Arsenic Bioaccumulation in Freshwater Fishes

The arsenic ambient water quality criterion (AWQC) for protection of human health via ingestion of aquatic organisms is currently 0.14 μ g/L. This AWQC is derived using a bioconcentration factor (BCF) of 44, which is a consumption-weighted average based on two data points for oysters and fish that was proposed by the U.S. Environmental Protection Agency in 1980 for broad application to freshwater and marine environments. This BCF is based on the assumption that bioaccumulation is a simple linear function of the exposure concentration. In the nearly quarter of a century since this BCF was promulgated, there have been additions to the arsenic bioaccumulation database and a broader scientific understanding of bioaccumulation mechanisms and how they can be applied to estimating tissue concentrations in aquatic organisms. From this database, we identified 12 studies of arsenic bioaccumulation in freshwater fishes in order to explore differences in laboratory-generated BCFs and field-generated bioaccumulation factors (BAFs) and to assess their relationship to arsenic concentrations in water. Our analysis indicates that arsenic concentrations in tissue and arsenic BAFs may be power functions of arsenic concentration in water. A power function indicates that the highest BCF values may occur at low background levels and may decrease as environmental concentrations increase above the ambient range.     

Age of menarche in pigtail monkeys (Macaca nemestrina): A cross-sectional survey of perineal tumescence

A four-month survey of perineal tumescence in 131 young female pigtail monkeys ($\text{Macaca nemestrina}$) revealed that most females had begun to swell by the time they were 3 years old. Those that had not begun to swell by that time were generally of lower weight than their peers. Those that tumesced before they were 3 years old tended to be heavier than their peers, but were not necessarily heavier than older, nonswelling females.     

Self-organizing maps: stationary states,metastability and convergence rate

We investigate the effect of various types of neighborhood function on the convergence rates and the presence or absence of metastable stationary states of Kohonen's self-organizing feature map algorithm in one dimension. We demonstrate that the time necessary to form a topographic representation of the unit interval [0, 1] may vary over several orders of magnitude depending on the range and also the shape of the neighborhood function, by which the weight changes of the neurons in the neighborhood of the winning neuron are scaled. We will prove that for neighborhood functions which are convex on an interval given by the length of the Kohonen chain there exist no metastable states. For all other neighborhood functions, metastable states are present and may trap the algorithm during the learning process. For the widely-used Gaussian function there exists a threshold for the width above which metastable states cannot exist. Due to the presence or absence of metastable states, convergence time is very sensitive to slight changes in the shape of the neighborhood function. Fastest convergence is achieved using neighborhood functions which are "convex" over a large range around the winner neuron and yet have large differences in value at neighboring neurons.     

Optimization of transverse alternating field electrophoresis for strain identification of Leuconostoc oenos

Genomic DNA of several strains oof oenological lactic bacteria belonging to the species Lactobacillus plantarum, Leuconostoc oenos and Pediococcus pentosaceus was digested by the rare-cutting endonucleases ApaI and SmaI. The restriction products were separated by transverse alternating field electrophoresis (TAFE). The size of the genome of L. oenos estimated by adding the molecular size of the ApaI fragments was on average 1320 kb. A strong polymorphism was observed between the strains, which could be easily differentiated except for two industrial strains of L. oenos. A simple modification of the TAFE apparatus is proposed to improve the separation of the DNA fragments. Correspondence to: J.-N. Hallet     

Effects of weaning age on mortality of colony-born Macaca nemestrina

In an effort to determine empirically the proper age for separation of pigtailed macaque (Macaca nemestrina ) infants from their dams in a large domestic breeding colony, we conducted a retrospective survey of 1,592 infants. Survivorship was highest for infants not separated from their dams at all and for those separated within the first four months of life. Survivorship was poor for animals separated during or after the fifth month. Thus, not weaning or weaning early are the most acceptable management strategies in terms of mortality risk. This result is paradoxical with regard to nutritional considerations, but appears to be related to a sensitive period in social development. The relative advantages and disadvantages of various weaning ages are discussed.     

Distribution and properties of NADPH-linked aldehyde reductases from rat brain synaptosomes

Studies on the subcellular distribution of NADPH-linked aldehyde reductase from rat brain showed that 10% of the total reductase activity is located in the mitochondrial-synaptosomal fraction. There are differences in the percentages of reductase activity found in the synaptosomes compared to cytosol in various regions of the brain. The NADPH-linked aldehyde reductase from the synaptosomal fraction exhibited a nonlinear Lineweaver-Burk plot. This nonlinearity is due to the presence of two distinct aldehyde reductases, which can be distinguished by Michealis constants forp-nitrobenzaldehyde of 4.1×10^–5 M and 2.6×10^–6 M. The two NADPH-linked aldehyde reductases isolated from synaptosomes were further characterized according to pH optima, andK _i values for inhibition by barbiturates. In addition regional distributions for the two enzymes were determined. TheK _i values for pentobarbital for the highK _m enzyme and the lowK _m enzyme were estimated to be 2×10^–5 M and 6×10^–5 M, respectively. It was concluded from the above studies that the lowK _m reductase is probably responsible for 3,4-dihydroxyphenylglycoaldehyde (derived from norepinephrine) reduction in brain and a role of the highK _m enzyme for protection of neurons from high concentrations of chemically reactive aldehydes was proposed.This work was supported in part by Grants from the National Institute of Mental Health, MH 18948 from the University of Colorado Council on Research and Creative Work and by an MBS Program Grant #081-39.This work was performed in partial fulfillment of the requirements for the Ph. D. thesis.     

Vascularization of plexus myentericus (Auerbach) in the large intestine of the cat

1. Coincidental preparation of the intramuscular vascular bed and the plexus myentericus (Auerbach) of the cat's large intestine by India-ink method and silverimpregnation allowed to demonstrate independent vascularisation of ganglia and nerve-branches of the plexus Auerbach. 2. Each ganglion is surrounded by a capillary network widely independently existing of the intramuscular capillary bed. The preferred innervated terminal arterioles and especially the sphincteric capillaries opening into the periganglionic capillary network and the numerous arterio-venous short-circuits in its marginal area suggest to conclude a differentiated regulation of blood supply.