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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
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↗
PubMed1988

Quantitative relationships between axoplasm and Schwann cell sheath in unmyelinated nerve fibres. An electron microscope study.

The quantitative relationships between the size of the Schwann cell sheath and that of its related axoplasm were studied by electron microscopy in cross sections of bundles of unmyelinated axons (Remak bundles) of the spinal roots of lizard (Lacerta muralis). It was found that (i) the cross sectional area of the Schwann cell sheath is directly proportional to that of its related axoplasm (correlation coefficient 0.84), and (ii) the ratio between the cross sectional area of the Schwann cell sheath and that of its related axoplasm tends to diminish as the cross sectional area of the latter increases. Thus, under normal conditions, in the bundles of unmyelinated axons of the spinal roots of lizard a quantitative balance exists between the nerve tissue and its associated glial tissue. These results agree with those previously obtained in the myelinated fibres of the same region and in the spinal ganglia of the lizard, gecko, cat and rabbit. Some of the mechanisms probably involved in the control of the quantitative balance between nerve tissue and its associated glial tissue in peripheral nerves are listed.

Animals↗
PubMed1988

The structure of Schwann cells in unmyelinated fibres. A qualitative and quantitative electron microscope study.

The structure, size and distribution of many cytoplasmic components of Schwann cells associated with unmyelinated axons in lizard thoracic spinal roots were analysed under the electron microscope. The percentages of Schwann cell cytoplasmic area occupied by the following cytoplasmic components were determined: mitochondria, Golgi apparatus, granular endoplasmic reticulum, multivesicular bodies, smooth endoplasmic reticulum, lipofuscin granules, peroxisome-like bodies, autophagic vacuoles, dense bodies and lipid droplets. A linear correlation was found between the sectional areas of the mitochondria and granular endoplasmic reticulum of the Schwann cell and both length of Schwann cell plasma membrane profile and size of the related axoplasm. The structure of Schwann cells associated with unmyelinated axons and that of Schwann cells associated with myelinated axons were compared in the same species and in the same region of the peripheral nervous system using the same fixative and the same preparation technique. Some differences were detected in the organization of the granular endoplasmic reticulum, in the presence of cilia and in the percentages of cytoplasm occupied by various components. The hypothesis that Schwann cell mitochondria and granular endoplasmic reticulum are involved in the production and storage of proteins for the plasma membrane of this cell as well as the hypothesis that these organelles are involved in the production and storage of protein metabolites which are subsequently transferred to the related axons seem applicable not only to Schwann cells associated with myelinated axons (Pannese et al., in press), but also to those associated with unmyelinated ones.

Animals↗
PubMed1987

An electron microscope study of quantitative relationships between axon and Schwann cell sheath in myelinated fibres of peripheral nerves.

The quantitative relationships between the cross-sectional area of the Schwann cell sheath (myelin included) and that of its related axon were studied by electron microscopy in the nerve fibres of the spinal roots of lizard (Lacerta muralis). In both ventral and dorsal roots the cross-sectional area of the Schwann cell sheath (myelin included) was found to be directly proportional to that of its related axon (correlation coefficients between 0.88 and 0.92). The ratio between the cross-sectional area of the Schwann cell sheath (myelin included) and that of its related axon tends to diminish as the cross-sectional area of the latter increases. Thus, under normal conditions, in myelinated fibres of the spinal roots of the lizard a quantitative balance exists between the nerve tissue and its associated glial tissue. This result agrees with those previously obtained in the spinal ganglia of the lizard, gecko, cat and rabbit. Some of the mechanisms probably involved in the control of the quantitative balance between nerve tissue and its associated glial tissue in peripheral nerves are presented and discussed.

Animals↗
PubMed1987

Mitotic Schwann cells in normal mature spinal roots.

Some rare mitotic Schwann cells (one in about a thousand) were found in normal mature spinal roots of adult lizards. Mitotic cells retained their relationships with unmyelinated axons, a finding consistent with the hypothesis that the stimulation of Schwann cell proliferation requires direct contact between axons and Schwann cells. The observation presented in this paper shows that Schwann cells and the satellite cells of sensory and autonomic ganglia behave in the same way also with regard to their mitotic activity.

Animals↗
PubMed1986

Association between microtubules and mitochondria in myelinated axons of Lacerta muralis. A quantitative analysis.

The spatial relationship between microtubules and mitochondria was studied in myelinated axons of the ventral and dorsal spinal roots of the lizard Lacerta muralis by use of quantitative methods in single and serial sections. Microtubules mainly occurred in groups of 3 to 10. The mean density of microtubules was found to be significantly higher close to mitochondria than in the rest of the axoplasm. In single sections, 59-62% (according to the root region examined) of the microtubule groups were found to be 'associated' with mitochondria; this percentage rose to 74-76% in serial sections. The examination in serial sections of progressively longer segments of the same microtubule groups showed that the longer the segments of microtubule groups examined the higher was the percentage of microtubule groups 'associated' with mitochondria. The results obtained show that in the axons studied in the present research a non-accidental spatial association exists between microtubule groups and mitochondria. This evidence supports the suggestion that the microtubule groups play a role in the movement of mitochondria along the axon, even though it does not clarify the precise nature of this role.

Animals↗
PubMed1984

A comparison of the density of microtubules in the central and peripheral axonal branches of the pseudounipolar neurons of lizard spinal ganglia.

The number and density of microtubules were determined in cross sections of the two branches (central and peripheral) of the bifurcating axon of the pseudounipolar neurons of the lizard thoracic spinal ganglia. In both the central and peripheral branches the average number of microtubules rose, while the microtubular density decreased with an increase in the cross-sectional area of the axonal branch: More precisely, a linear relationship was observed between the logarithm of the microtubular density and the cross-sectional area of the axonal branch. Both the average number of microtubules per cross section of the axonal branch and the microtubular density were found to be significantly lower in the central than in the peripheral branch. Since the amount of material carried by fast transport was found by other authors to be greater in the peripheral than in the central branch, a positive correlation seems to exist between microtubular density and the quantity of material carried by fast transport along the two branches of the axon in pseudounipolar neurons. Such a correlation suggests that microtubules may be somehow involved in the fast transport of material along the axon. The average densities of microtubules were found to be the same comparing two sets of unmyelinated and myelinated central (or peripheral) branches of corresponding size. Therefore, different microtubular densities usually observed in unmyelinated and myelinated axons appear to be correlated with the different size ranges of the two types of axon rather than with the absence or presence of the myelin sheath.

Animals↗
PubMed1984

A quantitative study of microtubules in motor and sensory axons.

The number, density and distribution of microtubules were compared in the myelinated motor and sensory axons of the spinal roots of lizard (Lacerta muralis). In both motor and sensory axons the average number and density of microtubules were found to be related to the axonal size: the average number of microtubules rose, while the microtubular density decreased with an increase in the cross-sectional area of the axon. More precisely, a linear relationship was observed between the logarithm of the microtubular density and the cross-sectional area of the axon. No significant differences in the microtubular number and density were found between motor and sensory axons of corresponding size. Microtubules were unevenly distributed throughout the cross section of both motor and sensory axons. In particular, a nonaccidental association between microtubules and mitochondria was found in both axon types.

Animals↗