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PubMed2000

Spatial distribution and sampling plans for Thrips palmi (Thysanoptera: Thripidae) infesting fall potato in Korea.

The spatial distribution of adult and immature Thrips palmi Karny on fall potato, Solanum tuberosum L., on Cheju Island, Korea, was studied over a 2-yr period by visually inspecting potato leaves. The majority of thrips collected from the leaves were observed in the top one-third of the plant. The within-field spatial patterns of adults and immature thrips were aggregated. The slopes and intercepts of Taylor's power law did not differ among adults and immature thrips. A fixed-precision-level sampling plan was developed using the parameters from Taylor's power law and was tested with resampling simulations using eight independent data sets. Over a wide range of densities, the simulation demonstrated that actual sampling precision (d = SEM/mean) values at d = 0.25 averaged < 0.24 in all cases. A binomial sampling plan for estimating mean density was developed using an empirical model evaluated at tally thresholds (the minimum number of insects present before a leaf is considered infested) of one, three, five, and eight thrips per leaf. Increasing sampling size had little effect on the precision of the estimated mean regardless of tally threshold (T). However, increasing T had a dramatic effect on precision. The best tally threshold for estimating thrips density based on the applicable density ranges and the precision of the model was T = 5. A binomial sampling plan with a tally threshold of five and a fixed sample size of 30 leaves should be an effective replacement for enumerative counts when thrips average < 10 per leaf.

Animals↗

PubMed1994

Prediction of asymptotic threshold shift caused by hearing aid use.

This study used a well-verified mathematical model to predict asymptotic temporary threshold shift (ATS) caused by hearing aid use. The model determined the amounts of ATS to be expected if real ear insertion gains (REIGs) recommended by the current National Acoustic Laboratories (NAL) procedure are used. It also determined the consequences of use of excess REIG and of high input levels to hearing aids. If recommended REIGs are used and input levels are normal (average A-weighted input levels of about 61 dB SPL), ATS is unlikely to occur for clients who have typical audiograms with three-frequency average pure-tone thresholds (PTAs) less than 60 dB HL. For people with PTAs greater than 60 dB HL, small amounts of ATS can be expected to occur during hearing aid use, but these amounts of ATS are safe, that is, unlikely to be associated with permanent threshold shift (PTS) for individuals with all PTAs except those greater than about 100 dB HL. If REIGs are 15 dB greater than those recommended, the amounts of ATS will be unsafe for people with PTAs greater than about 80 dB HL. It appears unwise for clients who have this degree of hearing loss to use excess REIG. The use of excess REIG in high ambient levels of sound (average A-weighted input levels of about 75 dB SPL) is likely to cause PTS for hearing aid users with PTAs of about 50 dB HL or greater. Clients who prefer to use excess REIG should therefore avoid high ambient sound levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Audiometry, Pure-Tone↗

PubMed1988

Hormonal considerations in women with seizures.

The relationships between seizures in epileptic women and the hormones estrogen and progesterone are under increasing study. Serum concentrations of estrogen and progesterone parallel cerebrospinal concentrations, and circulating sex hormones are concentrated in specific areas of the brain that regulate sexual behavior. These centers include two potentially epileptogenic regions--the amygdala and hippocampus. Many of these structures are physiologically affected in vitro by estrogen and progesterone. Exogenous sex hormones change the seizure threshold in animal models of epilepsy. Cyclical hormonal variations may influence electroencephalographic activity and affect seizure frequency in women with epilepsy. Hormonal therapy may be appropriate adjunctive anticonvulsant treatment, particularly for women with seizures that are catamenial or associated with a menstrual or reproductive endocrine disorder.

Brain↗

PubMed2001

Accuracy evaluation of surface-based registration methods in a computer navigation system for hip surgery performed through a posterolateral approach.

