The merkel cell in the labial ridge epidermis of anuran tadpole. I. Fine structure, distribution and cytochemical studies

Abstract

A B S T R A C TThe labial ridge epidermis of the anuran tadpole, which is the formative site of horny teeth, was studied with the electron microscope. The triangular epidermis covering the apex of the labial ridge was composed of horny teeth cells arranged in a columnar shape, keratinocytes, secretory epidermal cells, two kinds of non-epidermal cells and Merkel cells. Individual non-epiderma1 cells were identified as neutrophils and macrophages respectively.In addition, the fine structure, distribution and cytochemistry of the Merkel cell were studied. The fine structure of Merkel cells in the labial ridge epidermis was not so different from those of other vertebrates reported previously by other workers, except for the presence of numerous glycogen particles. The presence of Merkel cells in the labial ridge epidermis was very frequent, and they were arranged in a line at a uniform level of the triangular epidermis. They were usually located in the third cell layer from the base of the epidermis.PAS and azure A stains were used on semithin epoxy sections t o reveal the Merkel cells, and both stained them intensely. On the other hand, though glutaraldehyde-silver techniques and permanganate fixation were used to detect monoamines in the Merkel cells ultracytochemically, a positive reaction was observed only on the pigment granules.It is known that the larval anurae have two different cornified organs for mastication; horny jaws and teeth. The first description of these organs was made by Schulze in 1869. Since then, several histological studies have been reported (Beaumont and Deunff, '59; Luckenbill, '65; Kaung, '751, whose studies were done on the differentiation of the horny jaws and teeth.The author studied the cell composition of the anuran labial ridge epidermis, which is the formative site of horny teeth, with electron microscopy. During the course of the studies, i t was found that many Merkel cells were present in the ridge epidermis.With regard to the Merkel cell, many problems relating to function and development need to be solved. It seems that the anuran tadpole is very useful material for Merkel cell studies.The present investigations demonstrate the cell composition of the labial ridge epidermis of the anuran tadpole, and show the fine struc- ture, the distribution and the cytochemistry of Merkel cells within the epidermis of the labial ridge. MATERIALS AND METHODSLarvae of Rana japonica raised from eggs in the laboratory a t 20°C were used in this study. The mouth parts of tadpoles from stages I to X were dissected and immersed in 2.5% glutaraldehyde (pH 7.2 phosphate buffer). Tadpoles were selected according t o the table of Rana pipiens by Taylor and Kollros ('46). The dorsal and ventral lips of the mouth were then dissected and divided into small pieces. These small pieces of tissue were fixed with 2.5% glutaraldehyde for two hours at 4"C, then postfixed with 1% osmium tetroxide fo one hour. Specimens were then dehydrated and embedded in Epon 812. Ultrathin sections were cut in the transverse pl...

Merkel cell development in the wound healing in the labial mucosa of adult rabbits.

“…showed that the Merkel cell of the labial mucous membrane of the rabbit developed in the epithelial layer via a cell which showed a transitional structure between the Merkel cell and the keratinocyte during the course of postnatal development of the rabbit. Certain workers have suggested that the neuro-ectodermal cells may be irrelevant to the development of the Merkel cell in the larval amphibian skin (TWEEDLE, 1978;TACHIBANA, 1979;. The same thing may be expected in mammals too.…”

“…A lot of papers on the Merkel cell have appeared during the last two decades (CAUNNA, 1962;MUNGER, 1965MUNGER, , 1977MUSTAKALLIO and KIISTALA, 1967;SMITH, 1967SMITH, , 1970IGGO and MUIR, 1969;KUROSUMI et al, 1969;BREATHNACH, 1971;LYNE and HOLLIS 1971;HASHIMOTO, 1972 a, b;ANDRES and DURING, 1973;NAFSTAD, 1971a, b;WINKELMANN and BREATHNACH, 1973;ENGLISH, 1974ENGLISH, , 1977WHEITEAR, 1974;BUDTZ and LARSEN, 1975;HALATA, 1975;SAXOD, 1978;TWEEDLE, 1978;TACHIBANA, 1978TACHIBANA, , 1979, and many others). But the life history, including the developmental origin, of the Merkel cell is not necessarily clear.…”

“…Several investigators have contributed to this field by developmental and experimental approaches (BREATHNACH, 1971;LYNE and HOLLIS, 1971;HASHIMOTO, 1972a;ENGLISH, 1974;TACHIBANA, 1979;; TACHIBANA, SAKAKURA *A part of this research was supported by scientific research fund from the Ministry of Education of Japan. 151 and NAWA, 1980).…”

Ultrastructures of mechanoreceptors in the oral mucosa

“…(1969), Robins (1970), Smith (1970), Andres and During (1973) and Breathnach and Winkelmann (1973). Merkel cells have been reported in the oral mucosa of several animal species by Halata (1970), Tachibana (1978, 1979), Watanabe (1979/80), Tachibana and Nawa (1980) and Tachibana et al . (1983).…”

A light and electron microscopic study of lamellated nerve endings found in the rat cheek mucosa.

“…WATANABE andYAMADA (1979) andWATANABE andYAMADA (1983) have similary described encapsulated nerve endings in the rat gingiva, and BERKOVITZ et al (1983) have found like corpuscles in the periodontal ligament. NIKAI et al (1971) described the fine structure of Merkel cells in the rat gingiva; HASHIM0T0 (1972) did the same in the human oral mucosa; SAXOD (1978) in the palate mucosa of chicken; TACHIBANA (1978) in the labial ridge epidermis of the anuram tadpole; GARANT et al (1980) in the palate mucosa of the squirrel monkey and TACHIBANA et al (1982) in the labial mucous epithelium of adult rabbits.…”