Search PubMed⌕ Search

Biomedical subjects

M Pollock

Publications and source records attributed to M Pollock.

At least 37 records · Page 2Linked to original sources
PubMed1987

Decay of the oocyte-type heat shock response of Xenopus laevis.

Xenopus oocytes have a complex heat shock response. During transition of the oocyte into fertilized egg, the heat shock response undergoes several qualitative and quantitative changes culminating in its complete extinction. Heat shock induces oocytes to synthesize four heat shock proteins (hsps): 83, 76, 70, and 57. After ovulation, two additional proteins (hsps 22 and 16) are inducible. The heat shock response of spawned eggs can be modified by changing the ionic configuration of the external medium and by adding pyruvate and oxaloacetate to the media. Since Xenopus eggs do not synthesize mRNA, these modifications to the external medium apparently alter the utilization of preexisting messenger RNAs in protein synthesis. Artificial activation terminates inducibility of hsps 76, 57, and 16 and diminishes the hsp 70 response. Two new heat shock proteins-66 and 48-are also inducible in artificially activated eggs. Fertilization, on the other hand, terminates the heat shock response; no hsps can be induced. However, hsp 70 appears to be made constitutively in fertilized eggs. RNA blot analyses reveal that oogenic hsp 70 messenger RNA is retained in eggs and early embryos. This messenger is apparently used for heat-induced synthesis of hsp 70 before fertilization and for constitutive synthesis of hsp 70 in zygotes.

Animals↗
PubMed1987

Collagen synthesis in axotomized peripheral nerve: evidence against Schwann cell involvement.

To explore the role of Schwann cells in nerve collagen formation, fascicular collagen was measured in axotomized rat sciatic nerve after regeneration or permanent axotomy. The same increase in fascicular collagen was seen in both paradigms. Thus there is no evidence that Schwann cells unassociated with axons make an important contribution to nerve collagen synthesis after transection.

Animals↗
PubMed1987

Occurrence of multiple sclerosis in the north and south of New Zealand.

An impression that multiple sclerosis is commoner in southern parts of New Zealand than in the north has never been tested rigorously. Identical methods were used to determine the prevalence and incidence of multiple sclerosis in two regions: the Waikato (in the North Island) and Otago and Southland (in the South Island). No cases were found in Maoris, while the expected number was 11.7. The prevalence rate of multiple sclerosis (excluding possible cases) in non-Maoris was 24 per 100,000 in the northern region and 69 per 100,000 in the south. The incidence rate was also more than twice as high in the southern region. These findings are considered in relation to genetic and environmental hypotheses about the aetiology of multiple sclerosis.

Adolescent↗
PubMed1986

Morphological and functional effects of triiodothyronine on regenerating peripheral nerve.

The functional and morphologic consequences of treatment of peripheral nerve lesions with exogenous 3,3',5-triiodo-L-thyronine (T3) are unclear. In this study adult Wistar rats with sciatic nerve crush lesions were treated with 20 micrograms/kg/day of T3. The treated animals gained weight though more slowly than vehicle-treated rats. Ten control and 10 experimental animals assessed 4 days postoperatively for sensory axon regeneration by the "pinch test" showed no significant difference in distance regenerated. Motor function recovery was monitored for 21 days after nerve crush lesions by the vestibular placing response and also showed no significant difference. Light microscopy of transverse epoxy sections of the sciatic nerve 5 mm distal to the lesion showed no significant difference in whole nerve area or myelinated fiber density but quantitative electron microscopy revealed a significant increase in axolemma, myelin spiral length, whole nerve fiber area, and nerve fiber perimeter in T3-treated rats. Statistically nonsignificant increases in axonal area and myelin periodicity were also noted. These results are interpreted as indicating that although T3 treatment is not functionally beneficial in the regeneration of adult mammalian peripheral nerve it nonetheless has subtle morphologic effects that indicate a stimulating effect on membrane synthesis.

Animals↗
PubMed1986

Proximal and distal changes in collagen content of peripheral nerve that follow transection and crush lesions.

Collagen content of rat sciatic nerve was measured 10 weeks after either nerve transection or nerve crush. Nerve transection led to a significant increase in fascicular collagen in nerve segments 2.5 mm proximal and distal to the injury site. Remote from the transection, fascicular collagen was also significantly increased, this effect being most marked distally. Nerve crush by comparison resulted in only a small increase in fascicular collagen, significantly less than after transection. The greater amount of fascicular collagen far distal to the nerve injury could relate to a predominantly caudal endoneurial flow of inflammatory or growth factors. Differences in the amount of fascicular collagen formed after nerve transection compared with nerve crush are clearly due to factors other than axonal degeneration, and may relate to collagen synthesis by denervated Schwann cells or to the severity of the nerve injury.

