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Biomedical subjects

J Bell

Publications and source records attributed to J Bell.

At least 343 records · Page 19Linked to original sources
PubMed1986

Numerical solution of a nonlinear advance-delay-differential equation from nerve conduction theory.

A functional differential equation which is nonlinear and involves forward and backward deviating arguments is solved numerically. The equation models conduction in a myelinated nerve axon in which the myelin completely insulates the membrane, so that the potential change jumps from node to node. The equation is of first order with boundary values given at t = +/- infinity. The problem is approximated via a difference scheme which solves the problem on a finite interval by utilizing an asymptotic representation at the endpoints, cubic interpolation and iterative techniques to approximate the delays, and a continuation method to start the procedure. The procedure is tested on a class of problems which are solvable analytically to access the scheme's accuracy and stability, then applied to the problem that models propagation in a myelinated axon. The solution's dependence on various model parameters of physical interest is studied. This is the first numerical study of myelinated nerve conduction in which the advance and delay terms are treated explicitly.

Animals↗
PubMed1986

Interface of panic and depression: clinical and sleep EEG correlates.

Four groups of subjects were compared with respect to their clinical and demographic status and electroencephalographic (EEG) characteristics, namely: primary major depressive disorder (PRI MDD); panic disorder (Panic); "Mixed" group comprising patients meeting full syndromal criteria for MDD and panic occurring concomitantly; and normal controls. The "Mixed" (MDD + Panic) patients were characterized by earlier age of onset of psychiatric illness, longer duration of current episode, greater intensity of symptoms, higher impairment of functioning, increased miscellaneous psychopathology, and greater objective stress and anger. With respect to sleep EEG variables, PRI MDD patients were clearly different from the other three groups. The sleep profile of the "Mixed" group occupies an intermediate position between the "pure" Panic and MDD groups. Classification of the "Mixed" patients based on the discriminant function coefficients of the Schedule for Affective Disorders and Schizophrenia and sleep analysis of the "pure" groups (PRI MDD and Panic) reveals that some patients are classified as true PRI MDD while others are classified as falling somewhere along the PRI-MDD/Panic spectrum. The separation of the PRI MDD from Panic and Normals, however, is clear, suggesting that sleep can be successfully used as a physiological marker in the separation of these conditions.

Adult↗
PubMed1986

The nucleotide sequence, localization and transcriptional properties of a tRNALeuCUG gene from Drosophila melanogaster.

The nucleotide sequence of a tRNALeuCUG gene from Drosophila melanogaster has been determined and compared with available tRNALeuCUG sequences from other eukaryotes, as well as with the tRNALeuUUG gene of D. melanogaster. The genomic location, determined by in situ hybridization, was found to be at site 66B on chromosome 3L. This localization probably places it within one of the known, but uncharacterized, clusters of tRNA genes in this organism. In addition, the transcriptional behaviour of this tRNALeuCUG gene in various in vitro systems is described and it seems that, although the gene is transcribed in all test systems, the very A + T-rich 5'-flanking sequence of this particular gene may be somewhat inhibitory to transcription in vitro.

Animals↗
PubMed1986

A nonlinear model for transduction in hair cells.

Based on the experimental observations of the mechano-electrical transduction in hair cells, we formulate a model of the receptor potential utilizing a simple model circuit and ideas of stretch activation that have been developed for other mechanoreceptors. The stereociliary displacement-response relation is developed based on the cilia crosslinking, thus incorporating notions of bidirectional sensitivity, asymmetry, saturation, and adaptation into the model. We then give some simulation results involving periodic stimuli to the hair bundle as well as current stimuli of study latency behavior and other qualitative properties of the model.

Animals↗
PubMed1986

Proliferation-dependent regulation of base excision repair in normal and SV-40 transformed human cells.

The effect of SV-40 viral transformation of human cells on the proliferation-dependent regulation of base excision repair was examined. Normal human diploid WI-38 fibroblasts and SV-40 transformed WI-38 cells were used to examine whether the process of transformation perturbed the regulation of base excision repair. The regulation of excision repair enzymes in each cell type was examined by quantitating: the specific activities of the base excision repair enzymes uracil DNA glycosylase and hypoxanthine DNA glycosylase as a function of cell growth; and immunological analysis of the uracil DNA glycosylase using monoclonal antibodies to human uracil DNA glycosylase. In each cell type, both DNA glycosylase activities were increased as a function of cell proliferation; the extent of enhancement being greater in the transformed cells. As defined by ELISA and immunoblot analysis, the induced uracil DNA glycosylases in both cell types share the same determinants. Although other repair processes are altered upon SV-40 transformation, these results suggest that the proliferation-dependent regulation of these base excision repair enzymes is retained in SV-40 transformed human cells.

Cell Division↗
PubMed1986

Parametric dependence of conduction speed for a diffusive model of a myelinated axon.

