Department of Zoology, Banaras Hindu University, Varanasi 221005, India.
Gen Comp Endocrinol. 2013 Sep 1;190:203-13. doi: 10.1016/j.ygcen.2013.06.019. Epub 2013 Jul 10.
This article is focused on the effect of specific phase relation of serotonergic and dopaminergic oscillations on the gonadal responses of different avian species. These species include (i) summer breeding birds - Red headed bunting (exhibiting post-reproductive absolute photorefractoriness) and Indian Weaver bird (which lacks absolute photorefractoriness), (ii) autumn breeding - Spotted munia and Lal munia (photoperiodic responses of which are distinctly different from that of any long day birds described thus far) and (iii) domesticated Japanese quail (which under natural day length breeds in summer, exhibits relative photorefractoriness, but breeds continuously if maintained in long photoperiod). Previous experiments have shown that daily administration of serotonin precursor 5-hydroxytryptophan and dopamine precursor L-dihydroxyphenylalanine given 8h apart during progressive phase of gonadal cycle can lead to a significant decrease in gonadal activity. However, if given at an interval of 12h it leads to an increase in gonadal activity and the effect of other intervals (0-, 4-, 16- and 20-h) were not different from control. Similar effects were observed during regressive phase of the gonadal cycle of above species except in those which display absolute photorefractory phase in their breeding cycle. This shows that, gonad of such species not only develop post-reproductive photorefractoriness but also becomes insensitive to the stimulatory effects of 5-HTP and L-DOPA when given at the interval of 12h. It is suggested that, temporal phase relation of circadian serotonergic and dopaminergic oscillations is the basis of seasonality in birds and may alter the activity of neuroendocrine-gonadal axis not only under natural day length but also under experimental/different photoperiodic conditions. These results are in agreement with the internal coincidence model of photoperiodic time measurement and indicate that birds can detect specific phase relationship between the two neural oscillations for their reproductive regulations and circadian organization is intricately involved in the regulation of seasonality.
这篇文章主要关注的是血清素能和多巴胺能振荡的特定相位关系对不同鸟类物种的性腺反应的影响。这些物种包括(i)夏季繁殖鸟类-红额金翅雀（表现出产后绝对光感受性）和印度织布鸟（其缺乏绝对光感受性），(ii)秋季繁殖鸟类-斑文鸟和栗耳文鸟（其光周期反应明显不同于迄今为止描述的任何长日鸟）和(iii)家养日本鹌鹑（在自然日长下夏季繁殖，表现出相对光感受性，但如果维持在长光照下则连续繁殖）。先前的实验表明，在性腺周期的渐进阶段，每天相隔 8 小时给予血清素前体 5-羟色氨酸和多巴胺前体 L-二羟基苯丙氨酸，可以显著降低性腺活动。然而，如果间隔 12 小时给予，则会导致性腺活动增加，而其他间隔（0-、4-、16-和 20-小时）的效果与对照没有区别。在上述物种的性腺周期的退化阶段也观察到了类似的效果，除了那些在繁殖周期中表现出绝对光感受性的物种。这表明，这些物种的性腺不仅在产后发育出光感受性，而且在 12 小时的间隔下，对 5-HTP 和 L-DOPA 的刺激作用变得不敏感。这表明，昼夜血清素能和多巴胺能振荡的时间相位关系是鸟类季节性的基础，不仅可以改变自然日长下，还可以改变实验/不同光周期条件下神经内分泌-性腺轴的活动。这些结果与光周期时间测量的内部巧合模型一致，并表明鸟类可以检测到两种神经振荡之间的特定相位关系，用于它们的繁殖调节，而昼夜节律组织复杂地参与了季节性的调节。
