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L Alibardi

Publications and source records attributed to L Alibardi.

48 records · Page 3Linked to original sources
PubMed1995

Development of the axial cartilaginous skeleton in the regenerating tail of lizards.

In order to study the pattern of growth of regenerating cartilage, H3-thymidine was injected in individuals of the lizards Anolis carolinensis and Lampropholis delicata during advanced stages of tail regeneration. Light and electron microscopic autoradiographical analysis showed that the regenerating cartilaginous tube was mostly derived from the interstitial proliferation of chondroblasts. Appositional growth is limited during the initial stages of cartilage formation. Later, after the differentiation of an inner and outer perichondrium, a few cells were added to the cartilaginous tube while cellular degeneration of the calcifying areas was in progress. In this way a constant diameter of the cartilaginous tube was maintained. In order to study the rate of production of matrix protein (collagen), H3-proline was administered to other samples of Lampropholis. To the best of the author's knowledge this was done for the first time in the cartilage of a reptiles. The tracier was mostly localized in the apical-intermediate cartilage and one hour postinjection it was mostly concentrated in the ergastoplasm around the Golgi apparatus and its secretory vesicles. Three hours after the injection of H3-proline some of the tracier was found in the cytoplasm of chondrocytes and in the extracellular matrix.

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PubMed1995

Muscle differentiation and morphogenesis in the regenerating tail of lizards.

The differentiation of muscles in the lizards Anolis and Lampropholis with tails that had regenerated for 21-50 d was investigated by light and electron microscope autoradiography using tritiated thymidine. At the apex of the regenerating tail, groups of 4-8 myoblasts of the promuscle aggregates fused to produce bundles of myotubes whose multiple labelled and unlabelled nuclei appeared to be distributed at random. The formation of the first myotubes and their growth is responsible for the formation of the myotome primordia and their separation from the intermuscular connective myosepta. More nuclei were added with the lengthening of the myotubes--up to 14-18 nuclei in the oldest proximal myotubes. At 4-5 h after injection labelled nuclei were found outside the myotubes while at 2-6 d after injection many labelled nuclei were observed in the myotubes, particularly near the two ends of the myotubular sarcoplasm contacting the myoseptum. This change from the initial distribution suggests that the growth of the myotubes takes place mostly at their terminals. There is an apparent correlation between the number of nuclei and the final length of the myotubes and myotome. The insertion of fibres with a similar number of nuclei and lengths into the pinnated connective myoseptum of the original musculature, the autotomy plane, probably determines the wave-like shape of the muscles within the regenerated myotomes.

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PubMed1994

H3-thymidine labeled cerebrospinal fluid contacting cells in the regenerating caudal spinal cord of the lizard Lampropholis.

Australian scincid lizards (Lampropholis) were injected with a single dose of H3-thymidine during the early stages of tail regeneration in order to study later a possible differentiation of neurons and glial cells within the regenerating spinal cord. After 5 hours post-injection only electrondense or pale ependymal cells took up H3-thymidine. Light and electron microscopic analysis of later stages, 6, 12 and 20 days post-injection, revealed that labeled pale cells were occasionally recognizable 12-20 days post-injection. Many pale unlabeled and a few labeled cells contacted the central canal of the spinal cord and appeared as cerebrospinal fluid contacting cells. The electron microscope showed the presence of stereocilia in the apical cytoplasm of these pale cells, a typical characteristic of cerebrospinal fluid contacting neurons. After 12-20 days post-injection, among ependymal cells rare pale cells containing intermediate filaments were labeled. Other pale cells represented intermediate stages of differentiation between ependymal and neural or glial cells. Differentiated medium-high electrondense ependymal tanicytes were also labeled 6, 12 and 20 days post-injection. This analysis showed that a limited regeneration of cerebrospinal fluid contacting neurons occurs locally in the caudal spinal cord of the scincid lizard Lampropholis.

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PubMed1994

Modifications of the dermis during scale regeneration in the lizard tail.

During scale morphogenesis in the regenerating tail of lizards (Anolis and Lampropholis) the structure of the dermis undergoes changes in relation to the ingrowth of epidermal papillae to form the new scales. Cell proliferation in the dermis, as revealed by the uptake of 3H-thymidine, is high in the prescaling region of the regenerating tail but lower than the proliferation in the epidermis. Under the epidermis of the scaling region dermal cell proliferation rapidly drops down under the distal (apical) and proximal (caudal) sides of the infolding epidermal papillae. Dermal fibroblasts take up 3H-proline in high amounts, especially in the forming deep dermal layer, where many collagen fibrils are laid down forming dense connective. Electron microscopic study revealed that "anchoring filaments" link the basement membrane of the epidermis with the deep dermis, in particular in the sinking hinge region. As a result of the higher proliferation of the epidermis with respect to the dermis (heterochrony) and the presence of dermo-epithelial "anchoring filaments", the superficial laminar epidermis sinks into the dermis to produce new scales. The epidermal downpushing is evidenced by a characteristic distortion of the dermal fibrils under the distal and the proximal sides, and in the hinge region of the forming scales.

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PubMed1994

Fine autoradiographical study on scale morphogenesis in the regenerating tail of lizards.

