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Biomedical subjects

J L Homick

Publications and source records attributed to J L Homick.

At least 19 recordsLinked to original sources
PubMed1992

Treatment of motion sickness in parabolic flight with buccal scopolamine.

Treatment of acute motion sickness induced by parabolic flight with a preparation of scopolamine placed in the buccal pouch was investigated. Twenty-one subjects flew aboard a KC-135 aircraft operated by the National Aeronautics and Space Administration (NASA) which performed parabolic maneuvers resulting in periods of 0-g, 1-g, and 1.8-g. Each subject flew once with a tablet containing scopolamine and once with a placebo in a random order, crossover design. Signs and symptoms of motion sickness were systematically recorded during each parabola by an investigator who was blind to the content of the tablet. Compared with flights using placebo, flights with buccal scopolamine resulted in significantly lower scores for nausea (31%-35% reduction) and vomiting (50% reduction in number of parabolas with vomiting). Side effects of the drug during flight were negligible. We conclude that buccal scopolamine is more effective than a placebo in treating ongoing motion sickness.

Administration, Buccal↗
PubMed1987

Lack of effects of astemizole on vestibular ocular reflex, motion sickness, and cognitive performance in man.

Astemizole was orally administered to 20 subjects in a randomized, double-blind design to assess the efficacy of this peripherally active antihistamine as an antimotion sickness drug possessing no central side-effects. Measures of vestibular ocular reflex (VOR) were made to evaluate the agent as a selective vestibular depressant. Following 1 week of orally administered astemizole (30 mg daily), a Staircase Profile Test, a VOR test, and a variety of tests of cognitive performance were administered. These tests revealed no statistically significant effects of astemizole. This leads us to conclude that, although the drug probably reaches the peripheral vestibular apparatus in man by crossing the blood-vestibular barrier, a selective peripheral antihistamine (H1) action is inadequate to control motion sickness induced through cross-coupled accelerative semicircular canal stimulation in a rotating chair.

Adolescent↗
PubMed1986

Vestibulo-spinal response modification as determined with the H-reflex during the Spacelab-1 flight.

Our laboratory at the Johnson Space Center has employed the H-reflex recorded from the soleus muscle as a method of monosynaptic reflex testing in conjunction with vertical linear acceleration to assess modification of utriculo-saccular function induced through prolonged exposure to microgravity. It was hypothesized that exposure to free fall would reduce the necessity for postural reflexes in the major leg muscles, and that postural modification would reflect a change, not in the peripheral vestibular organs, but more centrally. This postural adjustment would reflect a sensory motor rearrangement where otolith receptor input was reinterpreted to provide an environmentally appropriate response. In addition to the H-reflex (which was the only inflight measurement), vestibulo-spinal EMG from the gastrocnemius, and self-motion reports were obtained in response to a sudden earth vertical fall. Preflight, inflight and postflight motion sickness reports were also recorded, and related to the H-reflex data. The results indicated that early inflight H-reflex amplitude was similar to that recorded preflight, but that measurements obtained later in the flight (day seven) did not show a change in potentiation as a function of the different drop to shock intervals. Immediate postflight H-reflex response in three of the four astronauts tested showed a rebound effect. Postflight gastrocnemius EMG in response to the sudden fall did not show a significant change from preflight values. However, one crewman who was tested early postflight did show an increase in EMG activity in response to the sudden fall. This immediate postflight effect returned to baseline rapidly. Self-motion perception obtained inflight suggested that the early inflight drops were perceived like those preflight. Drops later inflight were described as sudden, fast, hard and translational in nature. Immediately postflight the drops were perceived like those late inflight, and the astronauts said that they did not feel as though they were falling, rather the floor came up to meet them. Post hoc peak H-reflex amplitude, both preflight and postflight was related to inflight space motion sickness.

Humans↗
PubMed1985

Otolith tilt-translation reinterpretation following prolonged weightlessness: implications for preflight training.

Observations with three astronauts yielded two major findings. First, perceived self-motion during sinusoidal roll differed immediately postflight from preflight. Between 70 and 150 min after landing, roll was perceived primarily as linear translation. Secondly, more horizontal eye movement was elicited by roll stimulation immediately postflight relative to both preflight and later postflight observations. These results support an "otolith tilt-translation reinterpretation" hypothesis, which has clear implications for understanding astronaut reports of space motion sickness during the early period of orbital flight. A proposal for "prophylactic adaptation training" which may provide preflight adaptation to weightlessness, derives from this research.

