Modulation of collagen-induced arthritis in rats by non-RT1-linked genes

An immunogenetic analysis of the progeny of F1, F2, and (F1 x parental strain) test cross-matings between the CIA-susceptible DA(RT1av1) and the CIA-resistant BN(RT1n) rat strains was performed. Hybrid progeny were tested for susceptibility to CIA as induced by native calf type II collagen, and for immune response to native rat and calf type II collagens. The results show a minimum of one non-RT1-linked gene which modifies susceptibility to CIA in RT1a/a hybrid progeny. These hybrids have anti-collagen immune responses equivalent to those of the parental DA strain as measured by skin testing and IgG antibody titers. An affect of sex hormones on susceptibility to CIA is indicated, because hybrid females were more susceptible than were hybrid males of equivalent RT1 allotypes.     

A note on the use of the Catalasemetre in assessing the quality of milk

The Catalasemetre, for assessing the quality of raw and pasteurized milk, has been studied. No correlation was found between catalase activity and bacterial counts for farm bulk tank milks within the range 5.2 ± 10²-5.4 ± 10⁵ cfu/ml. Similarly, no relation was observed between catalase activity and somatic cell counts of milk (range of counts from 0.08 to 3.5). However, the catalase activity and bacterial count of pasteurized milks which had been pre-incubated at 21.C for 25 h in the presence of crystal violet-penicillin-nisin to inhibit Gram-positive bacterial growth were significantly related. Thus, the use of this pre-incubation procedure coupled with the Catalasemetre to estimate bacterial growth, has potential in assessing the keeping quality of pasteurized milk samples within 25.5 h of production. Results on the thermostability of native milk catalase are also presented.     

Yeasts in molecular biology. Spheroplast preparation withCanadida utilis,Schizosaccharomyces pombe andSaccharomyces cerevisiae

Efficient preparation of spheroplasts fromCandida utilis, Saccharomyces cerevisiae, andSchizosaccharomyces pombe, using a purified mixture of enzymes fromTrichoderma harzianum, is described. Limitations of other methods, and differences between yeasts are demonstrated.     

Sulfate inhibition of molybdate assimilation by planktonic algae and bacteria: some implications for the aquatic nitrogen cycle

Molybdenum is required for both dinitrogen fixation and nitrate assimilation. In oxic waters the primary form of molybdenum is the molybdate anion. Using radioactive [⁹⁹Mol Na₂MoO₄, we have shown that the transport of molybdate by a natural assemblage of freshwater phytoplankton is light-dependent and follows typical saturation kinetics. The molybdate anion is strikingly similar to sulfate and we present data to show that sulfate is a competitive inhibitor of molybdate assimilation by planktonic algae and bacteria. The ability of freshwater phytoplankton to transport molybdate is inhibited at sulfate concentrations as low as 5% of those in seawater and at sulfate: molybdate ratios as low as 50 to 100 times lower than those found in seawater, Similarly, the growth of both a freshwater bacterium and a saltwater diatom was inhibited at sulfate: molybdate ratios lower than those in seawater.The ratio of sulfate to molybdate is 10 to 100 times greater in seawater than in fresh water. This unfavorable sulfate: molybdate ratio may make molybdate less biologically available in the sea. The sulfate: molybdate ratio may explain, in part, the low rates of nitrogen fixation in N-limited salt waters.     

Numerical solution of a nonlinear advance-delay-differential equation from nerve conduction theory

A functional differential equation which is nonlinear and involves forward and backward deviating arguments is solved numerically. The equation models conduction in a myelinated nerve axon in which the myelin completely insulates the membrane, so that the potential change jumps from node to node. The equation is of first order with boundary values given at t=±. The problem is approximated via a difference scheme which solves the problem on a finite interval by utilizing an asymptotic representation at the endpoints, cubic interpolation and iterative techniques to approximate the delays, and a continuation method to start the procedure. The procedure is tested on a class of problems which are solvable analytically to access the scheme's accuracy and stability, then applied to the problem that models propagation in a myelinated axon. The solution's dependence on various model parameters of physical interest is studied. This is the first numerical study of myelinated nerve conduction in which the advance and delay terms are treated explicitly.Supported in part by NSF Grant MCS8301724 and by a Biomedical Research Support Grant 2SO7RR0706618 from NIH     

Growth Regulation In Multilayered Cultures of Human Diploid Fibroblasts: the Roles of Contact, Movement and Matrix Production

Abstract. Early subcultures of human embryonic lung fibroblasts are exceptional, as they grow far beyond confluence before growth ceases: the stationary dish may well contain 3-10 monolayer equivalents. Maximal growth rates, however, occur at about one-sixth confluence when doubling times are 15-20 hr; a density at which cell contacts begin to become frequent. the fact that a slowing down of growth is first apparent at such low densities argues against this regulation being due to diffusion effects. Confirmation of the role of short-range or contact interactions in growth regulation comes from an experiment using mixed cultures of fibroblasts: this shows that growth inhibition is not carried by medium-borne influences but depends on short-range (<1 mm) interactions. Evidence that cells can escape the effects of such contact interactions and so divide comes from time-lapse studies of dense cultures: there is a burst of motility soon after a fresh-medium change, which is followed by a burst of mitosis × 20 hr later. A medium change to conditioned medium supplemented with 10% foetal calf serum leads to neither the burst of motility nor the subsequent burst of mitosis, although this medium is better able to support the growth of sparse cells than is fresh medium. Data are also presented to show that the amount of collagen deposited in superconfluent cultures affects their growth: the stimulation of collagen production with ascorbic acid leads to an unexpectedly low stationary cell density and rather less movement in the culture. This result suggests that the collagen stabilizes cell contacts that are responsible for growth inhibition. the question of why these cells grow more slowly as density increases cannot be answered directly by these experiments; nevertheless, the results suggest that cell contact affects the permeability of the cell membrane to medium.     

Hippocampal electrical activity and gamma-aminobutyrate metabolism in brain tissue following administration of homocysteine

Abstract: The concentration of γ-aminobutyrate (GABA) and the activity of glutamate decarboxylase and GABA-transaminase were measured in extracts of mouse brain before the onset and during the course of generalized seizures induced by systemic administration of homocysteine thiolactone. The results indicate that whole brain GABA metabolism is unaffected by subconvulsive and convulsive doses of homocysteine at all stages of the generalized seizure. Electroencephalographic monitoring of rat brain electrical activity via hippocampal electrode implantation allowed the course of homocysteine-induced seizures to be followed and afforded a means of quantifying such seizures.