1. The amnesia induced by various stress stimuli through hypoxia and cerebral ischemia was evaluated by the shortening of the response latency in a step-through task in mice. 2. The hypoxia-induced amnesia was reduced by cromakalim, a K+ channel opener (KCO), given 10 min before or immediately after the hypoxic treatment. 3. Similarly, the ischemia-induced amnesia was also reduced by cromakalim given 30 min before the occlusion. 4. In ischemic-induced amnesic mice, pyknotic cells, indicating the condensation of chromatin, were observed histochemically at the dentate gyrus granule cells in hippocampal regions 96 hr after ischemic treatment. In addition, cromakalim inhibited the induction of pyknotic cells. 5. These results suggest that KCOs might produce prophylactically neuroprotective effects against hypoxia- and cerebral ischemia-induced amnesia.
