Effects of dietary phytol and phytanic acid in animals

Feeding of phytol in large doses (2-5% by weight in the diet) led to accumulation of phytanic acid in the mouse, rat, rabbit, and chinchilla, the degree of accumulation depending upon the level of dietary intake. The relative concentration of phytanic acid, expressed as a percentage of the total fatty acids, was as high as 20-60% in liver and 30-40% in serum. Phytenic acid, which may be an intermediate in the conversion of phytol to phytanic acid, also accumulated. When phytol was withdrawn from the diet, tissue and serum concentrations of phytanic acid fell rapidly, which indicates the ability of the normal animal to metabolize phytanic acid readily. At high dosages in the diet, phytol inhibited growth and caused death within 1-4 weeks. In the mouse, dietary phytanic acid and dietary phytol fed in equivalent amounts were of comparable toxicity. Accumulation of tissue phytanic acid occurred more rapidly when phytanic acid was fed than when phytol was fed in equal amounts. In none of the animals fed either phytol or phytanic acid were there any signs of neurological defects. Histologic examination of rats fed phytol showed some fat accumulation, glycogen depletion, and karyokinesis in the liver. There were no pathologic changes in the retina or in the peripheral and central nervous system such as those described in Refsum's disease.     

A nonstationary Poisson point process describes the sequence of action potentials over long time scales in lateral-superior-olive auditory neurons

The behavior of lateral-superior-olive (LSO) auditory neurons over large time scales was investigated. Of particular interest was the determination as to whether LSO neurons exhibit the same type of fractal behavior as that observed in primary VIII-nerve auditory neurons. It has been suggested that this fractal behavior, apparent on long time scales, may play a role in optimally coding natural sounds. We found that a nonfractal model, the nonstationary dead-time-modified Poisson point process (DTMP), describes the LSO firing patterns well for time scales greater than a few tens of milliseconds, a region where the specific details of refractoriness are unimportant. The rate is given by the sum of two decaying exponential functions. The process is completely specified by the initial values and time constants of the two exponentials and by the dead-time relation. Specific measures of the firing patterns investigated were the interspike-interval (ISI) histogram, the Fano-factor time curve (FFC), and the serial count correlation coefficient (SCC) with the number of action potentials in successive counting times serving as the random variable. For all the data sets we examined, the latter portion of the recording was well approximated by a single exponential rate function since the initial exponential portion rapidly decreases to a negligible value. Analytical expressions available for the statistics of a DTMP with a single exponential rate function can therefore be used for this portion of the data. Good agreement was obtained among the analytical results, the computer simulation, and the experimental data on time scales where the details of refractoriness are insignificant. For counting times that are sufficiently large, yet much smaller than the largest time constant in the rate function, the Fano factor is directly proportional to the counting time. The nonstationarity may thus mask fractal fluctuations, for which the Fano factor increases as a fractional power (less than unity) of the counting time.     

Autophagy proteins control goblet cell function by potentiating reactive oxygen species production

Delivery of granule contents to epithelial surfaces by secretory cells is a critical physiologic process. In the intestine, goblet cells secrete mucus that is required for homeostasis. Autophagy proteins are required for secretion in some cases, though the mechanism and cell biological basis for this requirement remain unknown. We found that in colonic goblet cells, proteins involved in initiation and elongation of autophagosomes were required for efficient mucus secretion. The autophagy protein LC3 localized to intracellular multi‐vesicular vacuoles that were consistent with a fusion of autophagosomes and endosomes. Using cultured intestinal epithelial cells, we found that NADPH oxidases localized to and enhanced the formation of these LC3‐positive vacuoles. Both autophagy proteins and endosome formation were required for maximal production of reactive oxygen species (ROS) derived from NADPH oxidases. Importantly, generation of ROS was critical to control mucin granule accumulation in colonic goblet cells. Thus, autophagy proteins can control secretory function through ROS, which is in part generated by LC3‐positive vacuole‐associated NADPH oxidases. These findings provide a novel mechanism by which autophagy proteins can control secretion.     

