Back Skin Of Rats Research Articles

Phosphatidylserine accelerates wound healing and reduces necrosis in the rats: Growth factor activation.

To examine the effect of topical phosphatidylserine (PS) on wound healing factors and tissue necrosis in in vivo models. Topical PS was applied to evaluate aspects of the wound healing process and growth factors production of vascular endothelial growth factors (VEGF) as well a necrosis reduction in the skin flap of rat models. Moreover, phenytoin (PHT) and cyclosporine A (CsA) were used topically as positive control treatments in wound and necrosis models, respectively. Immunohistochemistry (IHC) VEGF, transforming growth factor-β (TGF-β), fibroblast growth factor (FGF) and histopathology were analysed on the wounds of rats. In the necrosis assessment, necrotic areas were determined on photography taken from the back skin of rats. Results indicated that PS topically enhanced significantly (P < 0.05) numbers of fibroblasts and endothelium while inhibiting the neutrophils and macrophages during the 14 days of wound treatment. Moreover, higher values of collagen deposition and epithelialization scores as well as wound recovery percentage (near 80%) were determined significantly (P < 0.05) in the PS group compared with the control. IHC analysis determined that FGF and VEGF cytokine factors were elevated in the wound site by topical PS. Moreover, the necrotic area was significantly (P < 0.05) improved in the PS group. Our experiment indicated that wound improvement and flap survival values in PS treatments were superior to PHT and CsA control groups, respectively. In conclusion, these findings suggest the potential of PS application in the healing of wounds and control of necrosis development after surgery or skin injuries.

Poly-l-lactic acid microspheres delay aging of epidermal stem cells in rat skin.

Injectable skin fillers offer a wider range of options for cutaneous anti-aging and facial rejuvenation. PLLA microspheres are increasingly favored as degradable and long-lasting fillers. The present study focused solely on the effect of PLLA on dermal collagen, without investigating its impact on the epidermis. In this study, we investigated the effects of PLLA microspheres on epidermal stem cells (EpiSCs). Different concentrations of PLLA microspheres on epidermal stem cells (EpiSCs) in vitro through culture, and identification of primary rat EpiSCs. CCK-8 detection, apoptosis staining, flow cytometry, Transwell assay, wound healing assay, q-PCR analysis, and immunofluorescence staining were used to detect the effects of PLLA on EpiSCs. Furthermore, we observed the effect on the epidermis by injecting PLLA into the dermis of the rat skin in vivo. PLLA microspheres promote cell proliferation and migration while delaying cell senescence and maintaining its stemness. In vitro, Intradermal injection of PLLA microspheres in the rat back skin resulted in delayed aging, as evidenced by histological and immunohistochemical staining of the skin at 2, 4, and 12 weeks of follow-up. This study showed the positive effects of PLLA on rat epidermis and EpiSCs, while providing novel insights into the anti-aging mechanism of PLLA.

Preparation of Chitosan Nanoparticles Loaded with Vascular Endothelial Growth Factor and Its Application in the Treatment of Skin Injury

This research was aimed to explore the application of chitosan (CS) nanoparticles (NPs) loaded with vascular endothelial growth factor (VEGF) in rat skin injury. Method: the VEGF-loaded CS NPs (VEGF/CS-NPs) were prepared, and a skin injury model on the back skin of rats was established. The VEGF/CS-NPs were applied to the injury model to observe the skin changes in the wound area of each group, compare the healing rate, the number of micro-vessels, and VEGF expression in each group of rats, so as to explore the intervention effect of VEGF/CS-NPs in skin injury. Results: the prepared VEGF/CS-NPs were spherical or quasi-spherical in morphology, uniformly dispersed, with smooth surfaces and relatively uniform size. The average particle size (PS) of the blank CS-NPs was 267.5 nm± 25.3 nm, while that of the drug-loaded CS-NPs was 298.6 nm ±44.7 nm, and the PS distribution was also very concentrated. The genipin cross-linked NPs could effectively prevent the degradation of the spherical wall and achieve the slow release of VEGF. After VEGF was applied to rats in the form of NPs, its healing rate and micro-vessel count were markedly superior to those of VEGF injection alone and blank group (P &lt; 0.05), and VEGF expression in skin injury tissues was also greatly increased (P &lt; 0.05). Conclusion: VEGF/CS-NPs could improve the bioavailability of VEGF and promote the healing of rat skin injuries.

