Max-Delbrück Centre for Molecular Medicine, Department of Neuroscience, Robert-Rössle Str. 10, 13125, Berlin-Buch, Germany.
Department of Zoology and Entomology, University of Pretoria, Pretoria, Republic of South Africa.
J Physiol. 2018 Oct;596(20):4995-5016. doi: 10.1113/JP276608. Epub 2018 Sep 15.
An ex vivo preparation was developed to record from single sensory fibres innervating the glabrous skin of the mouse forepaw. The density of mechanoreceptor innervation of the forepaw glabrous skin was found to be three times higher than that of hindpaw glabrous skin. Rapidly adapting mechanoreceptors that innervate Meissner's corpuscles were severalfold more responsive to slowly moving stimuli in the forepaw compared to those innervating hindpaw skin. We found a distinct group of small hairs in the centre of the mouse hindpaw glabrous skin that were exclusively innervated by directionally sensitive D-hair receptors. The directional sensitivity, but not the end-organ anatomy, were the opposite to D-hair receptors in the hairy skin. Glabrous skin hairs in the hindpaw are not ubiquitous in rodents, but occur in African and North American species that diverged more than 65 million years ago.
Rodents use their forepaws to actively interact with their tactile environment. Studies on the physiology and anatomy of glabrous skin that makes up the majority of the forepaw are almost non-existent in the mouse. Here we developed a preparation to record from single sensory fibres of the forepaw and compared anatomical and physiological receptor properties to those of the hindpaw glabrous and hairy skin. We found that the mouse forepaw skin is equipped with a very high density of mechanoreceptors; >3 times more than hindpaw glabrous skin. In addition, rapidly adapting mechanoreceptors that innervate Meissner's corpuscles of the forepaw were severalfold more sensitive to slowly moving mechanical stimuli compared to their counterparts in the hindpaw glabrous skin. All other mechanoreceptor types as well as myelinated nociceptors had physiological properties that were invariant regardless of which skin area they occupied. We discovered a novel D-hair receptor innervating a small group of hairs in the middle of the hindpaw glabrous skin in mice. These glabrous skin D-hair receptors were direction sensitive albeit with an orientation sensitivity opposite to that described for hairy skin D-hair receptors. Glabrous skin hairs do not occur in all rodents, but are present in North American and African rodent species that diverged more than 65 million years ago. The function of these specialized hairs is unknown, but they are nevertheless evolutionarily very ancient. Our study reveals novel physiological specializations of mechanoreceptors in the glabrous skin that likely evolved to facilitate tactile exploration.
开发了一种离体制备方法来记录支配小鼠前爪无毛皮肤的单个感觉纤维。发现前爪无毛皮肤的机械感受器神经支配密度比后爪无毛皮肤高 3 倍。与支配后爪皮肤的机械感受器相比，支配 Meissner 小体的快速适应机械感受器对前爪缓慢移动的刺激反应更为敏感。我们在前爪无毛皮肤的中心发现了一组独特的小毛发，它们仅被方向敏感的 D 型毛发感受器支配。D 型毛发感受器的方向敏感性，但不是终末器官解剖结构，与毛发皮肤中的 D 型毛发感受器相反。后爪无毛皮肤中的毛发并非在所有啮齿动物中普遍存在，而是仅存在于 6500 多万年前分化的非洲和北美物种中。
啮齿动物用它们的前爪主动与它们的触觉环境相互作用。关于构成前爪大部分的无毛皮肤的生理学和解剖学研究在小鼠中几乎不存在。在这里，我们开发了一种从前爪的单个感觉纤维记录的制备方法，并将解剖学和生理学受体特性与后爪无毛和有毛皮肤进行了比较。我们发现，小鼠前爪皮肤配备了非常高密度的机械感受器；比后爪无毛皮肤多 3 倍以上。此外，与后爪无毛皮肤中的机械感受器相比，支配 Meissner 小体的快速适应机械感受器对缓慢移动的机械刺激要敏感得多。所有其他机械感受器类型以及有髓伤害感受器的生理特性都与它们所占据的皮肤区域无关。我们在小鼠后爪无毛皮肤的中间发现了一种新型的 D 型毛发感受器，它支配着一小群毛发。这些无毛皮肤 D 型毛发感受器具有方向敏感性，尽管其方向敏感性与描述的有毛皮肤 D 型毛发感受器相反。并非所有啮齿动物都有无毛皮肤毛发，但在 6500 多万年前分化的北美和非洲啮齿动物物种中存在。这些专门毛发的功能尚不清楚，但它们在进化上非常古老。我们的研究揭示了无毛皮肤机械感受器的新的生理特化，这些特化可能是为了促进触觉探索而进化的。
