Increased susceptibility to Pseudomonas aeruginosa infection under hindlimb-unloading conditions.

It has been reported that spaceflight conditions alter the immune system and resistance to infection [Belay T, Aviles H, Vance M, Fountain K, and Sonnenfeld G. J Allergy Clin Immunol 170: 262-268, 2002; Hankins WR and Ziegelschmid JF. In: Biomedical Results of Apollo. Washington, DC: NASA, 1975, p. 43-81. (NASA Spec. Rep. SP-368)]. Ground-based models, including the hindlimb-unloading model, have become important tools for increasing understanding of how spaceflight conditions can influence physiology. The objective of the present study was to determine the effect of hindlimb unloading on the susceptibility of mice to Pseudomonas aeruginosa infection. Hindlimb-unloaded and control mice were subcutaneously infected with 1 LD50 of P. aeruginosa. Survival, bacterial organ load, and antibody and corticosterone levels were compared among the groups. Hindlimb unloading had detrimental effects for infected mice. Animals in the hindlimb-unloaded group, compared with controls, 1). showed significantly increased mortality and reduced time to death, 2). had increased levels of corticosterone, and 3). were much less able to clear bacteria from the organs. These results suggest that hindlimb unloading may induce the production of corticosterone, which may play a critical role in the modulation of the immune system leading to increased susceptibility to P. aeruginosa infection.     

Time-resolved spectroscopy of hemoglobin and myoglobin in resting and ischemic muscle

Difficulties of quantitation of hemoglobin/myoglobin absorption changes in muscle have led to the development of a new approach using short pulses of light. This method uses input light pulses sufficiently short so that the time course of travel of light through the brain can be precisely measured. The time of arrival of light at the detector gives the optical path length, given the velocity of light in tissues. The intensity profile of photon migration in tissues permits determination of the path length that the exiting photons have traveled and the concentration change of the pigments. A cavity-dumped liquid dye laser illuminates the tissue with 130-ps pulses detected as 600-ps duration at a half height at 3.0-cm distance from the input point. The decay of intensity from the 50% point onward to 0.1% follows a logarithmic function of slope mu which is attributed to the total absorption coefficient of the tissue. Increments of mu due to deoxyhemoglobin absorption at 760 and 630 nm are used to calculate the concentration change. This permits the calculation of the path length for continuous light measurements of 2 cm for a particular geometry. Variation of the wavelength of the laser affords determination of a spectrum of changes in the tissue.     

Changes in the patterns of birefringence and filament deployment in the meiotic spindle ofNephrotoma suturalis during the first meiotic division

Summary A study combining polarizing and Nomarski differential interference microscopes was carried out onNephrotoma suturalis spermatocytes in order to correlate changes in the distribution of spindle birefringence with both the fibrillar organization of the spindle and movement of chromosomes within it. Records of fluctuations in birefringence obtained from measurements of retardation and analyses of ciné films show that there are significant transient fluctuations in birefringence during prometaphase (the so-called northern lights phenomenon) and gradual changes in the magnitude and distribution of birefringence from prometaphase through telophase. A negative correlation was found between the distribution of birefringence at the various stages of division and the amount of fibrillar organization in the spindle observed with the Nomarski system. Neither the transient nor gradual birefringence changes in theNephrotoma spindle can be explained adequately in terms of the number or distribution of spindle filaments. The possibility that these changes are associated with the forces developed within the spindle is discussed.