Biomedical subjects

P D Schreuders

Publications and source records attributed to P D Schreuders.

5 recordsLinked to original sources

PubMed1996

Characterization of intraembryonic freezing in Anopheles gambiae embryos.

Intraembryonic freezing (IEF) in Anopheles mosquito embryos has been evaluated by differential scanning calorimetry with respect to embryo age, temperature, rate and duration of cooling, and absence or presence of extraembryonic ice. The initial temperatures for intraembryonic ice nucleation were -30.1 +/- 0.3, -28.4 +/- 0.4, and -29.1 +/- 0.2 degree C for embryos incubated for 15 h at 17 degrees C, 15 h at 26 degrees C, and 24 h at 26 degrees C, respectively, after oviposition. The first value is slightly but significantly lower than the latter two. These values were obtained on embryos in which the surface water was removed by brief drying; however, the values were nearly identical when external water and ice were present. Not only were the embryos of all three ages able to supercool at least transiently to -26 degrees C, but they could remain supercooled for up to 4 h at -20 degrees C after being cooled to -20 degrees C at 10 degrees C/min or (in the case of embryos incubated for 15 h at 26 degrees C) at 100 degrees C/min. The amount of freezable water in single embryos has been calculated from the differential scanning calorimetry measurements to be 3.45 +/- 0.08, and 3.53 +/- 0.06 microgram for embryos incubated for 15 h at 17 degrees C, 15 h at 26 degrees C, and 24 h at 26 degrees C, respectively. The differences are not significant. The corresponding values for the total water contents for embryos of the three ages were 4.04 +/- 0.20, 3.72 +/- 0.16, and 3.98 +/- 0.10 microgram, values that also did not differ significantly. Water thus makes up approximately 74% of the total weight of the embryo (approximately 5.3 micrograms) and about 91% of that water is freezable. Total water contents were determined gravimetrically after extensive air and vacuum drying. The kinetics of dehydration were determined during the air drying. They differed substantially among the three ages. The embryos incubated for 15 h at 17 degrees C lost water at about four times the rate of those incubated for 15 h at 26 degrees C and 10 times the rate of the embryos incubated for 24 h at 26 degrees C.

Animals↗

PubMed1994

An analysis of coupled multicomponent diffusion in interstitial tissue.

A one-dimensional multicomponent kinetic model was developed to simulate the interstitial diffusion of macromolecules in a three component system, consisting of water, the macromolecule and the interstitial matrix. Movement of the individual components was modeled as occurring in finite jumps between discrete low energy wells along paths defined in terms of species occupation. The flow rate was expressed as a function of the local species concentration, the jump distance, and a kinetic frequency parameter. The model, implemented in pseudo-bond graph form, was examined by fitting it to data obtained for the transport of fluorescein tagged dextran to determine the kinetic constants for that specific system.

Animals↗

PubMed1993

Contributions of cooling and warming rate and developmental stage to the survival of Drosophila embryos cooled to -205 degrees C.

Because of their high susceptibility to chilling injury, permeabilized Drosophila embryos can not be cryobiologically preserved by slow freezing at rates low enough to prevent the formation of intraembryonic ice. Calculations indicated that to outrun the chilling injury they must be cooled and warmed rapidly at an estimated 20,000 degrees C/min or faster. Ordinarily, such cooling rates would inevitably produce lethal intracellular ice. To prevent this, embryos must contain and be surrounded by sufficiently high concentrations of glass-promoting solutes to induce vitrification on cooling and prevent devitrification on warming. Like Steponkus et al. (Nature 345, 170, 1990) we have used ethylene glycol as the solute and have exposed permeabilized 12-h embryos to it in two steps. (Permeabilization was effected by exposing dechorionated embryos to a mixture of 0.3% 1-butanol in n-heptane for 90 or 110 s.) The two steps were (i) a 30-min exposure to 2 M ethylene glycol at 23 degrees C and (ii) a 5-min exposure to 8.5 M ethylene glycol [+/- 10% polyvinylpyrrolidone (PVP)] at 5 degrees C. The volumetric response to the first step indicates that full permeation of the 2 M glycol has been approached by 30 min. The point of the second step is to raise the intraembryonic concentration of ethylene glycol to near 8.5 M ethylene glycol by osmotic dehydration. Survival based on hatching is some 45% at this point. When 12-h embryos in 8.5 M glycol containing 10% PVP are then cooled to -205 degrees C at approximately 100,000 degrees C/min and warmed at about that rate, an average of about 12% survive (hatch), although in about half the runs 15-29% survive. Survivals in the absence of PVP are usually poorer but have been as high as 40%. Currently, 5% of the surviving larvae develop to adult flies (Steponkus et al. reported 18% hatching and 3% development to adult). Embryos that develop but do not hatch show readily detectable abnormalities in mouth parts and dorsal closure. Very high warming rates are much more critical to survival than are very high cooling rates; for example, none survive when warming is 2000 degrees C/min. The deleterious effect of slow warming is exerted between -80 and -40 degrees C. The lack of reciprocity between the effects of time spent cooling and time spent warming argues against ascribing death to chilling injury. Rather, it and other data argue for ascribing death to the devitrification during warming of cytoplasm that vitrified during cooling.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Cryobiological preservation of Drosophila embryos.

The inability to cryobiologically preserve the fruit fly Drosophila melanogaster has required that fly stocks be maintained by frequent transfer of adults. This method is costly in terms of time and can lead to loss of stocks. Traditional slow freezing methods do not succeed because the embryos are highly sensitive to chilling. With the procedures described here, 68 percent of precisely staged 15-hour Oregon R (wild-type) embryos hatch after vitrification at -205 degrees C, and 40 percent of the resulting larvae develop into normal adult flies. These embryos are among the most complex organisms successfully preserved by cryobiology.

Animals↗

PubMed1988

Normal wound healing compared to healing within porous Dacron implants.

This study examined the hypothesis that healing within porous implants differs from that in normal connective tissue. Special attention was given to extracellular components including collagen, reticular fibers, and ground substance, and to enzymes associated with activated macrophages. Using Dacron velour and the rabbit as host, the healing of normal connective tissue and that of the tissue/implant interface were histologically compared 10 and 28 days postimplantation. The results exhibited significant differences between connective tissue healing, implant capsule formation, and granulation tissue generation. The healing of connective tissue and implant capsule formation were essentially complete at 28 days. However, tissue inside the implant was qualitatively different and did not significantly change between 10 and 28 days. It was characterized by macrophages and giant cells, a predominantly acid mucopolysaccharide ground substance, and qualitatively fewer and less well defined collagen and reticular fibers were observed than in normal wound healing. Thus we conclude that the connective tissue inside Dacron velour does not resemble normal connective tissue after 10 or 28 days of healing. Furthermore, the collagen never fully matures into orderly bundles, a phenomenon which may be related to an altered mucopolysaccharide composition and a diminished reticular network. The lysosomal enzymatic activity of the macrophages and perhaps the giant cells at the tissue/implant interface may be linked to these differences.

Alcian Blue↗