Morphological estimation of brain extracellular fluid dynamics in cold-induced edema from the aspect of cerebrospinal fluid-extracellular fluid communication.

Following the induction of cold injury in the parietal cortex of rats, the brain extracellular fluid dynamics under conditions of cryogenic edema were investigated morphologically from the aspect of extracellular fluid (ECF)-cerebrospinal fluid (CSF) communication using horseradish peroxidase (HRP) injected into the cisterna magna as a marker. About 24 h after the induction of cold injury, HRP was distributed in the subjacent white matter of the lesion and around the ventricle. Forty-eight hours after injury, the distribution of HRP around the lesion became distinctive. This distribution of HRP became more concentrated at the same location on day 3-4 after injury. At this time, HRP was observed to be distributed along the walls of small vessels, in the cytoplasm of a few neurons and in the neuropil around the lesion by light microscopy. At small vessels around the lesion, a dense deposit of HRP at the basement membrane and many abluminal vesicles were evident by electron microscopy. These findings indicate that ECF-CSF communication changes drastically under the influence of edema fluid dynamics. In particular, the dense distribution of HRP around the lesion on day 3-4 after injury can be attributed to active retrograde transport by vessels in this area, a phenomenon considered important for edema resolution.