Journal of Applied Physiology, Vol 73, Issue 2 107S-111S, Copyright © 1992 by American Physiological Society
Ventral horn cell responses to spaceflight and hindlimb suspension
B. Jiang, R. R. Roy, I. V. Polyakov, I. B. Krasnov and V. R. Edgerton
Brain Research Institute, University of California, Los Angeles 90024-1564.
Spaceflight or hindlimb suspension results in a loss of mass and
alterations of the metabolic and contractile protein profiles of skeletal
muscles toward that resembling faster muscles. Given the influence of
motoneurons on muscle properties, ventral horn cells of the lumbosacral
enlargement of the spinal cord were studied to determine whether similar
adaptations were present. Three groups of rats (5 per group) were studied:
control, 14-day spaceflight, and 14-day hindlimb suspension. Spinal cords
were quick-frozen, and the succinate dehydrogenase (SDH) activity and
cross-sectional area of the soma of ventral horn cells were measured using
a computer-enhanced image-processing system. Briefly, the optical density
for SDH activity was determined after 8 min of incubation in a medium that
gave a steady-state enzymatic reaction. Soma sizes were determined in cells
with a visible nucleus. Although there were no significant differences
among the three groups in mean cross-sectional area and SDH activity, the
population distributions of both variables shifted significantly. In the
flight rats, there was a shift toward smaller cells. Compared with control,
the population distribution of SDH activities in the flight rats shifted
toward higher activities, whereas the distribution shifted toward lower
activities in the suspended rats. When considering the interactive effects
within individual cells, there was a higher percentage of small cells with
high SDH activities in the flight than in the control or suspended rats.
These contrasting effects of spaceflight and hindlimb suspension suggest
that the changes observed in ventral horn cells were due to factors other
than simply the absence of weight support.
