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Biomedical subjects

M Ledda

Publications and source records attributed to M Ledda.

At least 37 records · Page 2Linked to original sources
PubMed1999

Amount and distribution of lipofuscin in nerve and satellite cells from spinal ganglia of young adult and aged rabbits.

The quantitative aspects of the age-related accumulation of lipofuscin were studied in the rabbit spinal ganglia by stereological methods using the electron microscope. Both neurons and their associated satellite cells were examined. In neurons, the shape and structure of lipofuscin bodies differed in young adults (12-months-old) compared to aged rabbits (79-months-old), whereas substantial changes were not observed in satellite cells. Both in nerve and satellite cells, lipofuscin bodies were scattered singly in young adults, but were often clustered in old animals. Lipofuscin occupied an average of 0.36% of neuronal perikaryal volume in the young adults and 2.55% in the aged rabbits; these percentages are much lower than those observed in the same neurons of other species. In the satellite cells, the corresponding values were 0.29% and 2.02%. In the young adults, the mean size of lipofuscin bodies was significantly greater in neurons than in satellite cells; the size of these bodies increased with age by about 2.7 times in neurons and by about 1.7 times in satellite cells. Consequently, in the old rabbits the mean size of lipofuscin bodies was about 2.2 times greater in neurons than in satellite cells. It has been suggested that lipofuscin bodies are transferred from the neuronal perikaryon to the surrounding satellite cells and then removed via the capillaries. However, the present findings suggest that lipofuscin located in satellite cells represents pigment formed by these cells rather than being transferred from neuronal perikaryon. It would appear that the age-related accumulation of lipofuscin in the rabbit spinal ganglia has little effect on neuronal metabolism.

Aging↗
PubMed1998

Age-related decrease in the overall extent of perikaryal projections in rabbit spinal ganglion neurons.

The overall extent of the perikaryal projections of sensory neurons from spinal ganglia of young adult and aged rabbits was estimated by a stereological method using the electron microscope. The extent of perikaryal projections was significantly smaller in the aged animals. This age-related decrease did not seem to depend on factors intrinsic to the neuron, but on the absence of a satellite cell covering over extensive portions of the nerve cell body surface. This decrease may influence the organization of the subplasmalemmal cytoskeleton, metabolic exchange between the nerve cell body and its environment and perhaps also neuronal metabolism.

Aging↗
PubMed1997

Age-related decrease of the perineuronal satellite cell number in the rabbit spinal ganglia.

This study was undertaken to establish whether a change in the perineuronal satellite cell number contributes to the age-related reduction of the volume ratio between the perineuronal glial sheaths and their associated nerve cell bodies, observed to occur in rabbit spinal ganglia. The volumes of the nerve cell bodies and the numbers of the related satellite cell nuclei were estimated on serial semithin sections from young adult and old rabbits. As satellite cells are mononucleate, the number of the nuclei corresponds to that of these cells. The satellite cell sheaths in both age groups were also examined under the electron microscope. The mean number of satellite cells was significantly smaller in the aged animals than in the young adults although the mean volume of the nerve cell bodies was significantly larger in the former. Cytoplasmic vacuoles, invaginations of the connective tissue and autophagic vacuoles were more frequent in the old rabbits. Satellite cells with pyknotic nuclei and remnants of degenerated satellite cells were only found in aged animals, although rather rarely. The decrease in the satellite cell number is one of the mechanisms by which the age-related reduction of the volume ratio between the perineuronal glial sheaths and their associated nerve cell bodies takes place. The decrease in the satellite cell number seems to occur, at least in part, through cell degeneration. However, other mechanisms (e.g., detachment of satellite cells from the perineuronal sheaths) cannot be excluded. Since satellite cells play a role in neuronal support, the significant decrease in their number probably has negative consequences for neuronal activity.

Aging↗
PubMed1997

Cell body volume of spinal ganglion neurons: estimation by three different methods.

