Koizumi Ryoko, Kiyokawa Yasushi, Tanaka Kazuyuki D, Kimura Goro, Tanikawa Tsutomu, Takeuchi Yukari
Laboratory of Veterinary Ethology, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan.
Present address: Wildlife Damage Management Group, Central Region Agricultural Research Center, National Agricultural Food Research Organization, 2-1-18 Kannondaira, Tsukuba, Ibaraki 305-8666, Japan.
J Vet Med Sci. 2021 Jan 14;83(1):78-83. doi: 10.1292/jvms.20-0568. Epub 2020 Nov 25.
Exposure to novel objects typically evokes avoidance behavior in wild animals, which is called neophobia. We previously found that wild brown rats (Rattus norvegicus) that were trapped in a park in downtown Tokyo, Japan, exhibited neophobia. We also found that this behavior was accompanied by the activation of the basolateral complex of the amygdala (BLA). Previous studies have suggested that genetic factors are the primary determinants of neophobia. Since rats in cities form populations with distinct genetic characteristics, it is reasonable to assume that wild rats caught at different locations in urban centers will exhibit different levels of neophobia. Here we assessed the intensity of neophobia in wild rats trapped at a wholesale market in Tokyo. Although we performed exactly the same experiment in which neophobia was observed in wild rats trapped at the park, the presence of novel objects did not affect the behaviors of wild rats trapped at the market. Conversely, laboratory rats showed approach and exploratory behaviors as seen in the previous study, suggesting that the experiment was performed appropriately. Compared to the laboratory rats, the lack of behavioral changes in the wild rats was accompanied by fewer Fos immunoreactive cells in the BLA. In addition, the numbers of Fos immunoreactive cells in the bed nucleus of the stria terminalis and ventromedial hypothalamus were similar between the two types of rats. The results demonstrated the existence of wild rats that were indifferent to novel objects.
接触新物体通常会引发野生动物的回避行为，这种行为被称为新物恐惧症。我们之前发现，在日本东京市中心一个公园捕获的野生褐家鼠（Rattus norvegicus）表现出新物恐惧症。我们还发现这种行为伴随着杏仁核基底外侧复合体（BLA）的激活。以往的研究表明，遗传因素是新物恐惧症的主要决定因素。由于城市中的老鼠形成了具有不同遗传特征的种群，因此可以合理推测，在城市中心不同地点捕获的野生老鼠会表现出不同程度的新物恐惧症。在此，我们评估了在东京一个批发市场捕获的野生老鼠的新物恐惧症强度。尽管我们进行了与在公园捕获的野生老鼠中观察到新物恐惧症完全相同的实验，但新物体的出现并未影响在市场捕获的野生老鼠的行为。相反，实验室老鼠表现出了如先前研究中所见的接近和探索行为，这表明实验进行得很恰当。与实验室老鼠相比，野生老鼠缺乏行为变化的同时，BLA中Fos免疫反应阳性细胞也较少。此外，终纹床核和腹内侧下丘脑的Fos免疫反应阳性细胞数量在两种老鼠中相似。结果表明存在对新物体无动于衷的野生老鼠。
