Bernstein S A, Breding D J, Fisher S K
J Cell Biol. 1984 Aug;99(2):379-89. doi: 10.1083/jcb.99.2.379.
The lizard, Sceloporus occidentalis has an all-cone retina. In lizards maintained on a 12-h light:12-h dark (12L:12D) cycle, a burst of cone outer segment (COS) shedding occurs 2 h after light offset (1400 h circadian time) (Young, R.W., 1977, J. Ultrastruct. Res. 61:172-72). In this investigation, we studied the effect of different lighting regimes on the pattern of cone disk shedding in this species. When lizards entrained to a 12L:12D cycle are kept in constant darkness (DD), the shedding peak is advanced approximately 2 h and the magnitude of shedding is reduced to 30% of control. COS increased in mean length from 12 micron in controls to 14 micron after one cycle in DD and maintained this length during a second cycle in DD. In constant light (LL), disk shedding was damped to approximately 10% of control values. Shedding synchrony in LL was also perturbed and therefore cyclic shedding bursts could not be distinguished. During LL there was a much larger increase in COS mean length than in DD. After one cycle of LL, COS length was 15 micron and after two cycles COS length exceeded 17 micron. When lizards entrained to 12L:12D are shifted to a 6L:18D regimen, the first shedding cycle is biphasic. The first peak of 5% shedding occurs 2 h after light offset whereas a second larger peak (13%) occurs according to the entrained schedule (1400 h). This manipulation separates out a dark-triggered and circadian shedding component, which is normally superimposed in lizards entrained to a 12L:12D cycle. When entrained lizards are placed in 36 h of LL followed by light offset, the peak shedding response after light offset is double the control response (53% vs. 27%). After 30 h of LL (lights off 90 degrees out of phase), there is a biphasic shedding response similar to the 6L:18D regimen although this time the dark-triggered shedding component is greater in magnitude then the circadian component. COS turnover is estimated by extrapolating from COS mean length increases during LL. From this method we obtained a 2.7-micron increase in COS length during each day in LL. If COS growth is not augmented during LL, this would yield a 4-5-d turnover time for the average 12.5-micron COS.
西部强棱蜥（Sceloporus occidentalis）具有全视锥视网膜。在维持12小时光照：12小时黑暗（12L:12D）周期的蜥蜴中，视锥细胞外段（COS）的脱落高峰在光照结束后2小时（昼夜时间1400小时）出现（扬，R.W.，1977年，《超微结构研究杂志》61:172 - 172）。在本研究中，我们研究了不同光照模式对该物种视锥盘脱落模式的影响。当适应12L:12D周期的蜥蜴处于持续黑暗（DD）环境中时，脱落高峰提前约2小时出现，且脱落幅度降至对照组的30%。COS的平均长度从对照组的12微米在DD环境中经过一个周期后增加到14微米，并在DD环境中的第二个周期保持该长度。在持续光照（LL）环境中，盘状结构的脱落被抑制至对照组值的约10%。LL环境中的脱落同步性也受到干扰，因此无法区分周期性的脱落高峰。在LL环境中，COS平均长度的增加幅度比在DD环境中要大得多。经过一个LL周期后，COS长度为15微米，经过两个周期后，COS长度超过17微米。当适应12L:12D的蜥蜴转移到6L:18D模式时，第一个脱落周期是双相的。5%脱落的第一个高峰在光照结束后2小时出现，而第二个更大的高峰（13%）则按照适应的时间表（1400小时）出现。这种操作分离出了一个黑暗触发的和昼夜节律性的脱落成分，这两种成分在适应12L:12D周期的蜥蜴中通常是叠加的。当适应环境的蜥蜴在LL环境中放置36小时后再进行光照结束操作，光照结束后的脱落高峰反应是对照组反应的两倍（53%对27%）。在LL环境中放置30小时（光照关闭相位相差90度）后，会出现类似于6L:18D模式的双相脱落反应，尽管此时黑暗触发的脱落成分在幅度上大于昼夜节律成分。通过从LL环境中COS平均长度的增加进行外推来估计COS的更新率。通过这种方法，我们得出在LL环境中每天COS长度增加2.7微米。如果在LL环境中COS的生长没有增强，那么对于平均12.5微米的COS来说，这将产生4 - 5天的更新时间。
