Biomedical subjects
N Kapur
Publications and source records attributed to N Kapur.
Studies on the mode of action of tolnaftate in Microsporum gypseum.
Studies were performed on the mode of action of tolnaftate and resistance to this drug in Microsporum gypseum. Cells grown in the presence of tolnaftate (at the IC 50) showed a reduced content of total phospholipids and sterols whereas there was an increase in total RNA content. Incubation of cells with tolnaftate (at 10 x MIC), followed by addition of different macromolecule precursors revealed inhibition of the biosynthesis of all macromolecules except for RNA. The activity of membrane-bound enzymes did not change on treatment with tolnaftate (10 x MIC) whereas an increase in the leakage of intracellular 32P was observed. The content of total phospholipids was higher in tolnaftate-resistant cells, whereas the content of total sterols, DNA, RNA and protein was comparable to that of susceptible cultures. Activity of phosphodiesterase decreased and 5'-nucleotidase increased in tolnaftate-resistant cells. Our results suggest that the antifungal activity of tolnaftate is due to differential action on various targets site(s) which are modified in strains resistant to the drug.
Amnesia in relation to fugue states--distinguishing a neurological from a psychogenic basis.
A case of transient amnesia is described in which a patient reported memory loss for five days, during which he had wandered extensively. Analysis showed that he did not have selective amnesia for the public events which had occurred during the five days for which he professed memory loss. This finding was incompatible with our case having a neurologically based global memory disorder during the fugue state. These findings offer support for a distinction between personal and public episodic memory.
The role of diencephalic pathology in human memory disorder. Evidence from a penetrating paranasal brain injury.
A patient (B.J.) is reported who developed severe memory impairment following a penetrating brain injury caused by a snooker cue which entered through his left nostril into the basal regions of the brain. Initially, his memory disorder had the clinical features of a dense amnesic syndrome, with both anterograde and retrograde amnesia, but B.J. subsequently showed significant recovery of memory function. Formal memory testing was carried out 21 months after injury. This demonstrated marked verbal memory impairment, as severe as that seen in patients with the amnesic syndrome. On nonverbal memory tests, his impairment was relatively mild and patchy. His retrograde amnesia had regressed mainly to affect a 6 month period before the injury. On other cognitive tasks, he performed at an average or above average level, and there was no neuropsychological evidence of frontal lobe dysfunction. Neuroradiological investigations at various stages after his injury failed to demonstrate a lesion in any of the thalamic nuclei. Magnetic resonance imaging showed a lesion in the hypothalamus in the region of the mamillary bodies. Our study demonstrates that marked, relatively focal, memory disorder after diencephalic injury can occur without direct pathology to the body of the thalamus. It also indicates that structures in or adjacent to the hypothalamus, such as the mamillary bodies, may play a more important role in human memory functioning than has hitherto been considered.
Korsakoff's psychosis.
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Focal retrograde amnesia: a long term clinical and neuropsychological follow-up.
A patient (E.D.) who had displayed a selective retrograde amnesia in association with transient amnesic episodes (Kapur et al., 1986) was reexamined five years after initial assessment. At the clinical level, his transient amnesic attacks continued, but some of these had clear epileptic features. In addition, EEG investigation indicated temporal lobe abnormality, more prominent in the left temporal region, and supported a clinical diagnosis of temporal lobe epilepsy. Both CT scanning and magnetic resonance imaging were unable to detect the presence of any structural lesion. At the neuropsychological level, there was no evidence of dementia in the form of generalized cognitive dysfunction nor significant deterioration in cognitive functioning since the earlier assessment. Our patient continued to show marked memory loss for public events over the past 20-30 years, in the context of normal or near normal performance on most tests of anterograde memory functioning. While memory for famous scenes and famous faces was markedly impaired, our patient's memory for famous cars was within normal limits and his memory for autobiographical events showed only patchy impairment. Although E.D. performed at an average or above average level on most standard tests of anterograde memory functioning, our patient did show evidence of significant memory loss for public events which had occurred over the past ten years (i.e. since the onset of his illness). The possibility is raised that E.D.'s memory disorder may represent a form of disconnection syndrome.
Genetic analysis of temperature-sensitive lethal mutants of Salmonella typhimurium.
