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Biomedical subjects

D Robertson

Publications and source records attributed to D Robertson.

At least 199 records · Page 11Linked to original sources
PubMed1995

A geminivirus induces expression of a host DNA synthesis protein in terminally differentiated plant cells.

Geminiviruses are plant DNA viruses that replicate through DNA intermediates in plant nuclei. The viral components required for replication are known, but no host factors have yet been identified. We used immunolocalization to show that the replication proteins of the geminivirus tomato golden mosaic virus (TGMV) are located in nuclei of terminally differentiated cells that have left the cell cycle. In addition, TGMV infection resulted in a significant accumulation of the host DNA synthesis protein proliferating cell nuclear antigen (PCNA). PCNA, an accessory factor for DNA polymerase delta, was not present at detectable levels in healthy differentiated cells. The TGMV replication protein AL1 was sufficient to induce accumulation of PCNA in terminally differentiated cells of transgenic plants. Analysis of the mechanism(s) whereby AL1 induces the accumulation of host replication machinery in quiescent plant cells will provide a unique opportunity to study plant DNA synthesis.

Base Sequence↗
PubMed1995

Contraction of isolated porcine coronary arteries is inhibited by high concentrations of propranolol.

Isometric tension responses of isolated porcine coronary artery rings were studied in the presence of concentrations of propranolol higher than those necessary to block effects mediated by beta-adrenergic receptors. Propranolol (50-300 microM) inhibited contractions induced by 30 mM KCl and by histamine, norepinephrine, and acetylcholine in a concentration-dependent, noncompetitive fashion. The (+) propranolol isomer and the racemic mixture were equipotent inhibitors of contraction. Propranolol inhibition was partly reversed by increased extracellular Ca++. These effects of propranolol thus appeared to be independent of beta-blockade and could be relevant to some of the drug's observed but still unexplained in vivo actions.

Acetylcholine↗
PubMed1995

Ultrastructural localization of ras-related proteins using epitope-tagged plasmids.

To determine the ultrastructural distribution of H-ras, the rho proteins rho-A, rho-B, rho-C, and the rac1 protein (members of the ras GTP-binding protein family), we used cDNA expression plasmids in which a short sequence coding for the epitope recognized by the anti c-myc monoclonal antibody 9E10 has been inserted at the N-terminus. Each of the expressed proteins has this epitope as a tag, allowing its localization by light and electron microscopy by the same antibody. After nuclear microinjection of these plasmids into MDCK or Rat 2 cells, expression of the protein (6-18 hr later) was confirmed by immunofluorescence labeling with 9E10 imaged by confocal microscopy. For ultrastructural localization of these tagged proteins, a method was devised to process microinjected cells in situ into low-temperature resin. The proteins were localized on the sections using 9E10 detected with colloidal gold conjugates. Ha-ras protein was localized almost exclusively on the cell membranes. Rho-A and rho-C were predominantly associated with the submembraneous actin network, and rho-B was found in association with multivesicular bodies. Rac1 protein induces the formation of large pinocytotic vesicles and was detected on the cytoplasmic face of these vacuoles. These experiments demonstrate the successful use of this approach for detection of de novo synthesized proteins from microinjected plasmids by both light and electron microscopy on a small (< 50 cells) sample size.

Animals↗
PubMed1995

Immunomorphological characterization and effects of 12-(S)-HETE on a dynamic intracellular pool of the alpha IIb beta 3-integrin in melanoma cells.

