Terrien Jeremy, Zizzari Philippe, Epelbaum Jacques, Perret Martine, Aujard Fabienne
Mecanismes Adaptatifs et Evolution, Brunoy, France.
Chronobiol Int. 2009 Jul;26(5):838-53. doi: 10.1080/07420520903044281.
Daily variations in core temperature (Tc) within the normothermic range imply thermoregulatory processes that are essential for optimal function and survival. Higher susceptibility towards cold exposure in older animals suggests that these processes are disturbed with age. In the mouse lemur, a long-day breeder, we tested whether aging affected circadian rhythmicity of Tc, locomotor activity (LA), and energy balance under long-day conditions when exposed to cold. Adult (N = 7) and aged (N = 5) mouse lemurs acclimated to LD14/10 were exposed to 10-day periods at 25 and 12 degrees C. Tc and LA rhythms were recorded by telemetry, and caloric intake (CI), body mass changes, and plasma IGF-1 were measured. During exposure to 25 degrees C, both adult and aged mouse lemurs exhibited strong daily variations in Tc. Aged animals exhibited lower levels of nocturnal LA and nocturnal and diurnal Tc levels in comparison to adults. Body mass and IGF-1 levels remained unchanged with aging. Under cold exposure, torpor bout occurrence was never observed whatever the age category. Adult and aged mouse lemurs maintained their Tc in the normothermic range and a positive energy balance. All animals exhibited increase in CI and decrease in IGF-1 in response to cold. The decrease in IGF-1 was delayed in aged mouse lemurs compared to adults. Moreover, both adult and aged animals responded to cold exposure by increasing their diurnal LA compared to those under Ta = 25 degrees C. However, aged animals exhibited a strong decrease in nocturnal LA and Tc, whereas cold effects were only slight in adults. The temporal organization and amplitude of the daily phase of low Tc were particularly well preserved under cold exposure in both age groups. Sexually active mouse lemurs exposed to cold thus seemed to prevent torpor exhibition and temporal disorganization of daily rhythms of Tc, even during aging. However, although energy balance was not impaired with age in mouse lemurs after cold exposure, aging was associated with lower LA and Tc during the night and delayed decrease in IGF-1. This might reflect that adaptive strategies to cold exposure differ with age in mouse lemurs acclimated to a summer-like photoperiod.
正常体温范围内核心体温（Tc）的每日变化意味着体温调节过程，这对于最佳功能和生存至关重要。老年动物对寒冷暴露的易感性更高，这表明这些过程会随着年龄增长而受到干扰。在小鼠狐猴（一种长日照繁殖动物）中，我们测试了衰老是否会影响在长日照条件下暴露于寒冷时Tc的昼夜节律、运动活动（LA）和能量平衡。将适应LD14/10的成年（N = 7）和老年（N = 5）小鼠狐猴暴露于25℃和12℃的环境中10天。通过遥测记录Tc和LA节律，并测量热量摄入（CI）、体重变化和血浆IGF-1。在暴露于25℃期间，成年和老年小鼠狐猴的Tc均表现出强烈的每日变化。与成年动物相比，老年动物夜间LA水平以及夜间和白天的Tc水平较低。体重和IGF-1水平不会随衰老而改变。在寒冷暴露下，无论年龄类别如何，均未观察到蛰伏发作。成年和老年小鼠狐猴将其Tc维持在正常体温范围内，并保持正能量平衡。所有动物对寒冷的反应都是CI增加和IGF-1减少。与成年动物相比，老年小鼠狐猴中IGF-1的减少延迟。此外，与Ta = 25℃时相比，成年和老年动物在寒冷暴露时均通过增加白天的LA做出反应。然而，老年动物夜间LA和Tc大幅下降，而成年动物的寒冷效应则很轻微。在两个年龄组中，低温的每日阶段的时间组织和幅度在寒冷暴露下都得到了特别好的保留。因此，即使在衰老过程中，暴露于寒冷的性活跃小鼠狐猴似乎也能防止蛰伏表现和Tc每日节律的时间紊乱。然而，尽管寒冷暴露后小鼠狐猴的能量平衡不会因衰老而受损，但衰老与夜间较低的LA和Tc以及IGF-1的延迟下降有关。这可能反映出，在适应类似夏季光周期的小鼠狐猴中，对寒冷暴露的适应性策略因年龄而异。