The combined use of photobiomodulation and curcumin-loaded iron oxide nanoparticles significantly improved wound healing in diabetic rats compared to either treatment alone

This experimental study examined the effects of curcumin-loaded iron oxide nanoparticles (CUR), photobiomodulation (PBM), and CUR + PBM treatments on mast cells (MC)s numbers and degranulation, inflammatory cells (macrophages, neutrophils), and wound strength in the last step of the diabetic wound repair process (maturation phase) in a rat model of type one diabetes mellitus (T1DM). T1DM was induced in 24 rats, and 1month later, an excisional wound was created on each rat's back skin. The rats were then distributed into four groups: (1) untreated diabetic control group (UDCG); (2) rats treated with CUR (CUR); (3) rats exposed to PBM (890nm, 80Hz, 0.2J/cm2) (PBM); (4) rats treated with CUR plus PBM (CUR + PBM). Fifteen days after surgery, skin tissue samples were taken for biomechanical and stereological evaluations. The biomechanical factor of maximum force was observed to be considerably improved in the CUR + PBM (p = 0.000), PBM (p = 0.014), and CUR (p = 0.003) groups compared to the UDCG. CUR + PBM, PBM, and CUR groups had significantly decreased total numbers of MC compared with the UDCG (all, p = 0.001). The results were significantly better in the CUR + PBM (p = 0.000) and PBM (p = 0.003) groups than in the CUR group. Inflammatory cell counts were significantly lower in the CUR + PBM, PBM, and CUR groups than in the UDCG (all, p = 0.0001). In all evaluating methods, the usage of CUR + PBM produced better results than the use of CUR or PBM alone (almost all tests, p = 0.0001). CUR + PBM, PBM, and CUR significantly improved the repair of diabetic skin wounds in type 1 DM rats through significant decreases of MC number, degranulation, and inflammatory cells as well as a noteworthy improvement in wound strength. The impact of CUR + PBM was superior to that of either PBM or CUR alone. It is suggested that CUR + PBM could be used as a MC stabilizer for the effective treatment of some related human diseases.

UJI EFEK EPITELISASI EKSTRAK BATANG WOLE WOE ASAL KABUPATEN HALMAHERA TENGAH TERHADAP PENYEMBUHAN LUKA BAKAR PADA TIKUS

Wole woe is a native plant of Indonesia which is widely used by the people of Central Halmahera as a medicinal plant. Empirically this plant is widely used for wound treatment. This study aims to determine the effect of epithelialization of wole woe stem extract and determine the effective concentration and duration of wound healing in rats after administration of wole woe stem extract. This research was conducted experimentally in a laboratory using 25 rats which were divided into 5 groups consisting of 1 control group, 1 comparison group, and 3 treatment groups of wole woe stem extract. Wound induction was carried out using a 100 0C hot plate measuring 2x2 cm and affixed to the surface of the rat's back skin for 2 seconds. After a burn is formed, the extract is applied 2 times a day for 21 days. Observations on wound healing were carried out macroscopically and measuring the surface area of the wound. The results showed that the administration of wole woe bark extract influenced healing second-degree burns in rats. The results of statistical analysis showed that there was no difference between the comparison group and the extract test group (p&gt;0.05). Based on the percent reduction in wound, the most effective concentration in wound healing was 5% (99.75%). Wound healing time in rats was 21 days.

Distinguishing tissue structures via polarization staining images based on different combinations of Mueller matrix polar decomposition parameters

Mueller matrix polarimetry is gaining wide attention in the field of biophotonics due to its great potential in detecting the microstructures and optical properties of tissue samples label-freely. Individual Mueller matrix derived parameters were often used to characterize certain kind of tissue structure. However, it is found that the individual Mueller matrix parameters only contain partial structural information. Thus, it is difficult to accurately and comprehensively indentify different structures using a single polarization parameter image. Here we introduce an image fusion method based on color spaces to combine different Mueller matrix derived parameters to provide multi-dimensional structural information pixel by pixel in a single polarization staining image. The results of rat back skin tissue specimens indicate that different fibrous structures can be easily distinguished using the polarization staining image. Then, in order to quantitatively analyze the texture characteristics of the polarization staining images for different structures, the Tamura image processing and the gray level co-occurrence matrix (GLCM) methods are adopted to provide various evaluation indices after the images segmentations. The experimental results confirm that the information provided by the polarization staining images based on different Mueller matrix derived parameters can be used for accurate tissue structures discrimination. Combining with machine recognition systems and fast developing artificial intelligence techniques, the strategy proposed in this study can be very helpful for precise abnormal tissues detection and pathological diagnoses.

