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PubMed1979

Morphological and morphometric studies with the electron microscope on the Merkel cells and associated nerve terminals of normal and denervated skin.

Merkel cells and associated nerve endings of dog snout skin as well as foot and toe pads of rats were studied with the transmission electron microscope. Normal Merkel cells are characterized by the following morphological features: 1) localization restricted to the basal layer of the epidermis, 2) adjoining afferent nerve endings containing many mitochondria, 3) specific small round granules usually accumulated in the cytoplasm on one side of the nucleus facing the junction of the nerve ending, 4) highly lobulated irregular shape of the nucleus, 5) well developed Golgi apparatus with a few immature granules situated on the side of the nucleus opposite the junction at the ending, 6) spine-like processes extending from the cell surface where no nerve endings abut, 7) desmosomes and desmosome-like membrane thickening on the cell surface both abutting the surrounding keratinocytes and the nerve endings. The Merkel cells with nerve endings were observed and measured at various days after denervation. The experiments were carried out on rats whose sciatic nerves were transected. The samples of skin of foot and toe pads of the denervated legs were taken almost every day from 1 to 30 days. Almost no changes were noticed after 24 hrs, but within the next day the nerves retracted and were no longer observed in the epidermis. The Merkel cell granules increased in number in 1--3 days but decreased again to about a half of the value of the control at 30 days. The polarity of granules distribution showing a strong accumulation in the cytoplasm near the nerve ending became less marked after denervation. Some cells sustained severe degeneration in the later stage of experiment. It was remarkable that the activity of Merkel cells might depend on the associated nerves, but they never completely disappeared even after a long period of denervation.

Animals↗
PubMed1988

Presence and coexistence of chromogranin A and multiple neuropeptides in Merkel cells of mammalian oral mucosa.

By the use of light microscopic (LM) immunohistochemistry, Merkel cells of the mammalian oral mucosa have been examined for the presence and coexistence of some neuropeptides and of the neuroendocrine marker chromogranin A (CG-A). Peptide and CG-A immunophenotypes of oral Merkel cells were found to vary between species and to depend on the developmental stage, as exemplarily revealed in the pig. Oral Merkel cells of adult cat, mouse and pig but not those of adult guinea pig stained for calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal polypeptide (VIP) and peptide histidine isoleucine (PHI). Pairs of adjacent sections alternately stained for SP, CGRP, VIP, PHI or for CG-A revealed mutual coexistence of these peptides and of CG-A (if expressed) in individual Merkel cells of hard palate, gingiva and buccal mucosa. CG-A immunoreactivity was restricted to Merkel cells of cat and pig. In adult pig and cat, a much lower number of Merkel cells stained for CG-A and peptide expression was inverse. These results indicate that the chemical coding of Merkel cells in mammalian oral mucosa is much more complex than previously described and depends on the developmental stage.

Animals↗
PubMed1990

Merkel cell tumor of the back detected during pregnancy.

Merkel cell tumor is an unusual, aggressive malignancy of skin that has been considered to be derived from cutaneous Merkel cells. We are reporting a case of Merkel cell tumor overlying the left scapula with metastases to the thoracic spine and pleura. The tumor was found incidentally in a 23-year-old pregnant black woman. The tumor recurred locally 5 months after initial wide excision. Subsequently, a second wide excision of the recurrent tumor with ipsilateral axillary dissection was performed. The course of the disease was complicated by local recurrence and formation of distant metastases to pleura and spine. At the end-stage of the disease, the patient was found to have a cardiac murmur, and echocardiography revealed a mass in the anterior wall of the right ventricle that was suspicious for a metastatic lesion. The patient expired from extensive distant metastases 23 months after diagnosis.

Adult↗
PubMed1984

A fluorescent microscopic study of the development of rat touch domes and their Merkel cells.

