Pyza E, Meinertzhagen I A
Zoological Museum, Jagiellonian University, Kraków, Poland.
J Neurobiol. 1997 May;32(5):517-29.
Screening pigment granules occur in the synaptic terminals of photoreceptors in the fly's (Musca domestica, L.) compound eye. The granules resemble ommochrome granules in the overlying photoreceptor cell body. There are also two types of invagination into receptor terminals: capitate projections (from glial cells) and invaginations from neighboring receptor terminals. The number of profiles of these organelles in the first optic neuropile, the lamina, have been counted using single-section quantitative electron microscopic methods. Pigment granules are concentrated proximally in the terminal, toward the brain. The numbers change, increasing during the night (1 h after lights off) up to values more than twice the number 1 h after lights on, apparently by longitudinal migration of granules from the cell body into the terminal. Files entrained to day/night conditions and then held under constant darkness continue to exhibit changes in the numbers of profiles. Even though overall there were 80-90% fewer granule profiles than under day/night conditions, the numbers attained a peak many times higher at the end of the subjective day. Thus, the changes are endogenous, showing circadian rhythmicity. Although their significance is unknown, these changes parallel previously described circadian rhythms in the receptor terminals and their lamina monopolar-cell targets. The invaginations from receptor terminals were more numerous under day/night conditions than under constant darkness, and cycled in constant darkness, peaking at the end of subjective night. Capitate projections, by contrast, failed to change significantly under the experimental conditions analyzed, a lack of responsiveness they share with photoreceptor tetrad synapses.
筛选色素颗粒出现在果蝇（家蝇，L.）复眼中光感受器的突触终末。这些颗粒类似于覆盖其上的光感受器细胞体中的眼色素颗粒。受体终末还有两种内陷结构：头状突起（来自神经胶质细胞）和相邻受体终末的内陷。利用单切片定量电子显微镜方法，对第一视觉神经纤维层（即神经纤维层）中这些细胞器的轮廓数量进行了计数。色素颗粒在终末近端朝向脑的方向聚集。其数量会发生变化，在夜间（熄灯后1小时）增加，达到开灯后1小时数量的两倍多，显然是通过颗粒从细胞体向终末的纵向迁移实现的。被调整到昼夜条件然后置于持续黑暗中的果蝇，其轮廓数量继续呈现变化。尽管总体上颗粒轮廓比在昼夜条件下少80 - 90%，但在主观日结束时数量达到一个高得多的峰值。因此，这些变化是内源性的，表现出昼夜节律性。尽管其意义尚不清楚，但这些变化与先前描述的受体终末及其神经纤维层单极细胞靶点中的昼夜节律相似。受体终末的内陷在昼夜条件下比在持续黑暗中更多，并且在持续黑暗中呈周期性变化，在主观夜结束时达到峰值。相比之下，头状突起在分析的实验条件下没有显著变化，它们与光感受器四联突触一样缺乏反应性。
