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Biomedical subjects

J A Walker

Publications and source records attributed to J A Walker.

At least 91 records · Page 5Linked to original sources
PubMed1987

How do the parietal lobes direct covert attention?

In cases of unilateral parietal damage patients have trouble with stimuli in the visual hemifield on the side opposite the lesion (contralesional). This deficit is clear when they are first cued to attend to a location on the side of the lesion (ipsilesional) and then given a target on the opposite side of fixation. Our first experiments indicated that these patients do worse when cued to a location in either field and then given a target in the contralesional as compared to the ipsilesional direction. The results of this experiment can be accounted for by a representational or a directional view. A second experiment seeks to discriminate between the two. The results tend to favor the directional view.

Attention↗
PubMed1987

The enkephalin response in human tooth pulp to orthodontic force.

Public perception is that dentistry and pain go hand in hand; thus, pain and pain control are important considerations to the profession. Recent studies have attempted to discover the precise metabolic events involved in neural transmission of nociceptive information. One focus has been the study of peptidergic pathways, which purportedly inhibit the firing of pain-conducting fibers. The research described in this article defined the existence of one enkephalin, methionine enkephalin (ME), in an extract of human tooth pulp tissue and the effect of orthodontic force on that ME concentration. One set of patients who had premolars extracted for orthodontic purposes served as controls. Another set, also diagnosed for premolar extractions, had a coil spring attached between the left and right maxillary premolars to supply an orthodontic force for a period of time prior to extraction. High-performance liquid chromatography, radioimmunoassay, radioreceptor assay, and mass spectrometry were used in a series of experiments to isolate, identify, and quantify ME in the pulp tissues. Principal results were as follows: for the first time ME was detected in human tooth pulp, orthodontic force caused a significant decrease in ME concentrations in the group of experimental teeth compared with controls, and ME levels of the first spring-attached tooth that was removed from each patient had a statistically significant inverse log-linear relationship to the amount of applied force. These data indicate that orthodontic force mobilizes at least one neuropeptidergic pathway in the human tooth pulp.

Chromatography, High Pressure Liquid↗
PubMed1987

Nucleotide sequence of the streptolysin O (SLO) gene: structural homologies between SLO and other membrane-damaging, thiol-activated toxins.

The complete nucleotide sequence of a cloned streptolysin O (SLO) gene and the amino acid sequence of SLO, predicted from the DNA sequence, are reported. SLO contains a single cysteine residue located close to the C terminus of the molecule and shares extensive structural homologies with other thiol-activated toxins, which allow us to predict functionally important features.

Amino Acid Sequence↗
PubMed1987

Molecular cloning, characterization, and complete nucleotide sequence of the gene for pneumolysin, the sulfhydryl-activated toxin of Streptococcus pneumoniae.

A recombinant lambda bacteriophage has been isolated that carries DNA from Streptococcus pneumoniae and expresses a potent hemolysin that has been shown to be pneumolysin, the sulfhydryl-activated toxin of the pneumococcus. Hemolytic activity is inhibited by cholesterol and neutralized by serum against streptolysin O. The cloned gene expresses two polypeptides (Mrs, 56,000 and 53,000) in an Escherichia coli in vitro transcription-translation system, and both are precipitated by the addition of anti-alveolysin serum and anti-streptolysin O serum in the presence of Staphylococcus aureus cells. Expression of pneumolysin occurs when the gene is cloned in both possible orientations in pUC8. The DNA sequence of a 5-kilobase ClaI fragment that carries the pneumolysin gene has been determined. An open reading frame was identified that encodes a polypeptide of 471 amino acids that is hydrophobic in character and has an N-terminal amino acid sequence which is identical to that deduced from amino acid sequencing of the purified protein. The predicted amino acid sequence of the polypeptide reveals a single cysteine residue located 44 residues from the C terminus. Putative promoter and ribosome binding sites have been identified 5' to the pneumolysin coding sequence.

Amino Acid Sequence↗
PubMed1987

Digoxin-like immunoreactive substance in chronic hemodialysis patients: effect on digitoxin radioimmunoassay.

