The surface structure of the epithelium of the hamster cheek pouch

Experimental oral candidiasis in animal models

Oral candidiasis is as much the final outcome of the vulnerability of the host as of the virulence of the invading organism. We review here the extensive literature on animal experiments mainly appertaining to the host predisposing factors that initiate and perpetuate these infections. The monkey, rat, and mouse are the choice models for investigating oral candidiasis, but comparisons between the same or different models appear difficult, because of variables such as the study design, the number of animals used, their diet, the differences in Candida strains, and the duration of the studies. These variables notwithstanding, the following could be concluded. (i) The primate model is ideal for investigating Candida-associated denture stomatitis since both erythematous and pseudomembranous lesions have been produced in monkeys with prosthetic plates; they are, however, expensive and difficult to obtain and maintain. (ii) The rat model (both Sprague-Dawley and Wistar) is well proven for observing chronic oral candidal colonization and infection, due to the ease of breeding and handling and their ready availability. (iii) Mice are similar, but in addition there are well characterized variants simulating immunologic and genetic abnormalities (e.g., athymic, euthymic, murine-acquired immune deficiency syndrome, and severe combined immunodeficient models) and hence are used for short-term studies relating the host immune response and oral candidiasis. Nonetheless, an ideal, relatively inexpensive model representative of the human oral environment in ecological and microbiological terms is yet to be described. Until such a model is developed, researchers should pay attention to standardization of the experimental protocols described here to obtain broadly comparable and meaningful data.

Differential expression of type I cytokeratins in hamster cheek pouch epithelium following treatment with dimethylbenzanthracene

Cytokeratin (CK) expression in untreated, paraffin-treated or dimethylbenzanthracene (DMBA)-treated hamster cheek pouch epithelium was investigated utilizing monoclonal antibodies AE1 or AE3, which react with type I or type II CKs, respectively, and by in situ hybridization utilizing type I CK-specific probes. The latter were isolated from a cDNA library of hamster cheek pouch mRNA and designated CK 13 and CK 10 based on their respective homologies (> 95% amino acids) with murine CK 13 and human CK 10. Treatment of hamster cheek pouch epithelium with DMBA resulted in increased expression of type I CK, detected immunohistochemically with monoclonal AE1, but decreased expression of type II CKs detected with AE3. Despite an overall increase in type I CKs, in situ hybridization demonstrated differential expression of type I CKs with altered distribution of CK 13 mRNA and reduced expression of CK 10 mRNA, providing additional sensitive markers for DMBA-associated changes in CKs. These changes were constant at 2 to 22 weeks in the pre-neoplastic and neoplastic epithelium following the initial application of DMBA.

Scanning electron microscopy of dimethylbenzanthracene (DMBA)-treated hamster cheek pouch

The aim of the present study was to describe changes which could be regarded as a result of neoplastic rather than inflammatory processes. Fifty-five weeks after 6 weeks of DMBA application to the cheek pouches of 5 male hamsters there were 4 types of lesion: larger ulcerated sessile; smaller non-ulcerated sessile; non-ulcerated pedunculated; conical projections. These and the rest of the pouches were examined by scanning electron and light microscopy. The interlesional mucosa, non-ulcerated sessile lesions and conical projections were covered by flat polygonal cells with either a honeycomb surface pattern of interconnecting microridges, or microridges arranged into more parallel lines. Cell imprints and boundaries were formed by linear ridges, grooves or both. Pedunculated lesions had flat smooth-surfaced cells and cells with a honeycomb surface pattern. None of these lesions were carcinomas by light microscopy but the ulcerated sessile lesions were. The appearance of the cells on the ulcerated lesions varied: flat, with a variable number of short microvilli that were often knob-like, isolated short microridges, or both; plump, giving a cobblestone appearance with surfaces that were smooth, covered by microvilli, short microridges or both. Such appearances have been described as characteristic for dysplastic and malignant stratified squamous epithelium in a number of sites. Further study of both experimental and naturally occurring mucosal disease is needed to validate this.

