The studies on the brain mechanisms relating to the spatial learning disorder in aged and dmentia model rats.

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The present studies examined the acquisition of spatial learning using Morris water maze in the chronically scoporamine injected rats and aged rats.Scoporamine was injected subcutaneously by means of osmotic pump(2.5μl/hr)for 28 days before starting the task of spatial learning of the Morris water maze. And also 30 rats were reared and divided into three group, that is, 12 month(12A) 18 month(18A), and 24 month(24A) old group.All rats were trained to learn the position of a hidden escape platform(place learning)for four trials per day, with an intertrial interval of approxiamately 10 minutes, for a total of 4 days.On each trial, rats swam for 90 seconds or until they found the platform.The fifth day was a probe test in which the platform was retracted, and rats swam for 60 seconds.Then cue learning was tested subsequently in a single session of 4 trials in which rats swam to the visible escape platform that protruded above the surface of the pool, for 90 seconds on each trial.In the sc … More oporamine injected rats, the escape latency to the hidden platform significantly increased only in the early stage of the place learning. Additionally, the volume of the hippocampal mossy fiber terminals at the rostral portion increased exclusively in these learning impaired rats.These results suggested that the chronic injection of scoporamine might induce the neurogenesis of the rostral part of the dentate granule cells and also augment the volume of the mossy fiber terminals to supplement the cholinergic depletion.In the 24A group, the escape latency to the platform was significantly prolonged in the place learning but not in the cue learning.And a significant negative correlation between the escape latency and the mean swimming time was observed in the 24A group. In the 12A and 18A group, these results were observed, but not significant, as those in the 24A group. Also in the preaent study, percent time staying in quadrant 03 in which the escape platform was located during the place learning task was significant decreased in all aging group.These results suggest that the spatial learning deficits begin to appear around 1.2 months old and gradually go from bad to worse in later stages, and these deficits in 12A and 18A groups are probably related to the similar background mechanisms to the 24A group or more elderly groups in which the morphologi-cal and functional deteriorations are observed in the entorhinal-hippocampal networks. Less