A probabilistic model for designing and assessing the performance of eDNA sampling protocols

Environmental DNA (eDNA) sampling, the detection of species‐specific genetic material in water samples, is an emerging tool for monitoring aquatic invasive species. Optimizing eDNA sampling protocols can be challenging because there is imperfect understanding of how each step of the protocol influences its sensitivity. This paper develops a probabilistic model that characterizes each step of an eDNA sampling protocol to evaluate the protocol's overall detection sensitivity for one sample. The model is then applied to analyse how changes over time made to the eDNA sampling protocol to detect bighead (BH) and silver carp (SC) eDNA have influenced its sensitivity, and hence interpretation of the results. The model shows that changes to the protocol have caused the sensitivity of the protocol to fluctuate. A more efficient extraction method in 2013, new species‐specific markers with a qPCR assay in 2014, and a more efficient capture method in 2015 have improved the sensitivity, while switching to a larger elution volume in 2013 and a smaller sample volume in 2015 have reduced the sensitivity. Overall, the sensitivity of the current protocol is higher for BH eDNA detection and SC eDNA detection compared to the original protocol used from 2009 to 2012. The paper shows how this model of eDNA sampling can be used to evaluate the effect of proposed changes in an eDNA sampling and analysis protocol on the sensitivity of that protocol to help researchers optimize their design.     

Behavioral thermoregulation of the toad, Bufo marinus: effects of air humidity

Two experiments were performed. The first tested the hypothesis that the toad, Bufo marinus, will select a lower ambient temperature under dry environmental conditions. This behavioral response would reduce evaporative water loss and facilitate survival on land. The second experiment measured the effects of temperature on evaporative water loss. In the first experiment, toads were placed in a thermal gradient (11-40 degrees C) for 3 days. On days 1 and 3, water-filled dishes were placed along the temperature gradient and humid air was circulated through the chamber. On day 2, water dishes were removed, and dry air was circulated through the chamber. Body temperature (Tb) was recorded with a cloacal thermistor. Selected Tb was approximately 8.6 degrees C lower during the dry conditions than during the humid conditions. The behavioral hypothermia took about 6 h to develop. In the second experiment, a reduction in Tb from 17.7 to 12 degrees C reduced evaporative water loss by 42%. Consequently, behavioral hypothermia of the toad is an important adaptation to dry environmental conditions.     

The effect of Gymnema sylvestre extracts on the sweetness of eight sweeteners

Although numerous experiments have demonstrated the sweetness-inhibitingeffects of Gymnema sylvestre extracts, no human psychophysicalstudies have been done to quantitatively assess G.sylvestre'seffects across a set of natural and intensive sweeteners. Thepresent study evaluated the sweetness-inhibiting effects ofG.sylvestre extracts on three concentrations each of acesulfameK, aspartame, sodium cyclamate, fructose, glucose, sucrose,stevioside and xylitol. Subjects made sweetness judgements ofthe stimuli following pretreatment with either distilled water,commercial tea or G.sylvestre extracts. Gymnema sylvestre pretreatmentreduced the sweetness of the stimuli by an average of 77% withno evidence for a differential effect across sweeteners. Thepercentage reduction in sweetness was constant across the low,medium and high concentrations of the sweeteners. Kinetic plotsof the data fit the Michelis-Menten model for non-competitiveinhibition, but statistical results did not permit competitiveor uncompetitive mechanisms to be ruled out. A receptor occupancy/blockingmechanism is unlikely. The results support disruption of a moregeneral aspect of sweetness transduction and fit a type of ‘mixed’inhibition involving an effect on the breakdown of the stimulus/receptorcomplex. Inhibition of a later step in a sequential-step transductionsystem and/or a change in the physicochemistry of the environmentof the stimulus/receptor complex are possible. ²Present address: Department of Chemistry, Clark University,Worcester, MA 01610, USA. ³Present address: Department of Psychology, University of Rochester,Rochester, NY 14627, USA     

Regulated translation termination at the upstream open reading frame in s-adenosylmethionine decarboxylase mRNA.

The upstream open reading frame (uORF) in the mRNA encoding S-adenosylmethionine decarboxylase is a cis-acting element that confers feedback control by cellular polyamines on translation of this message. Recent studies demonstrated that elevated polyamines inhibit synthesis of the peptide encoded by the uORF by stabilizing a ribosome paused in the vicinity of the termination codon. These studies suggested that polyamines act at the termination step of uORF translation. In this paper, we demonstrate that elevated polyamines stabilize an intermediate in the termination process, the complete nascent peptide linked to the tRNA that decodes the final codon. The peptidyl-tRNA molecule is found associated with the ribosome fraction, and decay of this molecule correlated with release of the paused ribosome from the message. Furthermore, the stability of this complex is influenced by the same parameters that influence regulation by the uORF in vivo, namely the concentration of polyamines and the sequence of the uORF-encoded peptide. These results suggest that the regulated step in uORF translation is after formation of the peptidyl-tRNA molecule but before hydrolysis of the peptidyl-tRNA bond. This regulation may involve an interaction between the peptide, polyamines, and a target in the translational apparatus.