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Biomedical subjects

B Ahmed

Publications and source records attributed to B Ahmed.

At least 37 records · Page 2Linked to original sources
PubMed1999

Expression of the neuronal isoform of nitric oxide synthase (nNOS) and its inhibitor, protein inhibitor of nNOS, in pigment cell lesions of the skin.

Nitric oxide (NO) is involved in many physiological processes. In cancer, low levels of NO are thought to enhance tumour progression and metastasis. NO is generated from arginine by NO synthase (NOS); the Ca2+-dependent neuronal isoform or nNOS (expressed by neurones and inhibited by the protein inhibitor of nNOS, PIN), is also expressed by cultured normal melanocytes and by all malignant melanoma (MM) cell lines. We studied the expression of nNOS and PIN in paraffin sections of 177 and 58 pigment cell lesions, respectively, using immunohistochemistry; the activity of the necessary cofactor NADPH was studied in 26 frozen cases. Normal melanocytes in situ lacked nNOS and PIN expression, but were NADPH +. Almost half of common acquired benign naevi expressed nNOS; however, halo naevi and congenital naevi expressed nNOS very frequently. Dysplastic naevi and MM showed variable nNOS immunoreactivity in 72% and 83% of cases, respectively. Early (Clark I and Clark II) MM displayed nNOS staining most frequently, and all MM with an invasive radial growth phase expressed nNOS in the papillary dermis. In contrast, only 67% of metastatic MM were nNOS +. PIN was coexpressed with nNOS in 40 of 58 lesions. NADPH activity was present in all nNOS + naevi, but in two malignant cases, NADPH activity was not accompanied by nNOS expression. We conclude that nNOS expression is induced de novo in benign and malignant pigment cell lesions which have all the requirements (NADPH, PIN) necessary for the production and modulation of NO. We postulate that the frequent expression of nNOS in the junctional part of dysplastic naevi may be responsible for their particular histological features. NO generated by the neoplastic dermal cells in the invasive radial growth phase may contribute to the increased number of blood vessels in the papillary dermis.

Carrier Proteins↗
PubMed1999

Isolation of a flavone from Polygala stenopetala.

A flavones has been isolated from the roots of Polygala stenopetala. The structure was established on the basis of UV, Mass spectrum, 1HNMR, 13CHMR and NOE difference experiments as 5,7,4-trihydroxy-3, 5-dimethoxyflavone (tricin) This is for the first time that a flavones has been isolated from the species belonging to the family Polygalaceae.

Journal Article↗
PubMed1998

How long should Atrovent be given in acute asthma?

BACKGROUND: In acute asthma the optimal duration of treatment with combination beta agonist and anticholinergic nebuliser solutions is unknown; most studies have investigated single doses or treatment for up to 12 hours. To determine whether longer treatment with ipratropium bromide might aid recovery a study was undertaken in 106 patients with acute asthma. METHODS: A double blind, randomised, placebo controlled, three group study was performed with all patients receiving ipratropium for 12 hours and salbutamol for 60 hours after admission (both nebulised four hourly), systemic steroids and, if necessary, theophylline. At 12 hours ipratropium was stopped in group I (n = 35) but was continued in the other two groups, and at 36 hours ipratropium was also stopped in group II (n = 35) while patients in group III (n = 36) continued with ipratropium for 60 hours. Spirometric tests were performed before and after salbutamol, and again 30 and 60 minutes after ipratropium or placebo at 12, 36 and 60 hours. Peak flow rates (PEFR) were measured before and after each nebulisation. RESULTS: There were no differences between the groups in PEFR on admission (group I: 214 l/min, group II: 198 l/min, group III: 221 l/min), or mean forced expiratory volume in one second (FEV1) at 12 hours (group I: 1.81, group II: 2.01, group III: 2.21), 36 hours (group I: 2.11, group II: 2.31, group III: 2.41), or at 60 hours (group I: 2.21, group II: 2.31, group III 2.51). Despite this, median time to discharge was significantly higher for patients in group I (5.4 days) than for those in groups II (4.1 days) and III (4.0 days). CONCLUSIONS: Combination nebulised therapy can be continued beyond 12 hours and up to 36 hours after admission with improved recovery time. Lung function testing may not reflect the full benefit of treatment.