Animals↗
PubMed1985

Morphometric effects of use and disuse on peripheral nerve.

Rat peripheral nerve was evaluated morphometrically following hemicordotomy, tenectomy, or both to assess the effects of disuse and hyperactivity on the peripheral nervous system. Hemicordotomy resulted in an increase in diameter of nerve fibers supplying both "fast" and "slow" skeletal muscles in hypoactive and hyperactive limbs. Nerve fiber atrophy occurred only in nerve to "fast" muscle following disuse induced by hemicordotomy and tenectomy. The possible role of "motor nerve growth factor" or altered axoplasmic flow in bringing about these morphologic changes in peripheral nerve is discussed.

Animals↗
PubMed1985

Initial coping responses and psychosocial characteristics of children with insulin-dependent diabetes mellitus.

School-aged children with newly diagnosed insulin-dependent diabetes mellitus (IDDM) were studied longitudinally in order to document how they adjusted to the medical illness and to assess salient background factors. The extent of life stress and the prevalence of psychiatric disorders that predated the IDDM were within normative ranges, and there was no characteristic preexisting "diabetic personality." The initial strain of living with IDDM elicited two general modes of coping. The prototypical and subdued reaction (seen in 64% of the children) consisted of mild sadness, anxiety, feeling of friendlessness, and social withdrawal. The rest of the children (36%) exhibited reactions that met criteria for a psychiatric disorder; depressive syndromes were the most common presentations. Anamnestic factors and the parents' initial responses to their children's IDDM were unrelated to how the children themselves coped. However, psychiatrically diagnosable reactions were more likely among children whose parents were of low socioeconomic status and had marital distress. Coping with the diagnosis and the early impact of IDDM took no more than 7 to 9 months, no matter how severe the child's response was initially.

Adaptation, Psychological↗
PubMed1985

The intermediate filament protein desmin in cardiac and skeletal muscle from normal and dystrophic (BIO 14.6) hamsters.

Electrophoretic separation on polyacrylamide gels of polypeptides extracted from skeletal and cardiac muscle of BIO 14.6 dystrophic, carrier, and random-bred normal hamsters demonstrates similar quantities and electrophoretic mobility of a protein having a relative mass of 52 000 daltons (apparent isoelectric point 6.2) from all sources examined; we have tentatively identified this protein as the intermediate filament protein desmin. Reaction of such separated polypeptides transferred to nitrocellulose blots with antibodies raised against this protein fails to show immunological differences in this 52 000 dalton protein in cardiac and skeletal muscle from normal and dystrophic animals. Indirect immunofluorescence analysis of skeletal myofibrils from 30-to 60-day normal and dystrophic animals shows no differences in Z-line staining when immunoglobulins from anti-alpha-actinin serum are used as primary antibodies. Immunoglobulins from the putative anti-desmin serum also produce Z-line staining of skeletal myofibrils from normal animals, but fail to bind to the Z-lines of some skeletal myofibrils from dystrophic hamsters.

Animals↗
PubMed1984

Depressive disorders in childhood. II. A longitudinal study of the risk for a subsequent major depression.

As part of a longitudinal nosologic study of major depressive disorder, dysthymic disorder (DD), and adjustment disorder with depressed mood ( ADDM ) in a school-aged cohort, the predictive validity of each diagnosis was examined. Using all available data on the course of the disorders, the criterion was the first subsequent major depressive episode. Major depressive disorder and DD signaled a similarly high risk of a new bout of depressive illness. For the children who recovered from their first episode of major depression and then had their second one (40%), the free interval did not exceed two years; an underlying dysthymia increased the risk of recurrence. Major depression and dysthymia were distinct from ADDM and a set of control disorders; the latter two diagnostic groups were associated with a minimal risk for major depression.

Adjustment Disorders↗
PubMed1984

Peripheral nerve morphometry in stroke patients.

Sural nerve biopsy specimens from affected and non-affected limbs of stroke patients were examined morphometrically. Two principle abnormalities of peripheral nerve were found in hemiparetic and hemiplegic limbs. First, the frequency of abnormal teased nerve fibers was significantly increased with abnormal internodes frequently "clustered" and showing a 50% or more reduction in myelin thickness. Second, the mean diameter of myelinated nerve fibers was reduced. These results suggest a primary atrophy of peripheral nerve fibers in the affected limbs of stroke patients with secondary demyelination. Possible aetiological factors include disuse, transynaptic degeneration, ischemia, pressure effect, and decreased axoplasmic flow. It would seem that the structural integrity of peripheral nerve is frequently compromised following a cerebral lesion.