Exogenous L-carnitine ameliorates burn-induced cellular and mitochondrial injury of hepatocytes by restoring CPT1 activity

BackgroundImpaired hepatic fatty acid metabolism and persistent mitochondrial dysfunction are phenomena commonly associated with liver failure. Decreased serum levels of L-carnitine, a amino acid derivative involved in fatty-acid and energy metabolism, have been reported in severe burn patients. The current study aimed to evaluate the effects of L-carnitine supplementation on mitochondrial damage and other hepatocyte injuries following severe burns and the related mechanisms.MethodsSerum carnitine and other indicators of hepatocytic injury, including AST, ALT, LDH, TG, and OCT, were analyzed in severe burn patients and healthy controls. A burn model was established on the back skin of rats; thereafter, carnitine was administered, and serum levels of the above indicators were evaluated along with Oil Red O and TUNEL staining, transmission electron microscopy, and assessment of mitochondrial membrane potential and carnitine palmitoyltransferase 1 (CPT1) activity and expression levels in the liver. HepG2 cells pretreated with the CPT1 inhibitor etomoxir were treated with or without carnitine for 24 h. Next, the above indicators were examined, and apoptotic cells were analyzed via flow cytometry. High-throughput sequencing of rat liver tissues identified several differentially expressed genes (Fabp4, Acacb, Acsm5, and Pnpla3) were confirmed using RT-qPCR.ResultsSubstantially decreased serum levels of carnitine and increased levels of AST, ALT, LDH, and OCT were detected in severe burn patients and the burn model rats. Accumulation of TG, evident mitochondrial shrinkage, altered mitochondrial membrane potential, decreased ketogenesis, and reduced CPT1 activity were detected in the liver tissue of the burned rats. Carnitine administration recovered CPT1 activity and improved all indicators related to cellular and fatty acid metabolism and mitochondrial injury. Inhibition of CPT1 activity with etomoxir induced hepatocyte injuries similar to those in burn patients and burned rats; carnitine supplementation restored CPT1 activity and ameliorated these injuries. The expression levels of the differentially expressed genes Fabp4, Acacb, Acsm5, and Pnpla3 in the liver tissue from burned rats and etomoxir-treated hepatocytes were also restored by treatment with exogenous carnitine.ConclusionExogenous carnitine exerts protective effects against severe burn-induced cellular, fatty-acid metabolism, and mitochondrial dysfunction of hepatocytes by restoring CPT1 activity.

Wound healing effect of autologous fibrin glue and polyglycolic acid sheets in a rat back skin defect model

Fibrin glue from autologous plasma may prevent viral infection and allergic reaction. Moreover, this biomaterial contains growth factors such as TGF-β and VEGF that promote reconstruction of the mucous membrane by stimulating fibroblast proliferation and angiogenesis. Thus, autologous fibrin glue is predicted to improve healing better than commercial fibrin glue. Here, we evaluated the effects of autologous fibrin glue on the crucial early phase of wound healing. Epithelial defects were introduced in rats and covered with polyglycolic acid (PGA) sheets with or without commercial or autologous fibrin glue. Wound healing was assessed for six weeks by histology and immunohistochemistry. Our results demonstrate that wounds covered with PGA sheets and autologous fibrin glue achieved efficient wound healing without complications such as local infection or incomplete healing. The rate of recovery of the regenerating epithelium in this group was superior to that in wounds covered with PGA sheets and commercial fibrin glue. Immunohistochemistry of laminin, cytokeratin, and VEGF confirmed fine and rapid epithelial neogenesis. Collectively, our results indicate that covering surgical wounds with autologous fibrin glue promotes wound healing and epithelialization, improves safety, and reduces the risks of viral infection and allergic reaction associated with conventional techniques.