Acute Disease↗
PubMed1997

Map of the synapses onto layer 4 basket cells of the primary visual cortex of the cat.

The pattern of excitatory and inhibitory inputs to the inhibitory neurons is largely unknown. We have set out to quantify the major excitatory and inhibitory inputs to layer 4 basket cells from the primary visual cortex of the cat. The synapses formed with the soma, and proximal and distal dendrites, were examined at the light and electron microscopic levels in four basket cells, recorded in vivo and filled with horseradish peroxidase. The major afferents of layer 4 have been well characterised, both at the light and electron microscopic levels. The sizes of the synaptic boutons of the major excitatory inputs to layer 4 from the thalamic relay cells, spiny stellate cells, and layer 6 pyramidal neurons are statistically different. Their distributions were compared to those of the boutons forming asymmetric contacts onto the basket cells, which were assumed to be provided by the same set of excitatory afferents. The best-fit results showed that about equal numbers of synapses were provided by the layer 6 pyramids (43%) and the spiny stellates (44%), whereas the thalamic afferents contributed only 13%. A similar analysis on the symmetric synaptic input to the basket cells indicated that as much as 79% of the symmetric synapses could have originated from layer 4 basket cells. Thalamic and spiny stellate synapses were preferentially located on the soma and proximal dendrites, regions that also had 76% of all the symmetric contracts.

Animals↗
PubMed1997

An intracellular study of the contrast-dependence of neuronal activity in cat visual cortex.

Extracellular recordings indicate that mechanisms that control contrast gain of neuronal discharge are found in the retina, thalamus and cortex. In addition, the cortex is able to adapt its contrast response function to match the average local contrast. Here we examine the neuronal mechanism of contrast adaptation by direct intracellular recordings in vivo. Both simple (n = 3) and complex cells (n = 4) show contrast adaptation during intracellular recording. For simple cells, that the amplitude of fluctuations in membrane potential induced by a drifting grating stimulus follows a contrast response relation similar to lateral geniculate relay cells, and does not reflect the high gain and adaptive properties seen in the action potential discharge of the neurons. We found no evidence of significant shunting inhibition that could explain these results. In complex cells there was no change in the mean membrane potential for different contrast stimuli or different states of adaptation, despite marked changes in discharge rate. We use a simplified electronic model to discuss the central features of our results and to explain the disparity between the contrast response functions of the membrane potential and action potential discharge in simple cells.

Action Potentials↗
PubMed1996

The interaction of a type A retroviral particle and class II human leukocyte antigen susceptibility genes in the pathogenesis of Graves' disease.

We have previously reported that over 85% of patients with Graves' disease have detectable serum antibodies against a human intracisternal type A retroviral particle (HIAP), which are not present in age- and gender-matched controls, suggesting a role for HIAP in triggering the autoimmune process leading to Graves' disease. To investigate the interaction of this viral particle with genetic factors, 35 members of 3 kindreds, selected because of a high family prevalence of Graves' disease (a total of 11 members affected), were examined for clinical signs of thyroid dysfunction, goiter, and opthalmopathy. Thyroid function tests and autoimmune serological profiles were also obtained. In addition, subjects were tested for the presence of antibodies against HIAP by means of immunoblot analysis of their sera, and their human leukocyte antigen (HLA) class II alleles were determined by DNA methodology. Molecular genetic analyses enabled the detection of postulated HLA susceptibility haplotypes in each family. These families had 8, 4, and 5 members, respectively, with such apparent susceptibility genes and 11, 5, and 9 members, respectively, with immunological evidence of retroviral exposure. In the presence of both factors (codetected in a total of 15 members of the 3 kindreds), the incidence of Graves' disease was 100%, 67%, and 80%, respectively. One additional member of family B and 3 in family C with both viral and genetic susceptibility factors were found to have serological abnormalities and/or goiter and ocular signs consistent with evolving or preclinical Graves' disease. In families A and C, tight linkage between HLA haplotypes and Graves' disease was demonstrated in a manner consistent with recessive inheritance. The association between the occurrence of both anti-HIAP-I antibody positivity and HLA susceptibility and the presence of Graves' disease was highly significant (P < 0.001). The pathogenesis of Graves' disease in these families appears to be attributable to the interaction between the immune response to an intracisternal type A retroviral particle and immunogenetic susceptibility, leading to the autoimmune processes that underlie Graves' disease, with subsequent development of the characteristic features of the illness. Data from these families suggest that both of these factors are necessary for final disease expression. These results imply that serological evidence of retroviral exposure together with genetic HLA susceptibility are the two major predisposing factors underlying the pathogenesis of Graves' disease. Further studies will establish whether prospective identification of persons at risk for Graves' disease is possible by this means.

