The study of cerebral ischemia in animals is not easy, because cerebral circulation is not the same as in humans. Indeed, in most animals, there is a collateral circulation between the vertebral and carotid arteries before these arteries enter the brain. On the other hand, in gerbils, unilateral ligation produces ischemia in the ipsilateral forebrain and leads to death in 40-60% of the animals. Because the cerebral ischemia so produced is not effective in all gerbils, it is important to select "sensitive" gerbils by funduscopic examination. Only sensitive gerbils are retained for further experimentation. The nature of the aging process is the subject of some speculation. One hypothesis is referred to as the free radical theory. This theory postulates that free radicals are involved in aging and age-related disorders of the brain. Therefore, we have determined levels of neuromediators involved in cerebral ischemia and memory, including catecholamines (dopamine [DA], dihydroxyphenylacetic acid [DOPAC], hydroxyvanillic acid [HVA]) and indolamines (5-hydroxyindolacetic acid [5HIAA], serotonin [5-H1), amino acids (aspartate, glutamate and GABA), and free radicals ('OH). We have chosen for study the caudate nucleus, hippocampus, and retina, where changes after ischemiaheperfusion insult are well documented. In gerbil brain, levels of 'OH and neurotransmitters are low at birth, reach a plateau, and then decrease with aging. After cerebral ischemia (60 min) induced by left carotid occlusion, the reperfusion (30 min) symptoms are classified using a behavioral score (Stroke Index). Moreover, after ischemia/