Department of Psychology, Michigan State University, East Lansing, MI 48824, USA.
J Biol Rhythms. 2012 Aug;27(4):299-307. doi: 10.1177/0748730412449723.
The term masking refers to immediate responses to stimuli that override the influence of the circadian timekeeping system on behavior and physiology. Masking by light and darkness plays an important role in shaping an organism's daily pattern of activity. Nocturnal animals generally become more active in response to darkness (positive masking) and less active in response to light (negative masking), and diurnal animals generally have opposite patterns of response. These responses can vary as a function of light intensity as well as time of day. Few studies have directly compared masking in diurnal and nocturnal species, and none have compared rhythms in masking behavior of diurnal and nocturnal species. Here, we assessed masking in nocturnal mice (Mus musculus) and diurnal grass rats (Arvicanthis niloticus). In the first experiment, animals were housed in a 12:12 light-dark (LD) cycle, with dark or light pulses presented at 6 Zeitgeber times (ZTs; with ZT0 = lights on). Light pulses during the dark phase produced negative masking in nocturnal mice but only at ZT14, whereas light pulses resulted in positive masking in diurnal grass rats across the dark phase. In both species, dark pulses had no effect on behavior. In the 2nd experiment, animals were kept in constant darkness or constant light and were presented with light or dark pulses, respectively, at 6 circadian times (CTs). CT0 corresponded to ZT0 of the preceding LD cycle. Rhythms in masking responses to light differed between species; responses were evident at all CTs in grass rats but only at CT14 in mice. Responses to darkness were observed only in mice, in which there was a significant increase in activity at CT 22. In the 3rd experiment, animals were kept on a 3.5:3.5-h LD cycle. Surprisingly, masking was evident only in grass rats. In mice, levels of activity during the light and dark phases of the 7-h cycle did not differ, even though the same animals had responded to discrete photic stimuli in the first 2 experiments. The results of the 3 experiments are discussed in terms of their methodological implications and for the insight they offer into the mechanisms and evolution of diurnality.
术语“掩蔽”是指对刺激的即时反应，这种反应会干扰生物钟对行为和生理的影响。光和暗的掩蔽在塑造生物体的日常活动模式方面起着重要作用。夜行性动物通常对黑暗更活跃（正掩蔽），对光更不活跃（负掩蔽），而昼行性动物通常具有相反的反应模式。这些反应可以根据光强度和一天中的时间而变化。很少有研究直接比较昼行性和夜行性物种的掩蔽作用，也没有研究比较昼行性和夜行性物种掩蔽行为的节律。在这里，我们评估了夜行性小鼠（Mus musculus）和昼行性草原田鼠（Arvicanthis niloticus）的掩蔽作用。在第一个实验中，动物被安置在 12:12 光暗（LD）循环中，在 6 个 Zeitgeber 时间（ZT；ZT0 = 灯亮）呈现黑暗或光脉冲。在黑暗阶段的光脉冲在夜行性小鼠中产生负掩蔽，但仅在 ZT14 时出现，而在昼行性草原田鼠中，整个黑暗阶段的光脉冲都产生正掩蔽。在这两种物种中，黑暗脉冲对行为没有影响。在第二个实验中，动物被置于持续黑暗或持续光照中，并分别在 6 个生物钟时间（CT）呈现光或暗脉冲。CT0 对应于前一个 LD 循环的 ZT0。对光掩蔽反应的节律在物种间存在差异；在草原田鼠中，在所有 CT 都能观察到反应，但在小鼠中仅在 CT14 时观察到反应。在小鼠中仅观察到对黑暗的反应，在 CT22 时活动明显增加。在第三个实验中，动物被置于 3.5:3.5-h LD 循环中。令人惊讶的是，掩蔽仅在草原田鼠中明显。在小鼠中，即使同一批动物在前两个实验中对离散的光刺激有反应，在 7 小时循环的光和暗阶段的活动水平也没有差异。三个实验的结果从方法学的角度进行了讨论，并从机制和昼行性的进化角度提供了见解。
