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Osmotic‐hypertensive opening of the blood‐brain barrier in rats does not necessarily provide access for potassium to cerebral interstitial fluid
Author(s) -
Somjen GG,
Segal MB,
Herreras O
Publication year - 1991
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.1991.sp003516
Subject(s) - tonicity , blood–brain barrier , evans blue , hippocampus , interstitial fluid , neocortex , chemistry , anesthesia , interstitial space , cortical spreading depression , extracellular fluid , medicine , potassium , endocrinology , extracellular , central nervous system , biochemistry , organic chemistry , psychiatry , migraine
The blood‐brain barrier was breached in urethane anaesthetized rats by infusing hypertonic mannitol or NaCl at high rate under high pressure into one internal carotid artery. Opening of the blood‐brain barrier was confirmed by staining of the perfused hemisphere by intravenous Evans Blue dye. Orthodromic‐evoked potentials in CAl region of hippocampus were transiently extinguished, and the extracellular potential in hippocampus and neocortex shifted in the positive direction during hypertonic infusion. After the hypertonic infusion, the permeability of the barrier to K+ was tested by infusing into the internal carotid artery artificial cerebrospinal fluid in which K+ replaced most of the Na+, raising the concentration of K+ in the blood plasma in the superior sagittal sinus to 13‐17 mM. Extracellular potential and interstitial potassium concentration ([K+]O) in hippocampus and neocortex, and evoked potentials in hippocampus, remained unchanged during prolonged infusion of high K+, unless and until spreading depression occurred. After a wave of spreading depression, [K+]O returned to baseline in spite of continued high K+ infusion. We conclude that [K+]O in brain tissue is effectively regulated even when colloidal dye can penetrate the blood‐brain barrier, but excess K+ may have entered the cerebral interstitial space in scattered patches outside the region sensed by the ion‐selective microelectrodes, triggering spreading depression.