Adaptation, Physiological↗
PubMed1985

Efficacy of phosphatidylcholine in the modulation of motion sickness susceptibility.

This study evaluated the efficacy of pharmacological doses of phosphatidylcholine (lecithin) in the modulation of motion sickness induced by exposure to coriolis stimulation in a rotating chair. Subjects received daily dietary supplements of 25 grams of lecithin (90% phosphatidylcholine) and were tested for their susceptibility to motion sickness after 4 h, 2 d, and 21 d. A small but statistically significant increase in susceptibility (+ 15%) was noted 4 h after supplemental phosphatidylcholine, with four of nine subjects demonstrating a marked increase in susceptibility. We attributed this finding to choline's stimulatory action on cholinergic systems, an action which opposes that of the classical antimotion sickness drug scopolamine. Chronic lecithin loading revealed a trend towards reduced susceptibility, possibly indicating the occurrence of adaptive mechanisms such as receptor down-regulation. Withdrawal from lecithin loading, perhaps coupled with anticholinergic treatment, might prove to be a potent prophylactic regimen and ought to be tested.

Coriolis Force↗
PubMed1984

Vestibulospinal reflexes as a function of microgravity.

The idea that sustained microgravity will result in altered otolith input requiring a modification of postural control was explored by using the pathway that links the otolith organs and spinal motoneurons. Two related methods were used. First, the Hoffmann reflex was used to measure at specific times the excitability of the soleus-spinal motoneuron pool during a brief unexpected linear acceleration. Second, extensive dynamic postural testing with a moving platform was done before and after flight. The Hoffmann reflex amplitude, reflecting otolith-modulated motoneuron sensitivity, was low in flight after adaptation, and its postflight potentiation may have been dependent on rate of adaptation. The strength of inflight motion sickness symptoms was related to postflight Hoffmann reflex amplitude. Dynamic posture tests showed significant deviations from the results obtained before flight. The strategy used for balance on the moving platform was modified, and the behavior of the subjects suggested a decrease in awareness of the direction and magnitude of the motion.

Electromyography↗
PubMed1983

An appraisal of the value of vitamin B12 in the prevention of motion sickness.

Unpublished reports have suggested that hydroxycobalamin (B12, i.m.) prevents motion sickness. Some biomedical evidence supports this contention in that B12 influences the metabolism of histidine and choline; dietary precursors to neurotransmitters with established roles in motion sickness. Susceptibility to motion sickness was evaluated after B12 (1000 micrograms, i.m.). Subjects initially completed vestibular function and motion sickness susceptibility tests to establish normal vestibular function. The experimental motion stressor was a modified coriolis sickness susceptibility test. Subjects executed standardized head movements at successively higher RPM until a malaise III endpoint was reached. Following two baseline tests with this motion stressor, subjects received a B12 injection, a second injection two weeks later, and a final motion sickness test three weeks later. No significant differences in susceptibility were noted after B12. Hematological parameters revealed no B12 deficiency before injection. The possibility that patients with B12 deficiencies are more susceptible to motion sickness cannot be ruled out.

Aerospace Medicine↗
PubMed1983

Motion sickness: a modulatory role for the central cholinergic nervous system.

The present review has extended the general theory of motion sickness proposed by Wood and Graybiel [135, 136] by identifying specific neurophysiological mechanisms that are involved in motion sickness and by interpreting the actions of both scopolamine and amphetamine as effective anti-motion sickness drugs within this neurophysiological context. The neurochemical and neurophysiological effects of scopolamine have been reviewed in relationship to central cholinergic pathways. Cholinergic pathways have been associated with both the perception and expression of normal and excessive levels of motion stimuli. New approaches to the problem of the prevention of motion sickness have been considered. Efferent nicotinic innervation at the primary sensory hair cells and the medial vestibular nucleus were identified as sites where modulation by cholinergic drugs might exert a beneficial influence. However, it was generally conceded that the complexity of the cholinergic system and the interaction of scopolamine with that system left open the possibility that pharmacological doses of drugs specific to the cholinergic system might exert significant modulatory influences at alternative sites, as well.

Acetylcholine↗
PubMed1983

Effect of amphetamine on optokinetically evoked head and eye movements in the squirrel monkey.

