A scanning electron microscope study of the effect of an enterotoxin from Clostridium perfringens 8-6 on mice of different ages

Intestinal damage to mice caused by an enterotoxin from a coatless spore mutant of Clostridium perfringens type A (8-6) was examined by scanning electron microscopy. Two distinct types of damage were observed, both of which could be correlated with animal age. Damage appeared to occur in a specific sequence similar to that found in previous studies in rabbits. We conclude that the type of ileal tissue damage reflects the mode of toxin incorporation from the gut, which is a function of animal age.     

Pitfalls in the assay of carboxymethylcellulase activity

A purified endocellulase from Sclerotium rolfsii and a crude cellulase preparation from Trichoderma reesei are used to illustrate several pitfalls associated with the assay of carboxymethylcellulase activity and the subsequent attainment of linear enzyme dilution curves. It is shown that the nature of both the enzymes and the substrate make the assay unsuitable for use in the calculation of enzyme recovery and purity.     

Proteolytically active complexes of cathepsin L and a cysteine proteinase inhibitor; purification and demonstration of their formation in vitro.

Proteolytically active complexes of the proteinase cathepsin L, with an endogenous inhibitor of cysteine proteinases, were purified from sheep liver. The complexes were active against the synthetic substrate Z-Phe-Arg-NHMec and also the proteins azocasein and gelatin. The composition of the complexes was demonstrated by Western blotting, after reducing and nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis with monospecific antibodies raised against purified sheep liver cathepsin L and purified sheep liver cysteine proteinase inhibitor (probably stefin B). Similar complexes could be formed in vitro, by coincubation of purified sheep liver cathepsin L with the purified sheep liver cystatin at a pH of 5.5 or higher.     

Volatile anesthetics inhibit NMDA-stimulated45Ca uptake by rat brain microvesicles

We have previously shown that volatile anesthetics inhibit glutamate-stimulated [³H]MK-801 binding to the ionophore of NMDA receptor complexes in rat brain. In the present study, we examined the influence of enflurane and halothane on NMDA-stimulated⁴⁵Ca uptake by a microvesicle fraction isolated from rat brain. NMDA stimulated⁴⁵Ca uptake (30 sec) by rat brain microvesicles by up to 70% with an EC₅₀ of 1.4±0.5 M. The NMDA-stimulated⁴⁵Ca uptake was inhibited by MK-801 and D-AP-5 with IC₅₀'s of 10 M. Enflurane and halothane inhibited⁴⁵Ca uptake stimulated by 100 M NMDA by as much as 60–80% with IC₅₀'s of 0.2–0.3 mM, concentrations achieved during routine clinical use. Basal⁴⁵Ca uptake measured in the absence of agonist was not affected by the anesthetics. Glycine did not affect the level of NMDA-stimulated⁴⁵Ca uptake, but markedly reduced the inhibition of uptake caused by enflurane and halothane. Preincubation of microvesicles with NMDA resulted in a desensitization of NMDA-stimulated⁴⁵Ca uptake, with a t_1/2 of 20 sec. Enflurane and halothane diminished both the extent and rate of development of this desensitization, as did glycine. These findings support the idea that volatile anesthetic interference with neurotransmission at NMDA receptor complexes contributes to the development of the anesthetic state.     

Biosensors for environmental monitoring

Increasing environmental legislation which controls the release and the levels of certain chemicals in the environment has created a need for reliable monitoring of these substances in air, soil and especially water. Conventional analytical techniques, although highly precise, suffer from the disadvantages of high cost, the need for trained personnel and the fact that they are mostly laboratory bound. Biosensors because of their specificity, fast response times, low cost, portability, ease of use and a continuous real time signal, can present distinct advantages in certain cases. Their biological base makes them ideal for toxicological measurements which are suited for health and safety applications. Over the last 3-4 years there has been an increase in the number of publications concerning biosensors for environmental monitoring, especially in the field of pesticide measurements.This paper reviews some of the more important developments over the past 3-4 years.     

Photosynthetic responses of Zostera marina L. (Eelgrass) to in situ manipulations of light intensity

Summary Photosynthetic responses of the temperate seagrass, Zostera marina L., were examined by manipulations of photon flux density in an eelgrass bed in Great Harbor, Woods Hole, MA during August 1981. Sun reflectors and light shading screens were placed at shallow (1.3 m) and deep (5.5 m) stations in the eelgrass bed to increase (+35% to +40%) and decrease (-55%) ambient photon flux densities. The portion of the day that light intensities exceeding the light compensation point for Z. marina (H _comp) and the light saturation point (H _sat) were determined to assess the impact of the reflectors and shades. The H _comp and H _sat periods at the deep station shading screen were most strongly affected; H _comp was reduced by 11% and H _sat was reduced by 52%. Light-saturated photosynthetic rates, dark respiration rates, leaf chlorophyll content, chlorophyll a/b, PSU_{O 2} size, PSU density, leaf area, specific leaf area, leaf turnover times and leaf production rates were determined at the end of three sets of 1- to 2-week experiments. None of the measured parameters were affected by the photon flux density manipulations at the shallow station; however, at the deep station leaf production rates were significantly reduced under the shading screen and chlorophyll a/b ratios were higher at the reflector. These results indicate that adjustment to short-term changes in light regime in Z. marina is largely by leaf production rates. Further, the most dramatic changes in the periods of compensating or saturating photon flux densities had the greatest impact on the measured photosynthetic responses.     

Production and characterization of monoclonal antibodies to rabbit lymphocyte subpopulations. I. Tissue immunofluorescence and flow cytometric analysis

Nine monoclonal antibodies to rabbit T cells and B subpopulations have been generated from three separate fusions of spleen cells from mice immunized with fractionated populations of rabbit lymphocytes. These monoclonal antibodies, as well as a previously described rabbit T cell monoclonal antibody, 9AE10, have been analyzed by immunofluorescence staining on frozen tissue sections of rabbit thymus, spleen, and appendix. This screening method permits rapid identification of the lymphocyte subdomains in each tissue which is not possible by other screening methods. Each monoclonal antibody selected has a unique tissue staining pattern. Flow cytometric analysis of these monoclonal antibodies, using indirect immunofluorescence techniques on thymocytes, splenocytes, and PBL, revealed varying percentages of positive cells and individual mean fluorescence intensities indicating different epitope densities for each antigen. These monoclonal antibodies are now being used to characterize normal lymphocyte function and the role of specific lymphocyte subpopulations in experimental disease models in the rabbit.