猫薄荷为何让猫“疯狂”？

Why Does Catnip Make Cats Go Crazy?

文本难度：考研

刘立军供稿

Of the many bewildering behaviors cats display, one of the strangest is their obsession with a specific species of plant. After just one whiff, even the most stoic cat can start pawing, drooling, biting, and wriggling in a state of pure feline euphoria. So, why do cats go crazy for catnip? This is the question cat behavior expert Masao Miyazaki and chemist Toshio Nishikawa set out to answer in 2013. Along with their research teams from Iwate and Nagoya University, they began by studying silvervine – a plant that sparks a similar response to catnip.

猫咪有着许多令人费解的行为，其中最奇特的莫过于对某一特定植物的痴迷。即便是最冷静自持的猫，哪怕只是闻上一口，也会瞬间陷入抓挠、流口水、啃咬、翻滚的状态，沉浸在纯粹的猫咪欢愉中。那么，猫咪究竟为什么会为猫薄荷神魂颠倒？2013年，猫咪行为学家宫崎正夫与化学家西川俊夫便带着这一问题展开了研究。他们与来自岩手大学与名古屋大学的研究团队携手，先从木天蓼这种植物入手——这是一种同样能在猫身上引发和猫薄荷相似反应的植物。

First, the researchers painstakingly extracted chemical compounds from the plant and dribbled various combinations of them onto filter paper. Then they brought in some cats and studied which compounds they were drawn to. Overwhelmingly, their feline testers pounced on the papers containing nepetalactol. And when Miyazaki and his student Reiko Uenoyama ran blood tests on the cats who’d interacted with nepetalactol, they found their systems were flooded with endorphins. These hormones block pain signals, relieve stress, and generally create a happy, calming effect. And catnip triggers the same endorphin rush with a similar chemical called nepetalactone, and it’s this flood of happy hormones that gives catnip and silvervine their signature drug-like response.

研究人员先是费尽心力，从木天蓼中提取各类化合物，再把不同配比的提取物滴在滤纸上。随后，他们找来猫咪，观察哪些化学成分会吸引它们。结果显而易见，绝大多数受试猫咪都径直扑向含有荆芥内酯醇（nepetalactol）的滤纸。宫崎正夫和他的学生上野山怜子对接触过荆芥内酯醇的猫咪进行血液检测，发现它们体内会大量分泌内啡肽。这类激素能够阻断痛觉信号、缓解压力，带来愉悦、镇定的感受。而猫薄荷则是借助一种结构相近的物质——荆芥内酯，同样能刺激猫体内大量释放内啡肽。正是这种快乐激素的迸发，让猫薄荷和木天蓼产生了标志性的、类似药物带来的反应。

These compounds don’t just trigger this effect in small cats. When the researchers brought nepetalactol-treated filter paper to a few zoos, leopards, lynxes, and jaguars all dove face-first into the compound. This was big news. If these different cat species reacted to nepetalactol the same way, the response was likely a shared evolutionary trait, potentially something important to cat survival that stretched back millions of years. When the silvervine researchers presented their work at a conference, one evolutionary biologist raised a compelling theory. In chemical terms, both nepetalactol and nepetalactone are classified as iridoids – a type of natural compound known to contain insect-repelling properties. So perhaps cats rubbing their faces in silvervine and catnip were applying an ancient form of bug spray.

这类化合物并非只对小型猫科动物生效。当研究人员把滴有荆芥内酯醇的滤纸带到几家动物园时，豹子、猞猁和美洲豹全都一头埋上去嗅闻。这是一项重大发现。既然这么多不同种类的猫科动物都对荆芥内酯醇产生相同反应，说明该行为极有可能是共有的进化特征，或许关乎猫科动物生存的重要本能，其根源可追溯至数百万年前。当木天蓼研究团队在学术会议上展示成果时，一位进化生物学家提出了一个极具说服力的假说：从化学分类来看，荆芥内酯醇与荆芥内酯都属于环烯醚萜类化合物，这类天然物质具备驱虫特性。所以，猫咪把脸在木天蓼和猫薄荷上蹭来蹭去的行为，或许正是在涂抹一种古老的驱虫剂。

To test this, researchers set up cages of mosquitoes that cats could stick their heads into. And sure enough, the cats that had been treated with nepetalactol got fewer mosquito bites than the cats in the control group. The same effect was true for the scientists who’d volunteered their arms in solidarity with their feline subjects. These mosquito-repelling properties are currently our best explanation for why cats love silvervine and catnip. But researchers still had one more question: in their state of euphoria, cats tend to vigorously bite, lick, and rub against these plants. But do cats really need to go this crazy to get their bug-repelling effects?

