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 concentra tion changes of iontophoretically administered tetramethyl- and tetrae thylammonium (TMA(+) and TEA(+)). Spreading depression (SD) was provok ed by high K+, and hypoxic SD-like depolarization (HSD) was induced by withdrawing oxygen. 2. Probe ion concentrations increased dramaticall y and about equally during SD and HSD, except that in a few hypoxic tr ials signals became transiently smaller than control. Interstitial vol ume 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 me mbranes for a short time during hypoxic SD.