Effects of visceral inputs on the processing of labyrinthine signals by the inferior and caudal medial vestibular nuclei: ramifications for the production of motion sickness.
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The effect on motion sickness and oculomotor function of GR 38032F, a 5-HT3-receptor antagonist with anti-emetic properties.
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1. The 5-hydroxytryptamine (5-HT3) receptor antagonist, GR 38032F, which possesses potent anti-emetic properties in vomiting induced by cancer chemotherapeutic drugs, has been tested to determine its value in the prophylaxis of motion sickness induced by cross-coupled stimulation. The double-blind trial compared GR 38032F with both a placebo (lactose) and with hyoscine. In addition, studies of ocular pursuit and saccadic eye movements were carried out following the administration of each drug. 2. The prophylactic effect of GR 38032F on motion-induced nausea was indistinguishable from that of placebo, whereas following hyoscine subjects showed a highly significant (P less than 0.001) increase in tolerance to cross-coupled stimulation. Tests of oculomotor function showed no effect on saccadic eye movement from either drug. However, both drugs produced a significant (P less than 0.05) though small reduction in eye velocity gain during pursuit eye movement. 3. These findings suggest that the 5-HT3 receptor is not involved in the neural pathways that bring about motion sickness, but that it may have a role in the control of ocular pursuit. The absence of an anti-motion sickness effect from a drug that is effective in the treatment of vomiting induced by cancer chemotherapy serves to emphasize that different neural mechanisms are involved in the generation of motion sickness. (+info)
Adaptation to telescopic spectacles: vestibulo-ocular reflex plasticity.
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The vestibulo-ocular reflex (VOR) is a mechanism for the production of rapid compensatory eye movements during head movements. To investigate the adaptation of this reflex to spectacle magnifiers, the effect on the VOR of a brief period of wearing telescopic spectacles during head rotation was studied in normal subjects. VOR gain, as measured in darkness, was defined to be the ratio of compensatory slow phase eye velocity to head velocity. Initial VOR gain as measured for vertical axis sinusoidal head rotation at 0.1 Hz, amplitude 60 degrees/sec, was about 0.7. After 15 min adaptation by sinusoidal rotation during the viewing of a remote video display through X2, X4, or X6 binocular telescopic spectacles, 47-70% of subjects exhibited significant VOR gain increases of 7-46%. These increases were measured with occlusion of the unmagnified visual field peripheral to the telescopes during adaptation. There was considerable interindividual variability in adaptation to telescopic spectacles. Telescopic spectacle power had little or no effect on the amount of VOR change after adaptation, although all telescope powers produced a greater VOR gain change than did adaptation without telescopes. Testing of VOR gain at multiple frequencies indicated that adaptation to telescopic spectacles by rotation at a single sinusoidal frequency induces VOR gain changes across a broad spectrum of frequencies of head rotation. When the unmagnified peripheral visual field was unobstructed during adaptation, VOR gain increases were significantly less than when the unmagnified peripheral visual field was occluded, and were similar to those observed during adaptation without the wearing of telescopic spectacles at all. VOR gain adaptation was associated with amerlioration of symptoms of oscillopsia and motion discomfort initially experienced by about 20% of subjects wearing telescopic spectacles. (+info)
Space medicine--a review of current concepts.
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Space medicine deals with the branch of research involved with the adaptation of humans to the unique environment of space. More than 100 people have traveled in space. The day will come when some human beings will spend all their time in space. Medical problems encountered in space, such as motion sickness, negative nitrogen and calcium balance, anemia and radiation exposure, are issues that already affect medical practice outside aerospace medicine. (+info)
Response suppression produced by vestibular stimulation in the rat.
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Seven rats were trained to stable performance levels on either Fixed Ratio 47, Variable Ratio 47, Variable Interval 1-min, or Fixed Interval 1-min schedules of food reinforcement. Subjects were then tested for sensitivity to vestibular stimulation from rotation, using an ascending method of limits technique with increments in velocity of one revolution per minute every 5 min. Centrifugal forces were minimized by locating the test chamber over the axis of rotation. Response rates decreased in all subjects as a function of increasing rotation speed. In addition, characteristic differences in the patterns of response decrement were found between subjects on ratio and on interval schedules. Repeated tests indicated high intra-subject reliability in sensitivity to rotation. Similarities of these data to "motion sickness" phenomena in other species were noted. It is suggested that this behavioral approach provides a sensitive and quantifiable technique for assessing the effects of vestibular stimulation in animals. (+info)
Motion sickness-induced pica in the rat.
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Two experiments investigating the effects of motion sickness on pica (the consumption of non-nutritive substances) are reported. In the first experiment rats subject to rotational stimulation subsequently engaged in geophagia (clay consumption). In the second experiment use of a conditioned aversion paradigm confirmed that the method of rotational stimulation used in the first experiment causes motion sickness in rats. The results of these experiments indicate that simple gastrointestinal malaise in the absence of a deficiency state or acute toxemia will elicit pica. It is suggested that gastrointestinal distress may be a significant factor in the etiology of pica and its relationship to other causes of pica is discussed. (+info)
Clinical characteristics associated with the development of anticipatory nausea and vomiting in cancer patients undergoing chemotherapy treatment.
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Approximately one in four patients experiences nausea and/or vomiting in anticipation of a chemotherapy treatment by the time of their fourth treatment cycle. Anticipatory nausea and vomiting is a prevalent problem of clinical significance in the total management of chemotherapy side effects. While refractory to standard antiemetic treatment, anticipatory nausea and vomiting has been successfully treated with behavioral approaches such as systemic desensitization. The present study was designed to identify the characteristics of patients at high risk for developing anticipatory side effects. Early identification of cancer patients prone to developing anticipatory side effects could lead to preventive measures. One hundred seventy-six consecutive ambulatory patients with histologically confirmed cancer who were being treated at three geographically separate hospitals of the University of Rochester Cancer Center were studied at the time of their fourth chemotherapy treatment. Patients found to experience anticipatory nausea and vomiting were significantly more likely (P less than .001) to have four or more of the following characteristics than patients who did not report anticipatory side effects: (1) less than 50 years of age; (2) the experience of nausea and/or vomiting after their last chemotherapy treatment; (3) a description of nausea after the last treatment as "moderate, severe, or intolerable"; (4) a description of vomiting after the last treatment as "moderate, severe, or intolerable"; (5) the reporting of the side effect "warm or hot all over" after their last treatment; (6) a susceptibility to motion sickness; (7) the experience of "sweating after their last treatment"; (8) and the experience of "generalized weakness after their last chemotherapy treatment." Results support a view that anticipatory side effects are conditioned and point to practical interventions for their clinical control. (+info)