No abstract

No abstract

In this study, we compared the effects of MK-801 and hippocampal lesions on re-training of Morris water maze place task in familiar and novel environments in rats. In Experiment 1, rats were pre-trained with the place task. After acquiring the task, rats were re-trained with the same task in a familiar environment following MK-801 injection, and were then trained with the same task in a novel environment following MK-801 injection. In the familiar environment, MK-801 had no effect, but in the novel environment performance was impaired. In Experiment 2, after the place task training, the hippocampus was lesioned, and rats were re-trained with the same task in the familiar environment then retrained again in the novel environment. Rats showed severe impairment in both environments. These two experiments suggest different functions for NMDA receptors and the hippocampus. The results of Experiment 1 showed that NMDA receptors are not required for utilizing spatial representations but they play an important role in the construction of spatial representations. The results of Experiment 2 show that the hippocampus is necessary for both the utilization of spatial representations already formed and the formation of new spatial representations.

Summary:Purpose: Genetically epileptic model rats, Ihara epileptic rat (IER/F substrain), have neuropathologic abnormalities and develop generalized convulsive seizures when they reach the age of ∼5 months. Because the neuromorphologic abnormalities are centered in the hippocampus, we expected to observe spatial cognitive deficits. The present study aimed to evaluate emotionality and learning ability of the F substrain of IER.Methods: To determine whether deficits are caused by inborn neuropathologic abnormalities or by repeated generalized convulsions, we tested nine 6-to 12-week-old IER/F rats that had not yet experienced seizures (experiment 1) and nine 7-to 9-month-old IER/F rats that had repeatedly experienced seizures (experiment 2) with identical tasks: an open-field test and the Morris water-maze place and cue tasks.Results: Both groups of IER/Fs showed behaviors that were different from those of control rats in the open-field test, and extensive learning impairments were seen in both the place task, which requires spatial cognition, and the cue task, which does not require spatial cognition but requires simple association learning. Their impaired performance of the cue task indicates that their deficiency was not limited to spatial cognition.Conclusions: Because young IER/F rats without seizure experiences also showed severe learning impairments, genetically programmed microdysgenesis in the hippocampus was suspected as a cause of the severe learning deficits of IER/Fs.

No abstract