DIFFERENCES BETWEEN THE CIRCADIAN SYSTEM OF 2 STRAINS OF SENESCENCE-ACCELERATED MICE (SAM)

The aim of this study was to look for morphological or functional diff erences between the circadian system of two substrains of Senescence A ccelerated Mice (SAM): senescence-prone (SAMP8; average median surviva l time = 10.0 months) and senescence-resistant (SAMR1; average median survival time = 18.9 months). Neither the general structure nor the qu antitative analysis of the number of VP-positive neurons in matched se ctions revealed differences between SAMP8 and SAMR1 mice. Under LD 12/ 12 photoperiod, all animals showed the typical pattern of wheel runnin g activity with maximum activity in the first half of darkness period. The period of the locomotor activity in free running as well as the t ime course for synchronization after a 6 h phase delay of LD cycle wer e similar in both strains of SAM mice. However, SAMP8 animals reentrai ned significantly earlier (3.4 +/- 0.4 days) than SAMR1 (6.3 +/- 0.9 d ays) after a 6 h phase advance of LD cycle. We conclude that the circa dian system of SAMP8 mice presents some functional differences with th at of SAMR1, which could help to explain their different rate of agein g. (C) 1997 Elsevier Science Inc.