Department of Biology, Bates College, Lewiston, ME, 04240, USA.
Department of Biology, Bates College, Lewiston, ME, 04240, USA.
Respir Physiol Neurobiol. 2020 Sep;280:103483. doi: 10.1016/j.resp.2020.103483. Epub 2020 Jun 25.
Newborn mammals exhibit a biphasic hypoxic ventilatory response (HVR) in which an initial increase in ventilation is followed by a decline back toward baseline levels. The magnitude of the secondary decline diminishes with postnatal age, but this transition occurs earlier in rat pups reared in moderate hyperoxia. This pattern is consistent with heterokairy, a form of developmental plasticity in which environmental factors alter the timing of developmental events. The present study investigated whether this plasticity is specific to the HVR or if hyperoxia instead accelerates overall development. Rat pups reared in 60 % O (Hyperoxia) exhibited a less biphasic ventilatory response to 12 % O than pups reared in 21 % O (Control) at 4 days of age (P4) and transitioned to a sustained HVR by P10-11; Control rats exhibited a biphasic HVR at both ages. However, the average ages at which pups attained other key developmental milestones (i.e., fur development at P5, incisor eruption at P9, and eye opening at P15) were similar between treatment groups. Moreover, growth rates and maturation of the metabolic response to cooling were not accelerated, and may have been delayed slightly, relative to Control rats. For example, the capacity for pups to increase their metabolic rate at low ambient temperatures increased with age, but this thermogenic capacity tended to be reduced in Hyperoxia pups at both P4 and P10-11 (i.e., lower CO production rates below the lower critical temperature). Collectively, these data support the conclusion that hyperoxia specifically advances the age at which rat pups exhibit a sustained HVR, altering the relative timing of developmental events rather than compressing the entire period of development.
新生哺乳动物表现出双相缺氧性通气反应（HVR），其中通气最初增加，然后回落到基线水平。随着出生后年龄的增长，继发性下降的幅度减小，但在中氧环境中饲养的大鼠幼仔中，这种转变发生得更早。这种模式与异态性一致，异态性是一种发育可塑性形式，其中环境因素改变了发育事件的时间。本研究探讨了这种可塑性是否专门针对 HVR，或者高氧是否反而加速了整体发育。在 60%氧气中饲养的大鼠幼仔在 4 天大（P4）时对 12%氧气的通气反应表现出双相性比在 21%氧气中饲养的幼仔（对照组）弱，并且在 P10-11 时过渡到持续的 HVR；对照组大鼠在这两个年龄都表现出双相性 HVR。然而，幼仔达到其他关键发育里程碑的平均年龄（即 P5 时的毛发生长、P9 时的牙齿萌出和 P15 时的眼睛睁开）在处理组之间相似。此外，与对照组大鼠相比，冷却代谢反应的生长速度和成熟度没有加快，甚至可能略有延迟。例如，幼仔在低环境温度下增加代谢率的能力随着年龄的增长而增加，但在 P4 和 P10-11 时，高氧幼仔的这种产热能力往往会降低（即较低临界温度下的 CO 产生率较低）。总的来说，这些数据支持以下结论：高氧专门提前了大鼠幼仔表现出持续 HVR 的年龄，改变了发育事件的相对时间，而不是压缩整个发育时期。
