Extracellular apparent diffusion in rat brain

The apparent diffusion coefficients (ADCs) of a series of markers concentra ted in the extracellular space of normal rat brain were measured to evaluat e, by inference, the ADC of water in the extracellular space. The markers ( mannitol, phenylphosphonate, and polyethylene glycols) are defined as "comp artment selective" because tissue culture experiments demonstrate some leak age into the intracellular space, making them less "compartment specific" t han commonly believed. These primarily extracellular markers have ADCs simi lar to those of intracellular metabolites of comparable hydrodynamic radius , suggesting that water ADC values in the intra- and extracellular spaces a re similar. If this is the case, then it is unlikely that a net shift of wa ter from the extra- to the intracellular space contributes significantly to the reduction in water ADC detected following brain injury. Rather, this r eduction is more likely due primarily to a reduction of the ADC of intracel lular water associated with injury. (C) 2001 Wiley-Liss, Inc.