Temporal hampering of thyroid hormone synthesis just before hatching impeded the filial imprinting in domestic chicks.
Temporal hampering of thyroid hormone synthesis just before hatching impeded the filial imprinting in domestic chicks.
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DOI：
10.3389/fphys.2023.1084816
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发表时间：
2023
影响因子：
4
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中科院分区：
文献类型：
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甲状腺激素在亲子印记敏感期的启动中起着关键作用。雏鸡大脑中甲状腺激素的数量在胚胎后期会固有地增加，并在孵化前达到顶峰。孵化后，依赖印记的循环甲状腺激素在印记训练期间通过血管内皮细胞快速流入大脑。在我们之前的研究中，激素流入的抑制阻碍了印记，这表明孵化后依赖学习的甲状腺激素的流入对于印记的获得至关重要。然而，目前尚不清楚孵化前的固有甲状腺激素水平是否会影响印记。在这里，我们研究了胚胎第20天的暂时性甲状腺激素下降对印记训练期间接近行为和对印记对象的偏好的影响。为此，在第18-20天，每天给胚胎注射一次他巴唑(MMI；一种甲状腺激素生物合成抑制剂)，并测定血清甲状腺激素(T4)，以评估MMI的效果。在注射MMI的胚胎中，T4浓度在胚胎第20天有一过性下降，但在孵化后第0天恢复到对照水平。在孵化后第1天的印记训练开始时，对照雏鸟只有在印记对象移动时才接近印记对象。在训练的后期，对照雏鸟随后走近静态印迹对象。另一方面，给予MMI的雏鸡在训练的重复试验中接近行为减少，对印记对象的行为反应显著低于对照雏鸡。这表明，它们对印记物体的持续反应在孵化前受到短暂的甲状腺激素下降的阻碍。因此，服用MMI的雏鸡的偏好分数显著低于对照雏鸡。此外，测试中的偏好分数与训练中对静态印记对象的行为反应显著相关。这些结果表明，孵化前的内源性甲状腺激素水平对印记的学习过程至关重要。
Thyroid hormones play a critical role in the initiation of the sensitive period of filial imprinting. The amount of thyroid hormones in the brains of chicks increases intrinsically during the late embryonic stages and peaks immediately before hatching. After hatching, a rapid imprinting-dependent inflow of circulating thyroid hormones into the brain occurs via vascular endothelial cells during imprinting training. In our previous study, inhibition of hormonal inflow impeded imprinting, indicating that the learning-dependent inflow of thyroid hormones after hatching is critical for the acquisition of imprinting. However, it remained unclear whether the intrinsic thyroid hormone level just before hatching affects imprinting. Here, we examined the effect of temporal thyroid hormone decrease on embryonic day 20 on approach behavior during imprinting training and preference for the imprinting object. To this end, methimazole (MMI; a thyroid hormone biosynthesis inhibitor) was administered to the embryos once a day on days 18–20. Serum thyroxine (T4) was measured to evaluate the effect of MMI. In the MMI-administered embryos, the T4 concentration was transiently reduced on embryonic day 20 but recovered to the control level on post-hatch day 0. At the beginning of imprinting training on post-hatch day 1, control chicks approached the imprinting object only when the object was moving. In the late phase of training, control chicks subsequently approached towards the static imprinting object. On the other hand, in the MMI-administered chicks, the approach behavior decreased during the repeated trials in the training, and the behavioral responses to the imprinting object were significantly lower than those of control chicks. This indicates that their persistent responses to the imprinting object were impeded by a temporal thyroid hormone decrease just before hatching. Consequently, the preference scores of MMI-administered chicks were significantly lower than those of control chicks. Furthermore, the preference score on the test was significantly correlated with the behavioral responses to the static imprinting object in the training. These results indicate that the intrinsic thyroid hormone level immediately before hatching is crucial for the learning process of imprinting.
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影响因子：
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