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Biomedical subjects

J H Myers

Publications and source records attributed to J H Myers.

At least 19 recordsLinked to original sources
PubMed2007

Host-plant effects the expression of resistance to Bacillus thuringiensis kurstaki in Trichoplusia ni (Hubner): an important factor in resistance evolution.

Pathogens are thought to exert strong selection on their hosts leading to increased host resistance. Bacillus thuringiensis kurstaki (Bkt) is a ubiquitous entomopathogen that has become the mainstay of nonchemical control of Lepidopteran pests and thus, the potential exists for the evolution of resistance in targeted host insects. We have studied the expression of Btk resistance in the cabbage looper, Trichoplusia ni (Hubner). For this generalist insect herbivore, three common host plants, tomato, pepper and cucumber, vary in suitability for larval growth and development. Here we show that the host plant also affects the overall toxicity of Btk, the relative expression of resistance between a resistant and a susceptible line and their F(1) reciprocal crosses, and importantly, the dominance of the resistance trait. This study demonstrates that tri-trophic interactions involving an insect, host plants and a pathogen have the potential to strongly influence the evolutionary response of an insect host to a pathogen.

Animals↗
PubMed2001

Spatial and temporal patterns of dispersal of western flower thrips (Thysanoptera: Thripidae) in nectarine orchards in British Columbia.

Thrips were sampled from six nectarine orchards in the Dry Central Interior, British Columbia, Canada, between April and June 1993 using yellow sticky cards on posts spaced around the perimeter of each orchard. Although 12 identified species of thrips were captured, >90% of individuals were the western flower thrips, Frankliniella occidentalis (Pergande). The flight patterns and abundances of western flower thrips were compared between orchards located in two differently oriented valleys (N-S and E-W) and between orchards located close to or far from areas of wild land. Results indicate that densities of western flower thrips entering orchards, and their direction of movement, were related more to the external vegetation than either location within the two different valleys or general wind flow patterns. Western flower thrips tended to move into orchards close to ground level in early spring (late April and early May) but flew higher as ground cover grew taller and temperatures increased. Densities of western flower thrips at ground level were highest in an orchard with the densest dandelion ground cover. We conclude that the location of nectarine orchards in relation to wild areas is a major determinate of western flower thrips densities.

Animals↗
PubMed2000

Population dynamics of western flower thrips (Thysanoptera: Thripidae) in nectarine orchards in British Columbia.

Development of a control strategy for thrips attacking nectarine trees depends on an understanding of their phenology, distribution, and life history as related to characteristics of nectarine orchards. To this end, we compared the overwintering behavior, distribution, and abundance of western flower thrips, Frankliniella occidentalis (Pergande), among 11 nectarine orchards located in the dry central interior of British Columbia, Canada, during 1993 and 1994. Western flower thrips emerged from areas not previously used for agriculture (wild areas) and from within orchards before trees were out of dormancy. Flight of thrips within and around orchards peaked during early bud development, with a second major peak several weeks later after husk fall as the next generation emerged. Orchards protected from wild areas by other orchards had the lowest densities of thrips in buds. Density estimates of western flower thrips on trees were not affected by location of trees within orchards or buds within trees, but most thrips were found in the most developed buds on a tree at any one time. Thrips were not found within buds until petal was first visible on the buds. Larval feeding on buds at early petal fall resulted in serious surface russetting of fruit.

Animals↗
PubMed2000

Evaluation of sampling methodology for determining the phenology, relative density, and dispersion of western flower thrips (Thysanoptera: Thripidae) in nectarine orchards.

Western flower thrips, Frankliniella occidentalis (Pergande), cause serious economic damage to nectarines in the Okanagan and Similkameen Valleys, British Columbia, Canada. We evaluated several sampling methods for western flower thrips for their precision and ability to predict general population trends. Beating of branches, flicking of buds, and visual estimation methods were not accurate for estimating numbers of thrips in nectarine buds. Thrips caught on sticky cards indicated general population trends, but were less efficient than collecting nectarine buds and counting thrips. Searching for thrips from buds in the field underestimated the density of both adults and larvae, and for adults, underestimated the proportion of the pale morph of western flower thrips. Dispersion patterns of thrips populations among orchards were either random or aggregated dependent on the development stage of the nectarine buds.

