on plasma lipids were assessed in 22 healthy, normolipidaemic volunteers [mean age (SEM) 21.1 (0.2) years] of whom 11 were untrained and 11 endurance trained. Each subject walked for 2 h on a treadmill at a speed selected to elicit 30% [29.8 (3.9)%] of his or her maximal oxygen uptake. All subjects consumed a similar diet, i.e. 48% of energy from carbohydrate, for 2 days prior to the test. Pre-exercise, high-density lipoprotein (HDL) cholesterol concentration was higher in the trained group than in the untrained group [0.88 (0.06) mmol.l-1 vs 0.73 (0.09) mmol.l-1, P less than 0.05]. The walk elicited an increase in blood lactate concentration (P less than 0.01) but glucose homeostasis was well maintained by both groups. After 2 h of walking total cholesterol had increased by 13 (0.6)% (P less than 0.05). HDL cholesterol concentration increased by 17 (1.6)%, so that the ratio of total to HDL cholesterol was lower after the walk than pre-exercise (P less than 0.05). In the endurance-trained group HDL cholesterol concentration increased progressively, being 7.9 (2.4)% higher after 1 h and 19.7 (1.6)% higher after 2 h. A different response was evident in the untrained group where a rise after the 1st h [25.1 (2.3)%] was followed by a decrease towards pre-exercise values. These results show that one prolonged bout of low-intensity exercise modifies lipoprotein metabolism and hold out the interesting possibility that this response may differ in trained and untrained individuals.