No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Peripheral nerve repair is often compromised by a failure to restore the biomechanical integrity of a damaged nerve. An understanding of the mechanical architecture that underpins the tensile properties of peripheral nerves, in particular their ability to bend and stretch during movement, is an important consideration in the design of tissue engineered repair conduits and other repair approaches. Mechanical features are distributed heterogeneously within rat nerve tissue, with compliance increased at articulations. This study sought to explore which ultrastructural features of the rat peripheral nerve are likely to be associated with this biomechanical heterogeneity, to examine whether these features are present in the human peripheral nerve and to conduct pilot investigations into the feasibility of assessing the mechanical behaviour of joint and non joint regions of nerve in human volunteers. The anatomical features of fascicle number, nerve cross sectional area and perineurium thickness were assessed in joint and non joint regions of rat median and sciatic nerve. Regional comparisons of collagen, elastin and beta spectrin were also made at these joint and non joint locations. Collagen fibril diameter in rat and human nerves was analysed using transmission electron microscopy and the number density of fibrils examined. Ultrasound was used to image the dynamic human nerve in a pilot study. There was no difference in the amount of collagen or elastin in joint and non joint regions of rat peripheral nerve and beta spectrin was present at both locations. Cross sectional area, degree of fasciculation and perineurium thickness were similar in joint and non joint areas. A population of collagen fibrils with significantly reduced diameter was found at the joint region of the rat median nerve that corresponds to the location of increased compliance in this tissue, though this pattern was not observed in the rat sciatic nerve. The number density of collagen fibrils was significantly increased at joint regions of the median nerve, indicating a greater number of thinner fibrils at this location. Examination of cadaveric human median nerves revealed a similar trend towards regional variation of collagen fibril diameter, with thinner fibrils at the joint regions compared to the non joint, particularly at the elbow, though the ulnar and radial nerves did not show a similar pattern. When the human median nerve was imaged using high resolution sonography, measurement of the displacement of the nerve at joint and non joint locations was achieved with the use of a novel speckle tracking algorithm, suggesting that with future development of this method it may be possible to measure strain.

The generation of mature Schwann cells from their cells of origin, neural crest cells, proceeds through two transitional steps first neural crest cells are specified to form Schwann cell precursors, which then mature into immature Schwann cells. These then generate the myelinating and non-myelinating Schwann cells found in mature nerves. Each of these steps has been well characterised phenotypically in terms of antigenic profile, survival mechanisms and morphological changes. First of all, using adapted survival assays I found that there is a range of factors that supports the survival of crest-derived glial precursor populations that generate satellite cells and Schwann cells but not of crest cells themselves. I found also that satellite cells develop earlier than Schwann cells in a number of characteristics including survival mechanisms and antigenic profile. I then examined the role of the Notch signalling pathway in the Schwann cell lineage using different in vitro and in vivo studies. I found that only Schwann cell precursor maturation is regulated by Notch signalling during early Schwann cell development. Notch signalling is also important in regulating cell division in immature Schwann cells and it acts as a negative regulator of myelination. During normal development, Notch signalling is attenuated, by a mechanism likely to involve the transcription factor Krox-20, to allow myelination to occur. Finally, in collaboration with Professors W.F. Blakemore and R.J. Franklin (University of Cambridge), I made a comparative analysis of the transplant characteristics of Schwann cell precursors and Schwann cells in two animal models of Multiple Sclerosis. We found that Schwann cell precursors outperform Schwann cells in myelination potential, survival and migratory properties in these animal models.

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This project focused on understanding the mechanisms involved in CNS integration. The anatomy and physiology of mammalian olfactory system was investigated in order to develop an organotypic in vitro sensory system to increase our understanding of sensory processing at a neural network level. The olfactory network cultures grown on multielectrode arrays (MEAs) were found to only rarely exhibit electrical activity and it was decided this was an unsuitable preparation for the purposes of this study. The spinal cord was chosen as a secondary sensory system, initially in co-culture with dorsal root ganglia and then alone, with special interest in gap junction function. Gap junctions have received increasing attention as contributors to pattern generation in neuronal ensembles, including the generation or modification of highly coordinated, intense bursting states. The main result section of this study explored the effects of four gap junction blockers (carbenoxolone (CBX), halothane, I-octanol and oleamide) on the spontaneous activity of mouse and rat frontal cortex and spinal cord cultures grown on microelectrode arrays (MEAs). It was our hypothesis that the characteristic coordinated bursting seen in most frontal cortex and in some higher density spinal cord cultures would be influenced via gap junction communication. The four compounds tested generated interesting, and in one case paradoxical effects. Frontal cortex cultures were all inhibited in a dose-dependent manner, which included total cessation of activity by halothane, CBX, I-octanol, or oleamide (at concentrations 250 muM, 100 muM, 20 muM, 20 muM, respectively). All cultures showed spontaneous recovery at lower concentrations and reversibility after culture medium changes at higher concentrations. In addition, measurements of network burst rates and coefficients of variation of burst period indicate that burst coordination among channels was reduced by these compounds. These responses were generally mirrored in the spinal cord, except for CBX, which produced a paradoxical transient intense increase in network spike and burst production. The results of this study show the effect of the gap junction blockers to be not only tissue specific, but also to differ from species to species. It is still unclear whether these differences seen really are through the blockade of gap junctions, or due to the secondary effects of the blockers used. Further studies showed that strychnine (1 muM) prevented this transient activity increase in spinal cord networks, implying that CBX may temporarily block glycine inhibition. Blocking intracellular calcium mobility with thapsigargin (up to 5 muM) did not affect the effects of gap junction blockers used.