In metastatic B16a murine melanoma cells, alpha IIb beta 3 integrin was shown to be one of the key adhesion molecules responsible for matrix adhesion and spreading. Upon stimulation, alpha IIb beta 3 can be upregulated at the cell surface due to translocation of the receptor to the plasma membrane from an intracellular pool. Here we have characterized this integrin pool as a tubulovesicular structure (TVS) corresponding to endosomes. TVS was found to be associated temporarily with microtubules and intermediate filaments especially after protein kinase C (PKC) stimulation with a lipoxygenase metabolite of arachidonic acid, 12-(S)-hydroxyeicosatetraenoic acid [12-(S)-HETE]. After PKC stimulation, the predominantly vesicular TVS became elongated and alpha IIb beta 3 appeared at the apical plasma membrane and microvilli. Disruption of either the microtubules or intermediate filaments prevented the 12-(S)-HETE effect both on vesicular to tubular transition of TVS as well as on surface expression of this integrin. The connection with the Golgi system of the integrin-containing TVS was proved by a Golgi-inhibitor (brefeldin A) pretreatment, which prevented the PKC-stimulation-induced TVS elongation and subsequent receptor-upregulation at the cell surface. After a soluble ligand binding (mAb to the alpha IIb beta 3 complex) the surface receptor endocytosed back to the TVS indicating the presence of a dynamic, cytoskeleton associated integrin pool in melanoma cells.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1995

Carotid body tumors: a review of 30 patients with 46 tumors.

Minimal morbidity occurs with resection of most carotid body tumors (CBT). With larger tumors significant injury to the cranial nerves has been reported. In order to assess the operative sequelae rate, 30 patients with CBT were reviewed. Sixteen patients either presented with bilateral carotid body tumors or had previously undergone a resection of the contralateral carotid body tumors, for a total carotid body tumor count of 46. Sixteen patients demonstrated a familial pattern while 14 were nonfamilial. Within the familial group, 14 of 16 presented with multiple paragangliomas as compared to 6 of 14 in the nonfamilial group. Tumor size ranged from 0.8 to 12 cm. Vascular replacement occurred in 2 of 20 patients with tumors < 5.0 cm, compared with 5 of 9 with tumors > 5.0 cm. Four patients lost cranial nerves with the resection: superior laryngeal nerve (SLN), 4; cranial nerve X, 1; cranial nerve XII, 1. Ten patients developed baroreceptor failure secondary to bilateral loss of carotid sinus function. First-bite pain occurred in 10 of 25 operative patients. Cranial nerve loss can be minimal with resection of carotid body tumors, however, baroreceptor failure and first-bite pain are postoperative sequelae that are often disregarded in the postoperative period.

Adult↗
PubMed1995

Diagnosis and management of baroreflex failure.

Baroreflex failure has a range of presentations, varying from the acute onset of a hypertensive crisis to a chronically volatile blood pressure and heart rate with hypertensive surges in response to stress, punctuated by periods of normal or even low blood pressure during rest. Differentiating this syndrome from other causes of labile hypertension is essential in devising effective treatment.

Antihypertensive Agents↗
PubMed1995

Anti-dopamine beta-hydroxylase immunotoxin-induced sympathectomy in adult rats.

Anti-dopamine beta-hydroxylase immunotoxin (DHIT) is an antibody-targeted noradrenergic lesioning tool comprised of a monoclonal antibody against the noradrenergic enzyme, dopamine beta-hydroxylase, conjugated to saporin, a ribosome-inactivating protein. Noradrenergic-neuron specificity and completeness and functionality of sympathectomy were assessed. Adult, male Sprague-Dawley rats were given 28.5, 85.7, 142 or 285 micrograms/kg DHIT i.v. Three days after injection, a 6% to 73% decrease in the neurons was found in the superior cervical ganglia of the animals. No loss of sensory, nodose and dorsal root ganglia, neurons was observed at the highest dose of DHIT. In contrast, the immunotoxin, 192-saporin (142 micrograms/kg), lesioned all three ganglia. To assess the sympathectomy, 2 wk after treatment (285 micrograms/kg), rats were anesthetized with urethane (1 g/kg) and cannulated in the femoral artery and vein. DHIT-treated animals' basal systolic blood pressure and heart rate were significantly lower than controls. Basal plasma norepinephrine levels were 41% lower in DHIT-treated animals than controls. Tyramine-stimulated release of norepinephrine in DHIT-treated rats was 27% of controls. Plasma epinephrine levels of DHIT animals were not reduced. DHIT-treated animals exhibited a 2-fold hypersensitivity to the alpha-adrenergic agonist phenylephrine. We conclude that DHIT selectively delivered saporin to noradrenergic neurons resulting in destruction of these neurons. Anti-dopamine beta-hydroxylase immunotoxin administration produces a rapid, irreversible sympathectomy.