Animals↗
PubMed1998

Eradication and pest management.

Eradication is the elimination of every single individual of a species from an area to which recolonization is unlikely to occur. Cost-benefit analyses of eradication programs involve biases that tend to underestimate the costs and overestimate the benefits. In this review, we (a) highlight limitations of current cost-benefit analyses, (b) assess eradication strategies from biological and sociological perspectives by discussing particular cases of successful and failed eradication efforts, and (c) briefly contrast eradication and ongoing area-wide control as pest management strategies. Two successful eradication programs involve the screwworm and cattle ticks. Gypsy moth and medfly eradication programs have not been successful, and subsequent captures of insects recur in eradication areas. In situations where heterogeneity of land use patterns make it difficult to prevent reinvasion of the pest, education and area-wide suppression are probably more realistic goals than eradication.

Animals↗
PubMed1997

Anticholinergic poisoning in colicky infants treated with hyoscyamine sulfate.

Hyoscyamine, one of the principal alkaloid components of belladonna, is a potent anticholinergic agent. Because of its anticholinergic properties, hyoscyamine sulfate drops are often prescribed for the treatment of colic in infants. Anticholinergic poisoning in infants is rare. However, five cases are reported of infants with anticholinergic toxicity following the administration of hyoscyamine drops for the treatment of colic. Common presenting symptoms included irritability, tachycardia, and erythematous flushed skin. These cases emphasize the need for a heightened awareness by emergency physicians and pediatricians of possible anticholinergic toxicity caused by the use of hyoscyamine for infant colic.

Atropine↗
PubMed1996

Delayed pulmonary edema and bronchospasm after accidental lacrimator exposure.

Clinical manifestations of lacrimator exposure can be immediate or significantly delayed. In both phases, the sequelae can be severe and life-threatening. As personal protection devices, these agents have become readily available to the public in many areas of the country. Emergency physicians should gain a firm understanding of the presentation, management, and disposition of the lacrimator-exposed patient. A case of accidental prolonged lacrimator exposure inducing pulmonary edema and bronchospasm is presented.

Adult↗
PubMed1996

Vomiting, ataxia, and altered mental status in an adolescent: late-onset ornithine transcarbamylase deficiency.

A case of a 13-year-old boy with protracted vomiting, ataxia, and altered mental status, ultimately diagnosed with late-onset ornithine transcarbamylase (OTC) deficiency, is presented. OTC deficiency is the most common urea cycle defect and typically is diagnosed in male infants with irritability, poor feeding, vomiting, lethargy, and often death caused by the effects of hyperammonemia. Late-onset OTC deficiency has been described in patients of all ages. The presenting symptoms in these patients vary but the most common are vomiting and lethargy. The pathophysiology, clinical features, differential diagnosis, and treatment of this disorder are discussed. Because of the risks of serious consequences, early detection and treatment of OTC deficiency and hyperammonemic episodes are mandatory. Emergency physicians caring for children and adults need to be aware of the spectrum of clinical presentations of OTC deficiency, including late-onset disease.

Adolescent↗
PubMed1996

The ED on line: computerization of the pediatric emergency department.

Computers are becoming an increasingly important tool in the management of emergency departments across the United States. Many emergency physicians are unfamiliar with computer systems and are uncomfortable with the idea of implementing computer technology into their departments. This article summarizes the benefits of computerized patient tracking systems and outlines the process by which such a program can be selected and incorporated into an emergency center.

Adolescent↗
PubMed1993

Effect of ramipril on alpha-adrenoceptor-mediated oscillatory contractions in tail artery of hypertensive rats.