The effect of amphetamine sulfate injection on head and eye movements evoked by optokinetic stimulus was studied in squirrel monkeys. No change was found in the gain of optokinetic-oculomotor and optokinetic-caputomotor functions, even after the maximum dose (0.5 mg/kg) of amphetamine. Also, no change in eye-head coordination was found. However, amphetamine facilitated the frequency of head nystagmus, whereas that of eye nystagmus did not change. When the poststimulus responses were studied in the dark, both nystagmoid head movement and optokinetic after eye nystagmus showed first phase and second phase. A different effect was found in the duration of these two phases suggesting the existence of distinct generators. Moreover, the synchronized onsets of head and eye nystagmus in both phases, and synchronized occurrence of quick phases indicated the existence of shared neural circuitry between head and eye movements.

Amphetamine↗
PubMed1983

Transdermal scopolamine in the prevention of motion sickness: evaluation of the time course of efficacy.

This study evaluated the time course of efficacy of transdermal scopolamine in the prevention of motion sickness induced by exposure to coriolis stimulation in a rotating chair. We measured levels of efficacy, quantified side effects and symptoms, and determined inter- and intra-subject variability following use of transdermal scopolamine. The response to transdermal scopolamine was highly variable, although overall we recorded a 40% improvement (p less than 0.05) in test scores 16-72 h after application of the transdermal system. This variability could not be explained solely by the levels of scopolamine present in the blood. The improvement was not due to the artifactual repression by scopolamine of selected symptoms of motion sickness. An unexpectedly high incidence of side effects was reported. It was concluded that the therapeutic use of transdermal scopolamine be evaluated individually and that individuals be cautioned that subsequent usage may not always be effective.

Administration, Topical↗
PubMed1980

Piracetam and fish orientation during parabolic aircraft flight.

Goldfish were flown in parabolic Keplerian trajectories in a KC-135 aircraft to assay both the effectiveness of piracetam as an anti-motion sickness drug and the effectiveness of state-dependent training during periods of oscillating gravity levels. Single-frame analyses of infrared films were performed for two classes of responses--roll rates in hypogravity or hypogravity orienting responses (LGR) and climbing responses in hypergravity or hypergravity orienting responses (HGR). In Experiment I, preflight training with a vestibular stressor facilitated suppression of LGR by the 10th parabola. An inverse correlation was found between the magnitudes of LGR and HGR. Piracetam was not effective in a state-dependent design, but the drug did significantly increase HGR when injected into trained fish shortly before flight. In Experiment II, injections of saline, piracetam, and modifiers of gamma-aminobutyric acid (GABA)--aminooxyacetic acid (AOAA) and isonicotinic acid (INH)--did not modify LGR. AOAA did significantly increase HGR. Thus, the preflight training had a beneficial effect in reducing disorientation in the fish in weightlessness, but the drugs employed were ineffective.

Aminooxyacetic Acid↗
PubMed1979

Space motion sickness.

Space motion sickness, presumably triggered by sudden entry into a weightless environment, occurred with unexpected frequency and severity among astronauts who flew the Skylab missions. Recovery from symptoms was complete within 3-5 days, and as revealed by the Skylab M131 Human Vestibular Function Experiment, all crewmembers were immune to experimentally induced motion sickness after mission day 8. This syndrome has been recognized as a possible threat to the early mission well-being and operational efficiency of at least some individuals who will fly space missions in the future. The causes of space motion sickness are not clearly understood, nor have satisfactory methods been identified to date for its prediction, prevention and treatment. In order to minimize the potential impact of this syndrome on Space Shuttle crew operations the National Aeronautics and Space Administration has organized a broad program of inter-disciplinary research involving a large number of scientists in the United States. Current research on the etiology of space motion sickness is based to a large extent on the so called sensory conflict theory. Investigations of the behavioral and neurophysiological consequences of intralabyrinthine, as well as intermodality sensory conflict are being performed. The work in this area is being influenced by the presumed alterations that occur in otolith behavior in weightlessness. In addition to sensory conflict, the possible relationship between observed cephalad shifts of body fluids in weightlessness and space motion sickness is being investigated. Research to date has failed to support the fluid shift theory. Research underway to identify reliable test methods for the prediction of susceptibility to space motion sickness on an individual basis includes attempts to (a) correlate susceptibility in different provocative environments; (b) correlate susceptibility with vestibular and non-vestibular response parameters, the latter including behavioral, hemodynamic and biochemical factors and (c) correlate susceptibility with rate of acquisition and length of retention of sensory adaptation. Controlled studies are also being performed during parabolic flight as a means of attempting to validate predictive tests for susceptibility to this syndrome. Research to develop new or improved countermeasures for space motion sickness is underway in two primary areas. One of these involves anti-motion sickness drugs. Significant achievements have been realized with regard to the identification of new highly efficacious drug combinations, dose levels and routes of administration. Although pronounced individual variations must be accounted for in selecting the optimum drug and dose level, combinations of promethazine plus ephedrine or scopolamine plus dexidrine are presently the drugs of choice. Work is also underway to identify side effects associated with anti-motion sickness drug use and to identify new drugs which may selectively modify activity in central neural pathways involved in motion sickness. In addition to research on drugs, efforts are being made to develop practical vestibular training methods. Variables which influence rate of acquisition of adaptation, length of retention of adaptation and transfer of protective adaptation to new environments are being evaluated. Also, included in this area is the use of biofeedback and autogenic therapy to train individuals to regulate autonomic responses associated with motion sickness. While valuable new knowledge is expected to evolve from these combined research programs, it is concluded that the final validation of predictive tests and countermeasures will require a series of controlled space flight experiments.

