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Biomedical subjects

I R Griffiths

Publications and source records attributed to I R Griffiths.

At least 73 records · Page 4Linked to original sources
PubMed1991

Retarded Wallerian degeneration following peripheral nerve transection in C57BL/6/Ola mice is associated with delayed down-regulation of the P0 gene.

Wallerian degeneration is markedly retarded in C57BL/6/Ola mice, the majority of axons remaining intact for up to 10 days after sciatic transections. By 5 days after axotomy in normal mice P0 mRNA is markedly down-regulated, whereas high expression is present in the mutant mice at 7 days and is not reduced by a second distal axotomy. However, dissociated Schwann cells cultured without neurons down-regulate P0 in the normal manner. The data suggest that the continued expression of P0 mRNA is probably dependent on a relatively stable axonal signal with a low turnover that does not require continuous fast anterograde or retrograde transport. This may indicate an intrinsic axolemmal molecule(s) is involved in the neuronal signal.

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PubMed1991

P0 gene expression in cultured Schwann cells.

This study examines the expression of the major myelin protein gene P0 in cultured Schwann cells, grown on their own or in association with neurons. Many freshly dissociated Schwann cells from actively myelinating nerves express Po mRNA in high abundance. If neurons are not present, signal intensity falls markedly with time so that by 7 days in culture only a basal expression is evident which is negligible compared to the level in vivo. Dorsal root ganglia from embryo day 16 (E16) rats contain no significant levels of Po mRNA but when grown in full myelinating medium (containing serum and embryo extract) increasing expression is seen from 4 to 5 days onward even though myelination does not occur until after the second week. In this intervening period the intensity of P0 mRNA expression is lower than that found in the actively myelinating cell. Neurons from sympathetic ganglia are also capable of inducing P0 mRNA expression. Schwann cells in dorsal root ganglia explants grown in serum-free defined medium do not assemble a basal lamina and will not wrap or myelinate axons. Nevertheless P0 mRNA, but not protein, is expressed in levels similar to those found in full myelinating medium prior to myelination. Such Schwann cells also exhibit galactocerebroside and the sulphatide recognised by the 04 antibody. It appears that in defined medium or in myelinating medium prior to myelination axonal signals can induce P0 mRNA expression to a certain degree. However, full up-regulation is usually associated with the rapid membrane expansion accompanying myelination. Whether this augmented up-regulation is due to further axonal signalling or events in the Schwann cell is unknown, but the results suggest that P0 expression can be regulated at several stages of synthesis.

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PubMed1991

Expression of P0 mRNA in myelinating Schwann cells is related to fibre size.

This study examines whether there is a relationship between the abundance of expression for P0 mRNA in myelinated Schwann cells and fibre diameter. Individual teased sciatic nerve fibres from young adult rats were hybridized with radiolabelled probe for P0 mRNA which is expressed in the perinuclear cytoplasm of the mid-internode. Signal intensity was measured as optical density of the developed autoradiograms. A highly significant positive linear correlation was present between signal intensity and fibre diameter. In a companion study, individual fibres were mounted in Araldite resin and transversely serially sectioned at 4 microns for autoradiography. Grain densities were determined for fibres of different diameters. Again, larger diameter fibres were associated with higher grain densities. The results indicate that the abundance of P0 mRNA expressed by a myelin-producing Schwann cell is related to fibre diameter with axonal size probably being the critical determinant. Axons may regulate P0 expression through the number of signalling molecules exposed on or released from the axolemma.

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PubMed1991

Loss of axonal contact causes down-regulation of the PLP gene in oligodendrocytes: evidence from partial lesions of the optic nerve.

We have examined the influence that axons may have on the expression of proteolipid protein (PLP), the major myelin protein of the CNS. Partial transections were made of the optic nerve of adult rats to produce approximately a 50% loss of axons. Twenty-eight days after lesioning, sections of the distal nerves were immunostained for GFAP and neurofilament protein and hybridized for PLP mRNA. The area of astrocytosis, as defined by GFAP immunostaining, usually exceeded the extent of axonal loss. PLP mRNA expression in oligodendrocytes in the denervated area of the lesioned nerve was reduced compared to the innervated zones of the lesioned nerve and the contralateral intact nerve. This down-regulation correlated with the axonal loss rather than the area of astrocytosis. The data support the contention that axons are necessary for oligodendrocytes to maintain full expression of their major myelin protein genes.