Adrenergic Agents↗
PubMed1995

Resurfacing versus not resurfacing the patella during total knee replacement.

One hundred patients with osteoarthritic knees were randomized either to have their patella resurfaced or not resurfaced using the same total knee replacement. These patients were assessed preoperatively and a minimum 2 years postoperatively using disease-specific (Knee Society Clinical Rating System) and functional capacity (30 second stair climbing and knee flexor and extensor torques) outcome measures. Two patients in the not resurfaced group required reoperation because of anterior knee pain. At 2 years' followup, the not resurfaced group had significantly less pain and better knee flexor torques than did the resurfaced group, whereas the results of the Knee Society Function Scores, 30 second stair climbing, and knee extensor torques were similar. These results suggest that longer-term followup is required, but that one should keep an open mind regarding patellar resurfacing during total knee replacement.

Activities of Daily Living↗
PubMed1995

Recordings from slices indicate that octopus cells of the cochlear nucleus detect coincident firing of auditory nerve fibers with temporal precision.

Acoustic information in auditory nerve discharges is integrated in the cochlear nuclei, and ascends through several parallel pathways to higher centers. Octopus cells of the posteroventral cochlear nucleus form a pathway known to carry information in the timing of action potentials. Octopus cells have dendrites oriented to receive converging input from many auditory nerve fibers. In all 34 intracellular recordings from anatomically identified octopus cells in slices, shocks to the auditory nerve evoked brief, consistent, graded EPSPs. EPSPs were about 1 msec in duration. At all but the lowest shock strengths, the delays between shocks and the peaks of resultant EPSPs had SDs of 0.02 msec. Polysynaptic excitation, perhaps arising from the axon collaterals of octopus cells, was observed. No detectable glycinergic or GABAergic inhibition was evoked with shocks. The input resistances were low, around 10 M omega, voltage changes were rapid, with time constants of about 1 msec, and action potentials were small. The low input resistance resulted in part from a Cs(+)-sensitive conductance. In the presence of 10 or 15 mM extracellular Cs+ the time constants increased 20-fold in the hyperpolarizing voltage range. As several subthreshold inputs were required to produce suprathreshold responses, octopus cells detect the coincident firing of auditory nerve fibers. Under physiological conditions the low input resistance and resulting short time constant limit the time over which temporal summation of excitation from auditory nerve fibers can occur and thus provide temporal precision to electrical signaling.

Action Potentials↗
PubMed1995

Recent advances in the treatment of orthostatic hypotension.

Orthostatic hypotension is a fall in blood pressure on standing that causes symptoms of dizziness, visual changes, and discomfort in the head and neck. The goal of treatment is the improvement of the patient's functional capacity, rather than a target blood pressure. For treatment to be successful, it must be individualized. Non-pharmalogic interventions include carefully managed exercise, scheduled activities, and monitoring of the environmental temperature. Agents such as fludrocortisone, midodrine, and epoetin alfa offer successful pharmacologic interventions. Although these measures ease the symptoms of orthostatic hypotension, current approaches neither reverse nor stabilize the disease process in autonomic disorders.

Humans↗
PubMed1995

Nonmetallic foreign bodies of the skull base: a diagnostic challenge.

Cases of physical trauma have become more common in emergency departments, since life in modern society has become increasingly dangerous. Foreign bodies in the head and neck region are more common, therefore, and management principles are well-defined. Typically, these foreign bodies are metal, plastic, or glass and often easily diagnosed; however, wooden foreign bodies pose special problems for the physician and, therefore, warrant separate consideration. We present the case of a 21-year-old male who was stabbed in the submental region with a large wooden stake and discuss the surgical and follow-up treatment of this interesting case, including the roles and limitations of angiography, computerized tomography, and magnetic resonance imaging.

Adult↗
PubMed1994

Noradrenergic lesioning with an anti-dopamine beta-hydroxylase immunotoxin.

