Abraham Ute, Albrecht Urs, Brandstätter Roland
Max-Planck Research Centre for Ornithology, Andechs, Germany.
Chronobiol Int. 2003 Jul;20(4):657-69. doi: 10.1081/cbi-120022414.
While the site of the major circadian pacemaker in mammals, the suprachiasmatic nucleus (SCN) of the hypothalamus, is very well characterized, little is known about hypothalamic circadian organization in birds. This paper reviews recent findings on clock gene expression in the hypothalamus of several bird species focusing on circadian pPer2 expression in the house sparrow. In contrast to mammals, rhythmic Per2 gene expression in the house sparrow hypothalamus is not restricted to a single cell group but occurs in two distinct hypothalamic nuclei, the SCN and the lateral hypothalamic nucleus (LHN). The complex temporal and spatial distribution of pPer2 expression suggests a longitudinal compartmentalization of the SCN with period gene expression being initiated in the most rostral portion before lights on. In the lateral hypothalamus, phasing of pPer2-rhythmicity appeared delayed. In pinealectomized house sparrows, the overall circadian pPer2 expression pattern is maintained indicating that rhythmic pPer2 transcription in the SCN and LHN of the house sparrow are not driven by the pineal gland. Rather, they reflect the activity of autonomous hypothalamic circadian oscillators. Certain changes in peak expression levels and the expression phase, however, suggest that the pineal melatonin rhythm affects both the phase and the amplitude of rhythmic hypothalamic pPer2 expression.
虽然哺乳动物主要昼夜节律起搏器的位置，即下丘脑的视交叉上核（SCN），已得到很好的表征，但关于鸟类下丘脑的昼夜节律组织却知之甚少。本文综述了几种鸟类下丘脑时钟基因表达的最新研究结果，重点关注家麻雀中昼夜节律相关的Per2基因表达。与哺乳动物不同，家麻雀下丘脑中有节律的Per2基因表达并不局限于单个细胞群，而是发生在两个不同的下丘脑核团，即视交叉上核和下丘脑外侧核（LHN）。pPer2表达复杂的时间和空间分布表明视交叉上核存在纵向分区，周期基因表达在光照开启前最靠前的部分开始。在下丘脑外侧，pPer2节律的相位出现延迟。在松果体切除的家麻雀中，整体昼夜节律性pPer2表达模式得以维持，这表明家麻雀视交叉上核和下丘脑外侧核中pPer2的节律性转录并非由松果体驱动。相反，它们反映了自主的下丘脑昼夜节律振荡器的活动。然而，峰值表达水平和表达相位的某些变化表明，松果体褪黑素节律会影响下丘脑pPer2节律性表达的相位和幅度。
