Saunders D S
Institute of Cell, Animal and Population Biology, University of Edinburgh.
Invert Neurosci. 1997 Sep-Dec;3(2-3):155-64. doi: 10.1007/BF02480370.
Two clock-controlled processes, overt circadian rhythmicity and the photoperiodic induction of diapause, are described in the blow fly, Calliphora vicina and the fruit fly, Drosophila melanogaster. Circadian locomotor rhythms of the adult flies reflect endogenous, self-sustained oscillations with a temperature compensated period. The free-running rhythms become synchronised (entrained) to daily light:dark cycles, but become arrhythmic in constant light above a certain intensity. Some flies show fragmented rhythms (internal desynchronisation) suggesting that overt rhythmicity is the product of a multioscillator (multicellular) system. Photoperiodic induction of larval diapause in C. vicina and of ovarian diapause in D. melanogaster is also based on the circadian system but seems to involve a separate mechanism at both the molecular and neuronal levels. For both processes in both species, the compound eyes and ocelli are neither essential nor necessary for photic entrainment, and the circadian clock mechanism is not within the optic lobes. The central brain is the most likely site for both rhythm generation and extra-optic photoreception. In D. melanogaster, a group of lateral brain neurons has been identified as important circadian pacemaker cells, which are possibly also photo-sensitive. Similar lateral brain neurons, staining for arrestin, a protein in the phototransduction 'cascade' and a selective marker for photoreceptors in both vertebrates and invertebrates, have been identified in C. vicina. Much less is known about the cellular substrate of the photoperiodic mechanism, but this may involve the pars intercerebralis region of the mid-brain.
在丽蝇（Calliphora vicina）和果蝇（Drosophila melanogaster）中描述了两种受时钟控制的过程，即明显的昼夜节律和滞育的光周期诱导。成年果蝇的昼夜运动节律反映了具有温度补偿周期的内源性、自我维持的振荡。自由运行的节律会与日常的光照：黑暗周期同步（被夹带），但在高于一定强度的持续光照下会变得无节律。一些果蝇表现出碎片化的节律（内部不同步），这表明明显的节律性是多振荡器（多细胞）系统的产物。丽蝇幼虫滞育和果蝇卵巢滞育的光周期诱导也基于昼夜节律系统，但在分子和神经元水平上似乎涉及一种单独的机制。对于这两个物种的这两个过程，复眼和单眼对于光诱导夹带既不是必需的，昼夜节律时钟机制也不在视叶内。中枢脑最有可能是节律产生和视外光接收的部位。在果蝇中，一组侧脑神经元已被确定为重要的昼夜节律起搏器细胞，它们可能也对光敏感。在丽蝇中也发现了类似的侧脑神经元，它们对抑制蛋白染色，抑制蛋白是光转导“级联”中的一种蛋白质，也是脊椎动物和无脊椎动物光感受器的选择性标记。关于光周期机制的细胞底物了解得要少得多，但这可能涉及中脑的脑间部区域。
