Trigeminal projections to contralateral dorsal horn originate in midline hairy skin

The present study tested the hypothesis that the trigeminal (V) primary afferent projection to the contralateral dorsal horn originates in midline hairy skin. A prior study (Jacquin et al., 1990) showed that this crossed projection is heaviest to ophthalmic regions of medullary and cervical dorsal horns, and that it does not arise from V ganglion cells that innervate cornea, nasal mucosa, or cerebral dura mater. Here, retrograde double-labeling methods were used to show that many ophthalmic ganglion cells that innervate midline hairy skin via the supraorbital nerve project to the contralateral medullary and upper cervical dorsal horns. Diamidino yellow injections into the right dorsal horn labeled an average of 104 cells in the left V ganglion. Of these contralaterally projecting ganglion cells, an average of 45% were also labeled by horseradish peroxidase (HRP) injections into the left supraorbital nerve, and 25% were also labeled by HRP injections into the midline opthalmic hairy skin. However, only 2% were labeled by HRP injections restricted to left supraorbital vibrissae follicle nerves. Almost all of the double-labeled cells were located in the dorsal one-half of the V ganglion, and they did not differ in size from single-labeled cells. On the basis of these and prior data, we conclude that a high percentage of contralaterally projecting V ganglion cells originate in midline hairy skin. It is also likely that the contralaterally projecting V ganglion cells serve a low-threshold mechanoreceptive function, given the relatively large ganglion cells and axons giving rise to this pathway and their central terminations in dorsal horn laminae III-V.     

Trigeminal Projections to Contralateral Dorsal Horn Originate in Midline Hairy Skin

The present study tested the hypothesis that the trigeminal (V) primary afferent projection to the contralateral dorsal horn originates in midline hairy skin. A prior study (Jacquin et al., 1990) showed that this crossed projection is heaviest to ophthalmic regions of medullary and cervical dorsal horns, and that it does not arise from V ganglion cells that innervate cornea, nasal mucosa, or cerebral dura mater. Here, retrograde double-labeling methods were used to show that many ophthalmic ganglion cells that innervate midline hairy skin via the supraorbital nerve project to the contralateral medullary and upper cervical dorsal horns. Diamidino yellow injections into the right dorsal horn labeled an average of 104 cells in the left V ganglion. Of these contralaterally projecting ganglion cells, an average of 45% were also labeled by horseradish peroxidase (HRP) injections into the left supraorbital nerve, and 25% were also labeled by HRP injections into the midline opthalmic hairy skin. However, only 2% were labeled by HRP injections restricted to left supraorbital vibrissae follicle nerves. Almost all of the double-labeled cells were located in the dorsal one-half of the V ganglion, and they did not differ in size from single-labeled cells.

On the basis of these and prior data, we conclude that a high percentage of contralaterally projecting V ganglion cells originate in midline hairy skin. It is also likely that the contralaterally projecting V ganglion cells serve a low-threshold mechanoreceptive function, given the relatively large ganglion cells and axons giving rise to this pathway and their central terminations in dorsal horn laminae III-V.     

Hair follicle measurements in some tropical and temperate breeds of cattle in Nigeria

Anatomical studies of the skin of mature White Fulani, N'Dama, Muturu and the Friesian cattle showed that there are significant regional and breeds differences in hair follicle density and depth. The hair follicle distribution per cm² of skin was higher on the neck, ventral and the upper limb sites (2000 – 2496) than on the dorsal, midside and eye margins (1344 – 1920). Low densities were recorded on the horn margin, perineum and the lower limb sites (576 – 960). This regional distribution was consistent in all breeds except the White Fulani in which follicle densities were significantly lower for most body sites. Hair follicle depth was greater in the Friesians (1.63 ± 0.68 mm) than in the N'Dama (0.98 ± 0.13 mm), the White Fulani (0.91 ± 0.31 mm) and the Muturu (0.84 ± 0.25 mm) cattle. Among body sites, follicle depth was significantly greater on the horn margin, lower and upper limbs and the scrotum (1.16 – 1.48 mm) than on other body sites (0.86 – 0.98 mm). A significant negative correlation was found between hair follicle density and follicle depth.     

Substance P effects on spinal nociceptive neurones.

