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Biomedical subjects

M E Vargas

Publications and source records attributed to M E Vargas.

10 recordsLinked to original sources
PubMed1999

Enhanced sensitivity to N-methyl-D-aspartate receptor activation in transgenic and knockin mouse models of Huntington's disease.

We used two mouse models of Huntington's disease (HD) to examine changes in glutamate receptor sensitivity and striatal electrophysiology. One model, a transgenic, consisted of mice expressing exon 1 of the human HD gene and carrying 141-157 CAG repeat sequences (R6/2 line). The second model, a CAG repeat "knockin," consisted of mice with different lengths of CAG repeats (CAG71 and CAG94 repeats). The effects of glutamate receptor activation were examined by visualizing neurons in brain slices with infrared videomicroscopy and differential interference contrast optics to determine changes in somatic area (cell swelling). Striatal and cortical neurons in both models (R6/2 and CAG94) displayed more rapid and increased swelling to N-methyl-D-aspartate (NMDA) than those in controls. This effect was specific as there were no consistent group differences after exposure to alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate (KA). Intracellular recordings revealed that resting membrane potentials (RMPs) in the R6/2 transgenics were significantly more depolarized than those in their respective controls. RMPs in CAG94 mice also were more depolarized than those in CAG71 mice or their controls in a subset of striatal neurons. Confirming previous results, R6/2 mice expressed behavioral abnormalities and nuclear inclusions. However, CAG71 and CAG94 knockins did not, suggesting that increased sensitivity to NMDA may occur early in the disease process. These findings imply that NMDA antagonists or compounds that alter sensitivity of NMDA receptors may be useful in the treatment of HD.

Animals↗
PubMed1996

Occipital arteriovenous malformations: visual disturbances and presentation.

BACKGROUND: Occipital arteriovenous malformations (AVMs) cause a variety of visual disturbances and headaches. Early diagnosis may lead to treatment that reduces the risk of hemorrhages, visual field loss and other neurologic deficits, and death. METHODS: We reviewed the records of the 70 patients with occipital AVMs referred to New York University Medical Center to investigate the mode of presentation and the outcome of treatment. RESULTS: Sixty-eight patients presented with one or more symptoms, including homonymous visual disturbances in 39, headache in 39, seizures in 20, and hemorrhage in twenty-six. Visual field loss was more common (p = 0.0007) and more severe (p = 0.0002) in patients who bled than in those with unruptured AVMs (16/44). The frequency of visual field loss was not associated with calcarine artery supply to the AVM. Prior to treatment, the fields improved in five patients with visual loss associated with a hemorrhage. Forty-six patients were treated with embolization, surgery, radiosurgery, or a combination of therapies. The AVM was eliminated in 19 of 20 patients (nine with preoperative partial embolization) treated with surgery versus in 4 of 27 patients treated only with embolization. There were two AVM-associated deaths, two subarachnoid hemorrhages, and four new neurologic deficits after treatment. Visual fields were worse in 15 patients, unchanged in 22, and improved in eight. CONCLUSIONS: Whereas some features of headache and visual symptoms are similar for occipital AVMs and migraine, the two disorders are usually distinguishable. Visual field improvement can spontaneously occur in patients who have had loss secondary to an intracerebral bleed. Treatment with embolization or surgery, particularly with surgical excision of the AVM, can result in new or worse visual field loss.

Adolescent↗
PubMed1995

Homonymous field defect as the first manifestation of Creutzfeldt-Jakob disease.

PURPOSE: Although in the early stage of Creutzfeldt-Jakob disease most patients have obvious dementia, we found that the disease can be diagnosed in patients solely on the basis of a visual system disorder. METHODS: We examined three patients who initially complained of a nonspecific, insidious visual disturbance. RESULTS: The three patients were found to have Creutzfeldt-Jakob disease, confirmed by histopathologic analysis. Each patient had a homonymous hemianopsia on the first neuro-ophthalmologic examination. The initial neurologic, neuroimaging, and electrophysiologic examinations were not conclusive. The subsequent rapid deterioration in the neurologic status, including dementia and typical electroencephalographic changes, was suggestive of Creutzfeldt-Jakob disease. CONCLUSION: At onset of Creutzfeldt-Jakob disease, patients may have a homonymous hemianopsia despite normal results of magnetic resonance imaging of the brain and neurologic examination.

Aged↗
PubMed1995

Genetic variability in mitochondrial DNA of the screwworm, Cochliomyia hominivorax (Diptera: Calliphoridae), from Brazil.

Restriction fragment length polymorphism (RFLP) analysis of mitochondrial DNA (mtDNA) was used to examine genetic variation and population structure of screwworm flies in four populations from São Paulo State, Brazil. The total DNA of 405 individuals was digested with 15 restriction endonucleases and probed with five cloned HindIII fragments representing the entire mitochondrial genome of Cochliomyia hominivorax. The survey revealed that four enzymes (HaeIII, HindIII, MspI, and PvuII) were suitable to detect mtDNA variation among all populations. Based on the fragment patterns obtained for these four enzymes, a total of 15 haplotypes in combination was detected. Heteroplasmic individuals for the PvuII pattern were obtained in one of the populations. The estimated average for nucleotide sequence divergence (delta) was 0.92%. The cladogram of the geographical distribution among the observed haplotypes suggests that the sampled screwworms probably belong to a single evolutionary lineage with populations interconnected by reduced gene flow.

