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Abstract
Hyperbaric oxygen (HBO; 100% oxygen at 2 atmospheres absolute) was administered for
1 h to male Mongolian gerbils either for a single session or every other day for five
sessions. Two days after HBO pretreatment, the gerbils were subjected to 5 min of
forebrain ischemia by occlusion of both common carotid arteries under anesthesia.
Seven days after recirculation, neuronal density per 1-mm length of the CA1 sector
in the hippocampus was significantly better preserved in the five-session HBO pretreatment
group (n = 10: 175.7 (47.8/mm, 54.9% of normal) than in the ischemic control group
(n = 10: 26.2 (11.6/mm, 8.0% of normal) and in the single-session HBO pretreatment
group (n = 7: 37.3 (21.7/mm, 11.4% of normal). Immunohistochemical staining for the
72-kDa heat-shock protein (HSP-72) in the CA1 sector performed 2 days following pretreatment
revealed that the five-session HBO pretreatment increased the amount of HSP-72 present
compared with that in the ischemic control group and in the single HBO pretreatment
group. These results suggest that tolerance against ischemic neuronal damage was induced
by repeated HBO pretreatment, which is thought to occur through the induction of HSP-72
synthesis.