Schmidt Kim L, Macdougall-Shackleton Elizabeth A, Soma Kiran K, Macdougall-Shackleton Scott A
Department of Biology, University of Western Ontario, London, Ontario, Canada; Advanced Facility for Avian Research, University of Western Ontario, London, Ontario, Canada.
Department of Biology, University of Western Ontario, London, Ontario, Canada; Advanced Facility for Avian Research, University of Western Ontario, London, Ontario, Canada.
Gen Comp Endocrinol. 2014 Jan 15;196:72-80. doi: 10.1016/j.ygcen.2013.11.014. Epub 2013 Nov 26.
Variation in early environmental conditions can have long-term effects on physiology and behavior, a process referred to as developmental programming. In particular, exposure to early-life stressors can have long-term effects on regulation of the hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-gonadal (HPG) axes. Although these effects have been well documented in mammals, less is known about how early-life stress affects regulation of these endocrine systems in non-mammalian species. In the current study, we determined the long-term effects of early-life food restriction or corticosterone (CORT) treatment on the HPA axis of song sparrows (Melospiza melodia), including the responses to restraint stress, dexamethasone challenge, and ACTH challenge. In addition, we assessed long-term effects on the HPG axis by measuring sex steroid levels (testosterone in males and 17β-estradiol in females) before and after a gonadotropin-releasing hormone (GnRH) challenge. Subjects treated with CORT during development had larger increases in CORT in response to ACTH challenge than food-restricted or control subjects. Neither treatment affected the responses of CORT to restraint or dexamethasone. CORT-treated males also had higher initial testosterone levels, but neither treatment affected testosterone levels post-GnRH. Lastly, although GnRH challenge failed to increase circulating estradiol levels in females, females exposed to food restriction or CORT treatment had lower estradiol levels than control females. These results show that exposure to stress can developmentally program the endocrine system of songbirds and illustrate the importance of considering developmental conditions when determining the factors responsible for inter-individual variation in endocrine regulation.
早期环境条件的变化会对生理和行为产生长期影响,这一过程被称为发育编程。特别是,早年暴露于应激源会对下丘脑-垂体-肾上腺(HPA)轴和下丘脑-垂体-性腺(HPG)轴的调节产生长期影响。尽管这些影响在哺乳动物中已有充分记录,但对于早年应激如何影响非哺乳动物物种中这些内分泌系统的调节,我们了解得较少。在当前研究中,我们确定了早年食物限制或皮质酮(CORT)处理对歌带鹀(Melospiza melodia)HPA轴的长期影响,包括对应激、地塞米松刺激和促肾上腺皮质激素(ACTH)刺激的反应。此外,我们通过测量促性腺激素释放激素(GnRH)刺激前后的性类固醇水平(雄性中的睾酮和雌性中的17β-雌二醇)来评估对HPG轴的长期影响。在发育过程中接受CORT处理的个体,在ACTH刺激下CORT的增加幅度大于食物限制组或对照组个体。两种处理均未影响CORT对应激或地塞米松的反应。接受CORT处理的雄性个体初始睾酮水平也较高,但两种处理均未影响GnRH刺激后的睾酮水平。最后,尽管GnRH刺激未能增加雌性个体的循环雌二醇水平,但经历食物限制或CORT处理的雌性个体的雌二醇水平低于对照雌性。这些结果表明,暴露于应激会在发育过程中对鸣禽的内分泌系统进行编程,并说明了在确定内分泌调节个体间差异的影响因素时考虑发育条件的重要性。