McNaughton F J, Dawson A, Goldsmith A R
Institute of Terrestrial Ecology, Huntingdon, United Kingdom.
Gen Comp Endocrinol. 1995 Jan;97(1):135-44. doi: 10.1006/gcen.1995.1013.
The reproductive system of juvenile European starlings appears to be similar to that of photorefractory adults, yet the increase in plasma luteinizing hormone (LH) in juveniles in response to gonadotrophin-releasing hormone (GnRH) is much less than that of photorefractory adults. To investigate this apparent anomaly, the effects of age, reproductive state, and sex on the increase in plasma LH concentration in response to im injections of GnRH were investigated. The results show that photorefractory juveniles needed 10 times the dose of GnRH to elicit the same increase in LH as photorefractory adults, and the response of photosensitive juveniles to 10 micrograms GnRH was at least 15 times as great as that of photorefractory juveniles (e.g., 6.14 micrograms/liter compared to 0.35 microgram/liter 2 min after injection). However, the response of photosensitive adults was not greater than that of photorefractory adults. These differences were not due to differences in the amount of LH stored in the pituitary: this was 298 +/- 34 and 306 +/- 51 ng/gland in photorefractory juveniles and adults, respectively, and 367 +/- 47 in photosensitive juveniles. Repeated weekly treatment with GnRH enhanced LH responses: LH levels 3 min after GnRH treatment increased in birds on short days from 7.7 micrograms/liter after the first treatment to 24.6 micrograms/liter after the sixth treatment and in birds on long days it increased from 0.54 to 1.8 micrograms/liter. The greater response of photorefractory adults compared to photorefractory juveniles may therefore be due to the self-priming effect of GnRH during a preceding period of photosensitivity and/or photostimulation. The response to exogenous GnRH depends more on age and history than on prevailing physiological state. There was also a marked sex difference: females showed a sevenfold greater response to GnRH.
幼年欧洲椋鸟的生殖系统似乎与光不应性成年鸟的相似，然而，幼年鸟对促性腺激素释放激素（GnRH）产生反应时，其血浆促黄体生成素（LH）的增加量远低于光不应性成年鸟。为了研究这一明显的异常现象，研究了年龄、生殖状态和性别对肌肉注射GnRH后血浆LH浓度增加的影响。结果表明，光不应性幼鸟引发与光不应性成年鸟相同LH增加量所需的GnRH剂量是其10倍，而光敏性幼鸟对10微克GnRH的反应至少是光不应性幼鸟的15倍（例如，注射后2分钟，分别为6.14微克/升和0.35微克/升）。然而，光敏性成年鸟的反应并不比光不应性成年鸟大。这些差异并非由于垂体中储存的LH量不同：光不应性幼鸟和成年鸟垂体中LH的储存量分别为298±34和306±51纳克/腺体，光敏性幼鸟为367±47纳克/腺体。每周重复用GnRH处理可增强LH反应：短日照鸟类在第一次GnRH处理后3分钟时LH水平为7.7微克/升，第六次处理后升至24.6微克/升；长日照鸟类则从0.54微克/升增至1.8微克/升。因此，与光不应性幼鸟相比，光不应性成年鸟反应更大可能是由于在之前的光敏期和/或光刺激期GnRH的自我启动作用。对外源性GnRH的反应更多地取决于年龄和经历，而非当前的生理状态。此外，还存在明显的性别差异：雌性对GnRH的反应比雄性大7倍。
