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Biomedical subjects

S Geuna

Publications and source records attributed to S Geuna.

At least 19 recordsLinked to original sources
PubMed2003

Schwann-cell proliferation in muscle-vein combined conduits for bridging rat sciatic nerve defects.

Among the various grafting procedures that have been studied as alternatives to traditional fresh nerve autografts for the repair of severed peripheral nerves, muscle-vein-combined graft conduits have recently been devised and successfully employed. In the present study, the early presence, origin, and proliferation activity of Schwann cells (SCs) along this particular type of biological graft conduit have been investigated, using antibodies directed against glial fibrillar acid protein (GFAP), a protein that is specifically expressed in glial cells, and proliferating cell nuclear antigen (PCNA), a protein that is expressed by cells during DNA synthesis. Results showed that the muscle-vein-combined graft was progressively invaded by a number of GFAP-immunopositive SCs, many of which were also found to be immunopositive for PCNA, thus demonstrating that their proliferation continues to occur inside the graft. Among the molecules that could be involved in the stimulation of Schwann-cell proliferation is neuregulin-1 (NRG-1) that mediates its effects by binding to the ErbB receptor tyrosine kinase family. In the present study, the authors report on the RT-PCR analysis for NRG-1 and ErbB3 mRNAs, showing an overall increase in the content of these transcripts inside the muscle-vein-combined graft. These results suggest that the muscle-vein-combined graft conduit constitutes an environment favorable to potentiate Schwann-cell proliferation during the early regeneration phases.

Animals↗
PubMed2002

The use of brainstorming for teaching human anatomy.

Interactive teaching techniques have been used mainly in clinical teaching, with little attention given to their use in basic science teaching. With the aim of partially filling this gap, this study outlines an interactive approach to teaching anatomy based on the use of "brainstorming." The results of the students' critique of the teaching techniques are also included. Seventy-five students from the first-year nursing curriculum were tested by a structured questionnaire after three brainstorming sessions. The overall response to these sessions was very positive, indicating that students perceived this interactive technique as both interesting and useful. Furthermore, this approach may provide a useful strategy when learning the clinical courses of the upcoming academic years.

Anatomy↗
PubMed2001

Unscheduled DNA synthesis in rat adult myenteric neurons: an immunohistochemical study.

Unscheduled DNA synthesis refers to DNA synthesis not followed by cell division. Previous studies have suggested that this phenomenon may occur in neurons from peripheral myenteric ganglia in conditions of functional hyperstimulation. In order to verify these observations, we have carried on an immunohistochemical study on myenteric neurons from the hypertrophic intestinal loops upstream from a partial obstruction (an experimental condition that induces a relevant increase of the neuronal workload) after labelling with two different markers: the proliferating cell nuclear antigen (PCNA), that is specifically expressed in cell nuclei during the S-phase, and the protein gene product 9.5 (PGP 9.5), a specific marker of nerve cells. While no myenteric neuron immunopositive for the anti-PCNA antibody was found in the control intestine, in the hypertrophic myenteric ganglia some neurons were positive for PCNA. These results provide an unequivocal evidence on the existence of unscheduled DNA synthesis in myenteric neurons from the hypertrophic intestine.

Animals↗
PubMed2001

Adult stem cells and neurogenesis: historical roots and state of the art.

Over the last few years, an impressive number of papers have addressed the stem cell issue. However, as often occurs when a scientific subject undergoes a period of fast growth, some confusion is generated. To help reduce the existing uncertainty, this paper focuses on the concept of adult stem cells in relation to the classification of cell populations on the basis their proliferative behavior. Particular attention is dedicated to adult neural stem cells, an issue that has recently seen the most amazing advances. Finally, the concept of adult stem cells is differentiated from that of developmental stem cells in relation to the employment of stem cells for transplantation therapies.

Adult↗
PubMed2001

Confocal imaging of Schwann-cell migration along muscle-vein combined grafts used to bridge nerve defects in the rat.

Schwann cells guide axonal regrowth during peripheral nerve repair. In a case of a nerve lesion with substance loss, a graft conduit is necessary to enable axons to reach the distal nerve stump. If a non-nervous autograft is used, the question arises as to the presence and origin of Schwann cells along the grafted tube. We addressed this issue using a tubulization technique based on the use of an autologous vein filled with fresh skeletal muscle for the repair of sciatic nerve defects in the rat. We showed that both ends of the graft were early and progressively colonized by a number of glial fibrillar acid protein-immunopositive and S-100 immunonegative cells, an immunocytochemical pattern typical of immature Schwann cells. These cells, which were located in the interstice between grafted skeletal muscle fibers, are mainly organized into long chains oriented along the main axis of the graft and progressively colonize all the graft. Schwann cells coming from the distal nerve end are suitable for being responsible for guiding regeneration of nerve fibers along the graft toward the correct periphery (tissue specificity).

Animals↗
PubMed2001

Methodological issues in size estimation of myelinated nerve fibers in peripheral nerves.

