LONG-TERM SPATIAL COGNITIVE IMPAIRMENT AFTER MIDDLE CEREBRAL-ARTERY OCCLUSION IN RATS - NO INVOLVEMENT OF THE HIPPOCAMPUS

The behavioral and neurochemical changes in the chronic phase of perma nent occlusion of the right middle cerebral artery (MCA) in rats were investigated. One month after MCA occlusion, 23 rats were unable to so lve a radial eight-arm maze task during an entire 1-month period, wher eas seven rats were able to solve this task. Three months after occlus ion, 19 MCA-occluded rats failed to solve the task successfully again for at least 1 month (the cognitively impaired rats), whereas 11 MCA-o ccluded rats were able to solve it (the cognitively unimpaired rats). The rats that underwent behavioral testing were examined for any chang es in the acetylcholine (ACh) levels in the hippocampus using HPLC wit h electrochemical detection or the formation of longterm potentiation (LTP) in the population spike of the hippocampal CA1 field. The immuno histochemical distribution of either the microtubule-associated protei n 2 (MAP2) or glial fibrillary acidic protein (GFAP) in the hippocampu s of the cognitively impaired rats was also studied. In the cognitivel y impaired rats, neither the suppression of the induction of LTP, nor the degradation of MAP2, nor the increase in the GFAP immunoreactivity was observed in the hippocampus, The levels of ACh in the hippocampus did not change significantly among the cognitively impaired, unimpair ed, and the sham-operated rats. These results suggest that MCA occlusi on is capable of producing long-term spatial cognitive disturbance in rats without any evidence of neurobiological damage in the hippocampus .