Figure 2.

Effects of ischemia and hirudin on the survival of hippocampal CA1 neurons. After staining of brain slices, as shown in Fig. 1, intact pyramidal cells were counted within a 400-μm section of the hippocampal CA1 region. A severe ischemia (6-min occlusion) caused a massive neuronal cell death, which was decreased if hirudin (≈0.1 unit/ml) was injected ICV 20 min before the occlusion (A). If the animals were “preconditioned” by prior mild ischemic insults (two 2-min occlusions at 1-day interval 2 days before a severe ischemia), a marked ischemic tolerance was observed (B). Hirudin, applied before each mild insult but not before the severe occlusion, impaired the resistance. Each bar represents the mean ± SEM of n animals (n is between 5 and 20). *, P < 0.025.