Size estimation of myelinated nerve fibers in peripheral nerves is a very common task in neuromorphology and different dedicated morpho-quantitative procedures have been devised and used to date. Unfortunately, many reports on experimental nerve studies lack comprehensive information on the procedures that have been designed and applied for myelinated fiber size estimation. This paper addresses the issue in the light of the recent advances in quantitative morphology that have recognized the concept of unbiased estimates as the key methodological issue to be addressed in morpho-quantitative studies. The potential foundations of bias at various study levels are analysed together with indications on how to cope with them. In addition, the issue of the precision of size estimates is addressed and the various geometrical parameters that can be selected for myelinated nerve fiber size assessment are outlined. Taken together, information provided in this paper is expected to help investigators conduct an appropriate preliminary study design phase, the key step for setting up the most adequate morpho-quantitative procedure for any given research goal.

Animals↗
PubMed2001

Evidence of very early neuronal migration from the olfactory placode of the chick embryo.

Cell migration from the olfactory neuroepithelium is a very peculiar phenomenon in the development of the nervous system. In this paper, we provide evidence that, in the chick embryo, migration of cells from the olfactory neuroepithelium begins earlier than previously reported, namely at the same time as the first olfactory placode differentiation, that occurs several hours before the superficial ectodermal invagination that gives rise to the olfactory pit. Moreover, we provide evidence that very early migrating cells express the HuC/D RNA-binding protein antigen, a specific neuronal marker. These observations refocus our knowledge on the very first developmental stages of olfactory neuroepithelium.

Animals↗
PubMed2001

Confocal imaging of HuC/D RNA-binding proteins in adult rat primary sensory neurons.

HuC/D RNA-binding proteins are antigens that are specifically expressed in nerve cells. In the present study, immunocytochemistry and laser confocal microscopy were used to study the cellular distribution of HuC/D RNA-binding proteins in adult rat primary sensory neurons. Colocalization with the protein gene product 9.5 (PGP 9.5) was used to identify sensory neurons. Confocal laser imaging showed that HuC/D antigens are expressed in the cytoplasm of all rat primary sensory neurons. Most neurons also showed anti-HuC/D immuno-positivity in the nucleus. The demonstration of the ubiquitous expression of HuC/D antigens in primary sensory neurons gives us a possible explanation for the severe pathological lesions observed in dorsal root ganglia in association with the paraneoplastic Hu Syndrome.

Animals↗
PubMed2000

Appreciating the difference between design-based and model-based sampling strategies in quantitative morphology of the nervous system.

Quantitative morphology of the nervous system has undergone great developments over recent years, and several new technical procedures have been devised and applied successfully to neuromorphological research. However, a lively debate has arisen on some issues, and a great deal of confusion appears to exist that is definitely responsible for the slow spread of the new techniques among scientists. One such element of confusion is related to uncertainty about the meaning, implications, and advantages of the design-based sampling strategy that characterize the new techniques. In this article, to help remove this uncertainty, morphoquantitative methods are described and contrasted on the basis of the inferential paradigm of the sampling strategy: design-based vs model-based. Moreover, some recommendations are made to help scientists judge the appropriateness of a method used for a given study in relation to its specific goals. Finally, the use of the term stereology to label, more or less expressly, only some methods is critically discussed.

Animals↗
PubMed2000

Nerve repair by means of vein filled with muscle grafts I. Clinical results.

Peripheral nerve lesions with a long segment defect need a grafting conduit to heal. Although autogenous nerve grafting is still considered the best method for bridging nerve defects, several alternative types of conduits (biological and synthetic) have been studied. We have demonstrated in previous experimental research in rats that a graft made using a vein (providing a guide for nerve regeneration) filled with fresh skeletal muscle (to prevent vein collapse and support axon regeneration) gave similar results to traditional nerve grafts. On this basis, we decided to use the muscle-vein-combined grafts in clinical cases. From 1993 to 1997, this technique was applied for bridging both sensory and mixed nerve defects (21 cases). We report good results in 85% of our cases with a minimum follow-up of 14 months. These results, obtained on nerve defects ranging from 0.5 to 6 cm in length, seem to be superior to those reported with other kinds of artificial or biological conduits.

Adolescent↗
PubMed2000

Nerve repair by means of vein filled with muscle grafts. II. Morphological analysis of regeneration.

The morphological features of regeneration in long-distance (3 cm) muscle-vein-combined grafts were experimentally investigated in the rat sciatic nerve by means of light and electron microscopy. In the early phases of regeneration (14 days after surgery), many regenerating nerve fibers were detected along the muscle-vein-combined graft. Six months after surgery, quantitative morphometrical analysis of myelinated nerve fibers showed that both the total number and density of myelinated nerve fibers were significantly greater in regenerated nerves than in control nerves. The contrary appeared true for the mean fiber size, with fiber size significantly smaller in regenerated nerves. Ultrastructural observations allowed the description of some peculiar aspects of the relationship between muscle fibers, nerve fibers, and Schwann cells in both early and late phases of regeneration.

Animals↗
PubMed2000

Tissue specificity in rat peripheral nerve regeneration through combined skeletal muscle and vein conduit grafts.