In decerebrated spinal cats, the effects of iontophoretically applied acetylcholine (ACh) and substance P were examined on the responses of dorsal horn neurones to noxious stimulation and touch of the skin. Both agents, in amounts that did not have a significant direct effect on the neuronal firing rate, prolonged the response of the cells to noxious stimulation but did not alter that to touch stimulation. The peptide and ACh potentiated the late, but not the early, responses of dorsal horn neurones to sural A_δ and C afferent stimulation. Substance P-induced potentiation of the above responses was observed even when the agent did not produce a significant depolarization of nociceptive cells. In greater amounts, the peptide depolarized the neurones, an effect that was not associated with a detectable change in the membrane resistance. These results indicate that substance P facilitates nociceptive pathways by potentiating the subliminal fringe and, in greater amounts, by depolarizing the cells. The failure by the peptide to potentiate touch-induced excitation of the nociceptive neurones appears not to be due to the selectivity of the drug effect but due to the absence of subliminal fringe.     

Dermal β-catenin activity in response to epidermal Wnt ligands is required for fibroblast proliferation and hair follicle initiation

Dermal fibroblasts are required for structural integrity of the skin and for hair follicle development. Uniform Wnt signaling activity is present in dermal fibroblast precursors preceding hair follicle initiation, but the functional requirement of dermal Wnt signaling at early stages of skin differentiation and patterning remains largely uncharacterized. We show in mice that epidermal Wnt ligands are required for uniform dermal Wnt signaling/β-catenin activity and regulate fibroblast cell proliferation and initiation of hair follicle placodes. In the absence of dermal Wnt signaling/β-catenin activity, patterned upregulation of epidermal β-catenin activity and Edar expression are absent. Conversely, forced activation of β-catenin signaling leads to the formation of thickened dermis, enlarged epidermal placodes and dermal condensates that result in prematurely differentiated enlarged hair follicles. These data reveal functional roles for dermal Wnt signaling/β-catenin in fibroblast proliferation and in the epidermal hair follicle initiation program.     

Skin penetration of infective hookworm larvae. II. The path of migration of infective larvae of Ancylostoma braziliense in the metacarpal foot pads of dogs

The hairless metacarpal foot pads of six hookworm-free puppies were exposed to infective larvae of Ancylostoma braziliense. Serial sections of the biopts stained with Harris' haematoxylin and eosin showed that the infective larvae are able to penetrate the toughest region of canine skin. Pores of eccrine sweat glands did not seem to constitute sites of entry and no larvae were detected in these glands. Larvae were only observed in the epidermis. The histopathology of the infected skin of the foot pads of the puppies was similar to that in human skin with "creeping eruption" as described by Fülleborn (1927). The biopts appeared to consist of hairy skin as well. In the unexposed adjacent hairy skin of the foot pads, larvae were also observed. They were found in the epidermis, hair follicle systems and dermis, suggesting that the migration from the epidermis into deeper tissue depends on the presence of the hair follicle systems.     

Polyclonal origin and hair induction ability of dermal papillae in neonatal and adult mouse back skin

Hair follicle development and growth are regulated by Wnt signalling and depend on interactions between epidermal cells and a population of fibroblasts at the base of the follicle, known as the dermal papilla (DP). DP cells have a distinct gene expression signature from non-DP dermal fibroblasts. However, their origins are largely unknown. By generating chimeric mice and performing skin reconstitution assays we show that, irrespective of whether DP form during development, are induced by epidermal Wnt activation in adult skin or assemble from disaggregated cells, they are polyclonal in origin. While fibroblast proliferation is necessary for hair follicle formation in skin reconstitution assays, mitotically inhibited cells readily contribute to DP. Although new hair follicles do not usually develop in adult skin, adult dermal fibroblasts are competent to contribute to DP during hair follicle neogenesis, irrespective of whether they originate from skin in the resting or growth phase of the hair cycle or skin with β-catenin-induced ectopic follicles. We propose that during skin reconstitution fibroblasts may be induced to become DP cells by interactions with hair follicle epidermal cells, rather than being derived from a distinct subpopulation of cells.     

The TGF-beta2 isoform is both a required and sufficient inducer of murine hair follicle morphogenesis.

