| Objective:Our experiment was to evaluate the damage of CA1 area of hippocampus by different strength currents,including changes in behavior and morphological of CA1 area.Our experiments provided the theoretical basis for treatment of hippocampal lesions by neuro stem cells transplantation.Materials and Methods:Experimentally naive male Sprague Dawley rats (220-250gm),purchase from Animal Section of Kunming Medical College(China), were housed in group of eight in transparent cages with food and water available ad libitum.The rats were randomly assigned to the following treatment groups:2mA30s hippocampal lesions(n=12),2mA60s hippocampal lesions(n=14),3mA60s hippocampal lesions(n=13),controls with sham operations(n=12),controls with normal(n=13).The animals were anesthetized with 45mg of pentobarbital per kilogram of body weight,and placed in a stereotaxic frame.The skull was exposed, and holes drilled in the skull on its dorsal sides(AP:4mm,LR:2mm&3.5mm).We first inserted needle-like electrode in the previous holes vertically,depth of 4mm from the skull surface,and then,connected to 2mA direct current sustained 30 seconds (2mA30s hippocampal lesions),to 2mA direct current sustained 60 seconds(2mA60s hippocampal lesions),to 3mA direct current sustained 60 seconds(3mA60s hippocampal lesions),did not connected to direct current and sustained 60 seconds (controls with sham operations).All lesions were bilateral and were intended to be symmetrical.Motor function evaluation followed experimental current hippocampal injury,excluding rats of motor function injury at 21d in the postoperative.Training the rats to locate the platform in the Morris water maze started 28d after surgery.The rats were trained 4 times every day,continued to 7 days.Every day session consisted of four trials 120 sec apart.Each trial was begun by releasing rat into the water,with its face toward the pool wall,at one of 4 start positions.Vision was blocked until the go-signal.The program tracked the position of the rat until the rat entered the platform.If the rat failed to find the platform within 120 sec,it was guided onto it. The rat was always left on the platform for 60 see.Spatial probe test was started 36d after surgery.The rats were released form the quadrant opposite to the previous platform quadrant and swimming was tracked for 120 sec.Within a day after finishing the behavioral testing,the rats were killed with an overdose of equithesin and perfused intracardially with saline and 4%polyformaldehyde.The brains were removed and stored in polyformaldehyde.Frozen sections(10μm) were cut coronally and every tenth section stained with HE and Nissal.Morphological criteria were used to determine the volume of the lesions in the CA1 area.The results were evaluated with mixed-model repeater measures analysis of variance.Results:In all rats with acceptable CA1 area of hippocampus lesions,the damage was confined to the CA1 area of hippocampus bilaterally.With time,the animals in all groups learned to find the hidden platform progressive faster.However,control with sham groups and 2mA30s hippocampus lesions,affecting less than the hippocampal tissue,learned quickly and finally swam directly to the hidden platform,the rats with 3mA60s and 2mA60s currents lesions generally failed to learn the exact position of the target.Thiswas expressed in longer latency to find the platform and poor performance on the spatial probe test.Conclusions:The integrity of the CA1 area of hippocampal formation is necessary for spatial learning and memory,and necessary for acquisition and retrieval of spatial information.Lesions to CA1 area of hippocampus were shown to affect Morris water maze.We observed a relationship between the currents size and duration of the CA1 area of hippocampus lesions and the learning of the spatial task.The increasing learning deficit with larger CA1 area lesions by currents intensity suggests that activity of the CA1 area is required for full spatial learning abilities.
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