Amphibians have evolved a remarkable diversity of defensive mechanisms against predators. One of the most conspicuous components in their defense is related to their ability to produce and store a high variety of bioactive (noxious to poisonous) substances in specialized skin glands. Previous studies have shown that T. verrucosus is poisonous with the potential to truly harm or even kill would-be predators by the effect of its toxic skin secretions. However, little is known on form and function of the skin glands responsible for production and release of these secretions. By using light- and scanning electron microscopy along with confocal laser scanning microscopy, we show that T. verrucosus exhibits three different multicellular skin glands: one mucous- and two granular glands. While mucous glands are responsible for the production of the slippery mucus, granular glands are considered the production site of toxins. The first type of granular glands (GG1) is found throughout the skin, though its average size can vary between body regions. The second type of granular glands (GG2) can reach larger dimensions compared with the former type and is restricted to the tail region. Despite their different morphology, all three skin gland types are enwrapped by a distinct myoepithelial sheath that is more prominently developed in the granular (i.e. poison-) glands compared to the mucous glands. The myoepithelial sheath consists of one layer of regularly arranged slender myoepithelial cells that run from the gland pore to the basal gland pole. This study shows that the skin in the Himalayan newt T. verrucosus displays one mucus- and two poison gland types enwrapped by a myoepithelial sheath. Contraction of the myoepithelium squeezes the glands and glandular content is released upon the skin surface where the secretion can deploy its defensive potential.

中文翻译：

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喜马拉雅蝾螈 Tylototriton verrucosus 皮肤腺体的形态和功能

两栖动物已经进化出非常多样化的防御捕食者的机制。它们防御中最显着的组成部分之一与它们在专门的皮肤腺体中产生和储存多种生物活性（有毒至有毒）物质的能力有关。先前的研究表明，疣状疣猴是有毒的，通过其有毒皮肤分泌物的作用，它有可能真正伤害甚至杀死潜在的捕食者。然而，对负责产生和释放这些分泌物的皮肤腺体的形式和功能知之甚少。通过使用光学和扫描电子显微镜以及共聚焦激光扫描显微镜，我们发现 T. verrucosus 表现出三种不同的多细胞皮肤腺体：一个粘液腺和两个颗粒腺体。虽然粘液腺负责产生光滑的粘液，但颗粒腺体被认为是毒素的产生部位。第一种颗粒状腺体 (GG1) 遍布整个皮肤，但其平均大小可能因身体部位而异。与前一种相比，第二种颗粒腺体（GG2）可以达到更大的尺寸，并且仅限于尾部区域。尽管它们的形态不同，但所有三种皮肤腺体类型都被独特的肌上皮鞘包裹着，与粘液腺体相比，在颗粒状（即毒物）腺体中更显着地发育。肌上皮鞘由一层规则排列的细长肌上皮细胞组成，从腺体孔延伸到基底腺极。这项研究表明，喜马拉雅蝾螈 T. verrucosus 表现出一种粘液腺和两种毒腺类型，被肌上皮鞘包裹。肌上皮收缩挤压腺体，腺体内容物释放到皮肤表面，分泌物可以发挥其防御潜力。