Hair follicle development serves as an excellent model to study control of organ morphogenesis. Three specific isoforms of TGF-beta exist which exhibit a distinct pattern of expression during hair follicle morphogenesis. To clarify the still elusive role of these factors in hair follicle development, we have used a combined genetic and functional approach: analysis of hair follicle development in mice with disruptions of the TGF-beta1, 2, and 3 genes was coupled with a direct functional test of the effect of added purified factors on fetal hair follicle development in skin organ cultures. TGF-beta2 null mice exhibited a profound delay of hair follicle morphogenesis, with a 50% reduced number of hair follicles. In contrast to hair follicle development, growth and differentiation of interfollicular keratinocytes proceeded unimpaired. Unlike TGF-beta2-/- mice, mice with a disruption of the TGF-beta1 gene showed slightly advanced hair follicle formation, while lack of the TGF-beta3 gene did not have any effects. Treatment of wild-type, embryonic skin explants (E14.5 or E15.5) with TGF-beta2 protein in either soluble form or slow release beads induced hair follicle development and epidermal hyperplasia, while similar TGF-beta1 treatment exerted suppressive effects. Thus, the TGF-beta2 isoform plays a specific role, not shared by the other TGF-beta isoforms, as an inducer of hair follicle morphogenesis and is both required and sufficient to promote this process.     

Development and homeostasis of the skin epidermis

The skin epidermis is a stratified epithelium that forms a barrier that protects animals from dehydration, mechanical stress, and infections. The epidermis encompasses different appendages, such as the hair follicle (HF), the sebaceous gland (SG), the sweat gland, and the touch dome, that are essential for thermoregulation, sensing the environment, and influencing social behavior. The epidermis undergoes a constant turnover and distinct stem cells (SCs) are responsible for the homeostasis of the different epidermal compartments. Deregulation of the signaling pathways controlling the balance between renewal and differentiation often leads to cancer formation.     

Nerve-derived sonic hedgehog defines a niche for hair follicle stem cells capable of becoming epidermal stem cells

In adult skin, stem cells in the hair follicle bulge cyclically regenerate the follicle, whereas a distinct stem cell population maintains the epidermis. The degree to which all bulge cells have equal regenerative potential is not known. We found that Sonic hedgehog (Shh) from neurons signals to a population of cells in the telogen bulge marked by the Hedgehog response gene Gli1. Gli1-expressing bulge cells function as multipotent stem cells in their native environment and repeatedly regenerate the anagen follicle. Shh-responding perineural bulge cells incorporate into healing skin wounds where, notably, they can change their lineage into epidermal stem cells. The perineural niche (including Shh) is dispensable for follicle contributions to acute wound healing and skin homeostasis, but is necessary to maintain bulge cells capable of becoming epidermal stem cells. Thus, nerves cultivate a microenvironment where Shh creates a molecularly and phenotypically distinct population of hair follicle stem cells.     

Different Requirements for GFRα2-Signaling in Three Populations of Cutaneous Sensory Neurons

Many primary sensory neurons in mouse dorsal root ganglia (DRG) express one or several GFRα’s, the ligand-binding receptors of the GDNF family, and their common signaling receptor Ret. GFRα2, the principal receptor for neurturin, is expressed in most of the small nonpeptidergic DRG neurons, but also in some large DRG neurons that start to express Ret earlier. Previously, GFRα2 has been shown to be crucial for the soma size of small nonpeptidergic nociceptors and for their target innervation of glabrous epidermis. However, little is known about this receptor in other Ret-expressing DRG neuron populations. Here we have investigated two populations of Ret-positive low-threshold mechanoreceptors that innervate different types of hair follicles on mouse back skin: the small C-LTMRs and the large Aβ-LTMRs. Using GFRα2-KO mice and immunohistochemistry we found that, similar to the nonpeptidergic nociceptors, GFRα2 controls the cell size but not the survival of both C-LTMRs and Aβ-LTMRs. In contrast to the nonpeptidergic neurons, GFRα2 is not required for the target innervation of C-LTMRs and Aβ-LTMRs in the back skin. These results suggest that different factors drive target innervation in these three populations of neurons. In addition, the observation that the large Ret-positive DRG neurons lack GFRα2 immunoreactivity in mature animals suggests that these neurons switch their GFRα signaling pathways during postnatal development.     

