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Biomedical subjects

J C Hwang

Publications and source records attributed to J C Hwang.

At least 73 records · Page 4Linked to original sources
PubMed1983

Determination of myofibrillar diameter by light diffractometry.

Distinctive oscillations in the diffraction line intensity were observed when a laser beam was directed at selected spots on single skeletal muscle fibres of frog and normally to the fibres. These intensity oscillations were interpreted as the diffraction from cylindrical myofibrils because they followed the first-order Bessel function. This interpretation allowed a direct determination of the myofibrillar diameter from the first intensity minimum of the zerothorder diffraction line. The hypothesis that the intensity oscillations were related to the myofibrillar diameter was substantiated by further experiments. At fixed sarcomere length the measured myofibrillar diameter increased when the fibre was immersed in hypotonic solution and decreased in hypertonic solution. In another experiment the diameter decreased and the sarcomere volume remained constant when the fibre was stretched passively. Furthermore, there was excellent agreement between the myofibrillar diameters measured by light diffractometry and electron microscopy.

Animals↗
PubMed1983

Respiratory-related hypoglossal nerve activity: influence of anesthetics.

In decerebrate, vagotomized, paralyzed, and ventilated cats, phrenic and respiratory-related hypoglossal discharges were evident at normocapnic normoxia or hyperoxia. Both increased progressively in hypercapnia or hypoxia. With increasing drive, onset of inspiratory hypoglossal activity began earlier relative to phrenic onset; an early expiratory hypoglossal burst was also observed. Following subanesthetic doses of chloralose, halothane, ketamine, or pentobarbital, hypoglossal activity was depressed much more than phrenic discharge. In moderate hypercapnia or hypoxia, phrenic activity increased more than hypoglossal, whereas, at high drive, the latter rose more sharply in some cats. Electromyograms of the diaphragm and genioglossus were recorded in intact awake cats to determine if their responses and those of decerebrates are comparable. Respiratory-related genioglossal discharge was evident in normocapnia. We conclude that anesthesia suppresses hypoglossal motor activities much more than those of the bulbospinal-phrenic system. Data for decerebrate cats and unanesthetized cats or humans provide no evidence of a differential distribution of chemoreceptor afferents on hypoglossal and bulbospinal-phrenic neurons, as suggested by results in anesthetized animals.

Anesthetics↗
PubMed1983

Characterization of respiratory-modulated activities of hypoglossal motoneurons.

In decerebrate, vagotomized, paralyzed, and ventilated cats, activities of the phrenic nerve and single hypoglossal nerve fibers were monitored. The great majority of hypoglossal neuronal activities were inspiratory (I), discharging during a period approximating that of phrenic. Many were not active at normocapnia but were recruited in hypercapnia or hypoxia. Once recruited, discharge frequencies, which rose quickly to near maximal levels in early to midinspiration, significantly increased with further augmentations of drive. Also, the onset of activities became progressively earlier, compared with phrenic discharge, in hypercapnia or hypoxia. Smaller numbers of hypoglossal fiber activities, having inspiratory-expiratory (I-E), expiratory (E), expiratory-inspiratory (E-I), or tonic discharge patterns, were also recorded. Activities of E, I-E, and those I fibers that became I-E in high drive may underlie the early burst of expiratory activity of the hypoglossal nerve. It is concluded that the firing and recruitment patterns of hypoglossal neurons differ from those of phrenic motoneurons. However, responses to chemoreceptor stimuli are similar among the two neuronal groups.

Animals↗
PubMed1982

Effect of bite force on the masseteric electromyographic silent period in man.

The duration of the masseteric EMG silent period as induced by tapping on the chin was measured at different levels of sustained bite force. Under both open bite and normal occlusion, the duration of the silent period was inversely related to the magnitude of the bite force. For bite force of the same magnitude, the value of the silent period remained relatively constant for the same subject in different trials (SEM congruent to 1 per cent), whereas the absolute values of the silent periods ranged far and wide for different individuals even under similar experimental conditions.

Adolescent↗
PubMed1981

Estimation of changes in single muscle fibre diameter in different solutions by diffraction studies.

