INTERSTITIAL VOLUME CHANGES DURING SPREADING DEPRESSION (SD) AND SD-LIKE HYPOXIC DEPOLARIZATION IN HIPPOCAMPAL TISSUE-SLICES

1. Relative interstitial volume (ISV) was estimated from the concentration changes of iontophoretically administered tetramethyl- and tetraethylammonium (TMA(+) and TEA(+)). Spreading depression (SD) was provoked by high K+, and hypoxic SD-like depolarization (HSD) was induced by withdrawing oxygen. 2. Probe ion concentrations increased dramatically and about equally during SD and HSD, except that in a few hypoxic trials signals became transiently smaller than control. Interstitial volume appeared to decrease on the average by similar to 70%. 3. The ISV that remains patent in CA1 region at the height of SD is <4% of total tissue volume. Probe ions may occasionally have passed through cell membranes for a short time during hypoxic SD.