Effect and mechanism of astaxanthin on acute kidney injury in rats with full-thickness burns

Effect and mechanism of astaxanthin on acute kidney injury in rats with full-thickness burns

Effect of Bifunctional β Defensin 2-Modified Scaffold on Bone Defect Reconstruction

Bone tissue engineering has emerged as an effective alternative treatment to the problem of bone defect. To repair a bone defect, antibiosis and osteogenesis are two essential aspects of the repair process. By searching the literature and performing exploratory experiments, we found that β defensin 2 (BD2), with bifunctional properties of antibiosis and osteogenesis, was a feasible alternative for traditional growth factors. The antimicrobial ability of BD2 against Staphylococcus aureus and Escherichia coli was studied by the spread plate and live/dead staining methods (low effective concentration of 20 ng/mL). BD2 was also demonstrated to enhance osteogenesis, with higher messenger RNA (mRNA) and protein expression of the osteogenic markers collagen I (Col1), runt-related transcription factor 2 (Runx2), osteopontin (Opn), and osteocalcin (Ocn) in vitro (1.5–2.5-fold increase compared with the control group in the most effective concentration group), which was consistent with the alkaline phosphatase (ALP) and alizarin red S (ARS) staining results. We implanted poly(sebacoyl diglyceride) (PSeD) combined with BD2 and rat bone tissue-derived mesenchymal stem cells (rBMSCs) under the back skin of rats and found that the inflammatory response was significantly lower with this combination than with the PSeD/rBMSCs scaffold without BD2 and the pure PSeD group and was similar to the control group. Importantly, when assessed in a critical-sized in vivo rat 8 m diameter calvaria defect model, a scaffold we developed combining bifunctional BD2 with porous organic polymer displayed an osteogenic effect that was 160–200% greater than the control group. The in vivo study results revealed a significant osteogenic response and antimicrobial effect and were consistent with the in vitro results. In summary, BD2 displayed a great potential of simultaneously promoting bone regeneration and preventing infection and could provide a viable alternative to traditional growth factors applied in bone defect repair.

A microstructurally inspired constitutive model for skin mechanics.

This study investigates the link between the mechanical properties of skin and its microstructural characteristics. Rat back skin samples from different locations, orientations, and sexes were collected and subjected to quasi-static uniaxial tensile tests. Stress-stretch behavior at low stress ranges and rupture data at high stress ranges were collected. The influence of location, orientation, and sex on skin mechanical properties was examined by comparing the mechanical parameters (i.e., initial slope, maximum slope, ultimate tensile strength, rupture stretch, and toughness) evaluated from the tensile testing data. Location and orientation were both found to have a significant effect on the mechanical properties. Collagen structural data (i.e., fiber orientation distribution, relative content, and fiber straightness) were evaluated using histology images. It was found that the rat lower (caudal) back had higher relative collagen content when compared to the upper (cranial) back. A microstructurally based constitutive model was proposed to describe the mechanical behavior of preconditioned rat back skin. The constitutive model incorporated the distribution of collagen fiber bundle orientations and relative collagen content measured from histology, and showed good agreement with the tensile test data. The influence of location and orientation was also evident in the optimized constitutive parameters. This study was a comprehensive investigation that combines skin mechanical behavior, micro-structure, and constitutive modeling.

Wound Healing Activity of Ethanolic Extract Gel of Tawas Ut Tuber (Ampelocissus rubiginosa L.) in Incisional Model Wistar Rats

Tawas ut tuber (Ampelocissus rubiginosa Lauterb.) is empirically used in wound healing by Dayak community. The present study was undertaken to assess wound healing activity of gel from ethanol extract of A. rubiginosa tuber using parameters of the closure of wound length, tensile strength, and histopathological observations. This study used twenty-five male Wistar rats divided into five groups: positive control (Bioplacenton®), negative control (placebo gel), and three of testing groups with gel extract (concentrations of 1.5%, 2.0%, and 2.5%). Wound healing activity was evaluated to 4 cm length and ± 2 mm depth incision wound model on the back skin of rats. The measurement of wound length was observed on the day of 4th, 8th, 12th, 16th, and 20th used quantitative analyze. On the day of 20th, animal was anaesthetized and the skin has been taken for tensile strength evaluation and histopathological observations. This study showed that group treated with gel extract at the concentration of 2.5% experienced higher wound healing activity with average percentage of wound closure of 99.00% ± 0.16, tensile strength 3.8541 gram/mm2, and proved with the re-epithelization, neocapillarization, and increase collagen density appeared in histopathological observations. Based on this study, gel from ethanol extract of A. rubiginosa tuber possesses wound healing activity.

