Age-dependent memory impairments following transient global ischemia : relationship to hippocampal pathology

Most human stroke victims are part of an older population while most animal models of ischemia employ young adult rodents. To add generalizability to rodent models of global ischemia, and its associated neuropathology and memory impairments, to the human stroke population, this thesis examines the effect of a IS-minute global ischemia via four vessel occlusion (4VO) in rats that were 8-weeks, 20-weeks, and SO-weeks of age. Rats were tested for object-location memory, using a 24-hour retention delay and object-recognition memory, using IS-minute and 24-hour delays. Rats with sham-ischemia in all age groups showed a preference for the moved object during the novel-object-in-place (NOIP) test of spatial memory, and for the novel object during the IS-minute novel-object- preference (NOP) test and with the exception of the 20-week group, during the 24-hour NOP test. However, rats that received ischemia displayed impairments in all age groups in the NOIP, in the 20-week group during the IS-minute NOP test, and in the 20and SO-week groups in the 24-hour NOP test of object recognition. Ischemic rats in all age groups had significantly fewer cells in the CA1, CA2, and hilus subfields of the hippocampus, than did sham-ischemia controls. Only the SO-week ischemia group had significant damage in CA3 and the dentate gyrus. Performance in the NOIP test was correlated with cell counts in CA1, CA2, and the dentate gyrus, and with CA1 and CA2 in the IS-minute NOP test. These findings indicate that the severity of memory impairments and neuropathology due to ischemia are influenced by the age of the brain