Brain blood flow restoration 'rescues' chronically damaged rat CA1 neurons

Middle aged rats (13 months) were subjected to chronic cerebrovascular insufficiency (CVI) for 9 weeks using a 3-vessel occlusion technique. This CVI injury targets CA1 neuron damage selectively. Three groups of rats had their cerebral blood flow restored after 1, 2 or 3 weeks following CVI by removal of their carotid artery occluders. Another rat group did not undergo deocclusion for the 9 week observation period. Rats were tested for memory acquisition and retention 6 and 9 weeks after CVI using a modified water maze test. At the end of the 9 weeks, cerebral blood flow was measured in the fronto-parietal cortex and rats were killed by fixation-perfusion. Hippocampal morphometry was done to assess the % of damaged CA1 neurons and the density of GFAP-positive hyperplasia and hypertrophy. Results show that restoration of cerebral blood flow 1 and 2 weeks after CVI but not after 3 weeks of CVI, reversed a significant increase in reactive astrocytosis and prevented memory impairment in these deoccluded rats when compared to the non-deoccluded group. It appears from these results that 'neuronal rescue' of CA1 neurons is possible when cerebral blood flow is restored in rats subjected to chronic CVI during a 2 week (but not 3 week) 'window of opportunity'. This chronic brain ischemia model may be useful in screening potential therapy in patients with dementia where spatial memory impairment and hippocampal damage may be manifested.