Search PubMed⌕ Search

Biomedical subjects

J R Scott

Publications and source records attributed to J R Scott.

At least 127 records · Page 7Linked to original sources
PubMed1992

Scrapie in the central nervous system: neuroanatomical spread of infection and Sinc control of pathogenesis.

Following bilateral intraocular (i.o.) infection of Sinc s7 mice with ME7 scrapie, sequential tissue pools were taken from retina, optic nerve, superior colliculus (SC), dorsal lateral geniculate nucleus (dLGN), visual cortex and cerebellum. The infectivity levels in these pools were estimated by intracerebral (i.c.) assay in C57BL/FaBtDk mice. Infectivity was first detected in retina at 35 days post-injection (as an increase above residual injected inoculum), SC at 56 days, dLGN at 77 days and in optic nerve, visual cortex and cerebellum at 98 days. Pathological lesions were shown to develop in the same sequence later in the incubation period. Comparison of sequential retina and SC assays in congenic mice, which differ only in the vicinity of the Sinc locus, revealed a difference in the initial detection and progression of i.o. infection of between 60 and 100 days, indicating that Sinc acts by delaying the initiation of replication. Higher levels of infectivity were found in retina and SC of mice infected with 79A scrapie, which destroys the photoreceptor layer in the retina, than with ME7 scrapie, which does not. Retrograde transport of infection was indicated by the levels of infectivity in the retina after i.c. infection with ME7 or 79A scrapie. These results indicate that scrapie spread within the central nervous system is restricted to neuroanatomical pathways, and that Sinc controls the initiation, but not the rate of replication.

Animals↗
PubMed1992

CooB is required for assembly but not transport of CS1 pilin.

CS1 pili are filamentous proteinaceous appendages found on many enterotoxigenic Escherichia coli (ETEC) strains isolated from human diarrhoeal disease. They are thought to effect colonization of the upper intestine by facilitating binding to human ileal epithelial cells. We have identified a gene, cooB, which lies directly upstream of cooA, the gene that encodes the major structural CS1 protein. When translated in vitro, the protein product of cooB migrates in sodium dodecyl sulphate/polyacrylamide gel with an apparent molecular mass of 26 kDa, which is consistent with that predicted from its DNA sequence. We constructed a mutant allele (cooB-1) by insertion of the omega fragment, which inhibits transcription and translation, into the cooB gene in vitro. In a derivative of an ETEC strain with the cooB-1 mutation (JEF100) and a plasmid that encodes Rns (pEU2030), the positive regulator required for CS1 expression, no cooB and a greatly reduced level of cooA product was detectable in total cell extracts. The reduction of cooA in this strain appears to result from polarity of the cooB mutation because introduction of the wild-type cooA gene in trans causes production of CooA protein, which is found in cell pellet extracts, in extracts containing only surface proteins and in the culture supernatant. Therefore, in the absence of CooB, CooA is stable and it is transported through both inner and outer membranes. However, the cooB-1 strain with cooA in trans does not cause haemagglutination of bovine erythrocytes (the model system used to assay adherence mediated by coli surface antigen 1 (CS1) pili).(ABSTRACT TRUNCATED AT 250 WORDS)

Antigens, Bacterial↗
PubMed1992

Standardization of a technique for analysing the frequency of parasite-specific cytotoxic T lymphocyte precursors in cattle immunized with Theileria parva.

A limiting dilution microculture system was optimized to quantify the frequency of Theileria parva-specific cytotoxic T lymphocyte precursors (CTLp) in peripheral blood mononuclear cells (PBMC) from immune cattle. Optimal results were obtained with responder cell input levels ranging from 2 x 10(4)/well to 6.25 x 10(2)/well, along with 1-5 x 10(3)/well stimulator cells in standard supplemented RPMI 1640 medium containing 2.5-5% T cell growth factors. Thirty-six microtitre wells were established at each responder input level. Cultures were incubated for 7 days at 38 degrees C, at the end of which time individual wells were screened for cytotoxic activity in a 4-h 111indium oxine-release assay. Analysis of the cytotoxicity data, by a computer-programmed maximum likelihood estimation method indicated that they conformed to the Poisson model of single-hit kinetics. Estimates of frequencies ranged from 1:3600 to 1:5275 CTLp in PBMC of eight cattle between 1 and 24 months after immunization with T. parva. By contrast, no CTLp were detected in six naïve animals analysed to a responder cell input of 10(5)/well. Split-well analysis of individual microwells showed that the CTL clones generated under limiting dilution conditions displayed exquisite specificity for parasitized cells, were genetically restricted and in some animals were parasite strain-specific.

