Burke-Cornell Medical Research Institute, White Plains, New York, United States of America.
PLoS One. 2012;7(12):e51348. doi: 10.1371/journal.pone.0051348. Epub 2012 Dec 6.
Chicks are bipedal precocious vertebrates that achieve adaptive locomotor skill within hours after hatching. Development of limb movement has been extensively studied in the chicken embryo, but few studies have focused on the preparations leading to precocious locomotor skill. Chicks typically hatch after 21 days of incubation, and recent studies provided evidence that the neural circuits for intralimb control of stepping are established between embryonic days (E) 18-20. It has also been shown that variations in light exposure during embryogenesis can accelerate or delay the onset of hatching and walking by 1 to 2 days. Our earlier work revealed that despite these differences in time to hatch, chicks incubated in different light conditions achieved similar locomotor skill on the day of hatching. Results suggested to us that light exposure during incubation may have accelerated development of locomotor circuits in register with earlier hatching. Thus, in this study, embryos were incubated in 1 of 3 light conditions to determine if development of interlimb coordination at a common time point, 19 days of incubation, varied with light exposure during embryogenesis. Leg muscle activity was recorded bilaterally and burst analyses were performed for sequences of spontaneous locomotor-related activity in one or more ankle muscles to quantify the extent of interlimb coordination in ovo. We report findings indicating that the extent of interlimb coordination varied with light exposure, and left-right alternating steps were a more reliable attribute of interlimb coordination for embryos incubated in constant bright light. We provide evidence that morphological development of the leg varied with light exposure. Based on these findings, we propose that light can accelerate the development of interlimb coordination in register with earlier hatching. Our results lead us to further propose that alternating left-right stepping is the default pattern of interlimb coordination produced by locomotor circuits during embryogenesis.
小鸡是双足早熟的脊椎动物，在孵化后数小时内就能获得适应性的运动技能。肢体运动的发育在鸡胚中得到了广泛研究，但很少有研究关注导致早熟运动技能的准备。小鸡通常在孵化后 21 天孵化，最近的研究提供了证据，证明控制腿部运动的神经回路在胚胎期 18-20 天之间建立。也有研究表明，胚胎发育过程中光照的变化可以提前或延迟孵化和行走 1-2 天。我们之前的工作表明，尽管孵化时间存在差异，但在不同光照条件下孵化的小鸡在孵化当天都能达到相似的运动技能。研究结果表明，孵化期间的光照暴露可能加速了与更早孵化相吻合的运动回路的发育。因此，在这项研究中，我们将胚胎暴露在 3 种光照条件之一下，以确定在 19 天的孵化期，在共同的时间点，四肢之间的协调发展是否会因胚胎发育期间的光照暴露而有所不同。我们双侧记录腿部肌肉活动，并对一个或多个踝关节肌肉的自发性运动相关活动序列进行爆发分析，以量化胚胎孵化期间肢体之间协调的程度。我们报告的发现表明，肢体之间协调的程度因光照暴露而不同，左右交替的步伐是在恒定强光下孵化的胚胎肢体之间协调的更可靠特征。我们提供的证据表明，腿部的形态发育因光照暴露而不同。基于这些发现，我们提出光照可以与更早的孵化相吻合，加速肢体之间的协调发展。我们的研究结果进一步表明，左右交替的步伐是胚胎发育过程中运动回路产生的肢体之间协调的默认模式。