Structure of hamster palatal gingiva and intermolar mucosa after intraperitoneal dosing with N-methyl-N-nitrosourea: a scanning electron microscope study

The palatal gingiva and intermolar mucosa from normal hamsters and from hamsters that had received N-methyl-N-nitrosourea (NMU) intraperitoneally were examined by scanning electron microscopy over a 22-week period. The normal gingiva and rostral two-thirds of the intermolar mucosa were covered by flat polygonal cells that had a regular honeycomb surface pattern of interconnecting micro-ridges, distinct cell boundaries and imprints of cells that had been desquamated. The caudal third of the intermolar mucosa in normal and NMU-treated hamsters was covered by soft-palate type mucosa whose smooth surfaced cells surrounded scattered fungiform-like papillae. In NMU-treated hamsters changes were more common in the rostral two-thirds of the intermolar mucosa than in the gingiva. At 10 weeks there were sessile and conical surface projections and saucer-shaped and conical epithelial-lined depressions. At 16 weeks these projections and depressions were larger and more numerous, and groups of conical projections formed papillomatous-like lesions. At 22 weeks the projections and depressions were further increased in number and size and there were distinct papillomas. At 10 and 16 weeks the entire epithelium showed cells, cell boundaries and cell imprints resembling those in the controls, except that there were defects or dilated intercellular spaces at the base of the conical depressions and some of the cells were thicker. Much of the 22-week epithelial had a similar structure, but in some areas that did not show the projections or depressions the cells varied in size and shape and were covered by elongated micro-ridges. Here the surface was irregular as were the cell boundaries. Examination of sections by light microscopy, both from these irregular areas and from areas that appeared normal by scanning electron microscopy, revealed that the deeper epithelial strata could be either normal, dysplastic or at times malignant. However, scanning electron microscopy failed to reveal dysplastic or malignant epithelium.

A scanning electron microscopic study of rete ridges in the cheek pouch of normal young, adult and aged Syrian hamsters

Cheek pouches were removed from BIO 87.20 male hamsters 4 weeks, 8 months or 18 months of age. One pouch from each animal was routinely processed for light microscopy. The epithelium and connective tissue of the remaining pouches were separated with EDTA and routinely processed for scanning electron microscopy. Two types of rete ridge were found: simple, consisting of a single epithelial ridge or blunt projection and complex, made up of multiple interconnecting ridges. The simple type predominated at 4 weeks (90%) but the complex type predominated at 8 (58%) and 18 months (73%). Although the 8- and 18-month pouches were significantly larger than the 4-week ones, the total number of rete ridges was similar at all ages. This, taken in association with the shift in type with age, suggests that the simple rete ridges develop into the complex ones. With increasing age more of the complex rete ridges took on the characteristics of touch domes. These changes in the shape of the rete ridges with age need to be taken into account in studies on experimentally altered cheek pouches so that they are not mistaken as pathological changes.

A light and scanning electron microscope study of epithelial thickenings and rete ridges in the adult hamster cheek pouch

Cheek pouches from 8 adult male BIO strain hamsters were removed; half of them were routinely processed for light microscopy. The epithelium and connective tissue of the remaining pouches were separated using EDTA. These tissues were routinely processed for scanning electron microscopy and their separated surfaces examined; after this, some were reprocessed for light microscopy. A total of 1200 sections were examined by light microscopy and of these, 414 had at least one area showing rete ridges. Scanning electron microscopy confirmed the presence of isolated areas of either single or multiple rete ridges on both the separated epithelial and connective tissue surfaces. The presence of isolated areas of rete ridge formation in normal adult hamster cheek pouch mucosa needs to be taken into account in studies on experimentally altered cheek pouches so that the ridges are not interpreted as being part of a pathological change.