Animals↗
PubMed1992

Pregnancies following implantation of an artificial fallopian tube in rabbits.

The first cases of pregnancies obtained in vivo in animals after implantation of a Teflon artificial fallopian tube model are presented. The Teflon prosthesis was implanted into the uterine cornua of rabbits and fixed subcutaneously in the abdominal wall. Five to eight blastocysts obtained from donor rabbits were transferred through the tubing into each recipient animal's uterus 2 to 14 days after placement of the device. On posttransfer day 10, normally developed pregnancies were visible and confirmed histologically in 4 of 7 animals.

Animals↗
PubMed1992

Conjugative transposition of Tn916: the transposon int gene is required only in the donor.

Conjugative transposition of transposon Tn916 has been shown to proceed by excision of the transposon in the donor strain and insertion of this element in the recipient. This process requires the product of the transposon int gene. We report here the surprising finding that the int gene is required only in the donor during conjugative transposition. We find that Tn916 int-1, whose int gene has been inactivated by an insertion mutation, transposes when a complementing wild-type int gene is present only in the donor during mating. When the int+ gene is present in a plasmid and is expressed from the spac promoter, conjugative transposition is very inefficient. However, when the Int+ function is supplied from a coresident distantly linked Tn916 tra-641 mutant, which is defective in a function required for conjugation, efficient conjugative transposition of Tn916 int-1 occurs. This suggests either that Int is not required for integration of Tn916 in gram-positive bacteria or that the protein is transferred from the donor to the transconjugant during the mating event. When the nonconjugative plasmid pAT145 was present in the donor, it was rarely cotransferred with Tn916. This suggests that complete fusion of mating cells is not common during conjugative transposition.

Bacillus subtilis↗
PubMed1992

Environmental regulation of virulence in group A streptococci: transcription of the gene encoding M protein is stimulated by carbon dioxide.

We have found that different atmospheres can have significant effects on the transcription of emm, the gene that encodes M protein, the major virulence factor of the group A streptococcus (Streptococcus pyogenes). Expression of emm was monitored by constructing a transcriptional fusion of the promoter for emm6.1 from S. pyogenes JRS4 to a promoterless chloramphenicol acetyltransferase gene. Transcription, as measured by determining chloramphenicol acetyltransferase specific activity, was stimulated by as much as 25-fold by increased carbon dioxide tension. Expression was greater in the latter stages of growth and was not affected by growth at 30 instead of 37 degrees C. Insertional inactivation of mry, a gene encoding a positive regulator of emm6.1, reduced chloramphenicol acetyltransferase activity below the detectable level. We conclude that expression of emm is influenced by environmental factors and that the level of carbon dioxide is one signal that may influence expression of M protein during infection.

Antigens, Bacterial↗
PubMed1992

Transfer of Tn916 between Lactococcus lactis subsp. lactis strains is nontranspositional: evidence for a chromosomal fertility function in strain MG1363.

Lactococcus lactis subsp. lactis MG1363 can act as a conjugative donor of chromosomal markers. This requires a chromosomally located fertility function that we designate the lactococcal fertility factor (Laff). Using inter- and intrastrain crosses, we identified other L. lactis strains (LMO230 and MMS373) that appear to lack Laff. The selectable marker in our crosses was Tcr, carried by Tn916, a transposon present on the chromosome. The transfer of Tcr was not due to Tn916-encoded conjugative functions, because (i) L. lactis cannot act as a donor in Tn916-promoted conjugation (F. Bringel, G. L. Van Alstine, and J. R. Scott, Mol. Microbiol. 5:2983-2993, 1992) and (ii) transfer occurred when the Tcr marker was present in a Tn916 derivative containing a mutation, tra-641, that prevents Tn916-directed conjugation in any host. In addition, we isolated a strain in which Tn916 appears to be linked to Laff; this strain should be useful for further analysis of this fertility factor. In this strain, Tn916 is on the same 600-kb SmaI fragment as Clu, a fertility factor previously shown to promote lactose plasmid transfer in L. lactis. Thus, it is possible that Clu and Laff are identical.