We have isolated 440 mutants of Salmonella typhimurium that show temperature-sensitive growth on complex medium at 44 degrees. Approximately 16% of the mutations in these strains have been mapped to 17 chromosomal locations; two of these chromosomal locations seem to include several essential genes. Genetic analysis of the mutations suggests that the collection saturates the genes readily mutable to a ts lethal phenotype in S. typhimurium. Physiological characteristics of the ts lethal mutants were tested: 6% of the mutants can grow at high temperature under anaerobic conditions, 17% can grow when the medium includes 0.5 M KCl, and 9% of the mutants die after a 2-hr incubation at the nonpermissive temperature. Most ts lethal mutations in this collection probably affect genes required for growth at all temperatures (not merely during high temperature growth) since Tn10 insertions that cause a temperature-sensitive lethal phenotype are rare.
How to write your first book.
Many doctors have, at some time or other, the idea of writing a book. This article considers some of the practical problems involved, including dealing with publishers, the formulation of a book proposal, writing individual chapters and desirable features of computer software.
Selective sparing of memory functioning in a patient with amnesia following herpes encephalitis.
A patient with amnesia subsequent to herpes encephalitis was assessed on a series of tasks which have been shown to result in normal or near normal performance by amnesic subjects. On a pursuit rotor learning task, our patient performed normally, and continued to show evidence of memory for the skill after a period of 30 days. On a perceptual learning task, which involved the identification of line drawings, he also displayed evidence of learning and long-term retention, but his performance remained below that of control subjects. In two priming experiments, which employed a "case-control" paradigm, performance on homonym-spelling and category item-generation tasks was preceded by exposure to a selected list of words. There was no evidence of differential facilitation in respect of those words used in the initial priming task. The findings point to some degree of selectivity of preserved learning capabilities in amnesia. It is hypothesized that this selectivity may be determined by several variables, including the type of task, the etiology and site of pathology, and the severity of amnesia.
Reduplicative paramnesia: possible anatomical and neuropsychological mechanisms.
A patient is reported who presented with reduplicative paramnesia following a vascular lesion in the right frontal region. Neuropsychological examination revealed significant memory impairment, perservation on a problem solving task and marked left-sided inattention. Recovery from the paramnesic episode was accompanied by selective resolution of the original cognitive deficits. It is suggested that focal right frontal pathology may represent a sufficient condition for the occurrence of reduplicative paramnesia, and that the underlying mechanisms may be dependent on a particular combination and severity of memory, visuospatial and conceptual deficits.
Some comments on the technical acceptability of Warrington's Recognition Memory Test.
The technical merits of Warrington's Recognition Memory Test are reviewed. The test has a number of attractive features, but also a number of significant limitations including defects in the initial validation studies, ceiling effects for the verbal recognition memory test, and inadequate documentation of the effects of educational level so as to permit interpretation of individual test data. In addition, no reliability data, such as test-retest or inter-examiner reliability correlations, are reported. It is suggested, therefore, that in its present form the test has limitations as an instrument for use in routine neuropsychological assessment.
Amnesia can facilitate memory performance: evidence from a patient with dissociated retrograde amnesia.
A case is reported of a patient who experienced numerous episodes of transient global amnesia (TGA) during which anterograde amnesia was less prominent than usual, and who developed a permanent selective retrograde amnesia. On formal testing, he performed well on traditional verbal memory tests, but showed marked retrograde amnesia for verbal material, including items on a famous voices recognition test. He was administered a paired-associate learning test where the names of famous personalities for which he was amnesic were associated with incongruous activities (e.g. John Newcombe-singing). Our patient performed better on this task than a group of five matched control subjects. Our observations indicate that in the organization of human memory retrograde amnesia may be fractionated from anterograde amnesia and that in certain situations specific types of amnesia can produce a facilitation effect compared to the performance of control subjects.
Double dissociation between perseveration in memory and problem solving tasks.
This study reports a double dissociation between perseverative responses on a short-term verbal memory test and a card sorting task, as shown by two patients with cerebral tumours. The two patients were matched for number of correct responses on the memory task. The first patient, with a craniopharyngioma and associated dilatation of the third ventricle and lateral ventricles, showed perseveration on the short-term memory task but not on the card sorting task. The second patient, with a subfrontal tumour involving the anterior corpus callosum, perseverated on the card sorting task but not on the short-term memory task. The presence of this double dissociation demonstrates the functional specificity of perseveration in certain memory and problem solving contexts and suggests that distinct subcortical/frontal mechanisms may underly specific types of perseveration.