Studies of the effects of varying tonicity on the contraction of muscle fibres requires a knowledge of the corresponding changes in fibre diameters, if the observed mechanical changes are to be attributed to various factors, including that of the interfilamental spacing. Hitherto, measurements of such changes in fibre diameters involved tedious measurements of the diameters of the fibres at numerous points along its length. We now describe a technique whereby the change in fibre diameter can be deduced from measurements of the corresponding intensity ratio of laser diffraction lines when the fibre is bathed in solutions of differing tonicities.

Animals↗
PubMed1981

Brain stem genesis of automatic ventilatory patterns independent of spinal mechanisms.

Efferent activities on the phrenic and recurrent laryngeal (RLN) nerves were monitored during eupnea, apneusis, and gasping in decerebrate, paralyzed, and ventilated cats before and after spinal cord transection at the first cervical level. The vagi were sectioned caudal to the RLN being studied and at the midcervical level contralaterally. Before spinal transection, the onset of RLN inspiratory activity preceded that of the phrenic nerve during eupnea and apneusis; in gasping, phrenic activity began before the RLN. These results were the same in normocapnia, hypercapnia, and hypoxia. After spinal transection, no phasic phrenic activity was observed at normoxia or hyperoxia, whereas the RLN exhibited discharge patterns similar to those before transection. Upon end-tidal O2 partial pressure diminutions below 50 Torr, one or more "burst" of phrenic activity were recorded. These bursts were not synchronized with the phasic RLN discharge. It is concluded that automatic ventilatory activity may be generated by inherent brain stem mechanisms. These results further imply the processes underlying gasping neurogenesis may differ fundamentally from those of eupnea or apneusis.

Animals↗
PubMed1980

Response of central vestibular neurons to utricular stimulations in cats.

In decerebrated, spinal transected cats with neck and forelimbs immobilized by plaster cats, the visual and proprioceptive cues were minimized when the animal was tilted. The contralateral labyrinth was acutely destroyed. The ipsilateral semicircular canals were plugged and the ipsilateral saccule extirpated leaving the ipsilateral utricle intact. Neurons in the vestibular nuclear complex driven by electrical stimulation of the utricle were shown to be highly sensitive to static pitch. Results suggest that the observed response to static pitch was due exclusively to input from the utricle.

Animals↗
PubMed1980

Immediate return of sensation after digital nerve repair.

Ten patients with immediate return of sensation after digital nerve repair were tested for sensibility and showed an early improvement followed by deterioration at the third week. Animal experiments to test the electrophysiology of the sural nerves in the rabbit after microrepair failed to show nerve impulse conducted across the anastomosis immediately after repair. Further clinical observations including nerve blocks supported the hypothesis of overlap innervation as the explanation for immediate return of sensibility

Action Potentials↗
PubMed1979

Comparison of dynamic properties of canal-evoked vestibulospinal reflexes of the neck and forelimb in the decerebrate cat.

The responses of neck and forelimb muscles to sinusoidal polarization of the horizontal canal nerve were compared by recording from these muscles simultaneously. Contrary to results on the vestibulocollic reflex, the central phase lag in the vestibulo-forelimb reflex increases with increasing frequencies up to 3 Hz. This demonstrates a difference in the organization of vestibular-driven pathways to neck and forelimb muscles.

Animals↗
PubMed1979

Vestibular function of saccule in cats as indicated by the response of Deiters' nucleus to static tilts.

In ketamine anesthetized cats, the contralateral labyrinth, the ipsilateral utricle, the ipsilateral horizontal and anterior semicircular canal nerves were completely destroyed, leaving the ipsilateral saccule intact. Neurons in the Deiters' nucleus, driven by electrical stimulation of the superior saccule, were responsive to static tilts in the antero-posterior direction. Results suggest that the saccule is capable of conveying information on head positional changes in the antero-posterior direction and that such information is retained at the level of the Deiters' nucleus.

Afferent Pathways↗
PubMed1979

Changes in diffraction patterns with length in single muscle fibres at rest.

