Rm. Lopachin et Pk. Stys, ELEMENTAL COMPOSITION AND WATER-CONTENT OF RAT OPTIC-NERVE MYELINATEDAXONS AND GLIAL-CELLS - EFFECTS OF IN-VITRO ANOXIA AND REOXYGENATION, The Journal of neuroscience, 15(10), 1995, pp. 6735-6746
Electron probe x-ray microanalysis was used to measure water content a
nd concentrations (mmol/kg dry weight) of elements (Na, P, S, Cl, K, C
a, and Mg) in myelinated axons and glial cells of rat optic nerve expo
sed to in vitro anoxia and reoxygenation. in response to anoxia, large
, medium, and small diameter fibers exhibited an early (5 min) and pro
gressive loss of Na and K regulation which culminated (60 min) in seve
re depletion of respective transmembrane gradients. As axoplasmic Na l
evels increased during anoxic exposure, a parallel rise in Ca content
was noted. For all axons, mean water content decreased progressively d
uring the initial 10 min of anoxia and then returned toward normal val
ues as anoxia continued. Analyses of mitochondrial areas revealed a si
milar pattern of elemental disruption except that Ca concentrations ro
se more rapidly during anoxia. Following 60 min of postanoxia reoxygen
ation, the majority of larger fibers displayed little evidence of reco
very, whereas a subpopulation of small axons exhibited a trend toward
restoration of normal elemental composition. Glial cells and myelin we
re only modestly affected by anoxia and subsequent reoxygenation. Thus
, anoxic injury of CNS axons is associated with characteristic changes
in axoplasmic distributions of Na, K, and Ca. The magnitude and tempo
ral patterns of elemental Na and Ca disruption are consistent with rev
ersal of Na+-Ca2+ exchange and subsequent Ca entry (Stys et al., 1992)
. During reoxygenation, elemental deregulation continues for most CNS
fibers, although a subpopulation of small axons appears to be capable
of recovery.