Diffusible factors from the distal stumps of transected peripheral nerves exert a neurotropic effect on regenerating nerves in vivo (specificity). This morphological study was designed to investigate the existence of tissue specificity in peripheral nerve fiber regeneration through a graft of vein filled with fresh skeletal muscle. This tubulization technique demonstrated experimental and clinical results similar to those obtained with traditional autologous nerve grafts. Specifically, we used Y-shaped grafts to assess the orientation pattern of regenerating axons in the distal stump tissue. Animal models were divided into four experimental groups. The proximal part of the Y-shaped conduit was sutured to a severed tibial nerve in all experiments. The two distal stumps were sutured to different targets: group A to two intact nerves (tibial and peroneal), group B to an intact nerve and an unvascularized tendon, group C to an intact nerve and a vascularized tendon, and group D to a nerve graft and an unvascularized tendon. Morphological evaluation by light and electron microscopy was conducted in the distal forks of the Y-shaped tube. Data showed that almost all regenerating nerve fibers spontaneously oriented towards the nerve tissue (attached or not to the peripheral innervation field), showing a good morphological pattern of regeneration in both the early and late phases of regeneration. When the distal choice was represented by a tendon (vascularized or not), very few nerve fibers were detected in the corresponding distal fork of the Y-shaped graft. These results show that, using the muscle-vein-combined grafting technique, regenerating axons are able to correctly grow and orientate within the basement membranes of the graft guided by the neurotropic lure of the distal nerve stump.

Animals↗
PubMed2000

Morphological analysis of peripheral nerve regenerated by means of vein grafts filled with fresh skeletal muscle.

Clinical data have shown that a vein segment filled with fresh skeletal muscle can be considered a good autologous grafting conduit for the repair of peripheral nerve lesions. In this study, the long-term morphological organization of rat sciatic nerve fibers regenerated along a muscle-vein-combined graft conduit is further analysed by light and electron microscopy. Regenerated nerve fibers were organized into fascicles of various sizes that were clearly delimited by perineurial-like shells made by long and thin cytoplasmic processes of perineurial-like bipolar cells and by densely packed collagen fibrils. Grafted skeletal muscle fibers were still detectable among nerve fiber fascicles. However, in spite of the persistence of skeletal muscle along the graft, regenerated nerve fibers showed a good morphological pattern of regeneration, providing further evidence that the muscle-vein-combined grafting technique represents an effective surgical alternative to the classical fresh nerve autograft for the repair of peripheral nerve defects.

Animals↗
PubMed2000

Verification of the two-dimensional disector, a method for the unbiased estimation of density and number of myelinated nerve fibers in peripheral nerves.

Quantification of the number of myelinated fibers in peripheral nerves is a common requirement in quantitative morphology. This parameter provides important information on the consequences of various physiological, pathological and experimental conditions on the nerve structure and is one of the main indicators of success of peripheral nerve repair. In this paper, the theoretical rationale for the application of stereological principles to obtain unbiased estimates of the density and total number of myelinated fibers in peripheral nerves is discussed and a simple stereological method is described. The method is applied together with a systematic random sampling scheme, that was optimized for the purposes of the present study, and with sampling scheme analysis by calculating the coefficient of error (CE). The stereological method, which consists of a two-dimensional variation of the classical disector procedure (two-dimensional disector), and the sampling scheme are verified by comparing estimates with the true density and total number of myelinated fibers in peripheral nerve trunks where true values have been accurately determined by extensive counting. The verification of the 2-D disector method, both of normal and regenerated nerves, showed that estimates of density and total number of myelinated nerve fibers are unbiased. The method also proved to be efficient (time-saving): Estimation of density and total number of myelinated fibers in a single nerve takes about 2-3 hours.

Animals↗
PubMed1998

Morphological and morphometrical changes in dorsal root ganglion neurons innervating the regenerated lizard tail.

The variations occurring in neurons from dorsal root ganglia that provide innervation to the regenerated tail of the lizard (vicarious ganglia) are analysed. Vicarious ganglion neurons, when compared to control ganglion neurons (i.e. ganglia from the same animal that were not involved in the reinnervation process), show a size increase of the soma (cell hypertrophy) which applies to all cell types and subtypes. No statistically significant differences in the relative percentage of neurofilament-poor (type D) and neurofilament-rich (type L) neurons were found between vicarious dorsal root ganglia compared to controls in all animals. On the contrary, within L neuron sub-types, a statistically significant increase in sub-type L2 (very rich in neurofilaments), and the appearance of sub-type L3 neuron which is not detectable in controls, were demonstrated in vicarious dorsal root ganglia. In spite of these variations in size and percentage distribution, no structural and ultrastructural differences of the various cell types and sub-types are detectable, except for the appearance of the sub-type L3 neurons. However, this neuron sub-type might not be considered specific of hypertrophy since the same morphological features have been observed, in normal conditions, in lizard dorsal root ganglia from cervical and lumbar spinal levels that provide innervation to limb plexuses.

Animals↗