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M Whitear

Publications and source records attributed to M Whitear.

At least 19 recordsLinked to original sources
PubMed1993

Spinal and facial innervation of the skin in the gadid fish Ciliata mustela (Teleostei).

The pattern of innervation of the skin of the rockling Ciliata mustela was investigated to sort out spinal from facial nerve innervation of cutaneous chemosensory and mechanosensory systems. This fish has a variety of appendages with different functional sensory specializations, i.e., the chin barbel, pelvic fin, anterior dorsal fin, and dorsal trunk skin. The carbocyanine dye, diI, was applied to nerve stumps in dissected aldehyde-fixed tissue. In the case of the chin barbel, the dye was applied to both the trigeminal and facial nerve components. In the other cases, the dye was applied either selectively to the spinal nerves, to the facial nerves, or to both components. In the chin barbel, diI labeled nerve fibers associated with taste buds (TBs) and solitary chemosensory cells (SCCs) as well as relatively blunt free nerve endings, which closely approach the epidermal surface. In the pelvic fin, anterior dorsal fin, and dorsal trunk skin, taste buds, solitary chemosensory cells, and their innervation were labeled only after diI was applied to the facial nerve stumps. Application of diI to spinal nerves labeled delicate, free nerve endings and nerve fibers associated with small cells deep in the epidermis with features characteristic of Merkel cells. Transmission electron microscopy supports these results; after denervation of the facial component of the anterior dorsal fin, synaptic contacts with Merkel cells remained intact, whereas the synapses with the SCCs vanished.

Animals↗
PubMed1990

Collagen turnover in regenerating barbels of a catfish.

In regenerating barbels of Heteropneustes fossilis, membrane-enclosed collagen fibrils, some within lysosomes, are found in fibroblasts, in old connective tissue at the wound site and also in the fibroblasts of the newly-formed core of the regenerate. The implication is that tissue remodelling can involve fibroblasts in phagocytosis of recently formed collagen fibrils. Cytological evidence suggests that individual fibroblasts are capable of synthesis and phagocytosis simultaneously.

Animals↗
PubMed1990

Cellular elements of the dermis and collagen remodelling during larval life of anurans.

The differentiation of the collagenous dermis has been followed by electron microscopy in larvae of three anuran species. Events can be divided into five phases, depending on the organization of the cellular elements. Initial secretion of collagen appears to be from the epidermis but fibroblasts are present from early stages. Apart from secretion, there is phagocytosis of fibrils by fibroblasts, seen most frequently when the operculum is formed and at metamorphosis. In most larval stages, the dermis consists of regular plies of collagen fibrils, penetrated by processes from underlying fibroblasts and crossed by nerves, with a cellular layer defining the deep face. In Rana, these cells contain enormous vacuoles and have been called "compartmented cells", but the vacuoles are absent in Bufo and Xenopus. Just before metamorphosis, fibroblasts and chromatophores migrate into the dermis, and establish a stratum laxum. A few plies of larval collagen fibrils are left under the epidermis, the bulk of the larval dermis becomes the stratum compactum. During larval life, the hypodermis contains chromatophores, blood capillaries and wandering leucocytes. The dermis gains a blood circulation only at metamorphosis, when subdermal lymph sacs and vertical smooth muscles are established.

Animals↗
PubMed1989

Merkel cells in lower vertebrates.

In lower vertebrates, Merkel cells are widely distributed in the epidermis. Dense-cored specific granules similar to those in mammalian Merkel cells are found in amphibians, dipnoans and lampreys, but only in some species of teleosts, others having few and small-cored vesicles. The characteristic microvilli are found in all these groups, but their number and disposition vary. In amphibians a Merkel cell is associated with a single nerve fibre, known to be mechanoreceptive, which forms reciprocal synapses at a varicosity against the cell and continues on in the epidermis. In lampreys most of the specific granules are grouped around spur-like processes of a nerve fibre which has other branches in the epidermis. In teleosts, one or more nerve fibres wind around a Merkel cell; synaptic modifications are variable. Fluorescence histochemistry shows the presence of quinacrine, neuron-specific enolase, met-enkephalin and serotonin in Merkel cells of some species that have been investigated, but experimental results from amphibians suggest that the receptive element may be the nerve fibre. The Merkel cell can act as a target for growing nerve fibres, but other functions, especially connected with the synapses, most of which are morphologically afferent, remain unknown. Merkel cells do not require trophic maintenance from the nerve. The basal cells of taste buds in teleosts and amphibians have been compared to Merkel cells, but are not identical, although in frogs the basal cells have dense-cored vesicles. In teleosts, both cell types qualify as paraneurons, but there are considerable differences in their cytology especially in the form of the synaptic specializations.