Adult↗
PubMed1983

Peripheral neuropathy in Tangier disease.

Peripheral nerve morphometry was assessed in four patients with Tangier disease. Three patients with a relapsing and remitting multiple mononeuropathy had prominent peripheral nerve demyelination and remyelination with affected internodes clustered along particular nerve fibres. Putative lipid vacuoles were almost exclusively confined in this multifocal neuropathy syndrome to Remak cells. By contrast a fourth patient with a slowly progressive syringomyelia-like neuropathy had advanced peripheral nerve degeneration and a more global distribution of lipid vacuoles within peripheral nerve. A review of Tangier disease in the literature indicated the possibility of additional peripheral nerve syndromes. The clinical heterogeneity raises the possibility of different metabolic errors in Tangier disease or a common metabolic error subject to genetic influences. The results of this study indicate that normal serum cholesterol levels do not exclude a diagnosis of Tangier disease. It is therefore advisable to determine both high density lipoproteins and serum cholesterol levels in patients with undiagnosed multifocal neuropathy or syringomyelia-like syndromes.

Adult↗
PubMed1981

Disulfiram neuropathy. A morphometric study of sural nerve.

This report describes peripheral nerve morphology in 3 patients whose acute polyneuropathy followed disulfiram therapy. In all patients a combination of axonal degeneration with segmental demyelination and remyelination was seen, suggesting a varying degree of toxicity to both cytons and Schwann cells. The observed randomness of abnormal internodes argued against primary axonal atrophy and secondary demyelination. While large myelinated fibres were preferentially lost, ultrastructural studies also suggested degeneration of unmyelinated fibres. Because of high chloral consumption at the onset of peripheral nerve disease in 2 patients, the possibility of disulfiram-chloral interaction was considered. Present evidence suggests that the combined use of chloral or its derivatives with disulfiram is best avoided.

Adult↗
PubMed1981

Experimental potassium depletion myopathy.

Myopathic morphological changes were observed in the calf muscles of rats maintained on a potassium-depleted diet for 30-50 days. Light-microscopic changes were more severe in the superficial gastrocnemius muscle fibres and included pallor, swelling and vacuolation, progressing to necrosis, mononuclear cell infiltration and phagocytosis. Mitochondrial disruption, transverse tubular dilatation, membranous body formation and vacuolation were seen on ultrastructural examination. Both vacuoles and subsarcolemmal membranous bodies were shown to be in continuity with the transverse tubular system. More advanced myopathic changes were those of sarcomere destruction and muscle fibre necrosis. Morphological changes resemble those of human potassium depletion myopathy. Ineffective energy metabolism and focal ischaemia due to impaired vasodilatation are proposed as mechanisms for the myopathy of potassium depletion.

Animals↗
PubMed1981

Experimental cold injury to peripheral nerve.

Focal non-freezing injury to rat sciatic nerve resulted in nerve conduction block and cessation of axoplasmic transport. Rats showed early functional recovery but subsequently developed a slowly progressive sciatic nerve paralysis. Horseradish peroxidase studies revealed prominent nerve oedema with early enhanced pinocytosis and later, passive leakage through damaged endoneurial capillaries. Detailed microscopy indicated a striking selective vulnerability to cold based on nerve fibre diameter. Unmyelinated fibres were spared while large myelinated nerve fibres showed severe axonal degeneration. Paranodal and segmental demyelination were infrequent findings and may have resulted from early axonal swelling. Possible pathogenic mechanisms to explain the degeneration of myelinated fibres in hypothermic injury are discussed. It is concluded that the gradient of clinical severity seen in limb hypothermic injuries has a pathological correlate in peripheral nerve.

Animals↗
PubMed1980

Clinical and morphological features of gold neuropathy.

Three cases of gold-related neuropathy are reported. Clinical features include an acute, symmetrically progressive polyneuropathy, focal or generalized myokymia and a tendency for initial neurological deterioration followed by improvement, after cessation of chrysotherapy. The degree of clinical recovery related to maximal disability. Morphological findings on sural nerve biopsies revealed both axonal degeneration and segmental remyelination. Similar peripheral nerve histology was seen in a parallel animal study in which the severity of the neuropathy was dose-related.

Adult↗
PubMed1979

Identical twins with papilloedema and cranial nerve palsies.

Central nervous system involvement has not been reported previously as a manifestation of sarcoidosis in monozygotic twins. Twin sisters developed multiple cranial nerve palsies and papilloedema within a two month period. Clinical features and the course of their diseases were remarkably similar.

Adult↗