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S J Robertson

Publications and source records attributed to S J Robertson.

34 records · Page 2Linked to original sources
PubMed1996

Characterization of a P2X-purinoceptor in cultured neurones of the rat dorsal root ganglia.

1. The electrophysiological actions of the P2-purinoceptor agonists, adenosine 5'-triphosphate (ATP), 2-methylthio ATP (2-meSATP) and alpha, beta-methyleneATP (alpha, beta-meATP) and of uridine 5'-triphosphate (UTP) were studied under concentration and voltage-clamp conditions in dissociated neurones of 1-6 day old rat dorsal root ganglia. 2. ATP (10 nM-100 microM) applied rapidly via a U-tube perfusion system (equilibration time < 10 ms) activated concentration-dependent inward currents with a latency to onset of a few ms, an EC50 of 719 nM and a Hill slope of 1.47. 3. 2-meSATP (10 nM- 100 microM) and alpha, beta-meATP (100 nM - 100 microM) also evoked transient inward currents. The EC50 and Hill slopes were 450 nM and 1.58 for 2-meSATP and 1.95 microM and 1.53 for alpha, beta-meATP respectively. There was no significant difference between the maximum currents evoked by the three agonists. 4. As the concentration of ATP increased so the rate of rise and decay of the currents also increased. At 100 and 300 nM ATP the decay of the current was best fitted by a single exponential, but at 1 microM and above two exponentials were required. Log-log plots of the rise time or time constants of decay versus concentration were linear. Currents evoked by 2-meSATP and alpha, beta-meATP showed a similar concentration-dependence in their kinetics. 5. Inward currents evoked by ATP, 2-meSATP and alpha, beta-meATP (300 nM) were abolished by the P2-purinoceptor antagonist, suramin (100 microM). 6. UTP (10 microM) evoked similar transient inward currents, which were sensitive to suramin (100 microM). ATP (10 microM), applied 2 min beforehand, reduced the response to UTP (10 microM) by 80 +/- 10%. 7. This study shows that ATP, 2-meSATP and alpha, beta-meATP act via a suramin-sensitive P2x-purinoceptor to evoke rapid, transient inward currents in dissociated neurones of rat dorsal root ganglia. The pyrimidine nucleotide, UTP, was also active. It is likely that the agonists were acting at the P2x3-subtype to produce these effects.

Adenosine Triphosphate↗
PubMed1996

Two separate envelope regions influence induction of brain disease by a polytropic murine retrovirus (FMCF98).

The major determinants involved in neurological disease induction by polytropic murine leukemia virus FMCF98 are encoded by the envelope gene. To map these determinants further, we produced four chimeras which contained neurovirulent FMCF98 envelope sequences combined with envelope sequences from the closely related nonneurovirulent polytropic virus FMCF54. Surprisingly, two chimeric viruses containing completely separate envelope regions from FMCF98 could both induce neurological disease. Clinical signs caused by both neurovirulent chimeras appeared to be indistinguishable from those caused by FMCF98, although the incubation periods were longer. One neurovirulence determinant mapped to the N-terminal portion of gp7O, which contains the VRA and VRB receptor-binding regions, while the other determinant mapped downstream of both of the variable regions. Western blot (immunoblot) analyses and immunohistochemical staining of tissue sections indicated that the variations in neurovirulence of these viruses could not be explained by differences in either the quantitative level or the location of virus expression in the brain.

Animals↗
PubMed1995

Characterization of the succinate dehydrogenase-encoding gene cluster (sdh) from the rickettsia Coxiella burnetii.

