Adly M A, Spiwoks-Becker I, Vollrath L
Department of Anatomy, Johannes Gutenberg University, Mainz, Germany.
Invest Ophthalmol Vis Sci. 1999 Sep;40(10):2165-72.
Electron microscopic sections through rod and cone ribbon synapses reveal mainly rodlike synaptic ribbon profiles, but a few unusual spherical and club-shaped profiles also occur. To elucidate the meaning of the latter two forms, the authors have investigated these ribbon synapses at different times during the 24-hour cycle and under various lighting conditions.
The various types of ribbon profiles were counted, and their sizes were measured by means of transmission electron microscopy in retinas of male BALB/c mice exposed to 12 hours light (lights on at 6 AM) and 12 hours dark (LD 12:12), continuous light, or continuous darkness for 4 days.
A 24-hour study of mice exposed to LD 12:12 showed that spherical and club-shaped profile numbers ranged from 0% to 29%, depending on the time of day. They reached a maximum at 3 hours after light onset, followed by a gradual decrease to approach zero at night and reappearing after light onset the next morning. After 4 days of continuous light, the spherical profiles were significantly decreased in number (examined at 9 AM). After continuous darkness, the spherical and club-shaped profiles were significantly reduced in number. Administration of 4 hours of light after 92 hours of continuous darkness restored the number of spherical and club-shaped profiles to normal values. The rodlike ribbon profiles were found to be longer in darkness than in light. In rod terminals containing spherical profiles, the rodlike ribbon profiles were shorter than in terminals without spherical profiles. CONCLUSIONS. The club-shaped and the spherical profiles were related to the turnover of the synaptic ribbons. Soon after light exposure in the morning, the synaptic ribbons formed distal swellings, giving rise to club-shaped profiles and a decrease in length. The swellings appeared to bud off, thus forming spherical synaptic bodies. This article discusses whether these changes are signs of degradation of spent ribbons, or whether they play a physiological role related to the inactivation of the ribbon synapses after light exposure.
通过对视杆和视锥细胞带状突触的电子显微镜切片观察，主要呈现出杆状突触带形态，但也会出现一些不寻常的球形和棒状形态。为阐明后两种形态的意义，作者在24小时周期的不同时间以及各种光照条件下对这些带状突触进行了研究。
通过透射电子显微镜对暴露于12小时光照（早上6点开灯）和12小时黑暗（LD 12:12）、持续光照或持续黑暗4天的雄性BALB/c小鼠视网膜中的各种类型的突触带形态进行计数，并测量其大小。
对暴露于LD 12:12的小鼠进行的24小时研究表明，球形和棒状形态的数量在一天中的不同时间从0%到29%不等。它们在光照开始后3小时达到最大值，随后逐渐减少，在夜间接近零，并在第二天早上光照开始后再次出现。持续光照4天后，球形形态的数量显著减少（上午9点检查）。持续黑暗后，球形和棒状形态的数量显著减少。在持续黑暗92小时后给予4小时光照，可使球形和棒状形态的数量恢复到正常值。发现杆状突触带形态在黑暗中比在光照中更长。在含有球形形态的视杆终末中，杆状突触带形态比没有球形形态的终末中的更短。结论。棒状和球形形态与突触带的更新有关。早上光照后不久，突触带形成远端肿胀，产生棒状形态并导致长度减少。这些肿胀似乎会脱落，从而形成球形突触小体。本文讨论了这些变化是已消耗突触带降解的迹象，还是它们在光照后与带状突触失活相关的生理作用。