OBJECTIVE: Many computer navigation systems have recently been developed for brain surgery, and the use of such systems in orthopedic surgery is increasing. Intraoperative registration of preoperative images is one of the most important steps in controlling the overall accuracy of computer navigation systems. Various parameters, such as CT-scan slice thickness, reconstruction pitch, intraoperative data sampling area, and data sampling volume, may affect the accuracy of registration. The purpose of this study was to evaluate the effect of the aforementioned parameters on the accuracy of registration for hip surgery performed through a posterolateral approach, and to find a clinically suitable trade-off between accuracy and surgical invasiveness. MATERIALS AND METHODS: One cadaveric pelvis and one cadaveric femur were used for this study. Four alumina ceramic balls with a diameter of 28 mm and within 1 micrometer of sphericity were attached to the pelvis, and three similar balls attached to the femur, to determine relative position. CT-scan images of the pelvis and femur were obtained with a helical scanner. Three sets of slice thickness and slice pitch were chosen for data acquisition, and two additional sets of reconstructed data were made. Bone contours were extracted by cutting out the surrounding substrate at a given CT number threshold, and surface models of the bone were made from the resultant data. The positions of the pelvis and femur were tracked by LED markers attached to the bone using an optical three-dimensional position sensor (OPTOTRAK). Registration of the computer models to the real objects was performed by measuring the position of a certain number of surface points on each object with an OPTOTRAK pen-probe. RESULTS AND CONCLUSION: Slice thickness and reconstruction pitch affected the accuracy of registration. As the sampling area was expanded from the periarticular area to the distant peripheral area, accuracy increased slightly. Accuracy did not increase when the whole area was used, but in fact decreased, especially in the femur. The positive effect of increasing the number of sampling points was saturated at 30 points when the surface of the periarticular area was sampled. The following trade-off between accuracy and invasiveness, in terms of various parameters of preoperative and intraoperative data, is proposed as clinically optimal: perform the CT scan with 3-mm slice thickness and 1-mm reconstruction pitch, and sample the periarticular area with 30 sampling points. With these parameters, the accuracy of registration was 1.2 mm and 0.9 degrees of bias with 0.7 mm and 0.3 degrees of RMS in the pelvis, and 1.4 mm and 0.6 degrees of bias with 1.3 mm and 0.3 degrees of RMS in the femur.

Cadaver↗

PubMed1998

Traumatic brain injury in the developing rat pup: studies of ICP, PVI and neurological response.

Diffuse brain swelling is a common complication in young victims of a seven head injury but, there is a lack of data on relevant models of injury. We produced diffuse brain injury in 21 day old Lewis rat pups (N = 33) by modifying a recently established weight-drop-model. The trauma threshold, neurological response, histological changes, intracranial pressure (ICP), and arterial blood pressure (ABP) were determined. In addition, the pressure-volume-index (PVI) was measured 15 min before, 2 min, and 1 h after brain injury. In the 1 m/100 g group 4 of 5 rats died, whereas in the 0.5 m/100 g only 4 of 28 died. The PVI increased at 2 min after traumatic brain injury (TBI) but ICP was unchanged, except for a minor increase immediately after injury. Histological studies revealed diffuse neuronal death, predominantly involving the cortex and hippocampus. The results of the present study indicate that determination of ICP in the developing rat pup during and after diffuse brain injury is possible. A 0.5 m/100 g weight-drop-trauma results in a morphologically severe injury but with low mortality. The increase in PVI can be attributed to a decrease of cerebral perfusion pressure (CPP) after injury. However, the absence of a further increase of ICP after injury in the developing rat indicates that this may not be a primary consequence of injury in paediatric patients.

Age Factors↗

PubMed1993

Evoked potentials and simple motor reaction times to localized visual patterns.

Spatially localized, contrast modulated visual stimuli evoke a monophasic, inion negative scalp potential (VEP) which can be recorded simultaneously with motor responses in simple reaction time experiments. VEP response time and median motor response latency are linearly related over a wide range of stimuli. We interpret our results to suggest that VEPs and motor response latencies arise from a common sensory system with different thresholds for detection and reaction. A model is introduced to predict detection thresholds from VEP response times which are usually more robust measures than VEP amplitudes.

Contrast Sensitivity↗

PubMed1995

Update on cellular transplantation into the CNS as a novel therapy for chronic pain.