Hairy Skin: Psychophysical Channels and Their Physiological Substrates

Experiments were conducted in which threshold-frequency characteristics were measured on the hairy skin of the forearm of human observers. Thresholds were measured with two stimulus probe areas (2.9 and 0.008 cm²) at three skin-surface temperatures (15d`, 30d`, and 40d`C). The results suggest that whereas glabrous skin uses four distinct channels of information, only three channels may be involved in mediating the sense of touch for hairy skin. The three channels are defined as P_h (Pacinian, hairy skin), NP_{h low} (non-Pacinian, hairy skin, low frequencies) and NP_{h mid} (non-Pacinian, hairy skin, middle frequencies). In addition, it is proposed that the neural substrates for the three psychophysically characterized channels are, respectively, the Pacinian corpuscle (PC) nerve fibers, the slowly adapting type II (SAII) fibers, and the rapidly adapting (RA) fibers.     

Laminin-10 is crucial for hair morphogenesis

The role of the extracellular matrix in cutaneous morphogenesis is poorly understood. Here, we describe the essential role of laminin-10 (alpha5beta1gamma1) in hair follicle development. Laminin-10 was present in the basement membrane of elongating hair germs, when other laminins were downregulated, suggesting a role for laminin-10 in hair development. Treatment of human scalp xenografts with antibodies to laminin-10, or its receptor beta1 integrin, produced alopecia. E16.5 Lama5 -/- mouse skin, lacking laminin-10, contained fewer hair germs compared with controls, and after transplantation, Lama5 -/- skin showed a failure of hair germ elongation followed by complete hair follicle regression. Lama5 -/- skin showed defective basement membrane assembly, without measurable increases in anoikis. Instead, Lama5 -/- skin showed decreased expression of early hair markers including sonic hedgehog and Gli1, implicating laminin-10 in developmental signaling. Intriguingly, treatment of Lama5 -/- skin with purified laminin-10 corrected basement membrane defects and restored hair follicle development. We conclude that laminin-10 is required for hair follicle development and report the first use of exogenous protein to correct a cutaneous developmental defect.     

Analysis of the expression pattern of involucrin in human scalp skin and hair follicles: hair cycle-associated alterations

Involucrin is a structural component of the keratinocyte cornified envelope that is expressed early in the keratinocyte differentiation process. It is a component of the initial envelope scaffolding and considered as a marker for keratinocyte terminal differentiation. The expression pattern of involucrin in human scalp skin and hair follicle cycle stages is not fully explored. This study addresses this issue and tests the hypothesis that "the expression of involucrin undergoes hair follicle cycle-dependent changes". A total of 50 normal human scalp skin biopsies were examined (healthy females, 51-62?years) using immunofluorescence staining methods and real-time PCR analysis. In each case, 50 hair follicles were analyzed (35, 10 and 5 follicles in anagen, catagen and telogen, respectively). Involucrin was prominently expressed in the human scalp skin and hair follicles, on both gene and protein levels. The protein expression showed hair follicle cycle-associated changes i.e. a very strong expression during early and mature anagen, intermediate to strong expression during catagen and prominent decline in the telogen phase. The expression value of involucrin in both anagen and catagen was statistically significantly higher than that of telogen hair follicles (p?相似文献   

Melanocyte stem cells: a melanocyte reservoir in hair follicles for hair and skin pigmentation

Most mammals are coated with pigmented hair. Melanocytes in each hair follicle produce melanin pigments for the hair during each hair cycle. The key to understanding the mechanism of cyclic melanin production is the melanocyte stem cell (MelSC) population, previously known as 'amelanotic melanocytes'. The MelSCs directly adhere to hair follicle stem cells, the niche cells for MelSCs and reside in the hair follicle bulge-subbulge area, the lower permanent portion of the hair follicle, to serve as a melanocyte reservoir for skin and hair pigmentation. MelSCs form a stem cell system within individual hair follicles and provide a 'hair pigmentary unit' for each cycle of hair pigmentation. This review focuses on the identification of MelSCs and their characteristics and explains the importance of the MelSC population in the mechanisms of hair pigmentation, hair greying, and skin repigmentation.     

Sensory Innervation of the Raccoon Forepaw: 1. Receptor Types in Glabrous and Hairy Skin and Deep Tissue

Electrophysiological recordings were made from the median, ulnar, radial, and dorsal ulnar nerves to determine the types of mechanosensory receptors serving glabrous and hairy skin surfaces of the raccoon forepaw. In addition to the cutaneous mechanoreceptors, fibers innervating deep tissues were also recorded from each of these nerves. These included sensory fibers innervating muscles, joints, claws, and the subcutaneous pulp.