为验证这一猜想，研究人员搭建了放有蚊子的笼子，猫咪可以把头伸进笼内。结果证实，体表接触过荆芥内酯醇的猫咪，被蚊子叮咬的次数少于对照组。就连主动挽起袖子、甘愿和猫咪一同参与实验的科研人员，手臂上的叮咬次数也同样大幅减少。目前，这种驱蚊特性是我们解释猫咪喜爱木天蓼与猫薄荷最合理的假说。但研究者还有一个疑问：当猫咪在亢奋状态下，往往会使劲啃咬、舔舐并用力蹭擦这类植物。可它们真的需要表现得如此“上头”，才能真正发挥驱虫功效吗？

To investigate rubbing, they provided cats with filter papers treated with microscopic amounts of nepetalactol. And sure enough, even these tiny doses made the papers irresistible, suggesting that microscopic amounts of bug repellent can be transferred by rubbing alone. As for biting and licking, the researchers found that when cats damage the plant, the leaves actually produce more mosquito-repellent chemicals. So your cat isn’t just ripping open their bags of catnip to be annoying; their evolutionary instincts are just trying to get even more of that bug protection.

为研究摩擦行为，研究人员向猫咪提供了只沾有微量荆芥内酯醇的滤纸。不出所料，即便剂量微乎其微，这些滤纸依旧对猫咪有着极强吸引力。这说明，仅靠蹭一蹭，就能沾上微量的驱虫物质。至于啃咬和舔舐，研究人员发现，当猫咪啃破植物组织时，叶片反而会生成更多驱蚊化学成分。所以，你的猫咪扒开猫薄荷袋子并不是故意捣乱，而是在进化本能驱使下，想要获取更多驱虫保护。

Cats are far from the only animal to use natural plants for purposes like this. Apes swallow scratchy and hairy leaves to dislodge parasites from their guts. Sheep munch on tannin-rich plants to kill intestinal worms, and monarch butterflies use toxic milkweed to kill parasites that normally impair their flight. Just like cats’ ability to find mosquito repellent, these behaviors can help humans identify useful plants and ingredients in the natural world. So, the next time you see your feline friend on a catnip binge, don’t worry – it’s only medicinal.

并非只有猫咪会利用天然植物达成这类目的。猿类会直接吞下粗糙多毛的叶片，借此刮擦并排出肠道寄生虫；绵羊会食用富含单宁的植物来杀灭肠道蠕虫；帝王蝶则会采食有毒的马利筋，清除会削弱自身飞行能力的体内寄生虫。和猫咪寻找天然驱蚊植物的本能一样，这类动物行为，也能帮助人类发掘自然界里有价值的植物与成分。所以，下次看到你的猫主子沉迷猫薄荷，不必担心——这只是它在“用药”而已。

【词汇】

1.stoic adj. 坚忍的；沉着的
2.whiff n. 一闻；一股气味
3.drool v. 流口水
4.wriggle v. 扭动；蠕动
5.feline adj. 猫科的；猫的
6.euphoria n. 欣快；极度愉悦
7.catnip n. 猫薄荷
8.painstaking adj. 煞费苦心的；极其仔细的
9.dribble v. 使滴下；滴落
10.pounce v. 猛扑；突然袭击
11.endorphin n. 内啡肽
12.lynx n. 猞猁
13.jaguar n. 美洲豹
14.dislodge v. 驱逐；移开
15.munch v. 大声咀嚼
16.intestinal adj. 肠的
17.milkweed n. 马利筋（一种植物）
18.binge n. 狂欢；放纵行为

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