The transplantation of cells that secrete neuroactive substances with analgesic properties into the CNS is a novel method that challenges current approaches in treating chronic pain. This review covers pre-clinical and clinical studies from both allogeneic and xenogeneic sources. One cell source that has been utilized successfully is the adrenal chromaffin cell, since such cells constitutively release catecholamines, opioid peptides, and neurotrophic factors; release can be augmented with nicotine. Other graft sources include AtT-20 and B-16 cell lines which release enkephalins and catecholamines, respectively. For grafting in rodents, adrenal medullary tissue pieces are transplanted to the subarachnoid space. Chromaffin cell transplants can decrease pain sensitivity in normal rats using standard acute pain tests (paw-pinch, hot-plate, and tail-flick). In addition, transplants can restore normal pain thresholds in rodent models of chronic pain (formalin, adjuvant-induced arthritis, and sciatic-nerve tie) which closely similate the pathologies of human chronic pain conditions. Xenografts have been studied due to concerns that future application for human pain may be limited by donor availability. Despite immune privileges of the CNS, xenografts require at least short-term immunosuppression to obtain a viable graft. Cell encapsulation is one method of sustaining a xenograft (in rat and human hosts) while circumventing the need for immunosuppression. Clinical studies have been initiated for terminal cancer patients with promising results as assessed by markedly reduced narcotic intake, visual analog scale ratings, and increased CSF levels of catecholamines and met-enkephalin.

Adrenal Cortex↗

PubMed2005

Revascularization of the right coronary artery: grafting or percutaneous coronary intervention?

BACKGROUND: The choice of myocardial revascularization strategy for the right coronary artery (RCA) in patients with multivessel disease and chronic stable angina remains controversial. Our aim was to determine the better strategy-hybrid, combining bypass of the left coronary network and percutaneous coronary intervention of the RCA, or exclusively surgical-and if the latter, the best conduit. METHODS: We used decision analysis, a modeling technique, to compare two RCA revascularization strategies: surgical grafting and percutaneous coronary intervention. A review of the English language literature determined the variables for each strategy. All possible outcomes of each strategy were analyzed to determine the baseline strategy yielding the highest expected effectiveness. Sensitivity analysis determined the most relevant elements in the model and indicated threshold values. RESULTS: Arterial grafting of the RCA led to the highest expected effectiveness, respectively 6% and 7% higher than that of percutaneous coronary intervention and the saphenous graft procedure. Of the arteries available-the radial, right gastroepiploic, and right internal thoracic artery-the most effective was the right internal thoracic artery, pedicled for the proximal part of the RCA and free connected as a Y or a T to the pedicled left internal thoracic artery for the distal part of the RCA. Sensitivity analysis showed surgery to be the appropriate strategy when the expected 1-year patency rate of the arterial graft exceeded 80%. CONCLUSIONS: This analysis shows arterial grafting of the RCA to have better outcomes than percutaneous coronary intervention, and the right internal thoracic artery to be the best conduit.

Angioplasty, Balloon, Coronary↗

PubMed1983

Plasma shielding by Q-switched and mode-locked Nd-YAG lasers.

Q-switched and mode-locked Nd-YAG lasers depend on beam divergence and plasma formation to reduce energy transmission below the retinal damage threshold. In a model system of physiologic saline, we investigated plasma "shielding" and found that plasma formation markedly reduces further energy transmission along the beam path once plasma formation occurs. The protective effect of plasma shielding appears similar for a Q-switched pulse and a train of mode-locked pulses in a physiologic saline medium.

Humans↗

PubMed1997

Automated lumen definition from 30 MHz intravascular ultrasound images.