Amphibians↗
PubMed1988

Chemosensory anterior dorsal fin in rocklings (Gaidropsarus and Ciliata, Teleostei, Gadidae): somatotopic representation of the ramus recurrens facialis as revealed by transganglionic transport of HRP.

The anterior dorsal fin in rocklings consists of a fringe of 50-80 delicate, vibratile rays, which are densely beset with epidermal chemosensory cells. The innervation of these cells is from the dorsal branch of the recurrent facial nerve, which also innervates all other fins and the skin of the trunk. This nerve carries at least three classes of fibres: small (0.5-1.5 micron in diameter), medium (1.5-4 micron), and large (greater than 4 micron). Approximately 12,000 small and weakly myelinated nerve fibres from the recurrent facial nerve innervate the anterior dorsal fin organ. Application of HRP at different locations of the recurrent facial nerve labelled three different sizes of sensory perikarya within the geniculate ganglion--small (6-15 micron in diameter), medium (18-24 micron), and large (greater than 25 micron)--which corresponds to the different size classes of fibres present within the nerve. Retrograde transganglionic transport of HRP revealed somatotopy within the brainstem facial lobe: the delicate nerve fibres innervating the chemosensory anterior dorsal fin terminate exclusively in a distinct, dorsal portion of the facial lobe. Fibres innervating the posterior dorsal fin, the anal and caudal fins, as well as the skin of the trunk terminate within caudal and dorsal areas of the ventral facial lobe; pectoral and pelvic fins are represented in the ventral and caudal portions of the ventral facial lobe. Innervation by a distinct type of fibre and exclusive representation within a distinct, dorsal part of the facial lobe may indicate a peculiar biological role in the anterior dorsal fin chemosensory organ in the rocklings.

Animals↗
PubMed1986

Genesis and regression of the figures of Eberth and occurrence of cytokeratin aggregates in the epidermis of anuran larvae.

In tadpoles of Rana temporaria, Bufo bufo and Xenopus laevis the development of the massive skeins of tonofilaments (cytokeratin intermediate filaments) that form the figures of Eberth follows a similar sequence in all species studied. Increase in the number of filaments is preceded by increase in polyribosomes and rER in the basal layer cells of the epidermis. A filamentous zone develops proximally in the cells concurrently with hemidesmosomes, which assume the typical larval bobbin form as the skeins occupy more of the cytoplasm. The figures of Eberth are at maximum development throughout mid-larval life. The first signs of regression appear before the climax stages, when aggregates of cytokeratin material are found among the filaments of the skeins. Such cytokeratin aggregates have previously been reported only from mitotic mammalian cultured or tumour cells, or in experimental situations. At metamorphic climax they are numerous in the basal layer cells and in some other cells of the epidermis, even when not dividing. This condition persists into the postmetamorphic stage when the figures of Eberth and the bobbin-type hemidesmosomes have gone. The formation of cytokeratin aggregates can be enhanced by chilling the animals before fixation, but does not depend on a drop in temperature, and takes place even if fixation is carried out at room temperature.

Animals↗
PubMed1983

Fine structure of the club cells in the skin of ostariophysan fish.

