PubMed Health⌕ Search

Biomedical subjects

J D Evans

Publications and source records attributed to J D Evans.

At least 19 recordsLinked to original sources
PubMed1998

Analytical solutions to a tapering multicylinder somatic shunt cable model for passive neurones.

A multicylinder somatic shunt cable model for passive neurones is considered in which one or more tapering equivalent cylinders emanate from a uniformly polarized soma. Each tapering equivalent cylinder approximates the loss of dendritic trunk parameter in the one or more dendritic trees that it represents, relaxing certain symmetry conditions necessary for the Rall equivalent cylinder concept and in particular allowing terminal branches to end at different electrotonic lengths. The case of exponential taper is considered in detail following the anatomical data on apical and basilar dendrites of CA1 and CA3 hippocampal pyramidal neurons obtained by Turner and Schwartzkroin [J. Neurophysiol. 44 (1980) 184; J. Neurosci. 3 (1983) 2381].

Dendrites↗
PubMed1997

Serum levels of insulin-like growth factors (IGF-I and IGF-II) and their binding protein (IGFBP-3) are not elevated in pancreatic cancer.

CONCLUSION: Serum levels of IGF-I, IGF-II, and IGFBP-3 are not elevated in pancreatic cancer and do not appear to have a significant role in glucose homeostasis in this group of patients. BACKGROUND: The insulin-like growth factors (IGFs) and their binding proteins (IGFBPs) have been implicated recently in the pathogenesis of pancreatic cancer, and increased serum levels of IGF-I or IGF-II have been reported previously in a number of other gastrointestinal malignancies. METHODS: Serum levels of IGF-I, IGF-II, and IGFBP-3 were measured by RIA in 20 patients with pancreatic cancer and 20 age-matched healthy control subjects and correlated with serum glucose, C-peptide, and glucose tolerance. RESULTS: No significant difference was observed in serum levels of IGF-I (13 vs 17 nmol/L, respectively), IGF-II (0.67 vs 0.91 U/mL), or IGFBP-3 (2.3 vs 2.3 mg/L) between the two groups of patients. Twelve (60%) patients had impaired glucose tolerance, but no correlation was observed between the serum levels of the IGFs and glucose tolerance.

Aged↗
PubMed1997

Factors affecting lactate and malate utilization by Selenomonas ruminantium.

Lactate utilization by Selenomonas ruminantium is stimulated in the presence of malate. Because little information is available describing lactate-plus-malate utilization by this organism, the objective of this study was to evaluate factors affecting utilization of these two organic acids by two strains of S. ruminantium. When S. ruminantium HD4 and H18 were grown in batch culture on DL-lactate and DL-malate, both strains coutilized both organic acids for the initial 20 to 24 h of incubation and acetate, propionate, and succinate accumulated. However, when malate and succinate concentrations reached 7 mM, malate utilization ceased, and with strain H18, there was a complete cessation of DL-lactate utilization. Malate utilization by both strains was also inhibited in the presence of glucose. S. ruminantium HD4 was unable to grow on 6 mM DL-lactate at extracellular pH 5.5 in continuous culture (dilution rate, 0.05 h-1) and washed out of the culture vessel. Addition of 8 mM DL-malate to the medium prevented washout on 6 mM DL-lactate at pH 5.5 and resulted in succinate accumulation. Addition of malate also increased bacterial protein, acetate, and propionate concentrations in continuous culture. These results suggest that 8 mM DL-malate enhances the ability of strain HD4 to grow on 6 mM DL-lactate at extracellular pH 5.5.

Animals↗
PubMed1997

Chronic pancreatitis and pancreatic carcinoma.

The differential diagnosis between pancreatic cancer and chronic pancreatitis is very important as the management and prognosis of these two diseases is different. In most patients with pancreatic disease, the diagnosis can be established but there is a subgroup of patients in whom it is difficult to differentiate between these conditions because the clinical presentation is often similar and currently available diagnostic tests may be unable to distinguish between an inflammatory or neoplastic pancreatic mass. This paper reviews the aetiology, pathology and clinical features of these diseases and discusses the limitations of conventional diagnostic methods and how newer techniques may be of value in the differential diagnosis.

Chronic Disease↗
PubMed1997

Role of matrix metalloproteinases and their inhibitors in pancreatic cancer.

