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The SAMP8 mouse strain shows an age-associated marked deficit in learning and memory, and is considered to be a useful animal model of age-related learning and memory disorders. We usually apply the passive avoidance task for selection of the offspring in maintenance and breeding of SAMP8 mice to maintain a stable phenotype compared with SAMR1 as the control. In the retention test of the passive avoidance task, almost all SAMR1 mice showed marked avoidance response, and showed a ceiling score of 300 s. In the SAMP8 strain, most animals showed short avoidance of 100–200 s, however, about 10–20% of animals showed long avoidance above 300 s, similar to the SAMR1 control group. We have continued to exclude these SAMP8 mice showing long avoidance from the offspring. At present SAMP8 mice show stable learning impairment, suggesting that breeding based on phenotype stability is critical to maintain the strain as an animal model of diseases. |
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