The ability of the fluorescent dye quinacrine to label epidermal Merkel cells was used to study the development of touch domes (Haarscheiben) in rat skin. In embryonic and early postnatal pups, sites of touch dome primordia were reliably located within strips of separated trunk epidermis by the occurrence of discrete clusters of fluorescent cells scattered across the basal cell layer. As in excised adult domes, most of these fluorescent (Merkel) cells lay caudal to the emerging tylotrich hair follicle and the cell cluster formed an annular or crescentric disc. Though all the touch domes that comprise the adult population appear to contain labelled Merkel cells by postnatal day 4, the number of these cells per dome continues to increase some 3-4 fold after birth to reach the average adult number (ca 90 cells) on the dorsal trunk around the fifth week. At about this time the adult size (ca 250 micron) of the dorsal Haarscheiben is also reached, as estimated by the length of the long axis of the fluorescent disc. The rostro-caudal orientation of this long axis varied from dome to dome, usually in the range 0-45 degrees clockwise or counterclockwise, and a functional correlate of this is suggested. The density of labelled dome primordia is higher on the dorsal than on the ventral trunk from as early as embryonic day E20-21 and remains higher although the density of domes decreases steadily across the skin during postnatal growth of the animal. This study utilizes a novel fluorescent labelling technique that is applicable to microscopic studies on the development of Merkel cells within their epithelial locations, in this instance the rat touch domes. Although the full population of domes is established early in development, the Merkel cells within a dome continue to increase in number for several weeks after physiological function is known to appear in this structure.

Animals↗
PubMed2003

Feline cutaneous neuroendocrine carcinoma (Merkel cell tumour): clinical and pathological findings.

A case of a feline Merkel cell tumour is described. An 8-year-old, female cat developed a round, alopecic, reddish mass on the nose. Wide excisional surgery was performed with cartilage resection. Histologically the mass was composed of solid islands of mostly basophilic densely packed cells with a scant cytoplasm, which was suggestive of a neuroendocrine origin. Results of immunohistochemical studies using antibodies against neurone-specific enolase, chromogranin, synaptophysin and pan-cytokeratin allowed classification of the lesion as a Merkel cell tumour. Ultrastructurally, dense core granules were identified in the cytoplasm. In a 2-year follow-up no relapses or metastases were observed. The clinical course recorded is in contrast with the malignant nature of a Merkel cell tumour recently described in a cat and of the human Merkel cell tumour, but is similar to the course of the canine Merkel cell tumour which is often benign. Early diagnosis along with the use of wide surgical excision might be considered an important factor in preventing relapse of this tumour.

Animals↗
PubMed1995

Merkel cells are integral constituents of desmoplastic trichoepithelioma: an immunohistochemical and electron microscopic study.

The incidence of Merkel cells has previously been investigated in a number of inflammatory and tumorous lesions of the skin. Special attention was given to tumors with follicular differentiation. In the present study we examined the localization of Merkel cells in another adnexal tumor, the desmoplastic trichoepithelioma (n = 15), as well as in its main differential diagnosis, the morpheiform basal-cell carcinoma (n = 30). Using immunohistochemical methods, we found Merkel cells as a stable constituent in desmoplastic trichoepitheliomas, but failed to detect them in morpheiform basal-cell carcinomas. These findings might therefore be an important tool in the sometimes very difficult but clinically imperative distinction between these two conditions. Furthermore, our study may be of interest in the discussion about the origin of desmoplastic trichoepitheliomas. High numbers of Merkel cells in desmoplastic trichoepitheliomas indicate a bulge-derived origin of this adnexal tumor, since high numbers of Merkel cells, especially in the bulge, were recently discovered. Although the significance of Merkel cell hyperplasia in desmoplastic trichoepithelioma is not presently understood, a regulatory role of the Merkel cell in growth and development of this adnexal tumor is suggested.

Basal Cell Carcinoma↗
PubMed2003

Merkel cell tumor presenting as a painful patch lesion on the right arm.

Primary small cell cutaneous neuroendocrine carcinoma (Merkel cell carcinoma) is an uncommon, highly malignant, primary cutaneous neuroendocrine carcinoma. Clinically it is seen as a 0.5- to 5.0-cm pinkish purple papule or nodule, usually not ulcerated, on the head, neck, or, less frequently, the roots of the limbs. We present the case of a woman with an atypical clinical presentation of a Merkel cell tumor.

Arm↗
PubMed1991

Light microscopic immunoenzyme and electron microscopic immunogold cytochemistry reveal tachykinin immunoreactivity in Merkel cells of pig skin.

Light microscopic (LM) immunoenzyme and electron microscopic (EM) immunogold cytochemistry were used to demonstrate the presence and subcellular distribution of tachykinin (substance P)-like immunoreactivity in Merkel cells of pig skin. Merkel cells of sinus hair follicles were strongly immunoreactive for tachykinins. In contrast, tachykinin-like immunoreactivity was absent from or very weak in epidermal Merkel cells while subepidermal and some intraepidermal nerve fibres were clearly immunopositive for tachykinins. Postembedding immunogold cytochemistry on the EM level revealed that tachykinin-like immunoreactivity was confined to the secretory granules in Merkel cells. Tachykinin immunoreactivity was clearly absent from the axon of the Merkel cell-axon complex. The selective presence of tachykinin immunoreactivity in secretory granules strongly suggests that tachykinins are synthesized in cutaneous Merkel cells, at least of pig. This is a further indication for the concept that the Merkel cell is a member of the diffuse neuroendocrine system. However, the functional role of tachykinins like substance P and neurokinin A and of other peptides present in Merkel cells remains enigmatic.