Base Sequence↗
PubMed1992

Outcome of children born to women treated during pregnancy for the antiphospholipid syndrome.

OBJECTIVE: To determine the rate of neonatal and childhood medical complications in the offspring of women with the antiphospholipid syndrome who are treated during pregnancy. METHODS: We compared 29 infants born to 23 mothers with antiphospholipid syndrome with a group of control children matched for year and gestational age at birth and route of delivery. During pregnancy, mothers with antiphospholipid syndrome were treated with accepted therapeutic regimens, including prednisone and low-dose aspirin, heparin and low-dose aspirin, and others. RESULTS: Neonatal complications in the study infants included hyperbilirubinemia (14), respiratory distress syndrome (three), bronchopulmonary dysplasia (two), necrotizing enterocolitis (two), intraventricular hemorrhage (two), neonatal sepsis (one), coarctation of the aorta (one), hypothyroidism (one), hypoglycemia (one), and death (one). Two children had feeding problems, four had delayed psychomotor development, and eight were small for their age. However, the overall rate of neonatal or childhood complications did not differ from that in the control children. CONCLUSIONS: Our data indicate that prematurity and neonatal problems are common, but the childhood course for these offspring is similar to that of other premature infants.

Antiphospholipid Syndrome↗
PubMed1992

Outcome of treated pregnancies in women with antiphospholipid syndrome: an update of the Utah experience.

OBJECTIVE: To determine the outcome of treated pregnancies in women with well-characterized antiphospholipid syndrome. METHODS: We reviewed 82 consecutive pregnancies in 54 women with antiphospholipid syndrome who were treated during pregnancy with the following: 1) prednisone and low-dose aspirin; 2) heparin and low-dose aspirin; 3) prednisone, heparin, and low-dose aspirin; or 4) other combinations of these medications or immunoglobulin. RESULTS: The overall neonatal survival rate was 73%, excluding spontaneous abortions, but treatment failures (fetal and neonatal deaths) occurred in all treatment groups. Patients with successful treated pregnancies had fewer previous fetal deaths than those with unsuccessful treated pregnancies. There were no significant differences in outcome among the four treatment groups. Preeclampsia and fetal distress occurred in half of all pregnancies, and fetal growth impairment occurred in nearly one-third. Preterm delivery due to maternal or fetal indications was required in 37% of the pregnancies. Four pregnancies were also complicated by postpartum thrombosis during treatment. CONCLUSIONS: Pregnancy in women with antiphospholipid syndrome appears to be improved by treatment, but fetal loss may occur despite treatment. Preeclampsia, fetal distress, fetal growth impairment, and premature delivery are common. Because of the clinically significant risk of thrombotic episodes, thrombosis prophylaxis should be considered in these patients.

Antiphospholipid Syndrome↗
PubMed1992

Lateral cervical radiographs and adenoid size: do they correlate?

Clinicians have questioned the value of lateral soft tissue neck x-ray (LSTN) in assessing adenoid size. Elaborate cephalometric assays have been devised to measure degree of nasopharyngeal obstruction secondary to adenoid hypertrophy. This study prospectively studied 73 children, aged 11 months to 13 years, with clinical evidence of adenoid hypertrophy to assess how well a LSTN correlates with direct intraoperative observation of adenoid size and nasopharyngeal obstruction. We found a relatively weak correlation (Pearson coefficient r = 0.34) between x-ray and operative observations. We conclude that LSTN is an appropriate examination in the preoperative assessment of children being considered for adenoidectomy. However, this test must be interpreted by recognizing the inherent limitations of evaluating a dynamic structure, such as the nasopharynx, through a non-dynamic modality.

Adenoids↗
PubMed1991

Evidence for intrinsic control of scrapie pathogenesis in the murine visual system.

Using the optic nerve to route scrapie infection into the brain reduces the initial spread of the disease to well-defined neuronal relays, and simplifies the observation of cause and effect of agent transport, replication and degeneration of the nervous system. One drawback of intraocular targeting of infection is the relatively long incubation periods required to produce clinical disease. By using highly-enriched fractions of infectivity and two models of murine scrapie, we have found that this time delay is not simply due to the limited amount of infective inoculum that can be injected into the eye. This provides evidence of intrinsic control of scrapie pathogenesis within the murine visual system.

Animals↗
PubMed1991

Scrapie inoculation of mice: light and electron microscopy of the superior colliculi.