We have identified and sequenced four genes that encode the protein subunits comprising the succinate dehydrogenase enzyme complex (Sdh) of the rickettsia Coxiella burnetii. The Sdh-encoding gene cluster (sdhCDAB) begins 3326 bp upstream from the citrate synthase-encoding gene (gltA) start codon and is read with opposite polarity. An open reading frame encoding the N-terminal 280 amino acids (aa) of 2-oxoglutarate dehydrogenase (SucA) begins 24 bp downstream from the stop codon of the gene specifying the iron-sulfur subunit (sdhB) of Sdh. The deduced aa sequence of Sdh subunits and the N-terminal portion of SucA revealed significant aa identity with the Esherichia coli homologues ranging from a low of 36.6% for SdhD to a high of 61.2% for SdhA and SdhB. Primer extension identified transcription start points (tsp) for sdh and sucA. The region upstream from the sdh tsp, but not the sucA tsp, displayed homology to promoter consensus sequences of E. coli. Further evidence that sucA transcription can occur independent of sdh transcription was provided by demonstrating that a TnphoA insertion disrupting sdhB had no effect on the production of SucA by an E. coli cell-extract-directed in vitro transcription/translation system. The plasmid clone pLPM60, which carries the C. burnetii sdhCDAB coding and upstream regulatory regions, rescued an E. coli sdhA mutant (MOB252), indicating functional expression of the rickettsial locus. A cell extract of MOB252 transformed with pLPM60 showed a sixfold greater level of Sdh enzyme activity over the E. coli wild type. A plasmid clone lacking the sdh upstream regulatory region did not complement nor produce sdh mRNA by dot blot analysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Induction of focal spongiform neurodegeneration in developmentally resistant mice by implantation of murine retrovirus-infected microglia.

FrCasE is a highly neurovirulent murine leukemia virus which causes a noninflammatory spongiform neurodegenerative disease after neonatal inoculation. The central nervous system (CNS) infection is wide-spread, involving several different cell types, whereas the lesions are localized to motor areas of the brain and spinal cord. Inoculation of FrCasE at 10 days of age (P10) results in viremia, but infection of the CNS is restricted and neurological disease is not observed (M. Czub, S. Czub, F. McAtee, and J. Portis, J. Virol. 65:2539-2544, 1991). In this study, we used this developmental resistance to restrict the extent and the distribution of FrCasE in the brain to examine whether the spongiform degeneration is a consequence of infection of cells in proximity to the lesions. Two approaches were used to infect the brain on or after P10. First, mice were inoculated with FrCasE at P10 to induce viremia and then at P17 were subjected to focal CNS injury within brain regions known to be susceptible to virus-induced spongiform degeneration. The injury resulted in local inflammation, glial activation, migration of inflammatory cells into the wound site, and high-level parenchymal infection about the wound site. However, no evidence of spongiform neurodegeneration was observed over a period of 3 months. The second approach involved the implantation of FrCasE-infected microglia into the CNS at > or = P10. This resulted in microglial engraftment and focal CNS infection unilaterally at the implantation sites and bilaterally along white matter tracts of the corpus callosum and pons and in cells of the subventricular layers of the lateral cerebral ventricles. Strikingly, focal spongiform degeneration colocalized with the sites of infection. In contrast to the wounding experiments, the implantation model was not associated with an inflammatory response or significant glial activation. Results of these studies suggest that (i) the developmental resistance of the CNS to infection lies at the blood-brain barrier and can be bypassed by direct introduction into the brain of virus-infected cells, (ii) the neuropathology induced by this virus is a consequence of local effects of the infection and does not appear to require endothelial or neuronal infection, and (iii) elements of the inflammatory response and/or glial activation may modulate the expression of neuropathology induced by neurovirulent retroviruses.

Age Factors↗
PubMed1994

The action of pyrantel as an agonist and an open channel blocker at acetylcholine receptors in isolated Ascaris suum muscle vesicles.

The anthelmintic pyrantel is believed to act as an agonist at acetylcholine receptors on somatic muscle from the parasite Ascaris suum. This study aimed to confirm this mode of action of pyrantel. Single-channel recordings from muscle vesicles formed from the extrasynaptic region of the bag of somatic muscle cells of Ascaris suum were made using the patch-clamp technique. Pyrantel (0.03-100 microM) activated cation-selective channels with at least 2 conductance levels: main conductance 41 +/- 2.04 pS (mean +/- S.E., n = 28), smaller conductance 22.4 +/- 0.34 pS (mean +/- S.E., n = 8). The current/voltage plots showed a linear relationship. Detailed kinetic analysis revealed that activation of the receptor by pyrantel resulted in at least 2 distinct open and burst states and at least 3 distinct closed states. The mean open time of the channel, with 0.1 microM pyrantel, was 1.53 +/- 0.22 ms (mean +/- S.E., n = 7) at -75 mV. We have previously shown that acetylcholine activated channels with similar properties to the pyrantel-activated channels (Pennington, A.J. and R.J. Martin, 1990, J. Exp. Biol. 154, 201) confirming that pyrantel is an acetylcholine agonist. With high concentrations (100 microM) of pyrantel a sequence of rapid openings and closings of the channel was observed, indicating the presence of an open channel block. Previous experiments have shown that the anthelmintic levamisole, which also acts as an acetylcholine agonist on this preparation, induced channel block at hyperpolarised potentials with high concentrations (Robertson, S.J. and R.J. Martin, 1993, Br. J. Pharmacol. 108, 170). A comparison is made of the actions of the 3 agonists pyrantel, levamisole and acetylcholine at the nicotinic receptor in Ascaris muscle, and implications for the therapeutic use of the compounds are discussed.