One prerequisite for standard clinical use of intravascular ultrasound imaging is rapid evaluation of the data. The main quantities to be extracted from the data are the size and the shape of the lumen. Until now, no accurate, robust and reproducible method to obtain the lumen boundaries from intravascular ultrasound images has been described. In this study, 21 different (semi-)automated binary-segmentation methods for determining the lumen are compared with manual segmentation to find an alternative for the laborious and subjective procedure of manual editing. After a preprocessing step in which the catheter area is filled with lumen-like grey values, all approaches consist of two steps: (i) smoothing the images with different filtering methods and (ii) extracting the lumen by an object definition method. The combination of different filtering methods and object definition methods results in a total of 21 methods and 80 experiments. The results are compared with a reference image, obtained from manual editing, by use of four different quality parameters--two based on squared distances and two based on Mahalanobis distances. The evaluation has been carried out on 15 images, of which seven are obtained before balloon dilation and eight after balloon dilation. While for the post-dilation images no definite conclusions can be drawn, an automated contour model applied to images smoothed with a large kernel appears to be a good alternative to manual contouring. For pre-dilation images a fully automated active contour model, initialized by thresholding, preceded by filtering with a small-scale median filter is the best alternative for manual delineation. The results of this method are even better than manual segmentation, i.e. they are consistently closer to the reference image than the average distance of all individual manual segmentations.

Catheterization↗

PubMedDate not supplied

Flow cytometry and cell cycle kinetics in continuous and fed-batch fermentations of budding yeast.

Cell size distributions, obtained either as protein distribution by flow cytometry or as cell volume distribution by a Coulter counter, give relevant information about the growth conditions of populations of budding yeast Saccharomyces cerevisiae. We have previously found a good correlation between these distributions and the growth rate in continuous cultures (Ranzi et al., Biotechnol. Bioeng. 1986, 28, 185-190). We now present determinations of the protein distributions and cell volume distributions during different fed-batch fermentations performed with a simple on/off controller. Since during the fed-batch fermentation a true steady state is not obtained, the distributions continuously change with time, but nevertheless we observed a good correlation between the average of both distributions and the actual growth rate. The behavior of the cell size distributions can be interpreted on the basis of a two-threshold cell cycle model in which both the critical protein content at budding (Ps) and the critical protein content for cell division (Pm) are differently modulated by the growth rate. Additional findings will be presented showing that this model can be used to successfully explain the insurgence and the maintenance of oscillatory states in continuous cultures.

Cell Cycle↗

PubMedDate not supplied

Spike-frequency adaptation of a generalized leaky integrate-and-fire model neuron.

Although spike-frequency adaptation is a commonly observed property of neurons, its functional implications are still poorly understood. In this work, using a leaky integrate-and-fire neural model that includes a Ca2+-activated K+ current (IAHP), we develop a quantitative theory of adaptation temporal dynamics and compare our results with recent in vivo intracellular recordings from pyramidal cells in the cat visual cortex. Experimentally testable relations between the degree and the time constant of spike-frequency adaptation are predicted. We also contrast the IAHP model with an alternative adaptation model based on a dynamical firing threshold. Possible roles of adaptation in temporal computation are explored, as a a time-delayed neuronal self-inhibition mechanism. Our results include the following: (1) given the same firing rate, the variability of interspike intervals (ISIs) is either reduced or enhanced by adaptation, depending on whether the IAHP dynamics is fast or slow compared with the mean ISI in the output spike train; (2) when the inputs are Poisson-distributed (uncorrelated), adaptation generates temporal anticorrelation between ISIs, we suggest that measurement of this negative correlation provides a probe to assess the strength of IAHP in vivo; (3) the forward masking effect produced by the slow dynamics of IAHP is nonlinear and effective at selecting the strongest input among competing sources of input signals.

Action Potentials↗

PubMed2002

Statistical analysis of sediment toxicity by additive monotone regression splines.

Modeling nonlinearity and thresholds in dose-effect relations is a major challenge, particularly in noisy data sets. Here we show the utility of nonlinear regression with additive monotone regression splines. These splines lead almost automatically to the estimation of thresholds. We applied this novel method to explore the relation between the toxicity of aquatic sediments, as observed in bioassays with Daphnia magna, Chironomus riparius and Vibrio fischeri, and the degree of contamination of the sediments. Despite the low signal-to-noise ratio in the data, some interesting thresholds and (non)linear effects were found. The method has added value compared to the linear multivariate methods applied earlier to these data. Percentages of explained variance remained low, but could be doubled by diminishing the effect of local variability.

Animals↗

PubMed1989

Roles of neurotransmitter receptors in behavior: recovery of function following decreases in muscarinic receptor density induced by cholinesterase inhibition.

