Jefimow Małgorzata, Wojciechowski Michał S, Tegowska Eugenia
Department of Animal Physiology, Institute of General and Molecular Biology, N. Copernicus University, ul. Gagarina 9, PL 87-100 Toruń, Poland.
J Exp Zool A Comp Exp Biol. 2005 Nov 1;303(11):976-86. doi: 10.1002/jez.a.225.
We studied the influence of light-dark (L:D) cycle reversal on daily variations in the brown adipose tissue (BAT) capacity for nonshivering thermogenesis (NST) in Siberian hamsters (Phodopus sungorus). Continuous and simultaneous measurements of BAT temperature (T(BAT)) and preferred ambient temperature (PT(a)) were made after noradrenaline (NA) injections administered every 4 hr. First, hamsters were acclimated for 4 weeks to an ambient temperature (T(a)) of 23 degrees C and 12L:12D, and then to a reversed photoschedule 12D:12L for 8 weeks. The same was done after a 4- and 8-week acclimation period at the same T(a). We found that after photoschedule reversal, the re-entrainment of T(BAT) and PT(a) rhythms preceded re-entrainment of the NST rhythm. The daily rhythms of T(BAT) and PT(a) were fully re-entrained after 4 weeks of acclimation to the reversed photoschedule, but rhythmicity of the response to NA disappeared. This rhythm was restored in hamsters acclimated to a reversed photoschedule for 8 weeks. We suggest that the daily rhythm of NST capacity is not responsible for generating the rhythm of body temperature (T(b)). Rather, it is a result of the daily rhythm of T(b), but adjusts to the new environment more slowly than the T(b) rhythm. When a daily rhythm of NST was present, the increase in T(BAT) after NA injection was inversely correlated with the pre-injection T(BAT). In addition, NA-induced changes in PT(a) reflected the intensity of NST in BAT; namely, increased T(BAT) was correlated with the post-injection decrease in PT(a). When the increase in T(BAT) was large, animals chose a lower T(a) to dissipate excessive heat and prevent overheating. In the course of the experiments, we recorded a decreased mean NST capacity and increased body mass of hamsters. These changes are representative of the time of photorefractoriness and a transition to a summer status. Despite prolonged exposure to an intermediate day length (12 hr of light) and photoschedule reversal, hamsters continued to change towards their summer condition and were able to acclimate to the new D:L cycle.
我们研究了明暗（L:D）周期反转对西伯利亚仓鼠（Phodopus sungorus）棕色脂肪组织（BAT）非颤抖性产热（NST）日变化的影响。每隔4小时注射去甲肾上腺素（NA）后，连续同时测量BAT温度（T(BAT)）和偏好环境温度（PT(a)）。首先，仓鼠在23摄氏度的环境温度（T(a)）和12小时光照:12小时黑暗（12L:12D）条件下适应4周，然后在12小时黑暗:12小时光照（12D:12L）的反转光照时间表下适应8周。在相同T(a)下经过4周和8周适应期后也进行了同样的操作。我们发现，在光照时间表反转后，T(BAT)和PT(a)节律的重新同步先于NST节律的重新同步。在适应反转光照时间表4周后，T(BAT)和PT(a)的日节律完全重新同步，但对NA反应的节律性消失。在适应反转光照时间表8周的仓鼠中，这种节律恢复了。我们认为，NST能力的日节律并非产生体温（T(b)）节律的原因。相反，它是T(b)日节律的结果，但比T(b)节律更慢地适应新环境。当存在NST日节律时，NA注射后T(BAT)的升高与注射前的T(BAT)呈负相关。此外，NA诱导的PT(a)变化反映了BAT中NST的强度；即，T(BAT)升高与注射后PT(a)降低相关。当T(BAT)升高幅度较大时，动物会选择较低的T(a)来散发过多热量并防止过热。在实验过程中，我们记录到仓鼠的平均NST能力下降和体重增加。这些变化代表了光不应期以及向夏季状态的转变。尽管长时间暴露于中间日长（12小时光照）和光照时间表反转，但仓鼠继续朝着夏季状态变化，并能够适应新的D:L周期。