The abdominal skin of female Sprague-Dawley rats is more sensitive than the back skin to drug-induced phototoxicity

In vivo phototoxicity studies are important to predict drug-induced phototoxicity in humans; however, a standard methodology has not established. To determine differences in sensitivity to drug-induced phototoxicity among various skin sites, we evaluated phototoxic reactions in the back and abdominal skin of female Sprague-Dawley rats orally dosed with phototoxic drugs (pirfenidone, 8-methoxysoraren, doxycycline, and lomefloxacin) or a non-phototoxic drug (gatifloxacin) followed by solar-simulated light irradiation comprising 18J/cm2 ultraviolet A. Tissue reactions were evaluated by macroscopic and microscopic examination and immunohistochemistry for γ-H2AX, and tissue concentrations of pirfenidone, doxycycline, and lomefloxacin were measured by tandem mass spectrometry. In addition, the thicknesses of the skin layers at both sites were measured in drug-naïve rats. The abdominal skin showed more severe reactions to all phototoxic drugs than the back skin, whereas the minimal erythema dose in drug-naïve rats and skin concentrations of each drug were comparable between the sites. Furthermore, histopathological lesions and γ-H2AX-positive cells in the abdominal skin were detected in deeper layers than in the back skin. The stratum corneum and dermis in the abdominal skin were significantly thinner than in the back skin, indicating a difference in the depth of light penetration and potentially contributing to the site differences observed in sensitivity to phototoxicity. Gatifloxacin did not induce any phototoxic reactions at either site. In conclusion, the abdominal skin is more sensitive to drug-induced phototoxicity than the back skin and may represent a preferable site for irradiation in this rat phototoxicity model.

Optimal dehydrothermal processing conditions to improve biocompatibility and durability of a weakly denatured collagen scaffold.

Collagen scaffolds are essential for tissue regeneration; however, preprocessing of these scaffolds is necessary because of their poor mechanical properties. The aim of this study was to determine the optimal condition for preparing a collagen scaffold with biocompatibility and durability. An atelocollagen fiber suspension was made and stored at -10°C in a container that could be cooled from the bottom to provide an orientation perpendicular to the collagen fiber and facilitate cell infiltration into the scaffold. After freeze-drying the frozen suspension, various collagen scaffolds were made by dehydrothermal (DHT) treatment under different conditions (processing temperature: 120-160°C for 0-28 h). Sections of the obtained materials were embedded under the back skin of rats, and the thickness and biocompatibility of the residual scaffold were evaluated after 2 weeks. The number of foreign body giant cells was counted to evaluate biocompatibility. Although the residual scaffold was thick, excessive DHT treatment caused a strong foreign body reaction. Weak DHT treatment resulted in a collagen scaffold with good biocompatibility but with reduced thickness. Overall, these results showed the restricted optimal conditions to make a collagen scaffold with good biocompatibility and ability to maintain sufficient space for tissue regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2301-2307, 2017.

Experimental study on pseudoallergic reaction of Qingkailing injection

Pseudoallergic reactions of Qingkailing injection (QKLI) was assessed by vascular hyperpermeability which were indicated by ear blue staining in ICR mice after single intravenous injection of QKLI mixed with Evans blue (EB) and skin blue spot formation in SD rats after intradermal injection of QKLI and intravenous injection of EB. In addition, QKLI-induced histamine, VEGF, TNF-alpha release was measured after ICR mice received the single dosing of QKLI iv. The mild vascular hyperpermeability characterized by ear blue staining could be observed in mice after intravenous injection of QKLI and EB. Intracutaneous injection of 50 micro L of test solution containing QKLI (25,50 microL) in rat back skin caused obvious local vascular hyperpermeability at the injection sites so as to result the larger diameters of blue spots than that in negative control group (P <0. 01). QKLI induced a significant increase of VEGF and a slight elevation of histamine in mice after intravenous administration, while TNF-alpha showed no change after QKLI iv. The results in this study indicated that both intravenous injection and intracutanous injection of QKLI could induce vascular hyperpemeability so as to cause pseudoallergic reaction in mice and rats. QKLI-induced pseudoallergic reaction may be associated with the release of histamine and VEGF.

Mechanical tension promotes skin nerve regeneration by upregulating nerve growth factor expression.

This study aimed to explore the role of mechanical tension in hypertrophic scars and the change in nerve density using hematoxylin-eosin staining and S100 immunohistochemistry, and to observe the expression of nerve growth factor by western blot analysis. The results demonstrated that mechanical tension contributed to the formation of a hyperplastic scar in the back skin of rats, in conjunction with increases in both nerve density and nerve growth factor expression in the scar tissue. These experimental findings indicate that the cutaneous nervous system plays a role in hypertrophic scar formation caused by mechanical tension.

