Large excisional wounds in mice prominently regenerate new hair follicles (HFs) and fat, yet humans are deficient for this regenerative behavior. Currently, wound-induced regeneration remains a clinically desirable, but only partially understood phenomenon. We show that large excisional wounds in rats across seven strains fail to regenerate new HFs. We compared wound transcriptomes between mice and rats at the time of scab detachment, which coincides with the onset of HF regeneration in mice. In both species, wound dermis and epidermis share core dermal and epidermal transcriptional programs, respectively, yet prominent interspecies differences exist. Compared with mice, rat epidermis expresses distinct transcriptional and epigenetic factors, markers of epidermal repair, hyperplasia, and inflammation, and lower levels of WNT signaling effectors and regulators. When recombined on the surface of excisional wounds with vibrissa dermal papillae, partial-thickness skin grafts containing distal pelage HF segments, but not interfollicular epidermis, readily regenerated new vibrissa-like HFs. Together, our findings establish rats as a nonregenerating rodent model for excisional wound healing and suggest that low epidermal competence and associated transcriptional profile may contribute to its regenerative deficiency. Future comparison between rat and mouse may lend further insight into the mechanism of wounding-induced regeneration and causes for its deficit.

Hairs and feathers are textbook examples of the convergent evolution of the follicular appendage structure between mammals and birds. While broadly recognized for their convergent thermoregulatory, camouflage and sexual display functions, hairs and feathers are rarely thought of as deadly defence tools. Several recent studies, however, show that in some species of mammals and birds, the integument can, in fact, be a de facto lethal weapon. One mammalian example is provided by African crested rats, which seek for and chew on the bark of plants containing the highly potent toxin, ouabain. These rats then coat their fur with ouabain-containing saliva. For efficient toxin retention, the rodents have evolved highly specialized fenestrated and mostly hollow hair shafts that soak up liquids, which essentially function as wicks. On the avian side of the vertebrate integumental variety spectrum, several species of birds of New Guinea have evolved resistance to highly potent batrachotoxins, which they acquire from their insect diet. While the mechanism of bird toxicity remains obscure, in a recently published issue of the journal, Dumbacher and Menon explore the intriguing idea that to achieve efficient storage of batrachotoxins in their skin, some birds exploit the basic permeability barrier function of their epidermis. Batrachotoxins become preferentially sequestered in their epidermis and are then transferred to feathers, likely through the exploitation of specialized avian lipid-storing multigranular body organelles. Here, we discuss wider implications of this intriguing concept.

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Macroscopic, histological, electron microscopic, microbiological, and immunological methods were used to study the healing of full-thickness skin wounds in laboratory rats under the influence of quercetin and its complex with 2-hydroxypropyl-β-cyclodextrin. It was revealed that under the influence of quercetin, the wound was completely covered with the epidermis almost a day earlier than in the control, and under the influence of a complex with 2-hydroxypropylβ-cyclodextrin 2.2 days earlier (p < 0.02). This was mainly due to the acceleration of marginal epidermization. There was no positive effect on the wound contraction. Quercetin and especially its complex with cyclodextrin had a stimulating effect on the phagocytic and metabolic activity of neutrophils both on the wound surface and in the blood of animals. The bacterial microflora present on the wound surface during healing coincided with the microflora of the intact skin. Neither the quercetin, nor the quercetin-2-hydroxypropyl-β-cyclodextrin significantly affected its composition.

A model was developed, on the basis of which the features of healing of a full-thickness skin wound were studied in laboratory rats using macro-, micro- and ultramicroscopic methods. It was found that during this process, two borders are formed on the surface of the wound ‒ one on the edge of the dermis and the second on the edge of the epidermis. It is shown that a granulation tissue can be formed not only due to the restructuring of fibrin, but also due to the reorganization of a subcutaneous tissue. It is hypothesized that the wound contraction occurs not only due to the contraction of collagen fibrils by myofibroblasts, but also due to the retraction of collagen fibers in the cytoplasm of these cells. Attention is drawn to the restoration of the elastic layer as an essential component of the skin regenerate. The reasons for the appearance of a longitudinal elongated shape and orientation along the sagittal line of the scar, which remains for life at the site of the former skin damage, are explained.