We estimated the mean volumes of two series of nerve cell bodies, one from rabbit and one from rat spinal ganglia by three different methods: a procedure we devised 25 years ago (the circle-fitting method), one of the new stereological methods (the nucleator method) and the method of serial sectioning--the most direct and accurate procedure presently available for estimating cell size. In the case of the rabbit, in which most spinal ganglion neurons have a single nucleolus, the mean volumes estimated by the first two methods are closely similar and deviate by less than 2% from the mean obtained by serial sectioning. In the case of the rat, in which approximately half of the spinal ganglion neurons have more than one nucleolus, the mean volumes estimated by the first two methods are again closely similar, but deviate by about 12% from the mean obtained by serial sectioning. These findings show that: a) both the nucleator method and the circle-fitting procedure are more accurate when applied to neurons with a single nucleolus; b) if certain conditions are respected, not all the methods previously used to estimate cell size give biased results. However, the new stereological procedures are easier and quicker to use than the earlier methods. These findings also show that our previous results obtained by the circle-fitting method are to be considered valid.

Animals↗
PubMed1996

Ultrastructural localization of actin in the cell body of rat spinal ganglion neurons.

We used phalloidin staining and immunocytochemistry at the light and electron microscope level to determine the localization of actin in the cell bodies of rat spinal ganglion neurons. The results show that actin is mostly concentrated along the periphery of the neuronal perikaryon, including the perikaryal projections. This localization places actin in a strategic position to be influenced by incoming signals and to produce mechanical tensions able to shape the perikaryal surface.

Actins↗
PubMed1996

Age-related reduction of the satellite cell sheath around spinal ganglion neurons in the rabbit.

The volumes of the nerve cell bodies and those of the enveloping satellite cell sheaths from spinal ganglia of young adult and aged rabbits were determined by morphometric methods using the electron microscope. The mean volume of the nerve cell bodies was greater in the old rabbits than in young adults; this is probably related to the larger body size of the old animals. The mean volume of the satellite cell sheaths was, however, smaller in the aged rabbits than in the young adults. Consequently the volume ratio between the satellite cell sheaths and the related nerve cell bodies was significantly smaller in the aged animals. Since satellite cells play an important role in the support of the neuron, the reduction in volume of the perineuronal sheath could be associated with a decrease in the trophic activity of satellite cells towards the enveloped neuron with consequences for neuronal activity. Furthermore, in the satellite cell sheaths of old rabbits, the number and extension of gaps that leave the neuronal surface directly exposed to the basal lamina were significantly increased. Since spinal ganglia lack a blood-nervous tissue barrier, only the satellite cell sheath controls the traffic of material to the nerve cell body. Because the neuronal surface unprotected by the satellite cell envelopment is significantly more extensive in the spinal ganglia of old rabbits than in those of young adults, the nerve cells of the former are more exposed to potential damage by harmful substances. A dense undercoating was seen very frequently beneath the portions of the neuronal plasma membrane not covered by satellite cells.

Aging↗
PubMed1995

On the influence of the perineuronal microenvironment on the outgrowth of perikaryal projections of spinal ganglion neurons.

While the outgrowth of the slender projections from the perikaryon of spinal ganglion neurons is an intrinsic property of these neurons, it is also influenced by the surrounding microenvironment. To obtain evidence concerning whether the outgrowth of these projections is influenced by one or both components of the perineuronal microenvironment (satellite cells plus extracellular matrix) we have taken advantage of a rare arrangement of these neurons. In the spinal ganglia of adult animals nerve cell bodies are occasionally arranged in pairs, the two nerve cell bodies of the pair being separated by a satellite cell sheet lacking a basal lamina, while along the remaining portions of their surfaces they are enveloped by a satellite cell sheath, in turn surrounded by a basal lamina and connective tissue. By studying these paired nerve cells we have been able to compare, in the same nerve cell body, the extent of the perikaryal projections in surface domains associated only with satellite cells and in surface domains associated with both satellite cells and extracellular matrix. In spinal ganglia of the rat and lizard we have found that the overall development of the perikaryal projections does not differ significantly in either of these surface domains. This finding suggests that neuron-satellite cell interactions rather than factors in the extracellular matrix play a role in promoting the outgrowth of perikaryal projections from spinal ganglion neurons.

Animals↗
PubMed1994

Perikaryal projections of spinal ganglion neurons: quantitative differences between membrane domains in contact with different microenvironments.