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PubMed1991

Rumpshaker: an X-linked mutation affecting CNS myelination. A study of the female heterozygote.

This study examines the myelin deficits found in the spinal cord and optic nerves of female mice heterozygotes for rumpshaker (rsh), an X-linked mutation causing hypomyelination. No clinical abnormalities were detected but morphological changes were evident, particularly in the spinal cord, which showed no evidence of resolving with age. In the spinal cord, scattered hypomyelinated axons, occasionally grouped in twos or threes, were the major feature; oligodendrocyte numbers were slightly elevated at all ages compared to normal male littermates and the total amount of myelin was reduced. Myelin protein composition of the sheaths was examined by immunostaining for myelin basic protein (MBP) and two peptide regions of PLP/DM-20 molecule; one being proteolipid protein (PLP)-specific and the other recognizing the c-terminal common to PLP-DM-20. The majority of myelin sheaths immunostained for MBP and PLP. Occasional MBP-positive sheaths failed to stain with PLP/DM-20 or PLP-specific antiserum. Therefore, at least two types of immunocytochemically-defined myelin sheaths are present in the heterozygotes. Changes in the optic nerves were much less obvious; glial cell numbers were increased but thinly myelinated axons were not detected although the total amount of myelin was reduced compared to normal littermates. In no instance were mosaic, amyelinated/hypomyelinated patches detected. Heterozygotes for rsh, therefore, are considerably different from those for other X-linked myelin mutations like the jimpy mouse and the myelin-deficient rat, both in regard to the severity of the lesions and their failure to recover with age.

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PubMed1990

Expression of myelin protein gene transcripts by Schwann cells of regenerating nerve.

The expression of many myelin-specific molecules in Schwann cells is profoundly decreased following denervation. This study examines the early reexpression of myelin protein genes associated with reinnervation. Following sciatic nerve crush, the distal, regenerated nerve was divided into appropriate (2.5 or 5 mm) consecutive lengths in which gene expression was monitored using Northern blotting, in situ hybridization, and immunostaining. The spatial separation of the distal axon tip and the more proximally located Schwann cells showing initial upregulation of P0 mRNA was constant over the period of 5-13 days after crush at approximately 3-4 mm in fixed, processed material. Axons associated with Schwann cells showing the initial upregulation were completely or partially enveloped in Schwann cell cytoplasm, with very few having any degree of ensheathment. It is probable that only a limited axon-Schwann cell contact is required for induction of the myelin protein genes. Myelin-associated glycoprotein mRNA was upregulated prior to those for P0 and myelin basic protein which had similar time courses. Reexpression of galactocerebroside also preceded that for P0 mRNA. Signal abundance for all myelin proteins decreased in a proximal to distal direction from the crush site, and with time the "wave" of upregulation moved distally down the nerve. In the more proximal, remyelinating zones, the signal intensity exceeded that of the contralateral normal nerve. Signal intensity also varied considerably between adjacent, expressing Schwann cells. The data provide further evidence of the strong temporospatial relationship between axons and the regulation of myelin protein genes in Schwann cells.

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PubMed1990

Rumpshaker mouse: a new X-linked mutation affecting myelination: evidence for a defect in PLP expression.

This report describes a new X-linked mutation in mice, named rumpshaker (rsh) which is associated with hypomyelination of the central nervous system. Myelination commences appropriately but the majority of sheaths fail to develop normally. Oligodendrocytes are increased in number and have prominent Golgi apparatus, rough endoplasmic reticulum and free ribosomes. Occasional cisternae of rough endoplasmic reticulum are distended. Some dense lamellar inclusions occur in oligodendrocytes but overall, degenerative changes and cell death are uncommon. Immunostaining demonstrates a major defect in expression of PLP DM-20. Using site-specific antisera directed at different portions of the PLP/DM-20 molecule, the major defect appears to be with PLP where virtually no myelin sheaths are positive. Antiserum against the C-terminal common to PLP and DM-20 shows reduced but definite myelin staining. Genetic analysis indicates a locus at or close to the PLP/jimpy (jp) locus. The rsh mutation, however, differs from jp in that affected mice have normal longevity, can breed, produce substantially more myelin and have increased numbers of oligodendrocytes.

