Biomedical subjects

M Lehrer

Publications and source records attributed to M Lehrer.

At least 19 recordsLinked to original sources

PubMed2001

Fluorescence polarization immunoassay: can it result in an overestimation of vancomycin in patients not suffering from renal failure?

It has been reported in scientific data that fluorescence polarization immunoassay (FPIA) results in overestimation of vancomycin in patients with renal failure. This overestimation is caused by interference of the degradation product, CDP-1, in this assay. Increases in vancomycin levels have also been reported in patients not suffering from renal failure (nonrenal failure patients) who are receiving vancomycin therapy for approximately 10 days or more. The authors tested whether this increase in vancomycin in nonrenal failure patients is a result of CDP-1 interfering with FPIA or a change in the pharmacokinetics of the drug. Serum vancomycin peak and trough samples were obtained from 10 adult (mean age +/- SD: 55.9 years +/- 17.5) nonrenal failure patients (mean ClCr +/- SD: 76.2 mL/min +/- 29.20) receiving vancomycin therapy for at least 10 days. These peaks and troughs were obtained at steady state and again at approximately 10 days of therapy. All serum samples were analyzed initially by fluorescence polarization immunoassay (FPIA, TDx) (Abbot Diagnostics; Irving, TX) and again by enzyme multiplied immunoassay (EMIT Vancomycin Assay) (Dade Behring; San Jose, CA). Statistical analysis (Wilcoxon signed-rank test) determined that there was no difference between the values obtained from the two assays. This demonstrates that the increase in vancomycin levels is not caused by the accumulation of CDP-1 and may be the result of a change in the pharmacokinetics of the drug.

Adult↗

PubMed2001

Vancomycin and ceftazidime bioactivities persist for at least 2 weeks in the lumen in ports: simplifying treatment of port-associated bloodstream infections by using the antibiotic lock technique.

The residual antibiotic concentration of vancomycin (2 mg/ml)- or ceftazidime (2 mg/ml)-heparin solutions instilled in ports in pediatric hematology-oncology patients 1 to 34 days earlier was measured. Antibiotic concentrations of > or = 100 microg of either antibiotic per ml persisted for at least 21 days. For treatment of lumenal port infections, antibiotic-heparin dwell times of > or = 2 weeks may be appropriate.

Adolescent↗

PubMed2000

The turn-back-and-look behaviour: bee versus robot.

Honeybees and social wasps departing from a novel food source perform stereotype flight manoeuvres, termed the turn-back-and-look behaviour (TBL). Based on results of behavioural studies, it is proposed that the image motion generated by the TBL provides the insect with information about the three-dimensional structure of the goal's surroundings, thus enabling it to select reliable landmarks that will guide it to the goal upon return. The colour, shape, and size of landmarks, on the other hand, are learned mainly during arrival at the food source. However, when bees are prevented from learning these cues on arrival, they learn them during the TBL, despite the fact that this performance does not require the use of image motion. A recently developed model shows that landmark learning can indeed be accomplished during the TBL by exploiting cues others than image motion. A mobile robot equipped with the appropriate software selects, during the TBL, reliable marks and returns to the site of departure from different locations by accomplishing image matching along a two-dimensional vector field.

Animals↗

PubMed1999

Honeybee memory: navigation by associative grouping and recall of visual stimuli.

Studies of navigation in bees and ants are beginning to reveal that foraging insects traveling repeatedly to a food source navigate by using a series of visual images of the environment acquired en route (Collett, 1996; Collett et al., 1993; Judd & Collett, 1998; Wehner et al., 1990, 1996). By comparing the currently viewed scene with the appropriate stored image, the insect is able to ascertain whether or not it is on the correct path and make any necessary corrections. If a bee happens to forage at more than one site, then she needs not only to memorize a separate set of images for each route that she has learned but also to retrieve the set of images that is appropriate to each route. Here we examine the bee's capacity to learn and later retrieve from memory two different sets of visual stimuli. Bees were trained to fly through a compound Y-maze where they were presented alternately with two different sequences of visual stimuli on their route to a food reward. We find that bees can indeed store two different sequences of images simultaneously. Furthermore, the trained bees are able to classify the memorized images into two groups, one pertaining to each three-stimulus set. Exposure to any of the images pertaining to one set triggers recall of all of the other images associated with that set. Associative grouping and recall of visual stimuli, demonstrated here for the first time in honeybees, provide an effective means of retrieving the appropriate navigational information from memory.

Animals↗

PubMed1999

Shape Perception in the Honeybee: Symmetry as a Global Framework.