The perikarya of spinal ganglion neurons display numerous slender projections. In the present investigation we have studied whether the extent of these projections is uniform over the entire perikaryal surface or whether there is a difference between the regions of the perikaryon in contact with different microenvironments. In spinal ganglia of the rat and the lizard we have analysed about 200 neuronal cell bodies arranged in pairs and have compared the extent of the projections quantitatively in the areas of interneuronal contact with that in the areas of neuron-to-satellite cell contact. In both species we have found that the projections are present over the entire perikaryal surface and that the overall development of the perikaryal projections is significantly greater in those portions of the surface in contact with satellite cells than in the portions in contact with another neuron. On the basis of these observations we conclude that the outgrowth of perikaryal projections is an intrinsic property of the nerve cell body which is manifested over the entire perikaryal surface; there is, however, an extrinsic influence from the microenvironment of the neuron, which may account for the quantitative differences in different domains of the perikaryal surface.

Animals↗
PubMed1993

The percentage of nerve cell bodies arranged in clusters decreases with age in the spinal ganglia of adult rabbits.

In the spinal ganglia of the rabbit the nerve cell bodies, which in early developmental stages are mutually in contact, come to be completely isolated from each other by a satellite cell sheath and by a connective envelope before birth. The present study demonstrates that in the early postnatal months some nerve cell bodies are still arranged in clusters, and that the percentage of these decreases progressively throughout adult life. This decrease probably arises because in some of the ganglion neurons the process of envelopment of the perikaryon by an individual sheath begins later, or takes place more slowly, than in the majority of cases. Therefore, the relationship between neurons and between neurons and satellite cells may change in certain clusters of nerve cell bodies under normal circumstances during adult life.

Aging↗
PubMed1991

Clusters of nerve cell bodies enclosed within a common connective tissue envelope in the spinal ganglia of the lizard and rat.

A careful search for groups of nerve cell bodies enclosed within a common connective envelope was made in the spinal ganglia of the lizard and rat using a serial-section technique. Nerve cell bodies sharing a common connective envelope were found to be more common in the lizard (9.4%) than in the rat (5.6%). These nerve cell bodies were arranged in pairs, or, less frequently, in groups of three. At times, they appeared to be in immediate contact, with no intervening satellite cells; at others, they remained separated from one another by a satellite cell sheet. The clusters of nerve cell bodies enclosed within a common connective envelope probably result from the arrest of developmental processes in the spinal ganglion. It is possible that, as a result of the cell arrangement here described, certain neurons electrically influence other sensory neurons at the level of the ganglion.

Animals↗
PubMed1991

Low doses of TRH in amyotrophic lateral sclerosis and in other neurological diseases.

30 subjects--23 with amyotrophic lateral sclerosis (ALS), 4 with Charcot-Marie Tooth atrophy, 2 with progressive spinal muscle atrophy and 1 with radiation myelopathy--were given chronic low-dose TRH therapy. The effects of treatment were assessed on the scale of Norris et al. (1974). The outcome of the study, in agreement with some and at variance with other studies, was that TRH induced a statistically significant neurological improvement in 17 of the 23 ALS patients but little or none in the other ALS patients and in patients with other neurological diseases.

Adult↗
PubMed1991

Ribosomes in myelinated axons of the rabbit spinal ganglion neurons.

To clarify whether, in the mature pseudounipolar neurons of mammalian spinal ganglia, a small number of ribosomes are dispersed in many or possibly all axons beyond their initial segments or if a large number of ribosomes is confined to a few axons only, three series of consecutive sections (of 449, 702 and 865 sections respectively) were cut from the sensory portion of rabbit spinal nerves very close to the ganglion. In these series of sections, portions (from 4.5 to 69.2 microns long) of 198 myelinated axons were examined. Clusters of ribosomes were detected only in three of the 198 axons examined, where they were present in 73-99% of the sections. In the nerves we studied ribosomes are not sparsely dispersed in many or possibly all axons, but are confined to a few axons only, where they are present in a high percentage of sections. Both size and density of axonal ribosomes were identical to those of adjacent Schwann cell ribosomes and clearly different from those of glycogen particles. The great majority of axonal ribosomes were localized within the subaxolemmal band of axoplasm whereas their frequency was lowest within the axonal core. The possible origin of the ribosomes found within the three axons is briefly discussed.