Adult↗
PubMed1995

Evidence for a retroviral trigger in Graves' disease.

An apparently high frequency of Graves' disease encountered in New Orleans, Louisiana, prompted an investigation for a possible infectious agent that might be triggering the disease in genetically susceptible individuals. We studied 40 patients with Graves' disease, and compared them to the following groups of controls: age and gender matched healthy subjects; patients with multinodular goiter (non-autoimmune thyroid controls); patients with chronic lymphocytic thyroiditis (autoimmune thyroid disease controls) and additional organ or tissue specific autoimmune controls exclusive of thyroid autoimmunity, including patients with Type I diabetes and other endocrine autoimmune complex disorders. Serum antibodies against a prototypic strain of a human intracisternal A-type retroviral particle type 1 (HIAP-1) were detected by a sensitive and specific immunoblotting assay. In 87.5% (35/40) of the Graves' disease patients there was a positive reaction against several HIAP-1-associated proteins, predominantly 97 Kd and 80 Kd, with only 5 showing no reactivity to any. In contrast, 2% (2/105) of sera from normal controls showed positive reactivity. Furthermore, only 10% (1/10) of sera from multinodular goiter control patients and 10% (1/10) of Hashimoto's patients showed reactivity (p < 0.0005). Sera from 3 of 20 (15%) of Type I diabetic patients none of whom had Graves' disease, showed reactivity but there was no reactivity in 9 other patients with one or more of the endocrine autoimmune complex disorders, including Addison's disease, vitiligo, myasthenia gravis and pernicious anemia. In addition we studied two individuals with Graves' disease from each of two families residing outside Louisiana, all of whom were positive for these antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Polyneuronal innervation of spiny stellate neurons in cat visual cortex.

Our hypothesis was that spiny stellate neurons in layer 4 of cat visual cortex receive polyneuronal innervation. We characterised the synapses of four likely sources of innervation by three simple criteria: the type of synapse, the target (spine, dendritic shaft), and the area of the presynaptic bouton. The layer 6 pyramids had the smallest boutons and formed asymmetric synapses mainly with the dendritic shaft. The thalamic afferents had the largest boutons and formed asymmetric synapses mainly with spines. The spiny stellates had medium-sized boutons and formed asymmetric synapses mainly with spines. We used these to make a "template" to match against the boutons forming synapses with the spiny stellate dendrite. Of the asymmetric synapses, 45% could have come from layer 6 pyramidal neurons, 28% from spiny stellate neurons, and 6% from thalamic afferents. The remaining 21% of asymmetric synapses could not be accounted for without assuming some additional selectivity of the presynaptic axons. Additional asymmetric synapses may come from a variety of sources, including other cortical neurons and subcortical nuclei such as the claustrum. Of the symmetric synapses, 84% could have been provided by clutch cells, which form large boutons. The remainder, formed by small boutons, probably come from other smooth neurons in layer 4, e.g., neurogliaform and bitufted neurons. Our analysis supports the hypothesis that the spiny stellate receives polyneuronal innervation, perhaps from all the sources of boutons in layer 4. Although layer 4 is the major recipient of thalamic afferents, our results show that they form only a few percent of the synapses of layer 4 spiny stellate neurons.