This study is concerned with the honeybee's spatial vision in light of the spatial signals that natural flowers display. A large amount of behavioral data shows that bees are perfectly adept at learning and exploiting a variety of spatial cues in the task of recognizing and discriminating between visual stimuli. These cues include spatial frequency, distribution of contrasting areas, orientation of contours, size and distance, different types of edges, and symmetry (or, in a broader sense, geometry). Symmetry constitutes a global feature that is only one of the cues that the target offers. Symmetrical stimuli always contain several further spatial cues that become relevant as the bee comes nearer to the stimuli. The results reviewed here show that the spatial signals used by the bee depend on whether the stimuli are presented on a horizontal or a vertical plane, on whether bees make their choices at a lesser or a greater distance, and on whether the target's image is stationary at the level of the eye, as opposed to moving. Further, it is shown that pattern recognition in the bee does not always require a learning process (i.e., several types of response to visual stimuli are based on hard-wired, innate behavioral programs). Finally, the results show that although it is not a prerequisite for spatial vision, color vision participates in spatial vision, whereas spatial cues extracted from image motion are processed by a color-blind system.

Journal Article↗

PubMed1998

Honeybee navigation: odometry with monocular input.

Recent studies have revealed that navigating honeybees, Apis mellifera, estimate the distance to a food source by integrating over time the image motion that they experience en route. Here we examine the ability of honeybees to gauge distance travelled when visual input is available primarily to one eye. Bees were trained to fly into a tunnel, lined with textured patterns, to collect a reward at a feeder placed at a certain distance. Their ability to estimate distance flown was then assessed by testing them in a fresh tunnel without the feeder. The results show that (1) bees can estimate distance flown under monocular conditions, performing nearly as accurately as when information is available to both eyes; (2) bees can learn to fly two different distances, where each distance is measured in terms of the image motion experienced by a different eye; and (3) bees that have acquired information on the distance to a food source using one eye can measure out the same distance when they are required to use the other (naive) eye. The need to measure distance using signals from a single eye becomes important when a bee flies to a food source along the face of a cliff or the edge of a forest. Furthermore, under such conditions, it is important to be able to deal with odometric signals that are transposed interocularly when the bee returns home from the food source. This is because, although distances are learnt primarily on the way to a food source, foraging bees monitor distance flown on the homebound as well as the outbound routes. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗

PubMed1998

Looking all around: honeybees use different cues in different eye regions

Based on results of early as well as recent behavioural studies, the present review compares the performance of different eye regions in exploiting information on shape, colour and motion, relevant to the honeybee's foraging task. The comparisons reveal similarities, as well as differences, among the performances of various eye regions, depending on the visual parameter involved in the task under consideration. The outcome of the comparisons is discussed in the light of anatomical and optical regional specializations found in the bee's peripheral visual pathway, as well as in the light of the foraging bee's natural habits. It is concluded that the functional differences found among different eye regions are based on neural mechanisms subserving the bee's natural needs, rather than on peripheral specializations.

Journal Article↗

PubMed1998

The role of gas chromatography/mass spectrometry. Instrumental techniques in forensic urine drug testing.

Appropriate GC/MS analytic techniques can provide conclusive confirmatory evidence for the presence of drugs and metabolites in forensic urine drug testing. Although forensic laboratories are required to utilize GC/MS, they have flexibility and freedom in selecting instrumentation, modes of operation, and actual analytic methods. It is incumbent on the laboratory to optimize analytic procedures so that reliability and accuracy are maximized. The laboratory needs to be aware of potential pitfalls in both the handling and the analyses of specimens. Specificity can be enhanced by utilizing mass spectrometric operating modes such as CI and full scan, which serve to complement SIM analyses. They are useful in solving difficult identification problems and in enhancing sensitivity as well as specificity. Newer types of GC/MS systems utilizing ion trapping or tandem mass spectrometry offer the promise of enhanced analytic performance and productivity gains. Knowledge of the advantages and potential pitfalls of different GC/MS systems as well as ionization and detection modes is helpful in optimizing the accuracy of compound identification.

Forensic Medicine↗

PubMed1997

A pharmacodynamic study of morphine and its glucuronide metabolites after single morphine dosing in cancer patients with pain.