Cholinergic neurotransmitter levels were elevated in rat brain by reducing its inactivating enzyme, acetylcholinesterase (AChE), with an anti-AChE agent. Elevated levels result in decreases in cholinergic (muscarinic) receptors. Withdrawal of agent after 10 days of chronic treatment began a gradual return of neurochemical variables toward normal states, yet not fully achieving them within the following 29 days of the experiment. All behavioral and physiological variables measured showed significant effects at the start of the treatment period, developing tolerance at different rates as treatments continued. They also recovered differentially during withdrawal. Results are consistent with a theoretical model in which thresholds for normal functioning of different behavioral and physiological processes are associated with different receptor densities.

Acetylcholine↗

PubMed1997

Max and inhibitory c-Myc mutants induce erythroid differentiation and resistance to apoptosis in human myeloid leukemia cells.

We have used the human leukemia cell line K562 as a model to study the role of c-myc in differentiation and apoptosis. We have generated stable transfectants of K562 constitutively expressing two c-Myc inhibitory mutants: D106-143, that carries a deletion in the transactivation domain of the protein, and In373, that carries an insertion in the DNA-interacting region. We show here that In373 is able to compete with c-Myc for Max binding and to inhibit the transformation activity of c-Myc. K562 cells can differentiate towards erythroid or myelomonocytic lineages. K562 transfected with c-myc mutants showed a higher expression of erythroid differentiation markers, without any detectable effects in the myelomonocytic differentiation. We also transfected K562 cells with a zinc-inducible max gene. Ectopic Max overexpression resulted in an increased erythroid differentiation, thus reproducing the effects of c-myc inhibitory mutants. We also studied the role of c-myc mutants and max in apoptosis of K562 induced by okadaic acid, a protein phosphatases inhibitor. The expression of D106-143 and In373 c-myc mutants and the overexpression of max reduced the apoptosis mediated by okadaic acid. The common biochemical activity of D106-143 and In373 is to bind Max and hence to titrate out c-Myc to form non-functional Myc/Max dimers. Similarly, Max overexpression would decrease the relative levels of c-Myc/Max with respect to Max/Max. The results support a model where a threshold of functional c-Myc/Max is required to maintain K562 cells in an undifferentiated state and to undergo drug-mediated apoptosis.

Apoptosis↗

PubMed1998

Primordial role of CD34+ 38- cells in early and late trilineage haemopoietic engraftment after autologous blood cell transplantation.

In order to better define which cell subset contained in graft products might be the most predictive of haemopoietic recovery following autologous blood cell transplantation (ABCT), the relationships between the amounts of reinfused mononuclear cells (MNC), CFU-GM, total CD34+ cells and their CD33 and CD38 subsets. and the successive stages of trilineage engraftment kinetics, were studied in 45 cancer patients, using the Spearman correlation test, a linear regression model and a log-inverse model. No relationship was found between the infused numbers of MNC, CD33+ and CD33- subsets observed and the numbers of days to reach predetermined absolute neutrophil (ANC), platelet and reticulocyte counts. The infused numbers of CFU-GM, CD34+ and CD34+ 38+ cells correlated inconstantly with haemopoietic recovery parameters. The strongest and the most constant correlations were significantly observed between the infused numbers of CD34+ 38- cells and each trilineage engraftment parameter. The log-inverse model determined a threshold dose of 0.05 x 10(6) (= 5 x 10(4)) CD34+ 38- cells/kg, below which the trilineage engraftment kinetics were significantly slower and unpredictable. Post-transplant TBI-conditioning regimens increased the low cell dose-related delay of engraftment kinetics whereas post-transplant administration of haemopoietic growth factors (HGF) seemed to abrogate this delay. This would justify clinical use of HGF only in patients transplanted with CD34+ 38- cell amounts lower than the proposed threshold value. This study suggests that the CD34+ 38- subpopulation, although essentially participating in late complete haemopoietic recovery, is also composed of committed progenitor cells involved in early trilineage engraftment.

ADP-ribosyl Cyclase↗

PubMed2003

Heritability of resistance against ectoparasitism in the Drosophila-Macrocheles system.

