Pyza E, Meinertzhagen I A
Zoological Museum, Jagiellonian University, Kraków, Poland.
J Comp Physiol A. 1998 Dec;183(6):719-27. doi: 10.1007/s003590050294.
Various organelles in the lamina terminals of housefly photoreceptors exhibit daily rhythms having a circadian basis. These include changes in the numbers of photoreceptor tetrad and L2 feedback synapses, and longitudinal movements of screening pigment. Circadian information has previously been suggested to spread from the clock to the lamina via widefield cells expressing either 5-hydroxytryptamine or pigment-dispersing hormone-like immunoreactivity. We examined the action of these neuromodulators, and other candidate neurotransmitters, 4 h after injecting either the transmitter or a control into the medulla. We counted electron microscope profiles of organelles that normally exhibit circadian changes, and two types of invagination into photoreceptor terminals, capitate projections and inter-receptor invaginations. No single substance mediated the changes observed. Injected pigment-dispersing hormone peptide decreased the number of pigment granules, implicating this peptide in screening pigment migration, but produced no changes in synapse-related organelles. alpha-Aminobutyric acid exclusively decreased the number of L2 feedback synapses. Responses to other transmitters were specific, and often large, but generally not statistically significant. Histamine, for example, may decrease the number of tetrads, possibly by direct autoregulation. The results suggest that there is likely to be more than one effector in the circadian pathways to the lamina.
家蝇光感受器的薄板终端中的各种细胞器呈现出具有昼夜节律基础的每日节律。这些包括光感受器四联突触和L2反馈突触数量的变化，以及遮光色素的纵向移动。此前有人提出，昼夜节律信息通过表达5-羟色胺或色素分散激素样免疫反应性的广域细胞从生物钟传播到薄板。在将递质或对照注射到髓质4小时后，我们研究了这些神经调节剂以及其他候选神经递质的作用。我们对通常呈现昼夜节律变化的细胞器以及两种类型的光感受器终端内陷（头状突起和感受器间内陷）的电子显微镜图像进行了计数。没有单一物质介导所观察到的变化。注射色素分散激素肽减少了色素颗粒的数量，表明该肽与遮光色素迁移有关，但对突触相关细胞器没有产生变化。α-氨基丁酸专门减少了L2反馈突触的数量。对其他递质的反应是特异性的，而且通常很大，但一般没有统计学意义。例如，组胺可能通过直接的自身调节减少四联突触的数量。结果表明，通向薄板的昼夜节律途径中可能存在不止一种效应物。