Eleven morphine naïve patients with cancer-related pain were given a single dose of either intravenous morphine (n = 5) or oral morphine (n = 6). Blood sampling was performed over a 24-hr period and serial pain assessments were made using a categorical scale. Plasma samples were analyzed for morphine, morphine-6-glucuronide (M-6-G), morphine-3-glucuronide (M-3-G), and normorphine using high-performance liquid chromatography. In neither the intravenous nor oral group was there a correlation between analgesia duration and the half-lives of morphine and M-6-G. There was no correlation between the time to peak analgesia and time to peak concentration for morphine or M-6-G. There was no significant difference in absolute concentrations of M-6-G or M-3-6 nor in the ratio of M-3-G to M-6-G at peak analgesia versus relapse.

Administration, Oral↗

PubMed1996

Honeybee navigation en route to the goal: visual flight control and odometry

Recent research has uncovered a number of different ways in which bees use cues derived from optic flow for navigational purposes. The distance flown to a food source is gauged by integrating the apparent motion of the visual world that is experienced en route. In other words, bees possess a visually driven 'odometer' that is robust to variations in wind load and energy expenditure. Bees flying through a tunnel maintain equidistance to the flanking walls by balancing the apparent speeds of the images of the walls. This strategy enables them to negotiate narrow passages or to fly between obstacles. The speed of flight in a tunnel is controlled by holding constant the average image velocity as seen by the two eyes. This avoids potential collisions by ensuring that the bee slows down when flying through narrow passages. Bees landing on a horizontal surface hold constant the image velocity of the surface as they approach it. This automatically ensures that flight speed decreases with altitude and is close to zero at touchdown. The movement-sensitive mechanisms underlying these various behaviours seem to be different, qualitatively as well as quantitatively, from those mediating the well-investigated optomotor response.

Journal Article↗

PubMed1996

Small-scale navigation in the honeybee: active acquisition of visual information about the goal

In a series of behavioural studies we found that bees use depth information extracted from self-induced image motion in several visual tasks involving pin-pointing the goal. Some of the results are reviewed here in an attempt to emphasise the active nature of this performance. They show that bees acquire depth information during free flight by employing two different strategies. One is to adapt flight behaviour, upon arrival at the food source, to the requirements of the task, a performance that is based on a learning process. The other is based on a stereotyped, innate flight pattern performed upon departure from the food source. The latter has probably evolved specifically for the acquisition of depth information.

Journal Article↗

PubMed1994

The effect of sucralfate on serum lipids and lipoproteins in normal volunteers [corrected].

Sucralfate is used in the treatment and prophylaxis of peptic ulcer disease. One possible mechanism of action is the binding of bile acids. Because the absorption of dietary fat and cholesterol is dependent on the presence of bile acids in the small intestines, sucralfate therapy may produce changes in serum lipoprotein composition qualitatively similar to bile acid sequestrants, such as cholestyramine, which reduce serum cholesterol levels. Although changes in total serum cholesterol have not been reported in sucralfate efficacy studies, the effect of sucralfate on serum lipoprotein composition has not been specifically addressed. The purpose of this study was to prospectively examine the effect of sucralfate on serum lipids and lipoproteins in normal volunteers. Eight healthy volunteers (six men, two women) were recruited for this 10-week study. Drugs known to affect cholesterol levels were not permitted before or during the study. Diet composition during the study period was unaltered from before the study. Subjects took 1 g sucralfate orally 1 hour before meals and at bedtime (four times a day) for 8 weeks, followed by a 2-week washout period. Fasting blood samples were obtained at baseline and weekly, and were analyzed for serum total and HDL cholesterol and for triglycerides. Levels of LDL cholesterol were estimated. After eight weeks of sucralfate, HDL cholesterol increased from baseline by 2.5 mg/dL (6.6%, from 37.6 +/- 9.5 to 40.1 +/- 8.69 mg/dL), and LDL cholesterol decreased by 7.6 mg/dL (6.4%, from 134 +/- 28.1 to 125.4 +/- 34.1). Total cholesterol decreased by 3.5 mg/dL (1.8%, from 192.9 +/- 34.3 to 189.4 +/- 37.2 mg/dL.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

Active vision in honeybees: task-oriented suppression of an innate behaviour.

In a pattern discrimination task, bees tend to fly along the contours contained in the patterns, as revealed by an earlier study. As opposed to this, in a task involving the detection of an edge between two striped surfaces placed at two different ranges, the bees avoid contour-following, as revealed by the present study. The study shows that, in the latter task, the bees learn to suppress the otherwise innate contour-following behaviour and adopt a flight strategy that provides them with the motion parallax cues necessary to cope with this task. Thus, the animal's active behaviour determines the type of visual information to be extracted from the environment.

Animals↗

PubMed1994

Spatial vision in the honeybee: the use of different cues in different tasks.