Digoxin-like immunoreactive substance(s) (DLIS) in the sera of patients with renal insufficiency may confound attempts to monitor serum digoxin levels. We investigated whether DLIS would affect the radioimmunoassay (RIA) for digitoxin. DLIS was detected by RIA in 9 of 38 chronic hemodialysis patients and in none of 25 healthy controls. Digitoxin levels were not elevated in either the control or dialysis group, and false-positive results for digitoxin by RIA were not obtained in any patient with DLIS. It is concluded that DLIS does not interfere with the digitoxin RIA, nor are digitoxin levels spuriously elevated in chronic hemodialysis patients. Digitoxin may be a preferable preparation for digitalis-dependent dialysis patients with DLIS.

Digitoxin↗
PubMed1986

Pattern-reversal visual-evoked potentials in the diagnosis of amblyopia in children.

We assessed the potential clinical usefulness of pattern-reversal visual-evoked potentials in the diagnosis of amblyopia. Twenty-seven children with anisometropic amblyopia and four children without amblyopia participated. Estimates of visual acuity for each eye (Snellen visual acuity) were obtained by conventional psychometric methods. Visual-evoked potentials to reversing checks subtending 15 minutes of visual arc were also obtained. Visual-evoked potential testing and interpretation were done in a masked fashion. Ten of the 31 children were retested seven to 21 days after the first test to estimate reliability of the procedures. Of the 27 amblyopic children, 22 were correctly identified by the visual-evoked potential test alone. In four patients initial visual-evoked potential tests failed to identify the disparity in visual acuity between the eyes and retests in two of the four again had false-negative results. In one child initial visual-evoked potential testing incorrectly identified the amblyopic eye but repeat testing did identify it. Of the four children with symmetrically good vision, three were correctly identified as normal by the initial visual-evoked potential test. The other normal child was incorrectly identified by the visual-evoked potential test as having amblyopia.

Adolescent↗
PubMed1986

The missing gap. A pitfall in the diagnosis of alcohol intoxication by osmometry.

An osmolal gap (a disparity between measured and calculated serum osmolality) may accompany alcohol intoxication. We encountered a patient with methanol toxicity in whom no such gap was present, despite a markedly elevated serum methanol level. Further investigation revealed that serum osmolality had been measured with a vapor pressure osmometer; this technique may not detect volatile solutes such as alcohols. In vitro testing confirmed the insensitivity of vapor pressure osmometry to toxic ranges of both methanol and ethanol. When alcohol toxicity is suspected, an osmolal gap should be sought only if freezing point osmometry is available.

Alcoholic Intoxication↗
PubMed1985

Thrombocytopenia associated with intravenous desferrioxamine.

Desferrioxamine (DFO) was administered intravenously to a 63-year-old chronic hemodialysis patient with osteomalacia believed secondary to aluminum intoxication. Thrombocytopenia was noted after five doses of DFO. Platelet counts normalized after DFO was withheld. Thrombocytopenia recurred upon two rechallenges with this drug. It is suggested that platelet counts be monitored in hemodialysis patients receiving intravenous DFO.

Aluminum↗
PubMed1984

Fimbria-fornix lesions impair spatial working memory but not cognitive mapping.

Three experiments were designed to evaluate the relative merits of two theories of hippocampal function, the cognitive mapping theory and the working memory theory. Rats were tested in a series of maze tasks that varied in memory requirements. In the experiments that required cognitive mapping but not working memory (Experiments 1 and 3), rats with fimbria-fornix lesions reached stable levels of performance that were as accurate as those of control rats, and they also performed accurately during transfer tests, results demonstrating that they used a cognitive mapping strategy to solve the discrimination. In the experiment that required working memory (Experiment 2), rats with fimbria-fornix lesions performed at chance levels during all of postoperative testing, and they distributed their choices randomly between the correct and the incorrect goals. These results are seen as generally refuting the predictions made by the cognitive mapping theory and supporting the predictions made by the working memory theory. Additional analyses (Experiment 3) examined the nature of a transitory impairment exhibited by rats with fimbria-fornix lesions in two tasks that did not require working memory. Postoperatively, the performance of the rats with lesions was initially impaired but recovered to normal levels with a time course similar to that seen during preoperative acquisition. These results are seen as requiring an extension of the working memory theory of hippocampal function, and discussion is focused on the possibility of a temporary retrograde amnesia following fimbria-fornix lesions and the distinctions between different types of memory abilities.