Sympathectomy has been achieved by a variety of methods but each has its limitations. These include lack of tissue specificity, incomplete lesioning, and the age range of susceptibility to the lesioning. To circumvent these drawbacks, an immunotoxin was constructed using a monoclonal antibody against the noradrenergic specific enzyme dopamine beta-hydroxylase (D beta H) coupled via a disulfide bond to saporin, a ribosomal inactivating protein. Three days after intravenous injection of the anti-D beta H immunotoxin (50 micrograms) into adult Sprague-Dawley rats, 66% of neurons in the superior cervical ganglia were chromatolytic. Superior cervical ganglia neurons were poisoned in 1 day old and 1 week old (86% of neurons) neonatal rats following subcutaneous injection of 3.75 and 15 micrograms, respectively. The anti-D beta H immunotoxin will be a useful tool in the study of the peripheral noradrenergic system in adult and neonatal animals.

Animals↗
PubMed1994

Enhanced resistance to nuclease degradation of nucleic acids complexed to asialoglycoprotein-polylysine carriers.

We have previously shown targeting of DNA to hepatocytes using an asialoorosomucoid-polylysine (AsOR-PL) carrier system. The AsOR-PL conjugate condenses DNA and facilitates entry via specific receptor-ligand interactions. In these studies, our objective was to determine if AsOR-PL conjugates protect bound DNA from nuclease attack. Double-stranded plasmid or single-stranded oligonucleotide DNA, alone or bound to conjugate, was incubated under conditions mimicking those encountered during in vitro and in vivo transfections. The results showed that complexed DNA was effectively protected from degradation by serum nucleases. Degradation of single-stranded oligonucleotides was inhibited 3- to 6-fold in serum during 5 hours of incubation. For complexed plasmids, greater than 90% remained full-length during 1.5 and 3 hour incubations in serum or culture medium containing 10% serum, respectively. Uncomplexed plasmid was completely degraded after 15 minutes in serum or 60 minutes in medium. In cell lysates, the conjugate was not effective in inhibiting endonuclease activity; plasmids were readily converted from supercoiled to open circular and linear forms. However, the resultant nicked forms were substantially protected from further degradation during one hour of incubation compared to plasmid alone. Under all conditions complexed DNA did not readily dissociate from the conjugate. Overall, for both single and double-stranded DNA, AsOR-PL conjugates conferred substantial protection from nuclease degradation.

Animals↗
PubMed1994

The anemia of primary autonomic failure and its reversal with recombinant erythropoietin.

OBJECTIVE: To determine if chronic sympathetic deprivation is associated with anemia and a low erythropoietin response. DESIGN: Survey of the prevalence and characteristics of anemia in patients with severe primary autonomic failure. SETTING: A referral service for autonomic failure in a tertiary teaching hospital. PATIENTS: 84 patients with primary autonomic failure who had symptomatic orthostatic hypotension. INTERVENTION: Open-label trial with human recombinant erythropoietin. RESULTS: Anemia was present in 32 of 84 patients (38%; 95% Cl, 27% to 50%). Plasma norepinephrine levels, measured in patients standing upright, were lower in the patient group with lower hemoglobin levels. Mean values in 22 patients with a hemoglobin level of less than 120 g/L were as follows: hemoglobin, 108 g/L (range, 87 to 118 g/L); hematocrit, 0.33; corrected reticulocyte counts, 0.008; mean corpuscular volume, 89 fL (89 microns 3); serum iron, 16.5 mumol/L (92 micrograms/dL); total iron binding capacity, 43.3 mumol/L (242 micrograms/dL); ferritin, 184 micrograms/L; serum vitamin B12, 410 pmol/L (556 pg/mL); and serum folate, 22.7 nmol/L (10 ng/mL). No relation was found between serum erythropoietin and blood hemoglobin levels. In seven of nine patients with autonomic failure who had hemoglobin levels less than 120 g/L, serum erythropoietin levels decreased below the 95% confidence interval corresponding to patients with iron deficiency anemia. Therapy with recombinant erythropoietin improved mean hemoglobin levels (from 108 to 133 g/L) in all patients treated (n = 5) at relatively low doses (25 to 50 units/kg body weight, subcutaneously, three times a week). CONCLUSIONS: Our data support the hypothesis that the sympathetic nervous system stimulates erythropoiesis in humans because anemia is a frequent occurrence in patients with severe autonomic failure and is associated with a blunted erythropoietin response.