Ectoparasites are abundant in natural communities, can have pronounced deleterious fitness consequences to their host and are important vectors of transmissible parasitic disease. Yet very few studies have estimated the magnitude of heritable genetic variation underlying resistance against ectoparasitism, which significantly limits our ability to predict the evolution of this ecologically important character. The present paper reports results of artificial selection for increased resistance in Drosophila nigrospiracula against ectoparasitic, haematophagous mites, Macrocheles subbadius. In this system, which occurs naturally in the Sonoran Desert of North America, ectoparasitism significantly damages the expression of host fitness traits, including longevity, fecundity and male mating success. In the present study, resistance, which was modelled as a threshold trait, responded significantly to selection applied on either sex. Realized heritability, calculated as a mean across four replicates, was estimated to be 0.152 +/- 0.014 (SE). The heritability estimate from selection on males did not differ from that on females, but both estimates differed significantly from zero. This documented presence of additive genetic variation for resistance, coupled with knowledge of the fitness consequences of ectoparasitism, indicates that the host population possesses significant evolutionary potential. Selection was applied on the pre-attachment phase, thereby targeting behavioural forms of defence. This study therefore establishes parallels between insects and other animals in their ability to protect themselves and evolve behavioural defences against ectoparasites.

Animals↗

PubMed2003

A comparison of the antinociceptive effects of xylazine, detomidine and romifidine on experimental pain in horses.

OBJECTIVE: To study the analgesic potency of the alpha2-agonist romifidine in the horse using both an electrical current and a mechanical pressure model for nociceptive threshold testing. In addition, a comparison was made with doses of detomidine and xylazine that produce equivalent degrees of sedation. STUDY DESIGN: Randomized, placebo-controlled, blinded cross-over study. ANIMALS: Six adult Swiss warmblood horses, one mare and five geldings, weighing from 530 to 650 kg and aged 6-15 years. METHODS: Nociceptive thresholds were measured using an electrical stimulus applied to the coronary band and using a pneumatically operated pin pressing on the cannon bone. Measurements were made immediately before and every 15 minutes for 2 hours after IV injection of the test substances. Lifting of the foot indicated the test end point. RESULTS: The three alpha2-agonists caused a temporary increase in nociceptive thresholds with a maximal effect within 15 minutes and a return to baseline levels within 1 hour. Using electrical current testing nociceptive thresholds were significantly different from placebo (mean +/- SD) for detomidine at 15 minutes (from control 5.8 +/- 0.9 to 23.3 +/- 3.9 mA, p = 0.0066) and 30 minutes (from control 6.6 +/- 1.1 to 18.8 +/- 3.3 mA, p = 0.0091). The difference was significant for romifidine at 15 minutes only (from control 5.8 +/- 0.9 to 18.7 +/- 3.8 mA, p = 0.0066). With mechanical pressure testing nociceptive thresholds were significantly different from control for detomidine at 15 minutes (from 3.2 +/- 0.2 to 6.2 +/- 0.5 N, p = 0.00076) and 30 minutes (from 3.2 +/- 0.7 to 5.7 +/- 0.8 N, p = 0.0167). The difference was significant for xylazine at 15 minutes (from control 3.2 +/- 0.2 to 5.6 +/- 0.7 N, p = 0.0079). At 15 minutes the order of magnitude of the measured antinociceptive effect was significantly different between the two pain tests for both romifidine and detomidine, but not for xylazine. For romifidine, the increase of mean thresholds compared to placebo was 4.0 +/- 1.3 times placebo levels with the electrical current test compared to 1.3 +/- 0.3 times for the mechanical pressure test (p = 0.037). For detomidine, the increase of mean thresholds compared to placebo was 5.4 +/- 1.7 times control levels with the electrical current test compared to 2.0 +/- 0.2 times for the mechanical pressure test (p = 0.040). This represents a 2.7 (romifidine) and 3.4 times (detomidine) greater increase in thresholds using electrical current testing compared to the use of mechanical pressure testing. CONCLUSION AND CLINICAL RELEVANCE: This study demonstrates the analgesic potential of alpha2-agonists in the horse for somatic pain and that they can have quantitatively different antinociceptive effects according to the antinociceptive test used.

Adrenergic alpha-Agonists↗