Much of the knowledge available on sensory performances in insects has been obtained from training experiments in honeybees. The present article reviews results of several behavioural studies on spatial vision in the bee. When considered jointly, they demonstrate the large amount of flexibility in the bee's visually guided behaviour. The visual cue that is used in a task depends on the experimental situation, e.g. the bee learns that particular cue that would most reliably guide it to its goal.

Animals↗

PubMed1991

Range perception through apparent image speed in freely flying honeybees.

When negotiating a narrow gap, honeybees tend to fly through the middle of the gap, balancing the distances to the boundary on either side. To investigate the basis of this "centering response," bees were trained to fly through a tunnel on their way to a feeding site and back, while their flight trajectories were filmed from above. The wall on either side carried a visual pattern. When the patterns were stationary vertical gratings, bees tended to fly through the middle of the tunnel, i.e. along its longitudinal axis. However, when one of the gratings was in motion, bees flying in the same direction as the moving grating tended to fly closer to it, while bees flying in the opposite direction tended to fly closer to the stationary grating. This demonstrates, directly and unequivocally, that flying bees estimate the distances of surfaces in terms of the apparent motion of their images. A series of further experiments revealed that the distance to the gratings is gauged in terms of their apparent angular speeds, and that the visual system of the bee is capable of measuring angular speed largely independently of the spatial period, intensity profile, or contrast of the grating. Thus, the motion-sensitive mechanisms mediating range perception appear to be qualitatively different from those that mediate the well-known optomotor response in insects, or those involved in motion detection and ocular tracking in man.

Animals↗

PubMed1990

Application of gas chromatography/mass spectrometry instrument techniques to forensic urine drug testing.

Appropriate GC/MS analytical techniques can provide conclusive confirmatory evidence for the presence of drugs and metabolites in forensic urine drug testing. Although forensic laboratories are required to utilize GC/MS, they have flexibility in selecting instrumentation, modes of operation, and actual analytical methods. Because a laboratory's accreditation status, reputation, and economic well-being depend on consistently accurate results, it is important to use optimal analytical procedures so that reliability and accuracy are maximized. Pitfalls in conventional EI SIM techniques can lead to high rates of false-positive and false-negative results. Different mass spectrometric operating modes such as CI and full-scan can be used to complement SIM analyses. These modes are useful in solving difficult identification problems and in enhancing both specificity and sensitivity. Newer types of GC/MS systems based on ion trapping offer the promise of technologic advances in enhanced analytical performance and productivity gains. Knowledge of the advantages and potential pitfalls of different GC/MS systems as well as different ionization and detection modes is helpful in optimizing the accuracy of compound identification.

Forensic Medicine↗

PubMed1989

[Argon laser trabeculoretraction in chronic open-angle glaucoma with normal pressure. A prospective study on the tonometric and perimetric effect].

A prospective randomised study was undertaken on sixty eyes, thirty five patients, (27 women, 8 men) followed in the Saint-Joseph hospital of Paris, with low tension glaucoma (LTG). The thirty five patients were selected at random and had either an argon laser trabeculoplasty (ALT) or received only vascular medications (medial). The first group (ALT) included 29 eyes. The second group (medical) included 31 eyes. The two groups were comparable: mean age, men/women distribution, mean intraocular pressure, mean C/D ratio, mean total visual capability (TVC) with the friedmann analyser. The mean follow up for the two groups was seven years. Nevertheless for the ALT group the mean follow up after ALT was four years. We compared for the two groups: --the aspect of the mean intraocular pressure (IOP) curve with time, --the evolution gradient of visual capabilities with time. For the ALT group we compared: --the mean IOP and 24 hours diurnal curves before and after laser treatment and the evolution gradient of visual capabilities before and after laser treatment. The introduction of ALT in the treatment of LTG had neither tonometric effect nor effect on the slope of visual field damage. We concluded that ALT is not recommended in LTG, but not that the IOP should not be reduced in this form of glaucoma.

Aged↗

PubMed1989

[Medium-term tonometric results of trabeculectomies performed after trabeculoretraction using an argon laser in chronic primary open-angle glaucoma].

Following unsuccessful Argon Laser Trabeculoplasty (ALT), 93 eyes were tracked for periods of 6 to 42 (mean: 24 months). The total failure rate of 20% is similar to the generally known failure rate of the trabeculectomies. However, failures are more frequent (37%) when trabeculectomy is performed between the second and third month after ALT. This may suggest not to operate on too soon after ALT or to perform filtering surgery with 5 Fluoro-uracil.

Adult↗