Animals↗
PubMed1990

Scanning electron-microscope observations of the perikaryal projections of rabbit spinal ganglion neurons after enzymatic removal of connective tissue and satellite cells.

The true surface of rabbit spinal ganglion neurons has been made directly accessible to scanning electron-microscope observation after removal of both the connective tissue and satellite cells that normally cover it. The neuronal surface is characterized by a profusion of slender projections whose shapes have been determined and whose length and width have been quantified. Controls carried out with transmission electron microscopy demonstrate that the procedure employed in this study satisfactorily preserves neuronal structure.

Animals↗
PubMed1990

The perikaryal projections of rabbit spinal ganglion neurons. A comparison of thin section reconstructions and scanning microscopy views.

Shape, length and width of the perikaryal projections of spinal ganglion neurons from adult rabbits fixed in situ by perfusion have been evaluated by means of serial section electron microscopy. The results thus obtained have been compared with those obtained by enzymatic removal of ganglionic connective tissue and satellite cells followed by direct observation of the true neuronal surface under the scanning electron microscope. The comparison has shown that the perikaryal projections exhibit a similar shape and similar size with both techniques.

Animals↗
PubMed1989

Internodal microvilli of Schwann cells of myelinated fibres in lizard spinal roots project onto unmyelinated axons.

Tufts of microvilli originating from the internodal cytoplasm of Schwann cells associated with myelinated axons in apparently normal lizard spinal roots have been studied under the electron microscope by means of both single and serial sections. More than one tuft of internodal microvilli may arise from a single Schwann cell. Sometimes mitochondria and more frequently an organelle resembling a multivesicular body with a clear matrix can be found in the Schwann cell cytoplasm underlying a tuft of internodal microvilli. The dimensions (length: 0.4-1.0 microns; diameter: 40-70 nm) and structure of internodal microvilli of the Schwann cell are very similar to those of nodal microvilli of the same cell. Each tuft of internodal microvilli projects towards an adjacent unmyelinated axon which at this site is partly devoid of its own Schwann cell sheath. Thus a single Schwann cell may be related to a myelinated axon and an unmyelinated axon at the same time. Patches of a dense axolemmal undercoating (which could be portions of the cytoskeleton) are present in the unmyelinated axon in close spatial correlation with internodal microvilli. The factors which could induce the formation of internodal microvilli as well as the possible role (or roles) of these microvilli are briefly discussed.

Animals↗
PubMed1988

Nerve fibres with myelinated and unmyelinated portions in dorsal spinal roots.

Series of 312-605 consecutive sections were prepared from apparently normal dorsal spinal roots of lizard (Lacerta muralis). Two axons which showed a segment enveloped by a compact myelin sheath and a segment devoid of myelin were followed in these serial sections. These provided the opportunity of analysing the structural features that an individual axon presents when it is myelinated and when it is devoid of myelin. Some structural features (e.g., axon calibre and microtubule density) were significantly different in the myelinated segment and in the unmyelinated segment. The factors which possibly influence these features are briefly discussed.

Animals↗
PubMed1988

Qualitative and quantitative observations on the structure of the Schwann cells in myelinated fibres.

Various morphological features of the Schwann cells of myelinated fibres in the lizard thoracic spinal roots were studied, and, when possible, quantified using morphometric methods. About 0.8% of the Schwann cells are binucleate and some display clusters of microvilli along the internodes. The percentages of the cytoplasmic area of the Schwann cell occupied by the following cytoplasmic components were determined: mitochondria, Golgi apparatus, granular endoplasmic reticulum, smooth endoplasmic reticulum, multivesicular bodies, dense bodies, autophagic vacuoles, peroxisome-like bodies, lipofuscin granules and lipid droplets. Linear relationships were found between the sectional areas of the mitochondria and granular endoplasmic reticulum of the Schwann cell and both the length of the profile of the Schwann cell plasma membrane and the size of the related axon. The results obtained are compatible both with the hypothesis that the mitochondria and granular endoplasmic reticulum of the Schwann cell are involved in the production and storage of proteins for the plasma membrane of this cell, and with the hypothesis that these organelles are involved in the production and storage of protein metabolites which are subsequently transferred to the related axons.

Animals↗