Rd. Andrew et al., EVIDENCE AGAINST VOLUME REGULATION BY CORTICAL BRAIN-CELLS DURING ACUTE OSMOTIC-STRESS, Experimental neurology, 143(2), 1997, pp. 300-312
The cell bodies of neurons and glia examined in culture respond to sev
ere osmotic stress (100 to 200 mOsm) by passive volume change that is
followed within several minutes by volume regulation, even in the face
of maintained osmotic change. However, in clinical situations, the br
ain does not experience such precipitous and severe changes in brain h
ydration. In this study we examined if there is evidence from the hipp
ocampal slice preparation supporting the type of volume regulation obs
erved in cultured brain cells. Within the CA1 region we imaged changes
in light transmittance (LT), recorded the evoked field potential, and
monitored tissue resistance (all measures of cell volume change) duri
ng the first hour of osmotic stress to search for evidence of volume r
egulation. During superfusion of hypo-osmotic aCSF (-40 mOsm), LT incr
eased 24 to 28% in the dendritic regions of CA1 neurons. The LT reache
d a plateau which was maintained throughout a 45-min application inter
val, more than enough time to reveal a regulatory volume decrease. Upo
n return to control saline, LT immediately returned to baseline and se
ttled there. Hypo-osmolality reversibly increased the relative tissue
resistance (RREL) measured across the CA1 region with a time course id
entical to the increase in LT. Conversely, hyperosmotic aCSF (mannitol
, +40 mOsm) decreased both RREL by 8% and LT by 15.5% with no indicati
on of a regulatory volume increase. The CA1 cell body layer showed onl
y slight hypo-osmotic swelling whereas exposure to the glutamate agoni
st quinolinic acid caused pronounced swelling in this region. Even whe
n osmolality was decreased by 120 mOsm for 20 min, dendritic regions r
esponded passively with no regulatory volume decrease. However, when a
CSF Cl- was substituted, the CA1 dendritic regions displayed immediate
swelling followed by a dramatic volume reduction under normosmotic co
nditions, indicating that such behavior can be evoked by extreme aCSF
dilution. We conclude that in the brain slice preparation, the cortica
l cells do not exhibit classic volume regulation in response to sudden
physiological changes in osmolality. Moreover it is the dendritic reg
ion, not the cell body region, that displays dynamic volume change dur
ing osmotic challenge. (C) 1997 Academic Press.