Acetylcholine↗
PubMed1993

Levamisole-activated single-channel currents from muscle of the nematode parasite Ascaris suum.

1. The patch-clamp technique was used to examine levamisole-activated channels in muscle vesicles from Ascaris suum. Cell-attached and isolated inside-out patches were used. 2. Levamisole (1-90 microM), applied to the extracellular surface, activated channels which had apparent mean open-times in the range 0.80-2.85 ms and linear I/V relationships with conductances in the range 19-46 pS. Ion-replacement experiments showed the channels to be cation selective. 3. The kinetics of the channels were analysed. Generally open- and closed-time distributions were best fitted by two, and three exponentials respectively, indicating the presence of at least two open states and at least three closed states. The distributions of burst-times were best-fitted by two exponentials. 4. Channel open- and burst-times were voltage-sensitive: at low levamisole concentrations (1-10 microM), they increased with hyperpolarization. At higher concentrations of levamisole (30 microM and 90 microM) flickering channel-block was observed at hyperpolarized potentials. Using a simple channel-block model, values for the blocking dissociation constant, KB were determined as 123 microM at -50 mV, 46 microM at -75 mV and 9.4 microM at -100 mV. 5. At the higher concentration of levamisole (30 microM and 90 microM) long closed-times separating 'clusters' of bursts were observed, at both hyperpolarized and depolarized membrane potentials and this was interpreted as desensitization.

Animals↗
PubMed1992

Distribution of a fluorescent ivermectin probe, bodipy ivermectin, in tissues of the nematode parasite Ascaris suum.

A fluorescent derivative of the anthelmintic ivermectin (4''-5,7-dimethyl bodipy proprionylivermectin, referred to hereafter as bodipy ivermectin) was synthesized for an investigation of the distribution of avermectins. Injected into adult Ascaris suum at doses greater than 0.1 micron per worm, it produced a dose-dependent immobilization. Fluorescent microscopy of frozen sections revealed the distribution of the probe in the whole nematode. Staining of collagenase-isolated muscle cells was studied using bath application of bodipy ivermectin. The trypan-blue quenching technique showed that the ivermectin probe was located in the outer monolayer of the muscle membrane. The cytoplasm was not stained. The interpretation of these observations is discussed in view of the known lipophilic nature of avermectins. Staining of the muscle membrane and nerve cord is consistent with the view that avermectins act at these sites. The significance of the hypodermal and lateral line staining is also discussed.

Animals↗
PubMed1992

Changes in ovarian NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase activity in pregnant and pseudopregnant rabbits.

The specific activity of NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) was found to increase in the ovaries of pregnant and pseudopregnant rabbits. The mean specific activity of cytosolic ovarian PGDH in 14- to 28-day pregnant rabbits was 24.3 +/- 8.1 nmol NADH formed/min/mg protein (n = 16) using PGE1 as substrate whereas in nonpregnant rabbits the specific activity was 1.5 +/- 0.8 nmol NADH formed/min/mg protein (n = 8). The reaction was dependent on NAD+; NADP+ did not support the reaction. In grouping the PGDH activities from pregnant rabbits into second (14-18 days) and third (2-28 days) trimester periods, no significant difference between values was found (26.1 +/- 8.9 vs 23.4 +/- 8.1 nmol NADH formed/min/mg protein, respectively). Western blot analysis of the ovarian cytosol using an antibody which was made to the purified lung PGDH of pregnant rabbits recognized an ovarian protein of identical molecular mass (30 kDa). Ovarian PGDH activities were also examined in rabbits treated with pregnant mare's serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG) to induce a state of superovulatory/pseudopregnancy and only on day 11 following hCG treatment was an increase in PGDH specific activity observed. On day 11, the specific activity was 14.8 +/- 4.3 nmol NADH formed/min/mg protein whereas values on days 10 and 12 were only 1.1 +/- 1.1 and 1.0 +/- 0.8, respectively. PGDH activities on days 3, 7 and 16 were also low.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Malacoplakia of liver: a case report.

