Immunohistochemical localization of Toll-like receptor 2 in skin Langerhans' cells of striped dolphin (Stenella coeruleoalba).

The skin is the primary interface between the body and the environment, and has a central role in host defence. In the epidermis, Langerhans' cells form an interconnecting network of dendritic cells, that play a central role within inflammatory and immune responses of terrestrial and aquatic mammals, but few studies aimed at their characterization have been carried out in cetaceans, so far. Toll-like receptors are crucial players in the innate immune response to microbial invaders. These receptors are expressed on immune cells, such as monocytes, macrophages, dendritic cells, and granulocytes. The aim of this preliminary study was to describe the expression of Toll-like receptor 2 in a stranded striped dolphin (Stenella coeruleoalba) skin. Immunoreactive cells were predominantly found within the stratified squamous epithelium. Other Toll-like receptor 2 positive cells of varying morphology, were found, and may help to increase the knowledge on the interaction occurring between dolphins and the environment in which they live at their most crucial interface: the skin.

Neuronal intermediate filaments in the developing tongue of the frog Rana esculenta.

The expression of several neuronal intermediate filament (NIF) proteins was investigated in the tongue of metamorphosing tadpoles (stage 38-45 of Gosner) and in adult individuals of the frog, Rana esculenta by means of immunohistochemistry. Results showed that nerve fibres at early stages of tongue development expressed peripherin (a NIF protein usually found in differentiating neurones) as well as the light- and medium molecular weight NIF polypeptide subunits (NF-L and NF-M, respectively); in the adult frog, peripherin was still found in nerve fibres reaching the fungiform papilla together with NF-M, but NF-L immunoreactivity was absent therein. Clusters of epithelial cells expressing peripherin were found in the early developing tongue before differentiation of taste organs, and NF-L and NF-H immunoreactivities were present in basal (Merkel) cells of the adult frog taste disc. Results indicate that neurones innervating the adult frog's taste disc maintain a certain plasticity in their cytoskeleton and that neuronal-like cells are present in the undifferentiated and differentiated tongue epithelium possibly playing a role in the developing and mature taste organ.

Two generations of the tongue and gustatory organs in the development of Hynobius dunni Tago.

In the development of Hynobius dunni there are two consecutive generations of the tongue and two generations of gustatory organs (taste buds and taste disks). The anlage of the developing secondary tongue appears just in front of the free ending of the primary tongue beginning at the larval developmental stage 62. From stage 67, a gradual reduction in the anterior part of the gill skeleton that supports the primary tongue occurs as the developing secondary tongue replaces the primary one. The lining of the entire oropharyngeal cavity of larvae contains only gustatory organs of the taste bud (TB) type. In younger larvae, the sensory area of a TB has a diameter of between 10 and 13 microm, while in older larvae, TBs reach 16-18 microm in diameter. After metamorphosis, some gustatory organs in the secondary tongue with a sensory area of 26-36 microm in diameter appear. In older animals they may reach as much as 56-71 microm. In other regions of the oropharyngeal epithelium than the tongue, these organs have an ellipsoid shape with a major axis of about 50 microm. On the basis of the cytomorphological criteria established previously, these organs were designated as taste disks. Thus, the presence of two generations of gustatory organs is characteristic of some urodeles, as well as frogs.

Development of mucous cells in taste discs of anurans.

Differentiation of the lingual taste discs (TDs) was studied in tadpoles of Rana esculenta, Hyla arborea and Pelobatesfuscus by means of LM, TEM, and SEM. The process of differentiation of mucous cells (MCs) within a TD anlage was investigated subsequently from 39th to 46th Gosner's developmental stage. In R. esculenta and P. fuscus, the MCs are distinguishable in TD anlages not earlier than at the 42nd tadpole Gosner's stage. At that stage TDs anlages are covered by a single layer of ordinary epithelial cells. Starting from the stage 44, tips of TDs progressively open outside and free surfaces of MCs can be distinguished as an area with numerous microfolds. At developmental stages 45 and 46, numerous electron-dense secretory granules can be seen in the supranuclear cytoplasm of MCs. The presence of mucopolysaccharides in H. arborea and P. fuscus was observed from the 44th-45th tadpole developmental stage.

