Ischemic tolerance can be induced repeatedly in the gerbil hippocampal neurons

We investigated whether ischemic tolerance can be induced repeatedly in the gerbil hippocampal neurons. The gerbils were firstly treated with two episodes of 2-min forebrain ischemia 1 day apart, which procedure is known to induce ischemic tolerance. After 4 weeks of recirculation, the animals were subjected to a 2-min period of preconditioning ischemia again and then to a 3-min period of ischemia after 3 days. The hippocampal CA1 neurons were destroyed 7 days after 3-min ischemia without the second preconditioning but not in animals with the second preconditioning. Thus, ischemic tolerance can be induced repeatedly when the first ischemic tolerance has disappeared.