Ito Akie, Kikusui Takefumi, Takeuchi Yukari, Mori Yuji
Veterinary Ethology, University of Tokyo, Japan.
Behav Brain Res. 2006 Jul 15;171(1):87-93. doi: 10.1016/j.bbr.2006.03.023. Epub 2006 May 4.
Environmental stimuli affect various aspects of the early physical and behavioral development in rats. One of the most important events in the early stage of life is weaning, and we recently reported that precocious weaning augments anxiety and aggressiveness in rats and mice. In the present study, we investigated the autonomic responses to stress in two groups of rats: the early-weaned group (weaned at 16 days of age), and the normally weaned group (weaned at 30 days) as a control. First, the early and normally weaned rats were subjected to an elevated plus-maze test to assess their anxiety levels. It was confirmed that early-weaned male rats, but not the females, showed a lower frequency of entry into and shorter duration of stay in the open arms of the maze compared to the normally weaned rats. Subsequently, the two groups were either placed in a novel clean cage or exposed to an unfamiliar conspecific, and their heart rates and core body temperatures were monitored to evaluate their autonomic stress responses. There was an exacerbation of autonomic responses, such as stress-induced hyperthermia and tachycardia, and an alternation of behavioral responses, including increased sniffing, and decreased grooming and resting. These effects of early weaning were significant only in males. In contrast, when rats encountered an unfamiliar individual, no significant differences were observed between the two groups in either sex. This suggests that stimuli emanating from an unfamiliar intruder were too intense to detect the augmentation of stress responses in the early-weaned rat. The results of the present study demonstrate that precocious weaning augments, not only behavioral but also autonomic responses, to stressful conditions with sexually dimorphic patterns, i.e. more profoundly in males than in females.
环境刺激会影响大鼠早期身体和行为发育的各个方面。生命早期最重要的事件之一是断奶，我们最近报告称，过早断奶会增强大鼠和小鼠的焦虑和攻击性。在本研究中，我们调查了两组大鼠对应激的自主反应：早期断奶组（16日龄断奶）和正常断奶组（30日龄断奶，作为对照）。首先，对早期断奶和正常断奶的大鼠进行高架十字迷宫试验，以评估它们的焦虑水平。结果证实，与正常断奶大鼠相比，早期断奶的雄性大鼠，但雌性大鼠没有，进入迷宫开放臂的频率较低，在开放臂停留的时间较短。随后，将两组大鼠分别置于一个新的干净笼子中或暴露于一个不熟悉的同种个体，并监测它们的心率和核心体温，以评估它们的自主应激反应。自主反应出现加剧，如应激诱导的体温过高和心动过速，行为反应也发生改变，包括嗅探增加、梳理和休息减少。早期断奶的这些影响仅在雄性大鼠中显著。相比之下，当大鼠遇到一个不熟悉的个体时，两组在性别上均未观察到显著差异。这表明来自不熟悉入侵者的刺激过于强烈，以至于无法检测到早期断奶大鼠应激反应的增强。本研究结果表明，过早断奶不仅会增强行为反应，还会增强对应激条件的自主反应，且具有性别差异模式，即雄性比雌性更明显。
