Mayer I, Bornestaf C, Wetterberg L, Borg B
Department of Zoology, University of Stockholm, Stockholm, S-106 91, Sweden.
Gen Comp Endocrinol. 1997 Dec;108(3):386-94. doi: 10.1006/gcen.1997.6985.
Breeding in the three-spined stickleback is stimulated by long but not by short photoperiods in many seasons. The aim of the present study was to test the hypothesis that melatonin plays a role in the inhibitory effect of short photoperiod in this species. Adult nonbreeding males were kept either under constant light (Experiment 1) or under a stimulatory long photoperiod (16L 8D, Experiment 2), in water containing 0, 20, or 80 microg/liter melatonin for 16 hr/day for 28 days during the spring. These melatonin treatments were intended to simulate the daily melatonin pattern of a nonstimulatory short photoperiod. In the second experiment, fish were also kept under a nonstimulatory short photoperiod (8L 16D). In the natural breeding season the only germ cells found in the stickleback testes are spermatozoa and spermatogonia, a condition found in many fish under all treatments. In the first experiment, spermatogenesis was not influenced by melatonin. However, testes also containing spermatocytes and spermatids were more common in fish kept under 8L 16D and fish treated with 80 microg/liter melatonin than in 16L 8D controls in Experiment 2. Kidney hypertrophy, an androgen-dependent male secondary sexual characteristic in the stickleback, appeared in most males kept under constant light or 16L 8D and was not influenced by melatonin treatment. In contrast, control males kept under 8L 16D in Experiment 2 did not display kidney hypertrophy. Therefore, the presence of an extended period of elevated melatonin did not prevent the stimulatory effects of long photoperiod on development of this secondary sexual characteristic in the stickleback.
在许多季节里，三刺鱼的繁殖是由长光照周期而非短光照周期刺激的。本研究的目的是检验褪黑素在该物种短光照周期的抑制作用中发挥作用这一假设。在春季，成年非繁殖期雄鱼被饲养在持续光照条件下（实验1）或刺激性长光照周期（16小时光照，8小时黑暗，实验2），每天在含有0、20或80微克/升褪黑素的水中饲养16小时，持续28天。这些褪黑素处理旨在模拟非刺激性短光照周期的每日褪黑素模式。在第二个实验中，鱼也被饲养在非刺激性短光照周期（8小时光照，16小时黑暗）下。在自然繁殖季节，三刺鱼睾丸中发现的唯一生殖细胞是精子和精原细胞，在所有处理下的许多鱼类中都发现了这种情况。在第一个实验中，精子发生不受褪黑素影响。然而，在实验2中，与16小时光照，8小时黑暗的对照组相比，饲养在8小时光照，16小时黑暗条件下的鱼以及用80微克/升褪黑素处理过的鱼，其睾丸中含有精母细胞和精子细胞的情况更为常见。肾脏肥大是三刺鱼中一种雄激素依赖性的雄性第二性征，在大多数饲养在持续光照或16小时光照，8小时黑暗条件下的雄鱼中出现，且不受褪黑素处理的影响。相比之下，实验2中饲养在8小时光照，16小时黑暗条件下的对照雄鱼未表现出肾脏肥大。因此，长时间升高的褪黑素的存在并未阻止长光照周期对三刺鱼这种第二性征发育的刺激作用。