Animals↗
PubMed1996

Cytoplasmic Ca2+ concentrations in intact Merkel cells of an isolated, functioning rat sinus hair preparation.

An isolated, functioning sinus hair preparation was developed to investigate cytoplasmic Ca2+ concentrations in intact Merkel cells using microfluorimetric techniques. Intracellular Ca2+ levels were monitored by means of photon counters in small groups of Merkel cells loaded with the calcium fluorescent indicators fura-2 or fluo-3. Mechanical stimulation of Merkel cells with fine glass rods resulted in small transient increases in intracellular Ca2+ levels (by about 20%) in the group of Merkel cells around the stimulating probe. A rise in Ca2+ is presumed to be essential for the postulated synaptic transmission to the afferent nerve terminal. Depolarization with a high concentration of potassium chloride (100 mM) caused increases in intracellular Ca2+ concentrations in Merkel cells (by about 70%) only in the presence of extracellular Ca2+, indicating an influx of Ca2+ through voltage-gated channels. The Ca2+ response was abolished neither by (+)-BayK8644 nor omega-conotoxin, suggesting that the Ca2+ channels are different from the classical L- or N-type channels. Extracellular application of ATP (10 microM to 5 mM) caused dose-dependent increases in intracellular Ca2+ levels in Merkel cells of up to sevenfold from the basal level of about 100 nM. Similar responses to ATP were also measured during superfusion with Ca(2+)-free medium, suggesting intracellular stores as the main Ca2+ source. Pre-incubation of Merkel cells with the purinoceptor antagonist suramin (100 microM) for 30 min reduced the Ca2+ responses to ATP by about 50% compared with control conditions. In conclusion, the results have demonstrated that a rise in intracellular Ca2+ in Merkel cells can be evoked by mechanical stimulation, membrane depolarization and chemical stimulation by ATP. These observations strongly suggest a possible contribution of Ca2+ to the normal responsiveness of Merkel cell mechanoreceptors, in turn supporting the hypothesis that Merkel cells are involved in the mechano-electric transduction process in sinus hair type I mechanoreceptors.

Adenosine Triphosphate↗
PubMed2001

Growth and characterization of a cell line from a human primary neuroendocrine carcinoma of the skin (Merkel cell carcinoma) in culture and as xenograft.

The primary neuroendocrine carcinoma of the skin or Merkel cell carcinoma (MCC) is a skin tumor with aggressive biological behaviour. Experimental models for investigating the biological properties of the tumor are prerequisite for developing new therapeutic approaches. In this study, we report the establishment and characterisation of a cell line derived from the lymph-node metastasis of a patient with highly aggressive MCC. Merkel carcinoma cells (MCC-1) grew as floating aggregates in suspension cultures for more than two years and over 70 subcultures. The proliferation rate in suspension cultures was rather moderate with a population doubling time of 69 h. The immunocytochemical pattern of the cultured MCC-1 was similar to that of the original tumor with expression of cytokeratin 18, neuron-specific enolase, neurofilaments, and synaptophysin. In addition, reverse transcriptase polymerase chain reaction (RT-PCR) revealed presence of chromogranin A mRNA in the MCC-1 cell line. Furthermore, electron microscopy yielded the rare finding of neuroendocrine granules in the cytoplasm of the cultured cells. The cell line MCC-1 was able to form colonies in soft agar. Nude mice developed solid tumors with similar histology to the original tumor after subcutaneous and intravenous injections of cultured MCC-1, and malignant ascites was seen after intraperitoneal injection. Also, two MCC-1 sublines were established by reculturing cells from the xenografts grown in vivo and immunocytochemistry confirmed their neuroendocrine origin. The MCC-1 line may thus serve as a model for studying the biology and the metastatic potential of Merkel cell carcinoma.

Aged↗
PubMed1989

Immunohistochemical analysis of chromogranin A and multiple peptides in the mammalian Merkel cell: further evidence for its paraneuronal function?