Aged↗
PubMed1994

Causes of chronic orthostatic hypotension.

OBJECTIVE: To determine the frequency of various causes of orthostatic hypotension. DESIGN: Survey. SETTING: Tertiary referral center. PATIENTS: One hundred patients with moderate to severe orthostatic hypotension. RESULTS: Twenty-seven percent of the patients had primary autonomic failure, 35% had secondary autonomic failure, and 38% had hypotension without evidence of generalized autonomic degeneration. CONCLUSIONS: In a tertiary referral center, only a minority of patients with severe orthostatic hypotension will have Shy-Drager syndrome or Bradbury-Eggleston syndrome as their primary disease. Occasional patients who initially appear to have Bradbury-Eggleston syndrome ultimately prove to have Shy-Drager syndrome or paraneoplastic autonomic failure. Antidepressant drugs, even in low doses, remain a major overlooked cause of orthostatic hypotension.

Adolescent↗
PubMed1994

Acute and chronic effects of unilateral elimination of auditory nerve activity on susceptibility to temporary deafness induced by loud sound in the guinea pig.

The involvement of crossed cochlear pathways in modulating the deafening effects of loud sound was investigated in the anaesthetized guinea pig. Auditory nerve activity was blocked unilaterally, either by surgical cochlear destruction or intracochlear perfusion of lignocaine, and the effect of a standard loud sound exposure in the untreated ear was then assessed using the compound action potential (CAP) audiogram technique. It was found that both cochlear destruction or lignocaine perfusion reduced the amount of threshold elevation in the untreated ear. The effect of lignocaine perfusion was significantly greater than acute cochlear destruction. In animals allowed to survive for 24 h and one week post-cochlear destruction before loud sound exposure, the protective effect was still present and was significantly greater than immediately post-destruction. This long-term protective effect of contralateral cochlear destruction was blocked by administering strychnine prior to the loud sound exposure. The results of lignocaine perfusion and chronic destruction make it unlikely that protection immediately post-destruction is the result of a transient barrage of primary afferent activity. We conclude that elimination of auditory nerve input can alter the effectiveness of brainstem circuitry responsible for protection (possibly the olivocochlear system). Since acoustic stimulation of the contralateral ear also has acute protective effects thought to be mediated by olivocochlear efferents, the circuitry responsible for protection appears to be subject to a complex balance between excitatory and inhibitory influences.

Action Potentials↗
PubMed1994

Ultrastructural localization of BHRF1: an Epstein-Barr virus gene product which has homology with bcl-2.

BHRF1 is an Epstein-Barr virus encoded protein which has a 38% sequence similarity with bcl-2 over the carboxyl portion. Like bcl-2, BHRF1 has been shown to suppress programmed cell death from apoptosis. Previously BHRF1 has been detected in mitochondrial, microsomal, and nuclear compartments by cell fractionation analysis. In this study we have used the technique of immunoelectron microscopy to define the ultrastructural distribution of the BHRF1 product in the EBV converted cell lines B95.8 and P3HR-1. The BHRF1 product was localized at the periphery of the mitochondria in a pattern similar to that of bcl-2 and by analogy with bcl-2 this is likely to be the functional destination. Sequence analysis of the BHRF1 protein disclosed similarity with the recently described bcl-2 homologues bcl-x (32%) and bax (34%) over the carboxyl portion, with several domains of complete identity. BHRF1 appears to be a member of a gene family involved in the regulation of programmed cell death. The identity between BHRF1 and bcl-2, an apparent shared ability to abrogate apoptosis, and the common ultrastructural localization is compelling and suggests that bcl-2 and BHRF1 are both functionally and mechanistically similar.

Amino Acid Sequence↗