Ultrastructural examination of the superior colliculi of mice intraocularly inoculated with the ME7 strain of scrapie showed vacuolation early in the course of infection. Brains were examined between 85-260 days after monocular inoculation with scrapie. The mean incubation period for the development of clinical disease was 302 days. Vacuolation was seen initially in the contralateral superior colliculus and subsequently in the ipsilateral colliculus. In coded trials light microscopical vacuolation was seen from 218 days but ultrastructural examination showed that sparse vacuoles were inconsistently present in either or both of the ipsilateral and contralateral colliculi from 85 days; frequent vacuoles were seen from 190 days. Scrapie-induced vacuoles were differentiated from vacuoles present in control tissue by the presence of loculation or by a limiting double membrane which showed protrusion or proliferation of the innermost lamella. Vacuolation was seen in neuronal perikarya, myelinated fibres, dendrites and axonal presynaptic terminals. Vacuoles of myelinated fibres were observed within myelin and possibly also in the inner tongue of oligodendroglial cytoplasm. Whorled membrane configurations were also seen. Tubulovesicular particles, 40 nm in diameter, were recognised in two scrapie-infected mice. It is suggested that some scrapie vacuoles arise as a result of incorporation of abnormal membrane into organelles, possibly mitochondria, in neuronal perikarya and neurites and probably also within oligodendroglial cytoplasm and myelin.

Animals↗
PubMed1991

Variation in resistance to isometamidium chloride and diminazene aceturate by clones derived from a stock of Trypanosoma congolense.

Nine clones were derived from a drug-resistant Trypanosoma congolense stock (IL 2856) and characterized in mice for their sensitivity to isometamidium chloride and diminazene aceturate. All clones were derived from the stock without drug selection and expressed high levels of resistance to isometamidium chloride (50% curative dose [CD50] values ranging from 1.5 to 5.1 mg/kg) and intermediate to high levels of resistance to diminazene aceturate (CD50 values ranging from 5.1 to 21.0 mg/kg). By contrast, the isometamidium chloride and diminazene aceturate CD50 values for a drug-sensitive clone, T. congolense IL 1180, were 0.018 mg/kg and 2.3 mg/kg, respectively. For both drugs, there appeared to be significantly different levels in expression of drug resistance amongst the 9 clones derived from IL 2856. Isoenzyme analysis of 7 enzymes showed that all 9 clones expressed the same electrophoretic variants. Thus, all 9 clones were identical for these phenotypic markers. The clone which expressed the highest level of resistance to isometamidium in mice (IL 3270) was transmitted to Boran cattle via the bite of infected Glossina morsitans centralis. IL 3270 produced an infection rate in tsetse of 5.0%. The resulting infections in cattle were shown to be resistant to intramuscular treatment with 2.0 mg/kg isometamidium chloride and 14.0 mg/kg diminazene aceturate. This contrasts with doses of 0.25 mg/kg isometamidium chloride or 3.5 mg/kg diminazene aceturate which are deemed sufficient to cure fully sensitive infections. Finally, 9 clones (subclones) were derived from IL 3270 and characterized in mice for their sensitivity to isometamidium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

The effect of two new immunosuppressive agents, FK506 and didemnin B, in murine pregnancy.

The purpose of this study was to investigate two promising immunosuppressive agents, didemnin B (DB) and FK506 (FK), during pregnancy to assess potential adverse maternal or fetal effects. Pregnant C3H mice were randomized into control and high- and low-dose treatment groups for each drug. Animals received daily injections from day 1 to day 16, and on day 17 of gestation the maternal condition, litter size, fetal resorption rates, and fetal/placental unit weights were determined. Immunoglobulin (IgG) levels were obtained for DB treatment groups. Delayed type hypersensitivity was assessed in virgin females. Both DB and FK had dose-dependent immunosuppressive activity in the DTH assay, and DB caused elevated IgG concentrations. High doses of DB caused diarrhea and maternal wasting with no fetal survival; with low-dose DB, maternal weight gain was depressed, but pregnancy outcome was not different from control animals. High-dose FK had no obvious detrimental effects on maternal health but caused resorption of all fetuses; administration of low-dose FK resulted in a higher number of resorptions, but fetuses that survived did not appear different from controls. We conclude that these immunosuppressive drugs can have adverse effects on pregnancy, but the maternal and fetal toxicity are dose-dependent.

Animals↗