BACKGROUND/AIMS: The matrix metalloproteinases are a family of proteolytic enzymes which normally have an important physiological role in tissue remodelling and wound healing, but more recently have been implicated in the proteolytic events which occur during tumour invasion. METHODS: The expanding family of matrix metalloproteinases and the specific tissue inhibitors of the matrix metalloproteinases are reviewed including their classification, structure, function, regulation of activity, and tissue expression with particular reference to pancreatic cancer. The effect of synthetic matrix metalloproteinases inhibitors in preclinical studies is reviewed together with the results of ongoing clinical trials in pancreatic cancer. RESULTS: Pancreatic cancer is associated with the overexpression of several matrix metalloproteinases with a reduced expression of their specific inhibitors. Orally bioavailable matrix metalloproteinase inhibitors have successfully completed phase I/II clinical trials with promising results. Multicentre randomised controlled phase IIb/III clinical trials aren currently under way in pancreatic cancer. CONCLUSIONS: Matrix metalloproteinase inhibition may represent a novel approach to the management of pancreatic cancer not only in advanced disease, but in the adjuvant treatment setting following tumour resection either alone or in combination with existing chemotherapeutic agents.

Clinical Trials as Topic↗
PubMed1997

Outcome of surgery for chronic pancreatitis.

BACKGROUND: In patients with chronic pancreatitis, surgery is indicated for the management of intractable pain or for the treatment of complications. METHODS: Sixty-three consecutive patients (49 men and 14 women of median age 40 (range 20-72) years) who had undergone surgery over an 8-year interval for chronic pancreatitis were studied. The mortality and morbidity rates associated with surgery were assessed and quality of life was reviewed based on relief of symptoms, analgesic use, employment and long-term sequelae. RESULTS: Forty-four patients (70 per cent) had alcoholic chronic pancreatitis. In 60 patients the principal indication for surgery was intractable pain. Eighteen patients had a duodenum-preserving resection of the pancreatic head (Beger operation); the other surgical procedures were Whipple resection (15), left-sided resection (13), total pancreatectomy (seven), pseudocystjejunostomy (five), pancreaticojejunostomy (one) and bypass procedures (four). The median inpatient stay was 12 days; 23 patients had postoperative complications including one death (2 per cent). There was improved pain control (P < 0.001), a reduction in opiate analgesia use, increase in percentage weight gain (P < 0.01 at 2 years) and return to employment following surgery. Although there was an increase in diabetes mellitus and need for enzyme supplementation these were easily controlled. CONCLUSION: Surgery is an effective treatment in carefully selected patients with chronic pancreatitis but must be tailored to the pattern of disease in each individual.

Adult↗
PubMed1996

Duodenal gangliocytic paraganglioma presenting as an ampullary tumor.

CONCLUSION: We report a case of a duodenal gangliocytic paraganglioma that had an unusual clinical presentation and atypical immunohistochemical features. BACKGROUND: Duodenal gangliocytic paragangliomas are rare tumors of the gastrointestinal tract with approx 70 cases reported in the literature. The most common presentation is with gastrointestinal bleeding, whereas obstructive jaundice is very uncommon. Immunohistochemistry typically shows positive epithelial cell staining for somatostatin, pancreatic polypeptide, and other neuroendocrine markers. METHODS: A 56-yr-old man presented with intermittent episodes of epigastric pain, vomiting, and obstructive jaundice. Upper gastrointestinal endoscopy revealed a pedunculated ampullary tumor that was subsequently confirmed by computed tomography. At operation, there was marked secondary obstructive chronic pancreatitis in the remaining pancreas necessitating a pylorus-preserving total pancreatectomy. RESULTS: Histology confirmed typical features of a duodenal gangliocytic paraganglioma, but immunohistochemistry demonstrated negative staining for somatostatin and other polypeptides, which is in contrast to most other reported cases. Two years after surgery, the patient remains alive and well on medical treatment with no evidence of recurrent tumor.

Ampulla of Vater↗
PubMed1996

A clinical and neuropsychological comparison of delusional disorder and schizophrenia.

