Direct Comparisons of 2D and 3D Dental Microwear Proxies in Extant Herbivorous and Carnivorous Mammals

The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately.     

Preparation and use of the poly-l-lysine-gold probe: a differential marker of glomerular anionic sites

Summary The conditions required for the production of a polylysine-coated gold (PL-G) complex, which shows optimal sensitivity for the demonstration of tissue anionic sites, expressed under different conditions of pH have been investigated. Problems encountered with this complex have been compared with those found with other methods of conjugation of polylysine to colloidal gold. The performance of a bovine serum albumin (BSA)-stabilized PL-G complex was examined against other PL-G conjugates, including complexes that are commercially available, for the detection of heterogeneous glomerular anionic site populations, expressed at pH 2.5 and pH 7.0.     

Cytochrome P-450-catalyzed desaturation of valproic acid in vitro. Species differences, induction effects, and mechanistic studies

The cytochrome P-450-mediated desaturation of valproic acid (VPA) to its hepatotoxic metabolite, 2-n-propyl-4-pentenoic acid (4-ene-VPA), was examined in liver microsomes from rats, mice, rabbits and humans. The highest substrate turnover was found with microsomes from rabbits (44.2 +/- 2.7 pmol of product/nmol P-450/15 min), while lower activities were observed in preparations from human, mouse, and rat liver, in that order. Pretreatment of animals with phenobarbital led to enhanced rates of formation of 4-ene-VPA in vitro and yielded induction ratios for desaturation ranging from 2.5 to 8.4, depending upon the species. Comparative studies in the rat showed that phenobarbital is a more potent inducer of olefin formation than either phenytoin or carbamazepine. The mechanism of the desaturation reaction was studied by inter- and intramolecular deuterium isotope effect experiments, which demonstrated that removal of a hydrogen atom from the subterminal C-4 position of VPA is rate limiting in the formation of both 4-ene- and 4-hydroxy-VPA. Hydroxylation at the neighboring C-5 position, on the other hand, was highly sensitive to deuterium substitution at that site, but not to deuteration at C-4. Based on these findings, it is proposed that 4-ene- and 4-hydroxy-VPA are products of a common P-450-dependent metabolic pathway, in which a carbon-centered free radical at C-4 serves as the key intermediate. 5-Hydroxy-VPA, in contrast, derives from an independent hydroxylation reaction.     

Enumeration of denitrifying microbial populations in turf

Summary Denitrifer populations of a silt and silt loam soil under a Kentucky bluegrass turf were enumerated using the most probable number (MPN) procedure. The influence of soil texture, soil depth, soil moisture, and additions of nitrate fertilizer on denitrifier populations were determined. Saturated soil conditions increased denitrifier populations 87-fold in the silt soil and 121-fold in the silt loam soil. Denitrifier populations did not differ significantly between soil depths and additions of fertilizer nitrate did not influence populations.