By the use of light microscopic immunohistochemistry, epidermal Merkel cells have been examined for the coexistence of some neuropeptides and chromogranin A (CGA). Peptide and CGA-immunophenotypes were similar in adult Merkel cells but variable in fetal skin, where CGA preceded the expression of peptides which were partly expressed only in a subpopulation of Merkel cells from hair follicles. Thus, only Substance P (SP) and calcitonin gene-related peptide (CGRP) were expressed in a subpopulation of Merkel cells from hair follicles. There were similar Merkel cell densities visualized on consecutive paraffin sections by the use of antisera against peptides, CGA and cytokeratin offering useful tools for a future systematical complementary mapping of Merkel cell populations in various species, locations and developmental stages. Electron microscopic immunohistochemistry has shown that CGA-immunoreaction is localized in the secretory granules which, again, supports the view that the Merkel cell is a paraneuron, i.e., neurosecretory in function.

Animals↗
PubMed1994

Ultrastructural study of the Merkel cell and its expression of met-enkephalin immunoreactivity during fetal and postnatal development in mice.

The morphological changes and the expression of met-enkephalin immunoreactivity of Merkel cells during fetal and postnatal development were investigated in touch domes and sinus hair follicles of mice by transmission electron microscopy. In prenatal fetal mice, the Merkel cells were mainly oval in shape and had slightly lobulated nuclei. These fetal Merkel cells (14, 16, 18 d gestation) which were not innervated showed a large number of accumulated dense-core granules in their cytoplasm as compared with the innervated Merkel cells which appeared in adult mice. No Merkel cells could be found in d 10 and d 12 fetuses. Innervation of Merkel cells was found to increase with age. The location of Merkel cells in juvenile, adult and even old mice was very similar, cells being found mainly in the basal layer of the epithelium. Using the electron-microscopic immunogold method, met-enkephalin-like substance was consistently located in the dense-core granule region of both innervated and noninnervated Merkel cells throughout the whole developmental stage. Interestingly, it was also found that the labelling intensity of met-enkephalin immunoreactivity was significantly higher in Merkel cells of younger age groups than in adult and old age groups. None of the nerve terminals associated with Merkel cells were labelled. The present study supports the theory of an epidermal origin of Merkel cells followed by the trophic growth of nerve fibers induced by the peptides.

Animals↗
PubMed1981

Merkel cells as targets of the mechanosensory nerves in salamander skin.

Previous investigations showed that the morphological basis of the low-threshold rapidly adapting mechanoreceptors in the salamander skin is neurite-Merkel cell complex located in the epidermis. We have now examined whether sensory nerves are required for the appearance of Merkel cells, and whether these cells act as specific targets for ingrowing sensory axons. Electronmicroscopic examination of denervated skin shows that Merkel cells survive in normal density and appearance in the epidermis for at least six months without nerves. In addition, mechanosensory function of such skin is restored when the skin become reinnervated either by collaterally sprouting (intact) nerves or by regenerating ones, and Merkel cells are then found to have nerve terminals associated with them. These experiments suggest that Merkel cells do act as targets for ingrowing nerves in these circumstances. Further experiments were done on skin that had regenerated in the total absence of any innervation to the limb; such new skin contained nerve-free Merkel cells that were normal in appearance, density and location. When nerves were allowed to innervate this new skin the sensory axons grew to the "new" Merkel cells and established typical neurite-Merkel cell complexes, and normal mechanosensory function. Since the new skin had developed without nerves, the sensory axons were not following "old" pathways to the Merkel cells. We conclude that the Merkel cells are the true targets for the mechanosensory axons; these cells attract the sensory axons to them and/or contain specific markers that allow the ingrowing axons to recognize them. Once a Merkel cell becomes innervated it loses this "target cell" quality. In addition, mechanosensory function of the sensory endings appears to occur only when the endings have developed a morphological association with a Merkel cell.

Animals↗
PubMedDate not supplied

Merkel cell carcinoma of the eyebrow extending into the orbit.

BACKGROUND: Merkel cell carcinoma is a rare and aggressive cutaneous neoplasm with high local recurrence and metastatic rates. PURPOSE: To highlight an unusual presentation of a Merkel cell carcinoma. CASE REPORT: We report a large Merkel cell tumor in an 85-year-old woman. It extended from the eyebrow into the upper nasal orbit posterior to the equator of the eye globe. Local resection resulted in microscopically complete removal of the tumor. During follow-up (20 months) no local recurrence was noticed but there was a metastasis in a lymphatic nodule. CONCLUSIONS: Merkel cell carcinoma often presents in the eyelids and periorbital region. However, extension from the eyebrow deep into the orbit is unusual.