A simple model of a myelinated axon, using ideas from cable theory and accounting for the diffusion of potential across the internode, is formulated and solved to obtain transcendental expressions relating conduction velocity and various model parameters. Numerical simulations are performed to obtain graphs of several parameter relationships.

Action Potentials↗
PubMed1986

Behaviour of a model for the synapse of an auditory receptor cell.

The purpose of this paper is to formulate a dynamical model of an auditory hair-cell synapse, coupled to a model of the hair cell's receptor potential through intracellular calcium concentration. The synaptic model includes a mechanism for auditory nerve discharge, which allows for the determination of the afferent nerve's firing rate from stimulation of the receptor cell's hair bundle. We show that the synaptic model has a periodic solution under certain conditions, given a constant current stimulus. We also show that the firing rate undergoes adaptation.

Adaptation, Physiological↗
PubMed1986

Pathophysiology involved in autonomic dysreflexia.

Autonomic dysreflexia has potentially life-threatening consequences in quadriplegics and high paraplegics. Seizures, subarachnoid hemorrhage, and fatal stroke may result. This article explains the pathophysiology of autonomic dysreflexia. Appropriate nursing interventions to prevent serious complications are described.

Autonomic Nervous System Diseases↗
PubMed1986

Vitamin D nutrition in pregnant Nigerian women at term and their newborn infants.

In view of the high incidence of rickets in infants of women practising purdah (the use of veils) in northern Nigeria we conducted a study on plasma calcium, phosphate, and serum 25-hydroxyvitamin D (25 OHD) concentrations in pregnant Nigerian women and in cord blood obtained from the newborns. Plasma calcium, phosphate, and serum 25 OHD concentrations were lower in practising women and their newborns than those not practising purdah and their infants, respectively. The concentrations of 25 OHD in all Nigerian women were greater than those observed in caucasian women in the United Kingdom. These data emphasise the role of exposure to sunshine in regulating serum 25 OHD concentrations and the adverse effect of deliberate exclusion of sunshine and are consistent with previous data indicating hypovitaminosis D in purdah clad women and their newborns in Saudi Arabia. These data do not, however, provide an explanation for the pathogenesis of the high incidence of neonatal rickets and tetany in infants born of purdah clad women as these women have 25 OHD concentrations greater than those in caucasian women in the United Kingdom.

Alkaline Phosphatase↗
PubMed1986

Intravascular detachable balloon embolization of intracranial aneurysms. Indications and techniques.

The treatment of intracranial aneurysms from a transvascular approach, with preservation of the parent vessel is now being performed in selected cases. From a transfemoral approach, a silicone detachable balloon is flow-directed up the carotid or vertebral-basilar artery, guided directly into the aneurysm and detached. The aneurysm is thus excluded from the circulation and the parent artery is preserved. Thus far, this technique has been successful in treating aneurysms in the cavernous carotid, carotid ophthalmic, posterior communicating, distal basilar, and posterior cerebral artery distributions. The indications and techniques of detachable balloon embolization therapy are presented.

Embolization, Therapeutic↗
PubMed1986

Further data supporting linkage between cystic fibrosis and the met oncogene and haplotype analysis with met and pJ3.11.

The linkage of cystic fibrosis (CF) and the polymorphic DNA markers pJ3.11, met, 7C22, DOCR1-917, COL1A2, and TCRB have jointly localized the mutation causing CF to chromosome 7q2.1-3.1. We report further linkage data with two polymorphic markers at the met oncogene locus, pmetH and pmetD, which supports the tight linkage found by White et al. between CF and met. One family shows evidence for meiotic recombination between CF and met. Analysis of haplotypes in CF pedigrees collected for linkage studies combined with data from single affected families requesting prenatal diagnosis (Farrall et al., Lancet i:1402-1404, 1986) shows CF and met to be in linkage equilibrium in our population while pJ3.11-CF haplotypes show a deviation from the equilibrium frequencies.

Cystic Fibrosis↗
PubMed1986

Genital rhabdomyosarcoma: current management and review of the literature.

Rhabdomyosarcoma is the most common soft tissue sarcoma in childhood and 20 per cent of these cancers involve the pelvis or genitourinary system. Radical pelvic surgery, such as exenteration, was considered at one time to be the standard treatment for this cancer which carried a very poor prognosis. Over the past 15 years, a combined modality approach to treating rhabdomyosarcoma, using chemotherapy, radiotherapy, and less radical surgery, has evolved and survival rates have improved. This paper presents a case of rhabdomyosarcoma involving the perineum which was treated by combination chemotherapy of Vincristine, Actinomycin-D, and Cytoxan, followed by wide local excision, interstitial and external beam radiotherapy, and postoperative chemotherapy. The literature on pelvic rhabdomyosarcoma is reviewed and the current approach to treating this cancer using multimodal therapy is discussed.

Adolescent↗