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PubMed1990

Effect of optic nerve transection upon myelin protein gene expression by oligodendrocytes: evidence for axonal influences on gene expression.

The effect of optic nerve transection on myelin protein gene expression was studied in rats following axotomy at two ages: during active myelination (17 days of age) and after peak expression of the genes (35 days of age). mRNA levels for proteolipid protein, myelin basic protein and myelin-associated glycoprotein were assessed by northern and dot blotting and by in situ hybridization using tissue sections and cultured individual oligodendrocytes. Transection at 17 days caused down-regulation of mRNAs for proteolipid protein, myelin basic protein and myelin-associated glycoprotein by 5 days after axotomy with an increase in GFAP mRNA. A more protracted change followed axotomy at 35 days of age. The abundance of mRNAs for proteolipid protein and myelin basic protein was significantly reduced by 28 days after transection in the affected nerve. Quantification of proteolipid protein mRNA expression in individual oligodendrocytes confirmed the down-regulation. However, in contrast to the effects on the major myelin proteins, the abundance of myelin-associated glycoprotein mRNA increased in the affected nerve for at least the initial month after lesioning at 35 days. The results show that optic nerve transection has significant effects on myelin protein mRNA expression in oligodendrocytes of optic nerve. However, the changes in myelin protein gene activity are relatively small and more protracted than those seen in Schwann cells after peripheral nerve section. Because axotomy also causes marked changes in the glial population of the optic nerve it is not possible unequivocally to ascribe the alteration in gene expression to loss of axons. However, the data may provide evidence that axons do influence myelin protein genes in oligodendrocytes and are necessary for them to develop their full expression.

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PubMed1989

Expression of myelin protein genes in Schwann cells.

The expression of myelin protein genes in Schwann cells has been studied in situ hybridization. 35S-UTP-labelled, antisense and sense RNA probes to the major protein Po, myelin basic protein (MBP), myelin-associated glycoprotein (MAG) and proteolipid protein (PLP) were employed with paraffin-embedded sections, teased fibres and dissociated Schwann cells from sciatic nerves of rats. Teased fibres were also prepared from cervical sympathetic trunks. Po mRNA was strongly expressed in the mid-internodal perinuclear area of Schwann cell cytoplasm. The degree of signal appeared to be related to fibre size. MBP mRNA showed a diffuse pattern along the Schwann cell internode with a marked increase in grains at the paranodal cytoplasm, particularly in larger fibres. This distribution suggests that the paranodal area is a major site of insertion of MBP into myelin membrane. The expression of MAG and PLP mRNA was markedly lower than Po and MBP. Both mRNAs were localized in the perinuclear cytoplasm and showed a dependence on fibre size. No significant signal was present in Schwann cells associated with unmyelinated axons. In addition to providing data on the cellular expression of myelin protein genes, these studies have shown that teased fibres are invaluable in allowing the localization of low abundance mRNAs.

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PubMed1989

The distribution of MAG in association with the axonal lesions of canine progressive axonopathy.

The distribution of myelin-associated glycoprotein (MAG) was examined by immunocytochemistry in the spinal cord, accessory cuneate nucleus and lumbar ventral nerve roots of dogs affected by progressive axonopathy. These areas were chosen because of the frequency of spheroids and the associated changes in the myelin sheath, including vacuolation, demyelination, remyelination and accumulation of a granular, amorphous material within the sheath. Normal animals demonstrated the expected distribution of MAG; periaxonal and associated with uncompacted membrane such as Schmidt-Lanterman incisures. The majority of early axonal spheroids were surrounded by a MAG-positive zone but in the larger swellings and longer duration cases this was sometimes absent in places even though the axon was associated with Schwann cell processes. Axons in vacuolated fibres were commonly surrounded by a single adaxonal process of Schwann cell and normal periaxonal space. This was immunoreactive for MAG but in situations where the process was incomplete or the space distorted, staining was absent. The granular material failed to stain for MAG. Distorted Schmidt-Lanterman incisures, a feature of the advanced disease, were strongly positive. In the CNS, spheroids without myelin sheaths or unassociated with oligodendroglial processes were negative for periaxonal MAG. The study confirms the localization of MAG at the periaxonal space. It also raises the question of how the distribution of periaxonal MAG is affected by axonal swelling with a consequent increase in axonal surface area.

