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The Journal of Neurophysiology Vol. 81 No. 5 May 1999, pp. 2501-2507
Copyright ©1999 by the American Physiological Society
Department of Physiology and Neuroscience, New York University Medical Center, New York, New York 10016
Tao, Lian
Effects of Osmotic Stress on Dextran Diffusion in Rat Neocortex
Studied With Integrative Optical Imaging. J. Neurophysiol. 81: 2501-2507, 1999.
Effects of osmotic stress on dextran diffusion in rat neocortex studied
with integrative optical imaging. This study investigated how
dextran (Mr = 3,000) diffused in rat cortical
slices when the osmolarity of the bathing artificial cerebrospinal
fluid was altered by varying the NaCl content. The apparent diffusion
coefficient, D*, was measured in the neocortex region using
fluorescent molecules and the integrative optical imaging (IOI) method.
The main results were: 1) the value of D* in rat
neocortex in the isotonic (300 mOsm) artificial cerebrospinal fluid at
34°C was D* = 0.68 ± 0.01 × 10
6
cm2 s
1 (mean ± SE, n = 78) and it could be changed within minutes by varying the extracellular
osmolarity. 2) Hypotonic stresses up to
100 mOsm decreased
D* by 35% and were fully reversible when the slices were
returned to the isotonic medium. Further hypotonic stress to
150 mOsm
caused further decrease in D* but after removal of the
stress, D* overshot its control value. 3)
Hypertonic stress of +50 mOsm increased D*, but the maximum
reversible increase in D* was only 15%. Further hypertonic
stress (to +200 mOsm) did not cause any further increase in
D* and, after removal of the stress, D* undershot
the control value. The changes in D* are thought to be
related to volume changes of cells in tissue: hypotonic solutions
caused cell swelling, resulting in reduced extracellular space and
compressed extracellular matrix so that the dextran diffusion was more
hindered. Hypertonic solutions had the opposite effect. Recordings of
extracellular field potentials in the hippocampal CA1 region
demonstrated that, on return to the isotonic solution after exposure to
an extreme hypotonic or hypertonic stress, the neurons retained their
ability to generate synaptic responses.
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