Recent studies indicate that norepinephrine-induced contractile oscillations in the tail artery from stroke-prone spontaneously hypertensive rats (SHRSP) may be a vascular phenomenon independent of blood pressure level. The objectives of this study were: (1) to characterize pharmacologically the alpha-adrenoceptor mediating norepinephrine-induced oscillations in tail artery; and (2) to investigate the relationship between blood pressure level, altered by treatments with hydralazine/hydrochlorothiazide or the angiotensin converting enzyme inhibitor ramipril, and the observation of norepinephrine-induced oscillations in tail artery. The alpha 2-adrenoceptor agonists clonidine and guanabenz potently stimulated oscillatory contractions in the tail artery while the alpha 1-adrenoceptor agonists phenylephrine and methoxamine were considerably less potent. Yohimbine, an alpha 2-adrenoceptor antagonist, but not the alpha 1-adrenoceptor antagonist prazosin demonstrated high affinity for the receptor mediating norepinephrine-induced oscillatory contractions. These results support the hypothesis that norepinephrine-induced oscillatory contractions in the tail artery from SHRSP occur primarily through stimulation of alpha 2-adrenoceptors. Ramipril lowered blood pressure in SHRSP after 4 weeks of treatment during 6-10 weeks of life but did not alter the ability of the alpha 2-adrenoceptor agonist clonidine (10(-5) M) to induce contractile oscillations in tail arteries from SHRSP, indicating these oscillations are not a secondary effect of high blood pressure. These studies suggest that norepinephrine-induced oscillations in tail artery from SHRSP may be a vascular trait separate and distinct from blood pressure level and angiotensin II expression early in life.

Animals↗
PubMed1993

Neuroanatomical differentiation in the brain of the spontaneously hypertensive rat (SHR). I. Volumetric comparisons with WKY control.

A series of measurements was made to assess the morphology of the brain of the spontaneously hypertensive rat (SHR). The SHR brain was smaller than that of age-matched normotensive Wistar-Kyoto (WKY) controls in a majority of measures of external surface landmarks. This reduction in size was evident in the youngest age group examined (94 days) and persisted in older groups (170, 240 and 350 days). The brain of the SHR was also smaller in terms of brain weight and brain weight:body weight ratios. Section-by-section digitized analyses of coronal histologic sections from 94-day-old rats revealed significant reductions in mean cross-sectional area and volume of midbrain/pons (10%) and hindbrain (11%) regions, but not of forebrain, in the SHR. Alterations in the mediolateral dimension, particularly within the pontomedullary brainstem, accounted for more of these volumetric changes than those in the dorsoventral dimension. Using the same coronal sections, it was found that surface areas and volumes of five individual nuclei/fiber tracts, selected for their involvement in central cardiovascular regulation, were significantly decreased in the SHR. The largest reduction in volume (30%) was found in the nucleus tractus solitarius, the primary site of termination of afferent baroreceptor fibers. No differences in surface area or volume were found in that portion of the cerebroventricular system (aqueduct of Sylvius) associated with the periventricular grey region, or in the inferior colliculus, which is not thought to be involved in cardiovascular control. These observations not only have practical implications, but suggest that the pathophysiological condition expressed as spontaneous hypertension in this widely-used model may be related to morphological alterations in the central nervous system.

Animals↗
PubMed1991

Effects of nontransmural ischemia on inner and outer wall thickening in the canine left ventricle.

The effect of ischemic subendocardial dysfunction on contractile function in the normally perfused subepicardium remains controversial. Accordingly, regional wall thickening (WT) was measured directly in the left ventricle of 10 open-chest dogs using epicardial echocardiography. Two silk sutures, used as echocardiographic targets, were inserted beneath the transducer to a depth of 25.0 +/- 0.7% (subepicardium) and 48.0 +/- 2.7% (midmyocardium) of transmural thickness. A hydraulic cuff, placed around the left anterior descending coronary artery (LAD) was then inflated slowly until transmural WT was reduced to 62 +/- 2% of baseline. Myocardial blood flow (MBF) was not significantly altered in the subepicardial third of the wall; however, flow to the midwall and subendocardial thirds decreased by 39% (p less than 0.001) and 50% (p less than 0.001), respectively. Nontransmural ischemia produced a small but significant decrease in epicardial WT (baseline = 0.77 +/- 0.08 mm, ischemia = 0.69 +/- 0.08 mm; p less than 0.05) and substantially larger decreases in midwall (baseline = 1.66 +/- 0.14 mm, ischemia = 1.03 +/- 0.09 mm; p less than 0.001) and subendocardial WT (baseline = 3.39 +/- 0.34 mm, ischemia = 2.10 +/- 0.26 mm; p less than 0.001). The degree of regional dysfunction was linearly correlated with tissue depth (r = 0.88, p less than 0.001). Thus the degree of dysfunction produced by nontransmural ischemia increased progressively from the subepicardium to the subendocardium, paralleling the pattern of perfusion. We conclude that perfusion, rather than transmural tethering, largely determines subepicardial function in the setting of nontransmural ischemia.