The club cells of the epidermis of a number of species of cyprinoid and siluroid fish have been examined by electron microscopy. As reported by previous authors, most cellular organelles are confined to a perinuclear zone. The outer cytoplasm, hitherto described as fibrillar or vesicular, is characterized by the presence of filaments of approximately 10 nm diameter, which have a spiral configuration. These helices are arranged in random directions. The coil diameter is about 50 nm, but the pitch varies widely, between species and even sometimes in different examples in a single specimen. The outer cytoplasm also contains amorphous electron-dense material, some vesicular profiles, especially at the periphery of the cell, and some ribosomes. Ribosomes are more numerous in the small club cells deep in the epidermis which are presumed to be relatively juvenile. The coiling filaments are associated with desmosome plaques, like the tonofilaments of the epithelial cells. A further resemblance to tonofilaments was noted in two species of topical catfish, where chilling the tissue induced felting of the tonofilaments and also of the helical filaments of the club cells, which aggregated to form a capsule of electron-dense material surrounding the perinuclear cytoplasm. The functions of club cells are briefly not yet experimentally established, and that the recognition of specific pheromones in ostariophysan fish is a secondary phenomenon. There is evidence suggesting that is some circumstances a club cell may discharge part of the outer cytoplasm, and then be re-enclosed in the epidermis. In damaged epidermis, club cells occasionally become confluent above the basal layers of epithelial cells.

Animals↗
PubMed1981

Fine structure of Merkel cells in lampreys.

The structure of Merkel cells occurring in the epidermis of adult and larval stages of Lampetra spp. is described; it is comparable to that reported from the gnathostome classes. The cells bear microvilli, grouped on the distal and proximal aspects, and are associated with sparsely branching and varicose nerve fibres. One branch of the neurite bears a spur-like process which indents the proximal side of the Merkel cell. Most of the specific Merkel granules are situated in the vicinity of this neurite projection; the cell membrane adjacent to the tip of the spur process bears structures resembling presynaptic densities. Occasionally, desmosome-like junctions are found between the neurite and the Merkel cell.

Animals↗
PubMed1981

Bar synapses in the end buds of lamprey skin.

The end buds of lamprey epidermis have been considered to be similar to taste buds, but the synapses on the receptor cells are of the type with a dense mass surrounded by lucent vesicles, which is not found in gustatory cells. It is suggested that the end buds may belong to the lateralis sensory system and be involved in the light sensitivity of lamprey skin.

Animals↗
PubMed1981

Sacciform cells in the skin of teleost fish.

The fine structure of sacciform gland cells of the epidermis is described in the number of species of teleost fish. In some of these the cell type had either not been found, or not recognized as such, before. Some histological and histochemical results are also reported. Despite considerable differences in the histochemistry and in the morphology of the sacciform cells over the range of species studied, some features of the fine structure are constant and can be used as diagnostic characters. The nucleus is peripheral, and there is a large membrane-limited lumen, into which the secretion is released from membrane-bounded vacuoles at the margin of the cytoplasm. It is probable that the secretion originates mainly in channels of endoplasmic reticulum which become swollen to form the vacuoles. Most sacciform cells open at the surface of the skin by an apical pore, but some have not been seen to open. The classification of the various unicellular glands of teleosts is discussed and it is concluded that attempts to categorise them by the nature of the secretion alone are unsatisfactory.

Animals↗
PubMed1981

Secretion in the epidermis of polypteriform fish.

Calamoichthys calabaricus possesses four types of epidermal secretory cell. Mucus is produced by the superficial epithelial cells and by goblet cells. Electron microscopical studies show that the other two types of unicellular gland present are structurally similar to the club cells and to the sacciform cells of teleost fish. The outer cytoplasm of the club cells contains filaments, coiled in spirals, which can be compared to the helical filaments previously described in club cells of eels, although they are less regularly arranged. Spiral filaments similar to those of Calamoichthys can be detected in some ostariophysan species studied by electron microscopy. The homologies of so-called club cells in various fishes are discussed. The lampreys and gadoids are now known not to have club cells; in eels the club cells contain a secretory vacuole in addition to cytoplasm with helical filaments. The club cells of ostariophysans have been distinguished, by some authors, as "alarm substance cells", but their cytological characteristics are so close to those of the club cells of Calamoichthys that, morphologically, they must be considered homologous. The sacciform cells are a separate type of unicellular gland; their fine structure in Calamoichthys is closely similar to that reported from certain teleost fish. In spite of the cell diversity, polypterid skin provides a model for a type of epidermis which is primitive in the actinopterygii.

Animals↗
PubMed1979

Keratinization of fish skin with special reference to the catfish Bagarius bagarius.

