Circadian remodeling of Neuronal circuits involved in rhythmic behavior(4/28/2008)

　今日は冷える。温暖なテキサスにいると寒さがこたえる。日本に帰ったら、寒さに耐えられるかな？今日のセミナーはアルゼンチンの研究グループが発表した論文紹介。ショウジョウバエの脳で側方ニューロンからdorsal protocerebrumにつながる神経の軸索の形が朝と夜では違う、という内容。この神経細胞は色素拡散ホルモンを分泌し、朝は夜と比べて軸索が伸びる。生物時計によって神経細胞の軸索の形態の変化が起こる。

Clock output pathways are central to convey timing information from the circadian clock to a diversity of physiological systems, ranging from cell-autonomous processes to behavior. While the molecular mechanisms that generate and sustain rhythmicity at the cellular level are well undrstood, it is unclear how this information is further structured to control specific behavioral outputs. Rhythmic release of PDF has been proposed to propagate the time of day information from core pacemaker cells to downstream targets underlying rhythmic locomotor activity. Indeed, such circadian changes in PDF intensity represent the only known mechanism through which the PDF circuit could communicate with its output. Here we describe a novel circadian phenomenon involving extensive remodeling in the axonal terminals of the PDF circuit, which display higher complexity during the day and significantly lower complexity at nighttime, both under daily cycles and constant conditions. In support to its circadian nature, cycling is lost in bona fide clockless mutants. We propose this clock-controlled structural plasticity as a candidate mechanism contributing to the transmission of information downstream of pacemaker cells.