Animals↗
PubMed1994

CNS effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides, 1986-1993.

The centrally mediated effects of peptides as published in the journal Peptides from 1986 to 1993 are tabulated in two ways. In one table, the peptides are listed alphabetically. In another table, the effects are arranged alphabetically. Most of the effects observed after administration of peptides are grouped, wherever possible, into categories such as cardiovascular and gastrointestinal. The species used in most cases has been rats; where other animals were used, the species is noted. The route of administration of peptides and source of information also are included in the tables, with a complete listing provided at the end. Many peptides have been shown to exert a large number of centrally mediated effects.

Central Nervous System↗
PubMed1993

Case report: hypercalcemia in a patient with AIDS and Pneumocystis carinii pneumonia.

Pneumocystis carinii infection is commonly seen in patients infected with HIV, and there is evidence of macrophage involvement in the disease process. Macrophage dysfunction can result in abnormal vitamin D metabolism as is often seen in a granulomatous disease such as sarcoidosis. This article describes a patient with AIDS who had P. carinii pneumonia and hypercalcemia and had elevated 1,25-dihydroxyvitamin D levels, the first such reported case in the literature. There was no other evidence of a granulomatous disease such as sarcoidosis or tuberculosis to account for this. It is suggested that the increase in 1,25-dihydroxyvitamin D level was secondary to P. carinii induced macrophage dysfunction. As the patient's P. carinii pneumonia resolved, his 1,25 dihydroxyvitamin D level normalized along with the resolution of hypercalcemia.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Estimation of population coverage in the 1990 United States census based on demographic analysis.

"This article presents estimates of net coverage of the national population in the 1990 [U.S.] census, based on the method of demographic analysis. The general techniques of demographic analysis as an analytic tool for coverage measurement are discussed, including use of the demographic accounting equation, data components, and strengths and limitations of the method. Patterns of coverage displayed by the 1990 estimates are described, along with similarities or differences from comparable demographic estimates for previous censuses....A final section presents the results of the first statistical assessment of the uncertainty in the demographic coverage estimates for 1990." Comments by Clifford C. Clogg and Christine L. Himes (pp. 1,072-4) and Jeffrey S. Passel (pp. 1,074-7) and a rejoinder by the authors (pp. 1,077-9) are included.

Americas↗
PubMed1992

How changes in components of growth affect the population aging of states.

We analyzed the demographic determinants of population aging for states of the United States between 1950 and 1980. Using the factorial projections method, we estimated the effects of population momentum and changes in mortality, fertility, and migration on changes in the proportion of persons age 65+. Declining mortality rates caused the population to age in virtually every state in every decade between 1950 and 1980, but the effects were very small. The effects of changes in fertility rates were considerably greater. Population momentum generally had a greater effect on population aging than changes in either fertility or mortality rates. Net migration was by far the most volatile component of population aging, both in terms of changes over time and state-to-state differences at a given point in time. We expect this trend to continue in coming decades.

Aged↗
PubMed1991

Orientation bias of cat dorsal lateral geniculate cells: directional analysis of the major axis of the receptive field centre.

The receptive field centre of cells in the dorsal lateral geniculate nucleus were mapped as iso-sensitivity contours. 94% of the cells were found to have elliptical centres, and analysis of the major axis orientation showed that 29% and 59% of units had their major axis oriented within +/- 20 degrees of the radial and horizontal directions, respectively. The data for Y-cells showed a greater dispersion in their orientation biases (R = 0.57) compared with X-cells (R = 0.79). Nevertheless, a horizontal orientation bias was found in both classes of cells: 47% of Y-cells and 73% of X-cells. In addition, an examination of the major axis orientations was undertaken for cells with receptive field centres located along the radial direction of 35 degrees below the horizontal meridian. In this 35 degree Radial Group a horizontal bias was also confirmed. Analysis of the dispersion of major axis orientations with eccentricity from the area centralis showed a statistically significant decrease in scatter and, hence, indicated an increase in the horizontal bias with eccentricity.