Aged↗
PubMed2004

Essential components for a glutamatergic synapse between Merkel cell and nerve terminal in rats.

The exact role of Merkel cells and their possible involvement in mechanosensation is unclear. The aim of this study was to determine, in the adult rat sinus hair follicle, the expression pattern of a number of vesicular proteins involved in neurotransmitter release to provide a clearer understanding of Merkel cell signalling mechanisms. We identified prominent expression and co-localization of the glutamatergic vesicle loading proteins VGLUT1 and VGLUT2 at the site of the sinus hair follicle known to be densely populated with Merkel cells. We also found expression of the vesicle recycling proteins synaptogyrin and syntaxin-6 in the same region of the hair follicle. Our data suggest that glutamate signalling is involved in Merkel cell mechanosensation and that vesicular trafficking is commonplace in the Merkel cell-neurite complex.

Animals↗
PubMed1985

Electron microscopy of Merkel cell carcinoma from formalin-fixed tissue.

Merkel cell carcinomas have characteristic, but not pathognomonic, histomorphologic features. The diagnosis can be confirmed by immunohistochemistry studies and electron microscopy. However, differential diagnostic problems often occur only after all tumor material has been fixed in formalin and embedded in paraffin, which gives poor tissue preservation for electron microscopy. Therefore, in addition to histologic and immunohistochemical studies, parallel ultrastructural investigations were performed on tumor specimens fixed in glutaraldehyde and routinely processed, for electron microscopy, on formalin-fixed tissue and on formalin-fixed paraffin blocks. Formalin fixation led to an almost complete loss of neurosecretory granules and cell membranes; however, the characteristic paranuclear whorls of intermediate filaments were retained in all tumors. Merkel cell carcinomas are immunoreactive for neuron-specific enolase (NSE), but NSE-antisera have only recently become commercially available. Cytokeratin is demonstrable as a paranuclear clump, and this feature was found in four out of six tumors. Thus histologic, immunohistochemical, and electron microscopy studies of formalin-fixed tissue are able to confirm the diagnosis of neuroendocrine Merkel cell carcinoma.

Adenocarcinoma↗
PubMed1991

Merkel cell carcinoma of the head and neck associated with Bowen's disease.

The Merkel cell carcinoma occurs primarily in the skin of the head and neck, and develops in the dermis with a trabecular growth pattern. Immunohistochemistry reveals positive staining for neuron-specific enolase, neurofilaments, cytokeratin and chromogranin A. Electron microscopically, the tumor cells contain dense-core granules, spinous cytoplasmic processes, desmosomes, zonulae adherentes and paranuclear filament aggregates besides frequent mitoses, focal necroses and lymphocyte and plasma cell infiltrates. The Merkel cell carcinoma is often co-existent with other malignancies such as squamous cell carcinoma or, as in the present study, with Bowen's disease. The definite diagnosis of the Merkel cell carcinoma can be effected only by electron microscopic examination of the tumor.

Aged↗
PubMed1989

The neural dependency of Merkel cell development in the rat: the touch domes and foot pads contrasted.

We have used the quinacrine labeling technique and electron microscopy to study the development of the Merkel cell population in the skin of the rat and how this is affected by denervation produced at birth and at various times thereafter. An unexpected difference was found between the Merkel cells of glabrous and hairy skin. In the paw pads of rats aged 1 day or older the Merkel cells differentiated normally and survived quantitatively in the absence of their nerves. In the touch domes however, denervation at 1-4 days prevented the differentiation of the normal Merkel cell population and led to the disappearance of all or most of the Merkel cells that were already present. The Merkel cells in touch domes of the lower leg were affected by denervation like those of the back skin, differing strikingly from the Merkel cells of the footpads, even though the hairy skin of the leg and the glabrous skin of the foot are innervated by the same anatomical nerve. In adult rats, axons regenerating to denervated paws reinnervated epidermal Merkel cells of the pads and restored essentially normal mechanosensitivity to them; thus the Merkel cells of mammalian glabrous skin, like their counterparts in the wholly glabrous skin of lower vertebrates (S. A. Scott, E. Cooper, and J. Diamond, 1981, Proc. R. Soc. London B211, 455-470; K. M. Mearow and J. Diamond, 1988, Neuroscience 26, 695-708), can act as targets for ingrowing nerves. However, even though the differentiation of Merkel cells in hairy skin is nerve dependent, they probably have in common with the Merkel cells of glabrous skin the role of acting as final targets for nerves during development and regeneration.

Aging↗