Karlsson K A, Kreider J C, Blumberg M S
Program in Behavioral and Cognitive Neuroscience, Department of Psychology, E11 Seashore Hall, University of Iowa, Iowa City, IA 52242, USA.
Neuroscience. 2004;123(2):575-82. doi: 10.1016/j.neuroscience.2003.09.025.
Infant mammals cycle rapidly between sleep and wakefulness and only gradually does a more consolidated sleep pattern develop. The neural substrates responsible for this consolidation are unknown. To establish a reliable measure of sleep-wake cyclicity in infant rats, nuchal muscle tone was measured in 2-, 5-, and 8-day-old rats, as were motor behaviors associated with sleep (i.e. myoclonic twitching) and wakefulness (e.g. kicking, stretching). Sleep-wake cycles of 2-day-old rats were characterized by short periods of muscle atonia followed by equally short periods of high tone. In 8-day-olds, sleep periods lengthened significantly and disproportionately in relation to awake periods. Next, locus coeruleus (LC) lesions in 8-day-olds resulted in rapid sleep-wake cycling similar to that exhibited by 2-day-olds; in addition, LC lesions had no effect on the duration of awake periods. Finally, transections caudal, but not rostral, to the anterior hypothalamus also reinstated rapid cycling in 8-day-olds, again without affecting the duration of awake periods. This last finding implicates neural structures within the anterior hypothalamus (e.g. ventrolateral preoptic area) in the modulation of sleep-wake cyclicity. The temporal coherence of atonia and myoclonic twitching was not disrupted by any of the manipulations. These results suggest the presence of a bistable mesopontine circuit governing rapid sleep-wake cycling that does not include the LC and that comes increasingly under hypothalamic control during the first postnatal week. This circuit may represent a basic building block with which other sleep components become integrated during ontogeny.
幼年哺乳动物在睡眠和清醒之间快速循环，一种更为稳定的睡眠模式是逐渐形成的。负责这种睡眠模式稳定的神经基质尚不清楚。为了建立一种可靠的测量幼鼠睡眠-清醒周期性的方法，研究人员测量了2日龄、5日龄和8日龄大鼠的颈部肌肉张力，以及与睡眠（即肌阵挛抽搐）和清醒（如踢腿、伸展）相关的运动行为。2日龄大鼠的睡眠-清醒周期的特点是短时间的肌肉张力缺失，随后是同样短时间的高张力。在8日龄大鼠中，睡眠时间相对于清醒时间显著延长且不成比例。接下来，对8日龄大鼠的蓝斑（LC）进行损伤，导致其睡眠-清醒快速循环，类似于2日龄大鼠；此外，LC损伤对清醒时间的持续时间没有影响。最后，在下丘脑前部尾侧而非头侧进行横切，也使8日龄大鼠恢复了快速循环状态，但同样不影响清醒时间的持续时间。这一最新发现表明，下丘脑前部（如腹外侧视前区）的神经结构参与了睡眠-清醒周期性的调节。任何操作都未破坏肌肉张力缺失和肌阵挛抽搐的时间连贯性。这些结果表明，存在一个双稳态的脑桥中脑回路，它控制着快速的睡眠-清醒循环，该回路不包括LC，并且在出生后的第一周越来越受下丘脑控制。这个回路可能是一个基本构建单元，在个体发育过程中，其他睡眠成分与之整合。