Regenerating scales in lizards originate as pockets in the epidermis instead of epidermal elevations as during embryo development. The morphogenesis of scales in the regenerating tail of the lizards. Anolis and Lamphropholis was studied after peritoneal injection of 3H-thymidine. The tracer was localized in the forming epidermis after progressive post-injection times, by means of autoradiography on plastic sections. After 4-5 hours post-injection of 3H-thymidine, the radioactivity was localized in the basal layer. After 2 to 4 days post-injection labelled cells were seen in the basal and intermediate spinosus layers but not in the uppermost keratinizing layers. Labelled cells were seen in the differentiating cornifying layers (pre-beta and pre-alpha) 6-8 days post-injection. At 12-14 days post-injection almost no radioactivity was seen in the basal layer or in the living part of the epidermis. A few labelled cells were present in the dense keratinizing layers of the sloughing wound and interscale lacunar layers. This study shows that scale formation and morphogenesis in the regenerating tail is brought about by a localized cell proliferation along the regenerating epidermis. In the forming scales the percentage of labelled cells in the distal side (future dorsal part of the new scale) is much higher than in the proximal side (the future ventral side of the scale), so that overlapped scales are generated.

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PubMed1993

3H-GABA administration during tail regeneration of lizards and autoradiographical localization.

Thirteen lizards (Anolis carolinensis and Scincella lateralis) were injected with 3H-GABA (tritiated gamma-aminobutyric acid) in order to study its localization inside the regenerating tail spinal cord (SC) by means of light and electron microscopic autoradiography. One and three hours after intraperitoneal injection, the radioactivity was essentially localized in regenerating nerves and pale cells, mostly contacting the central canal of the SC as typical Cerebrospinal-Fluid-Contacting-Neurons (CSFCNs). A smaller number of pale cells did not take up 3H-GABA and some of them appeared to be degenerating. Weaker radioactivity in regenerating SC was observed 6 hours post injection. Among non neural tissues, cells of the regenerating blastema, of the meninges and capillaries surrounding the regenerating SC, showed lower 3H-GABA uptake. This indicates that a certain amount of injected 3H-GABA has been converted to other metabolites. No 3H-GABA uptake was detected 1 or 6 hours post injection in normal SC and brain both in grey and white matter. This research indicates that CSFCNs of the regenerating tail in lizards uptake the aminoacid GABA or derived aminoacids, suggesting these cells subserve a high metabolic activity and may be GABA-ergic

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PubMed1992

Fine structure of cells in the young regenerating spinal cord of the lizard Anolis carolinensis after H3-thymidine administration.

H3-thymidine was injected in a single dose into adult lizards Anolis carolinensis during early stages of tail regeneration when the new tail measured in length 2-5 mm (about 3 weeks). Electron microscopic autoradiography revealed that in the regenerating spinal cord three different cell types were recognizable four hours post-injection. By far the most common type was the ependymal cell. Ependymal or roundish cells with clear electron-density or storing bundles of intermediate filaments were occasionally found. A second rarer, cell type devoid of intermediate filaments was a pale round cell, often highly labelled. This cell showed a very poor ultrastructural differentiation and probably represents the precursor of the few neurons and glial cells observed in older stages of regeneration. The third type was a neuroblast at different degrees of differentiation and did not uptake H3-thymidine revealing it was a post-mitotic cell. Despite the relatively advanced ultrastructural differentiation of these neurons, synapses were rarely seen after three weeks of SC regeneration in Anolis.

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PubMed1990

Fine structure of regenerating caudal spinal cord in adult tuatara (Sphenodon punctatus).

A report on the presence of cerebrospinal fluid contacting neurons (CSFCN) inside the regenerating caudal spinal cord of adult specimens of the tuatara Sphenodon punctatus is given. The cells in question are easily distinguished from amongst ependymal tanicytes of the regenerating cord. Large granules of high electron density are particularly common in these neural cells which generally show clear cytoplasm of low electron density. The ultrastructural findings strongly support the idea of a secretory activity of these neurons directed toward the central canal.

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PubMed1990

Fine observation on nerves colonizing the regenerating tail of the lizard Podarcis sicula.

During the regeneration of lizard tail, nerves sprouting from ganglia and the spinal cord invade the blastema as far as the apical epidermis. Electron microscopical observations reveal axons storing dense granules (dg) and dense core vesicles (dcv) which are concentrated in nerve terminals or in axoplasmatic regions. In the regenerating spinal cord (SC) these terminals resemble aminergic-peptidergic endings and grow as far as the distal portion of the SC, which is made up of irregularly arranged ependymal cells. Some axons storing dcv contact blastematic cells and other nerve terminals show a plasma membrane incomplete or broken. Whether this latter aspect is due to fixation artifacts or physiological rupture is unknown. Nerves containing dcv and a few dg also originate from spinal ganglia innervating the regenerating tail. The accumulation of material into these endings is probably slow and a possible trophic influence on the regeneration of lizard tail is discussed.

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PubMed1989

Comparative fine structure of the axial skeleton inside the regenerated tail of some lizard species and the tuatara (Sphenodon punctatus).

The regenerated tail of the New Zealand gecko Hoplodactylus maculatus is equipped with an elastic cartilaginous tube as skeletal axis. Other lizard species and Sphenodon punctatus possess variably developed hyaline cartilaginous tubes. Moreover, H. maculatus enhances the functional performance of its tail by long elastic fibres, which are arranged all around the central regenerated spinal cord. The different characteristics of the regenerated skeleton could be related to the different environments that the species studied occupy in nature.

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PubMed1989

Differentiation of liquor contacting neurons in the regenerating spinal cord of the newt Triturus.

This paper reports a detailed electron microscopic study of the ventricular cells in the growing spinal cord during the first two months of tail regeneration in Triturus vulgaris and T. cristatus. In the proliferating ependyma some cells undergo a neural differentiation in order to produce "Cerebro-Spinal-Fluid-Contacting-Neurons (CSFCNs). These round or pear-like cells store dense core vesicles, 80-100 nm in diameter, and show less electron-density than ependymal elements. The stereociliar apparatus is the last cytological differentiation of these elements and after two months of regeneration, synapse-like endings were occasionally found.

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