This is the first reported case in the English literature of malacoplakia of the liver. In common with other cases of malacoplakia, the patient was immunosuppressed secondary to steroid therapy for underlying systemic lupus erythematosus. The patient died 18 months after presentation; at autopsy, the histologic features included those of the late or fibrous stage of malacoplakia.

Female↗
PubMed1988

Hospital versus random digit dialing controls in the elderly. Observations from two case-control studies.

Finding an optimal source of controls is a major consideration in the design of case-control studies. While hospital patients can provide a relatively economical and convenient source of controls, hospital controls may have diseases independently associated with the exposures being studied. Results of a recent case-control study of multiple myeloma suggest that the problems of using hospital controls may be exacerbated in studies of diseases affecting the elderly, especially when considering risk factors which might be associated with chronic diseases. Apparently, the authors have encountered a modern analog of "Berkson's bias" in which cancer cases are referred to a tertiary care center for a single disease. On the other hand, noncancer patients who might serve as controls tend to be referred selectively if they have multiple diseases. This article reports some of the difficulties encountered in a case-control study whose mean case age was 63.4 years and suggests that community controls selected by random digit dialing may be preferable to hospital controls for hypothesis-generating case-control studies of diseases in the elderly.

Adult↗
PubMed1987

Familial Hodgkin's disease. A clinical and laboratory investigation.

A three to sevenfold increased risk of Hodgkin's disease has been noted in families of patients. We report the first family in which all four of a four member sibship had Hodgkin's disease. In these four sibling cases, we were able to explore markers of infectious etiologic factors by measuring antibodies to Epstein-Barr virus (EBV) and human T-cell lymphotropic virus (HTLV), and possible genetic risk factors by human leukocyte antigen (HLA) typing and chromosome analysis. All three men were diagnosed within six months of their 30th birthday. HLA typing revealed that all four siblings share the DR5 antigen, and two siblings share HLA-B27. Chromosome analysis on peripheral lymphocytes revealed no abnormalities. A detailed, structured interview failed to elicit evidence of unusual exposures. The EBV antibody titers are probably within the normal range and none of the family had antibodies to HTLV-III. Observations on this family suggest that genetic factors play a greater role than environmental factors in the etiology of familial Hodgkin's disease.

Adolescent↗
PubMed1976

Peer and college-student tutoring as reinforcement in a token economy.

Eighteen second-grade children initially received feedback in the form of nonredeemable tokens for reducing their disruptive classroom behavior. Four types of tutoring were then introduced in a Latin Square Design: noncontingent tutoring from fifth-grade peers, contingent peer tutoring, noncontingent college tutoring, and contingent college tutoring. No significant difference was found in the level of disruptive behavior of those children tutored by fifth-grade peers or college students, but contingent tutoring was significantly effective in reducing disruptive classroom behavior.

Journal Article↗
PubMedDate not supplied

MR imaging of middle cranial fossa arachnoid cysts: temporal lobe agenesis syndrome revisited.

MR studies in eight patients with extraaxial arachnoid cysts in the middle cranial fossa were reviewed in order to identify any associated structural defect in the ipsilateral temporal lobe. The study was prompted by the original theory that agenesis of the temporal lobe is the primary factor in the development of these cysts. Authors of subsequent studies proposed that the cysts are a consequence of embryological malformation of the meninges only and that the adjacent temporal lobe is compressed. Our findings suggest that middle cranial fossa cysts are associated with temporal lobe hypogenesis, and also that compression of the temporal lobe is an infrequent accompaniment.

Adolescent↗