Animals↗
PubMed1988

A computer model to study norepinephrine-induced oscillations of contraction in tail arteries of spontaneously hypertensive stroke-prone rats.

The purpose of this study is to develop a computer model of oscillatory contractions in isolated arteries from the tails of spontaneously hypertensive, stroke-prone rats (SHRSP). The computer simulation incorporates biologic data from experiments and mathematic expressions derived from an electric circuit model of the biologic system. The model characterizes the cellular mechanisms which have been proposed to be responsible for the oscillatory activity. Results indicate the ability of the model to provide results which closely match experimentally obtained data.

Animals↗
PubMed1987

Contractile responses to ouabain and potassium-free solution in vascular tissue from renal hypertensive rats.

This study characterizes contractions to ouabain and potassium-free solution in isolated vascular segments from two-kidney, one clip (2-K, 1C) hypertensive rats. Aorta, mesenteric artery, and vena cava from hypertensive rats were more sensitive (lower threshold) to ouabain than those from normotensive rats. Contractions of hypertensive vascular segments to potassium-free solution and to ouabain (10(-3) mol/l) were faster than those in normotensive vessels. Monensin potentiated contractions to ouabain and increased the rate of force development to potassium-free solution to a greater extent in normotensive aortae than in hypertensive aortae. Amiloride, low sodium solution, verapamil and calcium-free solution depressed contractions to ouabain and potassium-free solution in both hypertensive and normotensive aortae. These observations demonstrate augmented responsiveness to ouabain and potassium-free solution in hypertensive blood vessels. Interventions which influence transmembrane sodium and calcium movements altered contractions to ouabain and potassium-free solution. The results are consistent with the hypothesis that vascular cells of hypertensive rats have enhanced sodium pump activity.

Animals↗
PubMed1986

Genetic basis for altered vascular responses to ouabain and potassium-free solution in hypertension.

Many properties intrinsic to vascular smooth muscle are altered in hypertension. It is unknown whether these abnormalities are primary traits that may contribute to the etiology of hypertension or whether these vascular differences between the hypertensive and normotensive strains are inherited independently of genetic factors that predispose to hypertension. To determine if genetic factors responsible for the predisposition for hypertension may be the same as or linked to genetic factors determining a specific vascular response, adult stroke-prone spontaneously hypertensive rats (SHRSP), normotensive Wistar-Kyoto (WKY) rats, and progeny of genetic crosses of SHRSP and WKY rats (F1, F2, F1 X WKY, F1 X SHRSP) were studied. Rats were killed and helical aortic strips were mounted in a tissue bath for isometric force recording. Contractile responses to 10(-3) M ouabain (expressed as a percent of force generated to a maximal depolarizing stimulus) were greater in aortas from SHRSP (90 +/- 9%) compared with aortas from WKY rats (38 +/- 5%, P less than 0.05). The half time for contraction in K+-free solution was more rapid in aortas from SHRSP (21 +/- 4 min) when compared with aortas from WKY rats (48 +/- 4 min, P less than 0.05). A significant positive correlation between blood pressure (tail-cuff method) and the contractile response to 10(-3) M ouabain was observed in the segregating F2 progeny. In contrast, no correlation between blood pressure and the half time for contraction in K+-free solution was observed in the segregating F2 progeny.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