Animals↗
PubMed1994

Endovascular treatment of giant aneurysms which cause visual loss.

BACKGROUND: Progressive visual loss that results when a giant cerebral aneurysm compresses the anterior visual pathway requires treatment. When surgical clipping is not safely feasible, percutaneous methods of embolization of the aneurysm can be visual or life saving. METHODS: Endovascular techniques were used to treat 19 of 26 consecutive inoperable giant aneurysms in patients with visual loss, which included optic neuropathy (monocular in 13 patients and bilateral in 8) and optic tract dysfunction in five patients. Embolization of the aneurysm was performed with detachable balloons in 12 patients and with Guglielmi detachable electrocoils in 7. RESULTS: After treatment, vision improved in 7 patients, was unchanged in 11, and worsened in 1. Neurologic complications with balloons were temporary in four patients and severe and permanent in three. In contrast, only one temporary complication occurred with Guglielmi detachable electrocoils. The treatment results are contrasted with the outcome in the seven patients who refused intervention: three hemorrhaged (1 death); monocular blindness with dementia developed in two; a complete homonymous hemianopia and dementia developed in one; and one became bilaterally blind. CONCLUSION: Inoperable symptomatic giant aneurysms can be successfully treated with endovascular treatment.

Adolescent↗
PubMed1992

Ophthalmoplegia as a presenting manifestation of internal carotid artery dissection.

We present the case of a patient with an ipsilateral ophthalmoplegia as the presentation of a traumatic dissection of the internal carotid artery. We hypothesize that the cranial nerves dysfunction occurred because of interruption of the vascular supply to the nerves in the cavernous sinus from the inferolateral trunk of the cavernous carotid artery.

Adult↗
PubMed1992

[Adaptation and validation of a test on knowledge about diabetes mellitus].

OBJECTIVE: To adapt and validate a Spanish language medium test, of theoretical general knowledge of diabetes mellitus (questionnaire from the University of Michigan). To determine the validity of the concurrent and discriminatory content and establish reliability. DESIGN: The study was observational. Validity was verified prior to data collection. To analyse the concurrent and discriminatory validity, a questionnaire was used in personal interview with the patients, and the degree of knowledge evaluated on certain variables. SETTING: Hospital outpatient endocrinology consultations. PATIENTS: 167 diabetic patients were chosen at random, from the outpatient visits. 14 patients who had developed hearing, or language problems, or who had problems of a psychological nature, were excluded. Only 1 patient refused to answer the questionnaire. MAIN MEASUREMENTS AND RESULTS: Validity of the content was confirmed after careful analysis of the questions on the questionnaire by medical specialists in endocrinology. It was found that the test had adequate concurrence (p less than 0.01) when the average general knowledge levels of certain group of patients are compared. It also had acceptable discriminatory validity (r = 0.56: p less than 0.0001) and reliability (alpha: 0.84; p less than 0.45). CONCLUSIONS: Adaptation and validation has been obtained for a test of theoretical general knowledge on diabetes mellitus, and the test was found to be applicable to the population under study.

Adult↗
PubMed1984

[Methods for teaching problem-solving in medical schools].

The need to include in the medical curriculum instructional activities to promote the development of problem-solving abilities has been asserted at the national and international levels. In research on the mental process involved in the solution of problems in medicine, problem-solving has been defined as a hypothetical-deductive activity engaged in by experienced physicians, in which the early generation of hypotheses influences the subsequent gathering of information. This article comments briefly on research on the mental process by which medical problems are solved. It describes the methods that research has shown to be most applicable in instruction to develop problem-solving abilities, and presents some educational principles that justify their application. The "trail-following" approach is the method that has been most commonly used to study the physician's problem-solving behavior. The salient conclusions from this research are that in the problem-solving process the diagnostic hypothesis is generated very early on and with limited data; the number of hypotheses is small; the problem-solving approach is specific to the type of medical problem and case in hand; and the accumulation of medical knowledge and experience forms the basis of clinical competence. Four methods for teaching the solution of problems are described: case presentation, the rain of ideas, the nominal groups technique and decision-making consensus, the census and analysis of forces in the field, and the analysis of clinical decisions. These methods are carried out in small groups. The advantages of the small groups are that the students are active participants in the learning process, they receive formative evaluation of their performance in a setting conductive to learning, and are able to interact with their instructor if he makes proper use of the right questioning techniques. While no single problem-solving method can be useful to all students or in all the problems they encounter, teachers of medicine can improve their students' performance by adjusting these available methods to their particular needs and to those of their schools. The problem-solving methods described can help teachers shape the learning environment so as to develop in their students the most coherent, logical, concrete and complete set of skills possible. These methods can so be of value in improving the training of future doctors and the quality of their decisions to the benefit of their patients.

Curriculum↗