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PubMed1987

Feline dysautonomia: an ultrastructural study of neurones in the XII nucleus.

A feline dysautonomia of unknown aetiology has been reported in numerous cats in the United Kingdom since 1981. The consistent histological lesion is a chromatolytic-type change within the neurones of the autonomic nervous system, which is also found less frequently in non-autonomic regions, such as the XII nucleus. This study describes the ultrastructural changes in the XII nucleus within the first 2 weeks of clinical disease. In the abnormal neurones there is a dispersion of the Nissl substance, progressing to dilation of individual cisternae by an electron-dense floccular material. Such cisternae have lost the majority of their ribosomes. Normal Golgi complexes can be seen in neurones where there is only slight dispersion of the Nissl substance, but no Golgi complexes, either normal or abnormal, can be identified in any cell in which the Nissl substance is markedly disrupted. There is proliferation of smooth endoplasmic reticulum in several neurones, and there may also be an increased number of morphologically normal mitochondria. The nuclei of affected neurones are eccentric with crenations of the nuclear envelope, and in some cases nucleolar changes are also observed. Autophagic vacuoles are present in small numbers. Other organelles appear normal. These findings compare closely to those for the autonomic neurones, suggesting that the primary effect of the causal agent(s) is on the protein synthetic pathway of specific neurones.

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PubMed1987

Progressive axonopathy: an inherited neuropathy of boxer dogs. 4. Myelin sheath and Schwann cell changes in the nerve roots.

Changes in the myelin sheath have been studied in the nerve roots of dogs with Progressive axonopathy, an autosomal recessive inherited neuropathy. The earliest changes were attenuation of the sheath at the proximal paranode and adjacent internode, probably in response to the axonal swelling which occurs in this area. Myelin bubbles were frequently observed along internodes. As the disease developed, progressively more fibres demonstrated short internodes of irregular length and thin myelin sheaths suggesting extensive remyelination and remodelling of the sheath. Short lengths of axons devoid of myelin, and occasional macrophages were also encountered. Sheaths of both original and newly formed internodes were highly irregular in outline. Occasional intra-axonal projections of adaxonal Schwann cell cytoplasm were observed, but complex interdigitations were unusual. A moderately electron-dense, granular material accumulated within the myelin sheath, becoming more obvious in the advanced disease. This material of unknown origin and composition was located predominantly at the intraperiod line principally between the adaxonal cytoplasm and the inner major dense line, but also at Schmidt-Lanterman incisures and between paranodal loops. Xenografts of the canine nerves into athymic mice failed to demonstrate any of the myelin sheath changes. The temporal and spatial relationship of the myelin sheath and axonal changes and the failure to reproduce the natural lesion in grafts suggest that Schwann cell alterations probably occur in response to the axonal changes.

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PubMed1986

Progressive axonopathy: an inherited neuropathy of boxer dogs. 3. The peripheral axon lesion with special reference to the nerve roots.

