Differences between the circadian system of two strains of senescence-accelerated mice (SAM)

The aim of this study was to look for morphological or functional differences between the circadian system of two substrains of Senescence Accelerated Mice (SAM): senescence-prone (SAMP8; average median survival time = 10.0 months) and senescence-resistant (SAMR1; average median survival time = 18.9 months). Neither the general structure nor the quantitative analysis of the number of VP-positive neurons in matched sections revealed differences between SAMP8 and SAMR1 mice. Under LD 12/12 photoperiod, all animals showed the typical pattern of wheel running activity with maximum activity in the first half of darkness period. The period of the locomotor activity in free running as well as the time course for synchronization after a 6 h phase delay of LD cycle were similar in both strains of SAM mice. However, SAMP8 animals reentrained significantly earlier (3.4 +/- 0.4 days) than SAMR1 (6.3 +/- 0.9 days) after a 6 h phase advance of LD cycle. We conclude that the circadian system of SAMP8 mice presents some functional differences with that of SAMR1, which could help to explain their different rate of ageing.