Two-photon imaging of lymphocyte motility and antigen response in intact lymph node.
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Lymphocyte motility is vital for trafficking within lymphoid organs and for initiating contact with antigen-presenting cells. Visualization of these processes has previously been limited to in vitro systems. We describe the use of two-photon laser microscopy to image the dynamic behavior of individual living lymphocytes deep within intact lymph nodes. In their native environment, T cells achieved peak velocities of more than 25 micrometers per minute, displaying a motility coefficient that is five to six times that of B cells. Antigenic challenge changed T cell trajectories from random walks to "swarms" and stable clusters. Real-time two-photon imaging reveals lymphocyte behaviors that are fundamental to the initiation of the immune response. (+info)
Methods of measuring swimming speed of spermatozoa.
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Three basic approaches for determining the mean swimming speed of a suspension of microorganisms were compared, using bull and ram spermatozoa. Number fluctuation counting was performed automatically on a Quantimet 720 image analysing computer, the mean speed being obtained using 'probability after' statistics. The other two approaches were photomicrographic: number flux counting was performed on single photomicrographs; on the same photomicrographs, the mean speed was estimated from measurement of 'whole' and 'half' track lengths. These results were compared with each other and with the Quantimet results. The 'probability after' method was also compared, on additional samples, with cine-photomicrographic tracking. The mean speeds predicted by the 'probability after' method compared favourably with the other methods (range 68 mum/sec to 162 mum/sec). The results also suggested that, on single photomicrographs, measurement of 'half' track lengths or number flux counting were generally preferable to measurement of whole track lengths. (+info)
Fluorescence light microscopy of pulmonary surfactant at the air-water interface of an air bubble of adjustable size.
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The structural dynamics of pulmonary surfactant was studied by epifluorescence light microscopy at the air-water interface of a bubble as a model close to nature for an alveolus. Small unilamellar vesicles of dipalmitoylphosphatidylcholine, dipalmitoylphosphatidylglycerol, a small amount of a fluorescent dipalmitoylphosphatidylcholine-analog, and surfactant-associated protein C were injected into the buffer solution. They aggregated to large clusters in the presence of Ca(2+) and adsorbed from these units to the interface. This gave rise to an interfacial film that eventually became fully condensed with dark, polygonal domains in a fluorescent matrix. When now the bubble size was increased or decreased, respectively, the film expanded or contracted. Upon expansion of the bubble, the dark areas became larger to the debit of the bright matrix and reversed upon contraction. We were able to observe single domains during the whole process. The film remained condensed, even when the interface was increased to twice its original size. From comparison with scanning force microscopy directly at the air-water interface, the fluorescent areas proved to be lipid bilayers associated with the (dark) monolayer. In the lung, such multilayer phase acts as a reservoir that guarantees a full molecular coverage of the alveolar interface during the breathing cycle and provides mechanical stability to the film. (+info)
Mad scientists, compassionate healers, and greedy egotists: the portrayal of physicians in the movies.
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Cinematic depictions of physicians potentially can affect public expectations and the patient-physician relationship, but little attention has been devoted to portrayals of physicians in movies. The objective of the study was the analysis of cinematic depictions of physicians to determine common demographic attributes of movie physicians, major themes, and whether portrayals have changed over time. All movies released on videotape with physicians as main characters and readily available to the public were viewed in their entirety. Data were collected on physician characteristics, diagnoses, and medical accuracy, and dialogue concerning physicians was transcribed. The results showed that in the 131 films, movie physicians were significantly more likely to be male (p < 0.00001), White (p < 0.00001), and < 40 years of age (p < 0.009). The proportion of women and minority film physicians has declined steadily in recent decades. Movie physicians are most commonly surgeons (33%), psychiatrists (26%), and family practitioners (18%). Physicians were portrayed negatively in 44% of movies, and since the 1960s positive portrayals declined while negative portrayals increased. Physicians frequently are depicted as greedy, egotistical, uncaring, and unethical, especially in recent films. Medical inaccuracies occurred in 27% of films. Compassion and idealism were common in early physician movies but are increasingly scarce in recent decades. A recurrent theme is the "mad scientist," the physician-researcher that values research more than patients' welfare. Portrayals of physicians as egotistical and materialistic have increased, whereas sexism and racism have waned. Movies from the past two decades have explored critical issues surrounding medical ethics and managed care. We conclude that negative cinematic portrayals of physicians are on the rise, which may adversely affect patient expectations and the patient-physician relationship. Nevertheless, films about physicians can serve as useful gauges of public opinion about the medical profession, as tools for medical education, and as instruments of positive social change in efforts to reform managed care. (+info)
Dynamic stabilization of rapid hexapedal locomotion.