Neuropsychological analysis of a case of crossed dysphasia verified at postmortem.
A case is reported of crossed dysphasia in a right-handed monolingual patient, where neuropathological verification of the unilateral site of the lesion was obtained within a year of detailed neuropsychological assessment. The patient's pattern of language impairment was characterized by agrammatic speech and relatively preserved naming ability. In addition, the patient had good repetition, poor comprehension, and marked impairment on visuospatial tasks. Neuropathological investigations showed a large area of infarction affecting cortex, white matter, and subcortical structures in the right hemisphere. The possibility is discussed of a distinction between two types of crossed dysphasia with either dissociated or simultaneous language and visuospatial deficits due to reversed representation of hemispheric specific functions or transfer of most cognitive functions to the right hemisphere.
Slowly progressive aphasia without generalized dementia.
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Memory symptoms and memory performance of neurological patients.
The spontaneous memory symptoms of 100 brain-damaged patients suffering from a variety of conditions were elicited. The most frequent types of symptom related to memory for people's names, memory for recent events occurring a few days or weeks ago, memory for a spoken message and remembering to do something. The spontaneous symptoms from 50 non-brain-damaged patients were also elicited. There was a considerable degree of overlap between the type and incidence of symptoms in brain-damaged and control patients. Some symptoms (e.g. remembering people's names) were reported by a similar proportion of control as brain-damaged patients. A few symptoms (e.g. spatial disorientation, temporal disorientation) were reported by brain-damaged patients but not by any control patients. One symptom (remembering to do something) occurred more frequently in the control group of patients than in the brain-damaged group. The relationship between memory symptoms and memory performance was examined in a group of head-injured patients. A short questionnaire on memory symptoms was completed by each patient and by a close observer, and the head-injured subjects also performed tests of immediate and delayed recall. Although there was a highly significant correlation between degree of memory impairment as perceived by the patient and as perceived by an observer, there was generally a low correlation between subjective or observed memory impairment and scores on commonly used clinical memory tests.
Dysgraphia for letters: a form of motor memory deficit?
A case of pure dysgraphia is presented in which the patient could accurately copy letters which she could not write. The patient did not show any evidence of significant reading or speech impairment or any buccofacial or limb apraxia. Both oral and "block spelling" performance were intact. The writing impairment, which was bilateral, appeared to consist of a memory difficulty for the motor movements associated with letters. The dysgraphia was shown to be specific to letters as the patient was able to transcribe certain numbers and patterns which were similar to letters in their visuospatial complexity. It is suggested that dysgraphia for letters may represent a specific type of motor memory deficit, dissociable from copying skills and the ability to draw letter-like forms.
Role of free radicals in catecholamine-induced cardiomyopathy.
Effects of an antioxidant, vitamin E, and a membrane stabilizing agent, zinc, were examined on the isoproterenol-induced changes in the rat myocardium. Isoproterenol treatment (80 mg/kg given over 2 days in two equal doses) caused arrhythmias and 25% mortality within 24 h of the last injection. The ultrastructural changes in the subendocardium and in focal areas of the subepicardium included swelling of mitochondria, loss of myofibrils, cell necrosis, fibrosis, and infiltration of the affected areas by polymorphonucleocytes. Both creatine phosphate and adenosine triphosphate levels were markedly decreased in hearts from isoproterenol-treated animals. Pretreatment of the animals with vitamin E (10 mg X kg-1 X day -1 for 2 weeks) or zinc (10 mg/kg ZnSO4, twice a day for 7 days) prevented these deleterious effects of isoproterenol. Animals maintained on vitamin E deficient diet for 8 weeks were found to be more sensitive to isoproterenol-induced changes and this increased sensitivity was reversed by a 2-week feeding of the animals on the normal diet coupled with vitamin E treatment. Based on the data obtained in this study it is proposed that catecholamine-induced changes may involve free radicals, which by promoting lipid peroxidation may increase membrane permeability and lead to the development of cardiomyopathy.