Adaptation, Physiological↗
PubMed1979

Effect of macular ablation on vertical optokinetic nystagmus in the squirrel monkey.

After macular ablation in squirrel monkeys, a significant improvement of the slow-phase eye speed of vertical optokinetic nystagmus (VOKN) was found. This findings is in contrast to the result of our previous study in which horizontal optokinetic nystagmus (HOKN) was not improved following macular ablation. The different influence of macular ablation on HOKN and VOKN could be due to the directional characteristics of vestibular and visual interaction relative to the direction of gravity and to the difference in horizontal and vertical vestibulo-oculomotor neural pathways, including vestibular end-organs. The vertical directional dominance which was observed preoperatively was similarly observed in the postablative status; the upward slow-phase nystagmus was easier to provoke than the downward nystagmus by application of an identical stimulus.

Acoustic Maculae↗
PubMed1979

Effect of exercise upon locomotor balance modification after peripheral vestibular lesions (unilateral utricular neurotomy) in squirrel monkeys.

In this study, we placed unilateral utricular nerve section and measured the locomotor equilibrium function (deviation counts of the animal's trotting gait) by the squirrel monkey platform runway test. We applied physical exercise, both preoperatively (3 weeks) and postoperatively. 21 young adult squirrel monkeys were randomly assigned to three groups (7 each): rotating cage exercise (continuous trotting in the motor-driven rotating cage) group, rail-traversing exercise (60 running shuttles on the rotating rail) group, and control nonexercise group. After the statistical analyses on data it was found that the physical exercise showed some effect; however, the type, daily amount, and number of days applied must be quite substantial.

Animals↗
PubMed1977

Optokinetic nystagmus and vestibular stimulation in squirrel monkey model.

Simultaneous application of the rotatory stimulus with a constant angular acceleration (1 degree/sec2) did not clearly improve the optokinetic pursuing ability in squirrel monkeys, even though the directions of vestibular and visual stimuli matched. When the directions of vestibular stimulus and visual stimulus conflicted, the optokinetic pursuing ability markedly declined regardless of the stimulus magnitude. The inter-individual difference was large in that situation. For the vestibular-visual coordination, the active head movement condition is considered to be natural and important as a biological function.

Animals↗
PubMed1977

Effect of otolith end organ ablation on horizontal optokinetic nystagmus, and optokinetic afternystagmus in the squirrel monkey.

Horizontal optokinetic nystagmus (OKN) and optokinetic afternystagmus (OKAN) (stimulus speed 0-200 degrees/sec with 1 degree/sec constant angular acceleration) were examined before and after utriculo-sacculectomy (bilateral, two-stage) in squirrel monkeys. OKN exhibited a slight decline only after bilateral otolith and organ ablations. OKAN showed a minimal decline after unilateral operation but no change after bilateral operations. Severe OKN reduction and disappearance of OKAN after bilateral labyrinthectomy in primates should basically reflect the elimination of inputs from the cristae ampullares, and not from the maculae.

Animals↗