The authors evaluated 14 middle-aged and elderly patients with delusional disorder (DD) and 253 patients with schizophrenia (SC); all patients met DSM-III-R criteria. Because the DD patients were older and had a later age at onset of illness, a sub-sample of 50 SC patients with illness onset after age 40 was compared with the 14 DD patients on clinical and neuropsychological characteristics. The DD group had a less frequent history of past hospitalization but more severe overall psychopathologic symptoms. Level of neuropsychological impairment seemed somewhat lower in the DD group, but differences were nonsignificant because of small sample size. Diagnoses remained stable during up to 8 years' follow-up (average 4 years). These preliminary findings provide partial support to the clinical categorization of DD as a disorder distinct from SC.

Age of Onset↗
PubMed1995

Relatedness threshold for the production of female sexuals in colonies of a polygynous ant, Myrmica tahoensis, as revealed by microsatellite DNA analysis.

The genetic relationships of colony members in the ant Myrmica tahoensis were determined on the basis of highly polymorphic microsatellite DNA loci. These analyses show that colonies fall into one of two classes. In roughly half of the sampled colonies, workers and female offspring appear to be full sisters. The remaining colonies contain offspring produced by two or more queens. Colonies that produce female sexuals are always composed of highly related females, while colonies that produce males often show low levels of nestmate relatedness. These results support theoretical predictions that workers should skew sex allocation in response to relatedness asymmetries found within colonies. The existence of a relatedness threshold below which female sexuals are not produced suggests a possible mechanism for worker perception of relatedness. Two results indicate that workers use genetic cues, not queen number, in making sex-allocation decisions. (i) The number of queens in a colony was not significantly correlated with either the level of relatedness asymmetry or the sex ratio. (ii) Sex-ratio shifts consistent with a genetically based mechanism of relatedness assessment were seen in an experiment involving transfers of larvae among unrelated nests. Thus workers appear to make sex-allocation decisions on the basis of larval cues and appear to be able to adjust sex ratios long after egg laying.

Alleles↗
PubMed1995

Results of extensor tendon repair performed by junior accident and emergency staff.

The results of 46 extensor tendon repairs performed by junior accident and emergency doctors were assessed, with a minimum follow up of 6 months. Based on Miller's assessment, 80 per cent of the proximal injuries achieved excellent or good results. Only 18 per cent of distal injuries achieved excellent or good results. Neither grip or fingertip pinch strength were significantly reduced. Sixty-seven per cent of patients complained of no residual pain and only 7 per cent complained of the injured digit getting in the way.

Adolescent↗
PubMed1995

Techniques for the application of the analytical solution to the multicylinder somatic shunt cable model for passive neurones.

The general solution for the voltage response to a generic impulse current input in a multicylinder somatic shunt cable model for passive neurones has been developed in [1]. In this paper we consider the application of the multicylinder solution to examples previously considered by other authors for the single cylinder case: long and short current input and synaptic input modeled by an alpha-function and a multi-exponential function. Simple expansions appropriate for small and large times are found and efficient means of obtaining these expansions are clearly demonstrated. The dependence of the small and large time solutions upon the dimensionless parameters appearing in the conservation of current condition at the soma is investigated. Relevant limits of these dimensionless parameters which further simplify the small and large time solutions are related back to equivalent dimensional problems of interest to the practitioner. The well-posedness of the dimensionless inverse problem is investigated and a method proposed for the solution of the dimensional inverse problem for the somatic shunt.

Animals↗
PubMed1994

Compression neuropathy of the common peroneal nerve caused by a ganglion.

A case of compression of the common peroneal nerve caused by a ganglion herniating from the superior tibio-fibular joint is reported. MR imaging was partially helpful in making the diagnosis. The patient has made an almost complete recovery 3 months after excision of the lesion. Early diagnosis and treatment is required to ensure recovery.

Ganglia↗
PubMed1994

Analytical solutions to the multicylinder somatic shunt cable model for passive neurones with differing dendritic electrical parameters.

The multicylinder somatic shunt cable model for passive neurones with differing time constants in each cylinder is considered in this paper. The solution to the model with general inputs is developed, and the parameteric dependence of the voltage response is investigated. The method of analysis is straightforward and follows that laid out in Evans et al. (1992, 1994): (i) The dimensional problem is stated with general boundary and initial conditions. (ii) The model is fully non-dimensionalised, and a dimensionless parameter family which uniquely governs the behaviour of the dimensionless voltage response is obtained. (iii) The fundamental unit impulse problem is solved, and the solutions to problems involving general inputs are written in terms of the unit impulse solution. (iv) The large and small time behaviour of the unit impulse solution is examined. (v) The parametric dependence of the unit impulse upon the dimensionless parameter family is explored for two limits of practical interest. A simple expression for the principle relationship between the dimensionless parameter family is derived and provides insight into the interaction between soma and cylinders. A well-posed method for the solution of the dimensional inverse problem is presented.