Animals↗
PubMed1984

Cognition and the basal ganglia. Separating mental and motor components of performance in Parkinson's disease.

Central to the concept of subcortical dementia is the implication that the increased response latencies, which distinguish the syndrome, are due to a slowing of thought processes. The term 'bradyphrenia' has been applied to this presumed slowing of thought in Parkinson's disease and implies (1) that increased response latencies are not strictly motoric but are due to slowed information processing, and (2) that the mental slowing is analogous to the bradykinesia observed in the motor domain and, hence, attributable to dysfunction of dopaminergic basal ganglia mechanisms. The current study attempts to validate this definition of bradyphrenia by seeking a slowing of thought in Parkinson's disease which can be linked directly to bradykinesia. Six parkinsonian patients with end-of-dose akinesia were studied in three experiments which allowed separation of the speed of specific cognitive operations from the speed of motor responses. Serving as their own controls, they were tested both during the parkinsonian 'off' state, and when bradykinesia was alleviated by drug therapy. Four additional patients with newly diagnosed Parkinson's disease were studied before and following successful treatment with L-DOPA/carbidopa. The first experiment measured the rate of memory scanning, the second examined orientating of attention in the visual fields, and the third measured the time required to prepare a manual movement. The results show that overall reaction time increased when patients were in the untreated state, but without a concomitant slowing of purely cognitive components. The slowing of thought often reported in Parkinson's disease does not necessarily accompany bradykinesia and thus may not be related to dopaminergic dysfunction. These findings emphasize the need for caution in inferring a slowing of thought from increased response latencies in subcortical disorders.

Adult↗
PubMed1984

Effects of parietal injury on covert orienting of attention.

The cognitive act of shifting attention from one place in the visual field to another can be accomplished covertly without muscular changes. The act can be viewed in terms of three internal mental operations: disengagement of attention from its current focus, moving attention to the target, and engagement of the target. Our results show that damage to the parietal lobe produces a deficit in the disengage operation when the target is contralateral to the lesion. Effects may also be found on engagement with the target. The effects of brain injury on disengagement of attention seem to be unique to the parietal lobe and do not appear to occur with our frontal, midbrain, and temporal control series. These results confirm the close connection between parietal lobes and selective attention suggested by single cell recording. They indicate more specifically the role that parietal function has on attention and suggest one mechanism of the effects of parietal lesions reported in clinical neurology.

Adult↗
PubMed1983

Triad of glomerulonephritis, antinuclear antibodies, and positive skin immunofluorescence. Variant of systemic lupus erythematosus.

We are reporting findings in 13 patients who presented with glomerulonephritis without evidence of systemic disease, but who were found to have positive antinuclear antibody results and immunoglobulin and/or complement deposits at the dermal-epidermal junction of normal skin not exposed to light. There was no evidence of other organ involvement, and serologic tests for systemic lupus erythematosus (SLE) gave negative results. The renal disease is characterized by severe proteinuria, focal or diffuse proliferative glomerular lesions on biopsy, with variable patterns of immunoglobulin deposits. No clinical manifestations or serologic results typical of SLE have developed during prolonged observation. HLA phenotyping carried out in eight of the 13 patients revealed DR2 or DR3 alloantigens or both in seven of the eight patients, an incidence similar to that in patients with overt SLE. Because of the specificity of the skin biopsy immunofluorescence, the similarity of HLA-DR antigens, and a favorable response of the renal disease to therapy, we believe that these patients have a variant of SLE.

Adolescent↗
PubMed1982

Herbal medicine.

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Animals↗