Primary fixation of vervet monkey oral epithelium for ultrastructural investigation--SEM

Vervet monkey attached gingiva and alveolar mucosa was used to investigate the effect of primary fixative composition and osmolarity on the scanning electron microscope appearance and epithelial cell surface feature density. Primary fixation was obtained using 12 different fixatives with osmolarities varying between 320-2010mOsm followed by further standard SEM processing procedures. All primary fixatives investigated produced acceptably fixed oral epithelium for SEM study, showing all the morphologic features characteristic of either keratinized or non-keratinized oral tissue. Point counting revealed that the density of microvilli of attached gingiva epithelial cells when fixed at 2010mOsm was 72 +/- 8% of the cell surface area. This decreased to 40 +/- 5% when fixed at 320mOsm. Similarly the microplication density of the alveolar mucosa epithelial cells decreased from 70 +/- 5% at 2010mOsm to 43 +/- 7% at 320mOsm. Both these differences proved to be highly significant.

The morphology of keratohyalin granules in orthokeratotic and parakeratotic skin and oral mucosa

We compared morphologic features of keratohyalin granules (KHG) that were directly related to keratinization in oral mucosa (tongue, cheek, gums, palate; n = 4) with those in parakeratotic epidermis (psoriasis, n = 2; pityriasis rubra pilaris, n = 1; acute dermatitis, n = 1) and normal orthokeratotic epidermis. Among others, the ultrastructural features of globular KHG were observed in the cheek, nonspecialized tongue mucosa, and parakeratotic epidermis occurring in psoriasis, pityriasis rubra pilaris, and acute dermatitis, whereas gums and palate showed a mixture of characteristics, also resembling stellate KHG as seen in normal skin. From literature as well as from our studies, the impression was gained that globular KHG were found especially in quickly dividing epithelia and could easily be distinguished from the irregular or stellate KHG that were found in slowly dividing normal epidermis. Therefore, we studied keratinization features on days 3, 7, and 14 after autografting normal human skin (n = 4), thus inducing high cell turnover. Stellate KHG, present in granular cells of normal skin, were almost absent on the third day. Active cell division on the seventh day resulted in sparse keratohyalin formation inside globular granules of low electron density, whereas numerous, rather electron-translucent lipid droplets occurred in upper spinous and horny cells. These two phenomena seemed to be interrelated. After 14 days, round and increasingly electron-dense KHG were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental candidiasis in the hamster cheek pouch

Sixty-four adult male BIO 87.20 hamsters were divided into four equal groups. Animals in three groups had 1 ml of a thick aqueous suspension of either Candida albicans (ATCC 10261), Candida albicans (UO1) or Candida tropicalis (3100, Puna Culture Collection) placed in each of their cheek pouches. The fourth group were controls. Four animals from each group were killed 1, 2, 4 and 6 weeks following treatment. Specimens were removed from all left-cheek pouches and processed routinely for light microscopy. All animals treated with strain UO1 and 35 per cent of animals treated with either 10261 or 3100 strains exhibited changes. At 1 week, the epithelium had localized areas of neutrophilic leukocyte infiltration and some small discrete micro-abscesses. At 2 weeks, most micro-abscesses were larger. At 4 weeks, most micro-abscesses involved the more superficial epithelial layers. At 6 weeks, there were only a few superficial micro-abscesses. At 4 and 6 weeks, there were areas of thickened, often parakeratinized, stratum corneum. The connective tissue adjacent to the inflamed epithelium was infiltrated by varying numbers and types of chronic inflammatory cell. Hyphal invasion of the epithelium was not found. Thus the hamster cheek pouch is a suitable site for the study of experimental candidiasis. The occurrence of both an acute and chronic inflammatory response does not support the suggestion that the pouch is an immunologically-privileged site.

Touch domes and Merkel cells in hamster cheek pouch epithelium

Minute dome-shaped elevations on the epithelial surface of hamster buccal pouch were counted in full-thickness whole mounts of detached pouch epithelium. Domes were examined by light and electron microscopy. Each dome consisted of thickened epithelium containing numerous Merkel cells with associated unmyelinated terminal axons. The pouch domes have structural characteristics in common with Haarscheiben, or touch domes, described in hair-bearing skin in man and other mammals and must not be confused with focal hyperplastic or precancerous lesions.