Adult↗
PubMed1994

Solutions for transients in arbitrarily branching cables: IV. Nonuniform electrical parameters.

Solutions for transients in arbitrarily branching passive cable neurone models with a soma are extended to models with nonuniform electrical parameters and multiple dendritic shunts. The response to an injected current can again be represented as an infinite series of exponentially decaying components with system time constants obtained from the roots of a recursive transcendental equation. The reciprocity relations and global parameter dependencies are the same as for uniform models. Infinitely many "raw" electro-morphological models map onto a given "core" electrotonic model; local as well as global raw parameter trade-offs are now possible. The solutions are illustrated by means of biologically relevant examples: (i) the effects of nonuniform electrical parameters in a two-cylinder + soma cortical pyramidal cell model, (ii) the errors that can occur when uniformity is incorrectly assumed in a single cylinder model, (iii) nonsumming interactions between cells and electrodes that can dramatically increase the duration of the effective capacitative electrode artefact, and (iv) shunting inhibition and double impalements in a hippocampal CA1 pyramidal cell "cartoon" representation. These solutions should complement compartmental modelling techniques.

Animals↗
PubMed1993

Solutions for transients in arbitrarily branching cables: I. Voltage recording with a somatic shunt.

An analytical solution is derived for voltage transients in an arbitrarily branching passive cable neurone model with a soma and somatic shunt. The response to injected currents can be represented as an infinite series of exponentially decaying components with different time constants and amplitudes. The time constants of a given model, obtained from the roots of a recursive transcendental equation, are independent of the stimulating and recording positions. Each amplitude is the product of three factors dependent on the corresponding root: one constant over the cell, one varying with the input site, and one with the recording site. The amplitudes are not altered by interchanging these sites. The solution reveals explicitly some of the parameter dependencies of the responses. An efficient recursive root-finding algorithm is described. Certain regular geometries lead to "lost" roots; difficulties associated with these can be avoided by making small changes to the lengths of affected segments. Complicated cells, such as a CA1 pyramid, produce many closely spaced time constants in the range of interest. Models with large somatic shunts and dendrites of unequal electrotonic lengths can produce large amplitude waveform components with surprisingly slow time constants. This analytic solution should complement existing passive neurone modeling techniques.

Animals↗
PubMed1993

Solutions for transients in arbitrarily branching cables: II. Voltage clamp theory.

Analytical solutions are derived for arbitrarily branching passive neurone models with a soma and somatic shunt, for synaptic inputs and somatic voltage commands, for both perfect and imperfect somatic voltage clamp. The solutions are infinite exponential series. Perfect clamp decouples different dendritic trees at the soma: each exponential component exists only in one tree; its time constant is independent of stimulating and recording position within the tree; its amplitude is the product of a factor constant over that entire tree and factors dependent on stimulating and recording positions. Imperfect clamp to zero is mathematically equivalent to voltage recording with a shunt. As the series resistance increases, different dendritic trees become more strongly coupled. A number of interesting response symmetries are evident. The solutions reveal parameter dependencies, including an insensitivity of the early parts of the responses to specific membrane resistivity and somatic shunt, and an approximately linear dependence of the slower time constants on series resistance, for small series resistances. The solutions are illustrated using a "cartoon" representation of a CA1 pyramidal cell and a two-cylinder + soma model.

Animals↗
PubMed1993

Parentage analyses in ant colonies using simple sequence repeat loci.

In ants of genus Myrmica, female progeny may be the offspring of one to several different queens. In addition, both workers and queens are capable of producing haploid male offspring. Even in such complex colonies, parentage can be assigned on the basis of genotypic variation at highly polymorphic simple sequence repeat loci. Methods are described for isolating and screening dinucleotide repeat loci in ants. Three independent loci, Myrt2, Myrt3 and Myrt4, show expected heterozygosities of 0.94, 0.92 and 0.95, respectively. When used in parallel these loci should be sufficient to establish parentage in the vast majority of screened colonies. An initial screening indicates that males are produced by workers in the subalpine ant Myrmica 'near tahoensis'.

Animals↗