The array of receptors serving raccoon glabrous skin was the same as found in monkeys and humans: Rapidly adapting (RA), slowly adapting (SA), and Pacinian (Pc) fibers were characterized. Pacinian fibers have been rarely described in previous physiological studies of the raccoon peripheral nerves, but in the present study they composed between 14% and 18% of the glabrous skin mechanoreceptors recorded. A distal-proximal gradient in the density of skin innervation was evident for all three types of receptors.

Receptors characterized in the hairy skin of the dorsal paw were similar to those described in other mammals, and included both down and guard hair afferents, non-hair-associated RA fibers, and SA I and SA II fibers. The relative proportions of these fibers differed from those generally reported for the hairy skin of other mammals. SA hair-associated afferent fibers, which have been reported previously only in primate hairy skin, were also found in large numbers in the raccoon. Similarities and differences in the frequency and types of receptors innervating the raccoon forepaw, the forepaws of other mammals, and the hands of primates (including humans) are discussed.     

Segmental Igfbp5 expression is specifically associated with the bent structure of zigzag hairs

The murine hair coat consists of four different hair types that are characterised by hair length, the number of medulla columns, and the presence and number of bends. The molecular mechanisms underlying the establishment and maintenance of distinct hair follicle fates are unknown. We identify Igfbp5 as the first molecular marker that distinguishes among different hair follicle types. High-resolution expression analysis revealed that its expression in the medulla of hair shafts is associated with the bend-forming zones of zigzag hairs. To directly examine the functional importance of segmental gene expression in the hair follicle, we have generated transgenic mice expressing Igfbp5 in differentiating keratinocytes of the medulla and inner root sheath. Ectopic expression of Igfbp5 resulted in the appearance of remarkable curvatures and thinning of hair shafts, two hallmarks of hair bends. Both effects and the natural bending process are under negative control of IGF signalling. Thus, our data identify Igfbp5 as a central regulator of hair shaft differentiation and hair type determination.     

Feasibility of repairing skin defects by VEGF165 gene-modified iPS-HFSCs seeded on a 3D printed scaffold containing astragalus polysaccharide

The preparation of biodegradable scaffolds loaded with cells and cytokine is a feature of tissue-engineered skin. IPSCs-based tissue-engineered skin treatment for wound repair is worth exploring. Healthy human skin fibroblasts were collected and reprogrammed into iPSCs. After gene modification and induction, CK19⁺/Integrinβ1⁺/CD200⁺ VEGF₁₆₅ gene-modified iPS-HFSCs^GFP were obtained and identified by a combination of immunofluorescence and RT-qPCR. Astragalus polysaccharide-containing 3D printed degradable scaffolds were prepared and co-cultured with VEGF₁₆₅ gene-modified iPS-HFSCs^GFP, and the biocompatibility and spatial structure of the tissue-engineered skin was analysed by cell counting kit-8 (CCK8) assay and scanning electron microscopy. Finally, the tissue-engineered skin was transplanted onto the dorsal trauma of nude mice, and the effect of tissue-engineered skin on the regenerative repair of total skin defects was evaluated by a combination of histology, immunohistochemistry, immunofluorescence, RT-qPCR, and in vivo three-dimensional reconstruction under two-photon microscopy. CK19⁺/Integrinβ1⁺/CD200⁺ VEGF₁₆₅ gene-modified iPS-HFSCs^GFP, close to the morphology and phenotype of human-derived hair follicle stem cells, were obtained. The surface of the prepared 3D printed degradable scaffold containing 200 μg/mL astragalus polysaccharide was enriched with honeycomb-like meshwork, which was more conducive to the proliferation of the resulting cells. After tissue-engineered skin transplantation, combined assays showed that it promoted early vascularization, collagen and hair follicle regeneration and accelerated wound repair. VEGF₁₆₅ gene-modified iPS-HFSCs^GFP compounded with 3D printed degradable scaffolds containing 200 μg/mL astragalus polysaccharide can directly and indirectly participate in vascular, collagen, and hair follicle regeneration in the skin, achieving more complete structural and functional skin regenerative repair.