Histochemical reactions indicating keratinization have previously been demonstrated in parts of the epidermis of Bagarius bagarius. Fluorescence histochemistry and electron microscopy have now confirmed these results. Elevated areas of the epidermis are capped by a layer of dead cells with altered contents. On the outer aspect of these cells a dense layer, 18 nm thick, beneath the plasma membrane corresponds to the resistant envelope found in keratinized cells in tetrapod vertebrates. In Bagarius this layer does not extend to all faces of the keratinized cells, but a similar envelope has been detected in two other sites of piscine keratinized epidermis investigated, namely in the breeding tubercles of Phoxinus phoxinus and in the teeth of Lampetral fluviatilis. In the elevated areas of Bagarius-epidermis, the epithelial cells undergo progressive changes in cytoplasmic organization as they ;ecome more superficial. The second tier from the surface is sealed by tight junctions and is separated from the overlying keratinized cells by a sub-corneal space resembling that found in keratinized amphibian epidermis. Histochemical evidence of a high lipid content in the outer layers of the epidermis correlates with the presence of lipid inclusions and lamellated membranous profiles in the material studied by electron microscopy. Histochemical results show that the fin skin of Blennius pholis is not keratinized, but secretes a cuticle, histochemically reactive for both proteins and glycoproteins.

Animals↗
PubMed1978

Quinacrine fluorescence of Merkel cells in Xenopus laevis.

It has been shown by electron microscopy that, in Xenopus laevis, Merkel cells are usually situated near the ducts of the skin glands. Cells which fluorescence in ultra-violet light after treatment of the skin with quinacrine can be identified with these Merkel cells by their position, shape and size. The method indicates the presence of purine nucleotides, probably ATP. This result is consistent with the view that "large opaque vesicles" are sites of ATP storage.

Animals↗
PubMed1977

On the occurrence of Merkel cells in the epidermis of teleost fishes.

The ultrastructure of a differentiated cell type in the epidermis of two species of teleost fish, Ictalurus melas and Phoxinus phoxinus, is described. This cell type has a synaptic association with nerve fibres, microvillus-like peripheral processes, and membrane-bounded inclusions, which together are the diagnostic features of the Merkel cells of tetrapod vertebrates. Other cytoplasmic features are shared with the epithelial cells. The appearance of the membrane-bounded granules depends on the fixative used; after fixation with glutaraldehyde the granules are of a size and electron-density comparable to that found in tetrapod Merkel cells, but after fixing in osmium tetroxide the granules are inconspicuous.

Animals↗
PubMed1976

Identification of the epidermal "Stiftchenzellen" of frog tadpoles by electron microscopy.

Differentiated surface epidermal cells observed in the skin of tadpoles of Rana temporaria by electron microscopy have been identified with the Stiftchenzellen originally described by Kölliker in 1885. The cells have apical microvilli or a single apical projection and appear to have synaptic associations with nerve fibres in the epidermis. The distribution, dimensions and structure of the cells are in agreement with descriptions from le cells are sensory in nature. In addition, there are fine structural resemblances to the gustatory cells of fish and of amphibians which suggest that the Stiftchenzellen are chemoreceptors.

Animals↗
PubMed1976

Apical secretion from taste bud and other epithelial cells in amphibians.

Taste buds of the axolotl, Ambystoma mexicanum, contain cells, previously undescribed in this species, which have a long apical process, and are similar to the Type III cells of mammalian taste buds, and to the gustatory cells in fish. In the supporting cells, there is evidence of periodic decapitation, in addition to secretion by exocytosis. Bilaminar fragments, which are leaf-shaped bodies formed of two dense laminae separated by a lucent gap, protrude from the apical microvilli of the supporting cells and are found detached in the extracellular secreted layer. Their form and dimensions suggest that they represent secreted lipo-protein material. Similar bilaminar fragments have been seen, in much smaller numbers, on some other epithelial cells in amphibians, and in fish. A unique case, in which rough endoplasmic reticulum was found in the extracellular layer of the axolotl oral epithelium, is reported; it had apparently been ejected from the cell. It is suggested that the axolotl produces a copious secretion at the taste bud pore, in order to wash the surface, and that the bilaminar fragments represent material aiding this cleansing process. The condition in the axolotl is compared with that in some other species, particularly Rana temporaria.

Ambystoma↗
PubMed1975

Venomous fish.

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Animals↗