Extracellular diffusion parameters in the rat somatosensory cortex during recovery from transient global ischemia/hypoxia

Changes in the extracellular space diffusion parameters during ischemia are well known, but information about changes during the postischemic period is lacking. Extracellular volume fraction (alpha) and tortuosity (lambda) were determined in the rat somatosensory cortex using the real- time iontophoretic method; diffusion- weighted magnetic resonance imaging was used to determine the apparent diffusion coefficient of water. Transient ischemia was induced by bilateral common carotid artery clamping for 10 or 15 mins and concomitant ventilation with 6% O-2 in N-2. In both ischemia groups, a negative DC shift accompanied by increased potassium levels occurred after 1 to 2 mins of ischemia and recovered to preischemic values within 3 to 5 mins of reperfusion. During ischemia of 10 mins duration, a typically decreased to 0.07 +/- 0.01, whereas lambda increased to 1.80 +/- 0.02. In this group, normal values of alpha = 0.20 +/- 0.01 and lambda = 1.55 +/- 0.01 were registered within 5 to 10 mins of reperfusion. After 15 mins of ischemia, a increased within 40 to 50 mins of reperfusion to 0.29 +/- 0.03 and remained at this level. Tortuosity (lambda) increased to 1.81 +/- 0.02 during ischemia, recovered within 5 to 10 mins of reperfusion, and was increased to 1.62 +/- 0.01 at the end of the experiment. The observed changes can affect the diffusion of ions, neurotransmitters, metabolic substances, and drugs in the nervous system.