The development of the tongue and morphological and cytological changes in taste discs of Rana esculenta.

From the 38th developmental stage of the tadpole of Rana esculenta the process of tongue formation consists in the fast growth of the lining of the oral cavity floor anteriorly and faucially. This process is accompanied by the development of taste organs on the dorsal side of the tongue. At developmental stages 39-42 taste disc anlages are covered by a layer of ordinary epithelial cells. At these stages, in some cells of a taste disc single synaptic-like vesicles with an electron-dense core appear. Apart from that, as early as at stage 42 differentiation of the cells of a taste disc can be observed at the ultrastructural level. It is only at the 44th stage that all cell types characteristic for the mature TD can be distinguished in TEM (i.e., taste cells, basal cells and three kinds of associate cells: mucous, wing and sustentacular). Starting from that stage changes in the cell membrane can be observed indicating the presence of afferent synaptic junctions. The antibody used in the experiment was raised against neuron-specific enolase (NSE). At each of the developmental stages investigated (38, 42, 45) nerve fibres within the connective tissue beneath the epithelium of a taste disc anlage were immunopositive for NSE. From stage 42 onwards neural elements present in the basal part of the epithelium of a taste disc anlage were also NSE-positive. Basal cells did not show immuno-reactivity for NSE at any of the developmental stages investigated.

Morphological differentiation of taste organs in the ontogeny of Salamandra salamandra.

Morphological studies presented here provide additional cytological evidence that in the postnatal development of Salamandra salamandra there are two successive generations of taste organs: premetamorphic taste buds (TBs) in larval forms and taste disks (TDs) in postmetamorphic animals. The TBs have been found in the epithelium of the whole oropharyngeal cavity of larval forms, while in adults TDs appear only at the end of metamorphosis. The TDs can be papillary (or fungiform) on the soft (secondary) tongue and non-papillary outside the tongue. Two main cyto-morphological criteria distinguishing TDs from TBs have been established: (1) high differentiation of "nonsensory" components of a taste organ into several kinds of cells (often named "associate cells")--at least mucous cells and, separating them, wing cells; (2) a considerably larger area of the sensory epithelium than that in TBs, as the consequence of the large size of the mucous cells. In contrast to TDs each TB consists of longitudinally elongated supporting cells and taste cells, as well as of horizontally oriented basal cells, adjacent to the basement membrane. The sensory area in TBs measures 10-12 microm in diameter, while that in TDs has diameter of 45-90 microm. The anlage of the secondary tongue appears as a small folding of the floor epithelium just in front to the tip of the primary tongue in larvae 3 cm long, and is definitely formed in an animal with body length of about 6 cm.

Ultrastructure of premetamorphic taste organs of the Bombina variegata.

Ultrastructural studies of taste organs in tadpoles of Bombina variegata indicate that these are taste buds (TBs). They occur in the apical parts of papillae of the mouth cavity lining. Each taste bud consists of taste cells and supporting cells; no basal cells were found. In the sensory area of taste bud there are two types of sensory cells: cells with a tuft of short (approximately 1.5 m) microvilli and cells with a single, longer (up to 3.7 microns) process, definitely longer than in TBs of other studied species of Anura. Fairly often, twin TBs were observed.

Development of taste organs in Rana temporaria. Transmission and scanning electron microscopic study.

In tadpoles of Rana temporaria two successive generations of taste organs: taste buds (TBs) and taste disks were studied. The TBs are located in the apices of oral premetamorphic papillae. Each TB consists of vertically elongated receptor cells (probably taste) and supporting cells. No basal (Merkel) cells were observed there. Morphologically, two types of receptor cells have been distinguished in a TB. Complete synaptic structures were observed in the TBs between the 30th and 41st of Gosner's (1960) developmental stages, though synaptic vesicles occur already at stage 26. The taste disks consist of taste cells, supporting cells and basal cells. Dense-core synaptic vesicles occur in the gustatory cells at stage 41, but complete synaptic structures were not observed earlier than at stage 45. Synaptic junctions observed at some of the gustatory cells seem to be reciprocal (bidirectional).