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L S Mitchell

Publications and source records attributed to L S Mitchell.

14 recordsLinked to original sources
PubMed2000

Adenovirus 7a: a community-acquired outbreak in a children's hospital.

BACKGROUND: Adenoviruses produce many illnesses in children, particularly respiratory and gastrointestinal disease. The most common adenoviral respiratory infections in children are caused by types 1, 2, 3 and 5. Adenoviruses spread rapidly in closed environments often causing epidemic disease. Serotype 7a has been responsible for outbreaks of respiratory disease in children living in close proximity with one another. This report describes a large community-acquired adenovirus 7a epidemic in hospitalized children. METHODS: Evaluation of all patients with cultures positive for adenovirus from a children's hospital-based virology laboratory during a recognized adenovirus outbreak. All such adenovirus isolates were typed, and patients with adenovirus 7a are described by review of medical records. RESULTS: Between March 1 and July 26, 1997, 47 children admitted to the hospital were identified as infected with adenovirus. Of these 47 patients 26 (55%) were infected with adenovirus 7a. Twenty-four (92%) infections were community-acquired. The age range was 11 days to 10 years with a median of 9.5 months. Twenty-two patients (84%) had respiratory symptoms, and 21 (8%) had fever, making these the most common symptoms. The mean durations of fever and hospitalization were 5.5 and 7 days, respectively. One of 26 patients died. CONCLUSIONS: Adenovirus 7a can cause large community epidemics affecting children. The disease produced by adenovirus 7a in children is almost exclusively of the respiratory tract, and in some individuals it may be very severe and possibly fatal.

Adenovirus Infections, Human↗
PubMed1992

Developmental expression of major myelin protein genes in the CNS of X-linked hypomyelinating mutant rumpshaker.

Rumpshaker (rsh) is an X-linked mutation causing hypomyelination of the CNS of mice and has recently been identified as an allele of jimpy (jp). The mutation (known as jprsh) differs in several respects from other X-linked myelin mutants, including jp, in that mice have normal longevity, oligodendrocyte numbers are not decreased, and cell death is not a feature. Myelin sheaths are deficient in immunostainable PLP protein. The present study examines the developmental expression of the major myelin protein genes and translatability of PLP and MBP mRNA. Differences between the spinal cord and brain of mutants are evident in that mRNA levels are more markedly decreased in the brain. Protein levels are severely reduced in both locations and to a proportionately greater extent than the mRNA, particularly in the spinal cord where PLP RNA and protein are approximately 80% and 10-20%, respectively, of age-matched wild type mice. DM-20 protein, the other major product of the PLP gene, is disproportionately expressed in rumpshaker as is a 10 kDa proteolipid. In vitro translation studies indicate a marked decrease in PLP translation products from mutant RNA. There is no deficiency in the number of PLP mRNA-expressing oligodendrocytes although the abundance per cell is reduced. The data suggest that the phenotypic effects of the mutation may be associated with reduced translation of major myelin proteins, in particular PLP and its incorporation into compact myelin. However, the mutation is compatible with survival of oligodendrocytes and their differentiation to the stage of expressing PLP/DM-20 mRNA.

Aging↗
PubMed1992

Avoiding laparotomy in nonsurgical pneumoperitoneum.

Patients with free intraperitoneal air collections usually undergo emergency surgery, and the majority will have a gastrointestinal tract perforation. However, there is a subset of patients in whom no identifiable perforation is found at surgery. This entity of noniatrogenic, nonsurgical spontaneous pneumoperitoneum is being diagnosed more frequently at present and is commonly associated with other disease processes that, together, may suggest a benign process. Therefore, a diagnostic algorithm that would preclude operative intervention in this cohort of patients would be of paramount clinical importance. In this report, we present representative cases of the most common types of nonsurgical pneumoperitoneum, review the pathogenesis of this disorder, and discuss its relationship with pneumatosis cystoides intestinalis, pulmonary disorders, scleroderma, and gynecologic processes. Finally, we outline a diagnostic algorithm that may identify patients who can safely be observed, thereby reducing the incidence of negative laparotomies and, secondarily, the aggregate cost of health care.

Algorithms↗
PubMed1992

Temporal relationships between induced changes in c-myc mRNA abundance, proliferation, and differentiation in HL60 cells.

Changes in the relative abundances of c-myc mRNA have been related to changes in other parameters of differentiation (histochemical, clonogenic) during the course of the differentiation of HL60 cells to monocytes/macrophages or to granulocytes. Induction of differentiation to monocytes/macrophages was marked by a rapid rate of appearance of committed cells (80 to 90% in 24 hours) and a concomitant rapid loss of c-myc mRNA. Induction of granulocytic differentiation resulted in a much slower rate of appearance of committed cells (50% in 48 hours), and a much faster rate of loss of c-myc mRNA (tenfold in 1 hour). These data are consistent with there being a direct link between down-regulation of the expression of c-myc and the onset of proliferation arrest and monocytic differentiation, but show there is no such association of c-myc mRNA abundance and proliferation or differentiation during the maturation of HL60 granulocytes.

Cell Differentiation↗
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.

Animals↗
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.

Animals↗
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.

Animals↗
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.

Animals↗
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.

Animals↗
PubMed1990

Effect of cooling on the responsiveness of canine tracheal muscle.

Airway cooling causes bronchoconstriction in many persons who have asthma. To determine the direct effect of cooling on the response of tracheal muscle to parasympathetic and muscarinic stimuli in situ, the temperature of a segment of canine cervical trachea was adjusted to 37 degrees, 30 degrees, or 25 degrees C by superfusing temperature-controlled saline over its epithelial surface. The contractile response of the tracheal muscle to electrical stimulation of the vagus nerves and to intra-arterial acetylcholine was then determined. Cooling the segment to 25 degrees C decreased the contraction induced by parasympathetic stimulation. However, cooling did not alter the contraction induced by intra-arterial acetylcholine. Parallel studies were conducted in vitro using nine excised tracheal muscle strips taken from the same section of trachea in three additional dogs. Cooling the tracheal muscle to 25 degrees C in vitro increased the maximal contraction induced by both electrical field stimulation and by acetylcholine. Thus, cooling in situ does not alter the response of tracheal muscle to muscarinic stimuli and inhibits the response to parasympathetic stimuli. These data indicate that augmentation of the tracheal muscle response elicited by cooling in vitro does not reflect the response in situ. They suggest that a direct effect of cooling on airway smooth muscle response to parasympathetic and muscarinic stimuli does not account for cooling-induced bronchoconstriction in vivo.

Acetylcholine↗
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.

Animals↗
PubMed1984

Intracranial ultrasound diagnosis of neonatal periventricular leukomalacia.

Periventricular leukomalacia (PVL) is characterized by focal areas of white matter necrosis adjacent to the external angles of the lateral ventricles. The diagnosis of PVL has hitherto been limited to autopsy findings. The authors discuss pertinent literature and report in vivo diagnosis of nonhemorrhagic PVL by real-time intracranial ultrasonography. They recommend further study of ultrasound as a diagnostic method for evaluating infants at risk for PVL.

Brain↗