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To stabilize locomotion, animals must generate forces appropriate to overcome the effects of perturbations and to maintain a desired speed or direction of movement. We studied the stabilizing mechanism employed by rapidly running insects by using a novel apparatus to perturb running cockroaches (Blaberus discoidalis). The apparatus used chemical propellants to accelerate a small projectile, generating reaction force impulses of less than 10 ms duration. The apparatus was mounted onto the thorax of the insect, oriented to propel the projectile laterally and loaded with propellant sufficient to cause a nearly tenfold increase in lateral velocity relative to maxima observed during unperturbed locomotion. Cockroaches were able to recover from these perturbations in 27+/-12 ms (mean +/- S.D., N=9) when running on a high-friction substratum. Lateral velocity began to decrease 13+/-5 ms (mean +/- S.D., N=11) following the start of a perturbation, a time comparable with the fastest reflexes measured in cockroaches. Cockroaches did not require step transitions to recover from lateral perturbations. Instead, they exhibited viscoelastic behavior in the lateral direction, with spring constants similar to those observed during unperturbed locomotion. The rapid onset of recovery from lateral perturbations supports the possibility that, during fast locomotion, intrinsic properties of the musculoskeletal system augment neural stabilization by reflexes. (+info)
Motor control of nuclear bag and nuclear chain intrafusal fibres in isolated living muscle spindles from the cat.
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1. The behaviour of nuclear bag and nuclear chain intrafusal fibres in isolated cat muscle spindles was studied by direct observation during repetitive stimulation of the muscle nerve at different stimulus strengths. Contraction of intrafusal fibres and stretch of sensory endings was recorded on film. 2. Tenuissimus spindles are usually operated by a total of four or five fusimotor axons, and the individual action of all of them was studied in many cases. 3. The great majority of fusimotor axons produce activity at one spindle pole only. 4. In about 60% of spindles nuclear bag and nuclear chain intrafusal fibres are selectively controlled by different fusimotor axons, while in one third of these spindles the individual nuclear bag fibres are themselves controlled independently. The remaining 40% of spindles, in addition to some selective innervation, receive one non-selective axon which operates both nuclear chain and nuclear bag fibres though usually only one of the nuclear bag fibres is involved. Selective control is demonstrated in photographs. 5. The thresholds of fusimotor axons selectively innervating nuclear bag and nuclear chain fibres, and of non-selective fusimotor axons are not significantly different. 6. It is suggested that in spindles in which the nuclear bag fibres are controlled by the same axon, it is a 'dynamic' gamma, or occasionally beta, axon. Where one nuclear bag fibre is operated along with the nuclear chain fibres it is controlled by 'static' gamma axon(s), and the other nuclear bag fibre is selectively controlled by 'dynamic' gamma, and perhaps beta, axon(s). Where two nuclear bag fibres are separately operated one may be controlled by 'dynamic' axon(s) and the other by 'static' gamma axon(s). Nuclear chain fibres are always controlled by 'static' gamma axons. (+info)
Form of developing bends in reactivated sperm flagella.
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1. Dark-field, multiple-exposure photographs of reactivated tritonated sea urchin sperm flagella swimming under a variety of conditions were analysed. 2. The length, radius and subtended angle of bends increased during bend development. The pattern of development was essentially the same under all conditions observed. 3. The angles of the two bends nearest the base tend to increase at the same rate, cancelling one another, so that the development of new bends causes little if any net microtubular sliding. 4. The direction of microtubular sliding within a bend is initially in the same direction as that within the preceding bend, and reverses as the bend develops. (+info)
Malaria films: Motion pictures as a public health tool.
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I offer a historical examination of a group of malaria motion pictures, a subset of a larger genre of public health films. The majority of these more than 100 films were produced or coproduced by American and British agencies or production companies since 1940. The material is divided into 5 chronological periods, which include World War II, the postcolonial or DDT era (1946-1961), and the past 2 decades. The films themselves, I argue, represent a unique record of preventive measures, clinical techniques, and sociocultural biases, all within the context of a history of one of the greatest continuing challenges in public health. The malaria films, as a group, represent a large body of work that has not yet been brought together or analyzed as historical sources. (+info)