Animals↗
PubMed1990

Training of Kuwaiti medical doctors and their specialty choices: sociocultural impact.

Kuwait has a comprehensive and well-structured health care system. However, to deliver such care the country relies on expatriate medical doctors. This paper attempts to discuss the sociocultural influences on the training of Kuwaiti medical doctors and their specialty choices in order to gauge future requirements of the Kuwaiti Health Services.

Career Choice↗
PubMed1990

A demographic analysis of the population growth of states, 1950-1980.

Factors affecting regional differences in population growth in the United States are explored. "In this study, we estimated the contributions of births, deaths, and migration to changes in population size between 1950 and 1980 for the 48 contiguous states in the United States. We found that population momentum (i.e., the growth that would occur in a closed population if fertility and mortality rates remained constant) had the largest effect on population growth in most states, but that differences in net migration were the major cause of state-to-state differences in growth rates. We also found that net migration has been gaining in importance compared to natural increase as a component of population growth. We expect this trend to continue in coming decades." This is a revised version of a paper originally presented at the 1988 Annual Meeting of the Population Association of America (see Population Index, Vol. 54, No. 3, Fall 1988, p. 429).

Americas↗
PubMed1989

Orientation bias of cat retinal ganglion cells: a reassessment.

For cat retinal ganglion cells whose receptive field centres were distributed in specified sections of the left visual field, the deviations of the major axis from the radial, horizontal, and circumferential directions were determined. The percentage of cells with deviations within +/- 20 degrees from the radial, horizontal, and circumferential directions were, respectively, 33%, 68%, 16%. In addition, comparison between values of deviation from the horizontal direction for cells located at eccentricities of 10 degrees and 20 degrees from the area centralis showed a statistically significant trend; the bias for the horizontal increased with eccentricity.

Action Potentials↗
PubMed1989

Neural motion after-effects in the cat's striate cortex: orientation selectivity.

Single striate cortical neurones were recorded from adult cats, lightly anaesthetized with N2O/O2/halothane. The receptive fields for the dominant eye were subjected to direction-specific adaptation by a square-wave grating of optimal spatial frequency and velocity, drifting continuously in each neurone's preferred direction. Recovery of the neural motion after-effect induced by prior adaptation was assessed with the same grating pattern which now moved alternately in the preferred and opposite directions. In controls the same tests for recovery followed a period of exposure to a uniform field of identical luminance to the adapting grating. Three sets of measurements were made to establish whether the adaptation was orientation- as well as direction-specific. In the first, test grating orientation was maintained constant and optimal for each neurone whilst adapting orientation was systematically varied. In the second, test orientation was varied whilst maintaining adapting orientation constant. In the third set, adapting and test orientations were initially fixed at each neurone's optimum; they were next set, non-optimally to one side of the optimum. Results from the latter configuration were compared with similar tests in which the test grating remained at that non-optimal orientation whilst the orientation of the adapting grating was now altered to a new point on the other flank of each neurone's orientation tuning curve that was matched for strength of adaptation. Thus the degree of adaptation was identical in each case, but zero orientation difference between adapting and test gratings in one case was contrasted with a substantial orientation difference in the other. The results from all three sets of data were unequivocal: in simple neurones, and in standard and intermediate classes of complex neurones, but not in special complex neurones, the sequential effects of adapting gratings on the responses and sensitivity to subsequently presented test gratings were maximal when their orientations were matched and optimal for each neurone, less marked when orientations were matched but non-optimal. In conclusion, adaptation induced by pattern motion was orientation- as well as direction-specific only in standard (length summating) and intermediate complex neurones, and in simple cells; in special complex neurones it was not.

Adaptation, Ocular↗