Nanoreplica moulding of polyacrylamide hydrogels

Polyacrylamide (PAM) hydrogels are widely used in bioanalysis and biosensing applications. Scaling down of PAM patterns to micro/nanosize extends PAM applications to lab-on-a-chip, highly sensitive biosensors and cell/tissue analysis. Proposed is a replica moulding technique to pattern the PAM surface down to nanosize. Various patterns on silicon moulds successfully transferred to PAM with a minimum dimension of 60 nm and aspect ratio of up to ∼9. PAM is characterised as a platform for a single cell array and the analysis of cell responses to topographic cues. Moreover, micro/nanopatterned PAM samples were implanted under the back skin of rats to study the topological effects on immuno responses in vivo. Therefore the use of micro/nanoreplica moulding to pattern PAM hydrogel provides opportunities for studying the relationship between soft nanoscaled structures and cell/tissue.

Neovascularization of Porous Silk Fibroin Films(PSFFs) as Dermis Substitutes Implanted in Rats

Neovascularization in biomaterials plays a key role in wound healing. In this paper, porous silk fibroin films (PSFFs) whose structure was optimized, as dermis substitutes, were implanted in the back skin of rats for recovery of dermis loss. Results showed that a thin layer of loose connective tissue had formed at the interface between PSFFs and subcutaneous tissues, in which abundant blood vessels could be observed at 24 h after surgery. Whereafter the newly formed connective tissue thickened and the number of microvessels in the tissue increased. Furthermore, a few microvessels could be seen in PSFFs at day 5, most of which were capillaries. By day 10, the density of microvessels in PSFFs increased to a peak while the percentage of capillary decreased. At day 23, both the density of microvessels and the percentage of capillary was almost equal to those of normal tissues. In summary, wound healing with PSFFs as dermis substitutes is the neovascularization process of PSFFs. The process includes three major steps: (1) new formation and growth of loose connective tissue into the pores of PSFFs, (2) proliferation and migration of fibroblasts and endothelial cells, and (3) formation of functional microvessels and their networks.

A transcutaneous vaccination system using a hydrogel patch for viral and bacterial infection

One of the most important anthropic missions is preventing the global spread of infectious diseases. Vaccination is the only available preventive treatment for infectious diseases, but the availability of vaccines in developing countries is not adequate. We report a simple, easy-to-use, noninvasive hydrogel patch transcutaneous vaccination system. Antigen (Ag)-specific IgG production was induced by applying an Ag-immersed patch to non-pretreated mouse auricle or hairless rat back skin. Immunofluorescence histochemical analysis revealed that Langerhans cells resident in the epidermal layer captured the antigenic proteins delivered by the hydrogel patch, which promoted the penetration of antigenic proteins through the stratum corneum, and that Ag-capturing Langerhans cells migrated into draining lymph nodes. Humoral immunity elicited by our transcutaneous vaccination system demonstrated neutralizing activity in both adenoviral infection and passive-challenge tetanus toxin experiments. The use of this hydrogel patch transcutaneous vaccination system will facilitate the global distribution of effective and convenient vaccines.

Changes in the number of Merkel cells with the hair cycle in hair discs on rat back skin

Hair discs are known to contain a large number of Merkel cells and are ideal for investigating Merkel cell biology. Hair follicles, which are important elements of hair discs, undergo unique cyclical morphological and biological changes. To define the relationships between the number and the morphology of Merkel cells within the hair disc in association with the hair cycle on rat back skin. Merkel cells in hair discs were observed three-dimensionally using immunohistochemistry. Epidermal sheets were incubated with monoclonal murine antibody to CK20. As a result, Merkel cells in hair discs were clearly demonstrated as whole shapes and were counted under a light microscope. Merkel cells in hair discs increased during the early to middle phase of anagen and decreased during the middle phase of anagen to catagen and telogen in perinatal and postnatal rat back skin. We observed the morphological variation of Merkel cells in hair discs of rat back skin, and consequently divided them into two subtypes at the light microscopic level: the oval type and the dendritic type. The number of oval-type Merkel cells was not markedly affected by the hair cycle. In contrast, the number of dendritic-type Merkel cells markedly changed with the hair cycle. This difference of the hair cycle dependency between oval and dendritic-type Merkel cells suggests some functional differences, such as a secretory function, related to the hair cycle.