Brain injury improves survival of mice following brain ischemia.

Minor brain injury was inflicted with a small needle at 4 sites one week before the production of incomplete brain ischemia in the mouse. A bilateral carotid clamp was applied for 60 min under pentobarbital anesthesia, and the number of survivors at one week after the ischemic insult was compared with those in animals anesthetized only and those in a sham-operated group. The number of survivors in the brain-injured group was significantly higher than in the other two groups. The results suggest that anti-ischemic factors are released by the injured brain or that certain unknown protective mechanisms against ischemia become active following brain injury.