FAILURE IN LEARNING-TASK AND LOSS OF CORTICAL CHOLINERGIC FIBERS IN MICROSPHERE-EMBOLIZED RATS

The present study was undertaken to elucidate the pathological changes in learning and memory functions and in the metabolism of cortical ch olinergic neurons following microsphere embolism in the rat. Microsphe res (48 mu m) were injected into the right internal carotid artery of rats. Learning and memory functions were measured 7 or more days after the embolism by active and passive avoidance, and water maze tasks. I n the biochemical study, cortical acetylcholine and choline contents, and choline acetyltransferase activity were measured. Cortical acetylc holinesterase-containing fibers were quantitatively estimated in the e mbolized rat. The active and passive avoidance, and water maze tasks w ere impaired in the microsphere-embolized rat. In the histochemical st udy, the density of cortical acetylcholinesterase-containing fibers of the ipsilateral hemisphere of the microsphere-embolized rat was decre ased, but cell density was unchanged. Furthermore, microsphere embolis m decreased the cortical acetylcholine concentration and choline acety ltransferase activity and increased the choline concentration. The res ults suggest that microsphere embolism causes severe damage to cortica l cholinergic neurons, which may be, at least in part, related to the impairment of learning and memory functions in the sustained brain isc hemia.