Progressive axonopathy is an autosomal recessive inherited neuropathy of Boxer dogs with lesions in the CNS and PNS. This paper describes the axonal changes in the lumbar and cervical nerve roots and tibial nerve. By 2 months of age the proximal paranodal areas of many larger diameter fibres show small axonal swellings, sometimes with attenuation or loss of the associated myelin sheath. Axoplasmic changes within swollen and non-swollen fibres include disorganization of the peripheral neurofilaments and small accumulations of vesicles and vesiculo-tubular profiles, particularly in the sub-axolemmal area. Occasional fibres, more often in the cervical roots, are massively distended with disorganized neurofilaments. The frequency of the membranous accumulations decreases with progression of the disease. Many axons show a markedly irregular or corrugated outline and are surrounded by an attenuated sheath. The peripheral axonal cytoskeleton is disorganized and misaligned, whereas the central structures maintain a more normal arrangement. Regenerating axonal clusters are common in the cervical ventral roots but occur infrequently in the lumbar roots. Similar axonal changes occur in the peripheral nerves but at a much lower frequency. Any membranous accumulations or cytoskeletal disorganization are more probable in the proximal tibial nerves, while the frequency of axonal degeneration and regeneration increases distally. The morphological appearances indicate gross disturbances in axon-sheath cell relationships and suggest that abnormalities in the transport of various axoplasmic organelles may be involved in the pathogenesis of the axonal lesion.

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PubMed1986

Progressive axonopathy: an inherited neuropathy of boxer dogs. Quantitative and morphometric analysis of the peripheral nerve lesion.

Previous studies have described and illustrated the lesions in the peripheral nerves in progressive axonopathy, an inherited neuropathy of Boxer dogs. The present paper assesses these changes using quantitative techniques. Cervical and lumbar nerve roots and tibial, phrenic and medial cutaneous radial nerves have been studied in affected and age-matched normal dogs aged 2 months to 3 years. The dorsal and ventral nerve roots, and to a lesser extent the proximal nerves, contain a proportion of swollen myelinated axons whereas in the middle and distal nerves the larger diameter fibres fail to develop to their expected maximum calibre. The unmyelinated axons remain the same size as those in normal dogs. Myelin sheath changes, with attenuation or loss of the sheath and/or remyelination, become increasingly prevalent through the course of the disease, always maintaining a proximal to distal decrease in their frequency. Quantification indicates that, particularly in the ventral roots, many axons have disproportionately thin sheaths with shortened internodes. Axonal degeneration and regeneration increase in frequency in the distal nerves as the disease progresses. The cervical ventral roots prove an exception in that they contain large numbers of regenerating clusters at most stages. It is suggested that in progressive axonopathy an axonal transport failure may occur in the roots leading to the axonal swellings, as a result of which a developmental hypoplasia occurs in the more distal, larger diameter fibres. The prominent, but unevenly distributed, myelin sheath changes indicate a severe disturbance in axon-sheath cell inter-relationships.

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PubMed1983

Familial cerebellar ataxia with hydrocephalus in bull mastiffs.

A family of bull mastiff pups in which 16 animals developed certain neurological signs is described. It is probable that the disease is inherited in an autosomal recessive manner. Clinical and pathological examination of six animals revealed ataxia, behavioural abnormalities and a visual defect associated with symmetrical lesions in the cerebellar nuclei, lateral vestibular nucleus and inferior colliculus together with a communicating hydrocephalus. The cerebellar lesions consisted of vacuolation, gliosis and axonal degeneration. Evidence for both axonal and oligodendroglial abnormalities was present and these probably result from a genetically determined metabolic disturbance in the affected neurones.

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PubMed1983

Nerve fibres in spinal cord impact injuries. Part 1. Changes in the myelin sheath during the initial 5 weeks.

The spinal cords of cats were subjected to an impact injury using a "weight dropping" technique and sequential changes in the sheaths of non-degenerate myelinated fibres studied over a 3-week period. By 1 1/2 h after impact fibres showed retraction of some lateral loops from one paranode. The extent and severity of this change increased over the first week so that partial and full thickness demyelination were seen frequently. Partial demyelination most commonly resulted from the internodal termination of the innermost lamellae at an internodal location often associated with a Schmidt-Lantermann incisure. Remyelination by both Schwann cells and oligodendroglia occurred at the end of the second week. Oligodendroglial myelin showed many features of immaturity, similar to those found during development. It is suggested that the very earliest myelin damage is mechanical but is aggravated by other factor(s) one of which is probably ischaemia. Within the most severely injured areas there is death of oligodendroglia and any surviving axons are remyelinated principally by Schwann cells. In intermediate and minimally damaged areas of white matter oligodendroglial remyelination predominates.

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