Behavioral and histological changes after repeated brief cerebral ischemia by carotid artery occlusion in gerbils

The effects of repeated brief episodes of cerebral ischemia on passive avoidance learning and hippocampal neuronal degeneration were investigated in gerbils. Latency of step-through was shortened for the entire 7-day period when gerbils were trained at day 3 after 3 episodes of carotid artery occlusion for 2 min each at 60-min intervals. In addition, latency of passive avoidance was shortened for 63 days when gerbils were retrained at 14 days after occlusion. Severe neuronal degeneration in the CA1 regions of the hippocampus was observed 4 and 17 days after occlusion. A close correlation was seen between latency in the passive avoidance response and neurological degeneration of the hippocampal CA1 region. This fact was strongly supported by the results of another experiment that 1 2-min occlusion with almost no neuronal degeneration did not affect learning behavior while 3 1-min occlusions showed neuronal death and impairment of learning behavior of a moderate degree 4 days after occlusion. These results suggest that this gerbil model with carotid artery occlusion is useful for the quantitative measurement of functional changes in the chronic phase of repeated cerebral ischemia.