The addition of a simple X--Y sampling circuit to a closed circuit television system (CCTV) permits measurements of a narrow profile of the laser diffraction patterns from single frog muscle fibres at rest. Results confirm that maximum intensity occurs at 2.95-3.00 micron, but a positive linear relationship between the dispersions of sarcomeres and sarcomere lengths from 2.7--3.8 micron is obtained in four isolated single fibres.

Animals↗
PubMed1978

Correlative study of pain perception and masticatory muscle reflexes in man.

An attempt was made to explore the possibility of using the masticatory muscle reflexes as pain indices in human subjects. It was found that the digastric reflex, so readily evoked by electrodental stimulation in experimental animals, could not be consistently elicited in man. The reflex silent period of the masseteric muscles, on the other hand, may be used as a pain index for evaluating dental analgesia, provided that analgesic interference is anticipated at points along the reflex arc.

Adult↗
PubMed1977

Intracellular recordings from Deiters' neurons in response to saccular and oculomotor nucleus stimulations.

2 populations of cells were found in the Deiters' nucleus responsive to direct electrical stimulation of the ipsilateral saccule. Only those Deiters' neurons activated monosynaptically from the saccule could be driven antidromically from the oculomotor nucleus. Such an intracellular study provides strong evidence for a tri-neuronal arc in the sacculo-ocular reflex for vertical eye movements.

Action Potentials↗
PubMed1977

An experimental evaluation of regionally induced analgesia in dentistry.

A method for the assessment of induced regional dental analgesia in experimental animals is described. It is based on the validity of the electrodentally elicited digastric electromyogram as a pain index. This method has been applied to study the effectiveness of one local anesthetic and of "electroacupuncture" to suppress pain regionally.

Action Potentials↗
PubMed1977

In vitro measurement of rate of fluid secretion in rat isolated seminiferous tubules: effects of metabolic inhibitors and ions.

1. An in vitro technique for measuring secretory rate in rat isolated seminiferous tubules is described. 2. The basal rate of fluid secretion was 0-44+/-0-06 nl. cm-1 min-1 (S.E.) (n=21). The rate was found to be inhibited by cooling, addition of metabolic inhibitor 2,4-dinitrophenol (2-5 x 10(-4) M) and removal of glucose from the incubating solution. This indicates that fluid secretion in isolated rat seminiferous tubules is an energy dependent process. 3. Removal of K+ from the incubating medium inhibited the secretory rate in the isolated seminiferous tubules, whereas a fivefold increase in [K+]0 to 23-5 mM had no effect. The secretory rate was also unaffected by the absence of Cl- in the peritubular fluid. 4. Removal of Ca2+ from the peritubular medium caused a rise in the secretory rate. 5. Ouabain (10(-3) M) and acetazolamide (4 x 10(-5) M) caused a fall in the rate of fluid secretion in isolated seminiferous tubules. 6. These results are discussed in relation to the nature of the ionic secretion produced in the tubules.

Acetazolamide↗
PubMed1977

The force-velocity relationship in vertebrate muscle fibres at varied tonicity of the extracellular medium.

1. The relationship between active force and velocity of shortening was studied during tetanic contraction of isolated semitendinosus muscle fibres of the frog (0.5-2.0 degrees C). Measurements were carried out with the fibre immersed in isotonic (1.00R) Ringer solution and in solutions that were made hypotonic by reduction of NaCl (osmolality 0.62 and 0.81 of normal Ringer) and hypertonic by addition of sucrose (osmolality 1.22 and 1.44 of normal Ringer).2. The force-velocity relation was hyperbolic at loads lower than 80% of measured isometric force (P(0)) but exhibited a reversed curvature between 0.8P(0) and P(0). The maximum velocity of shortening was determined in two different ways: (i) by extrapolation to zero load from force-velocity data truncated at 0.8P(0) (computer fitting of hyperbola, leastsquares method) and (ii) by recording the time required to take up the slack of the fibre after a quick release during tetanus.3. Isometric force and maximum speed of shortening both changed inversely with the tonicity of the extracellular medium. Immersion of the fibre in 0.81R hypotonic solution caused active tension and shortening velocity to increase by 10 +/- 1% (mean +/- S.E. of mean, n = 14) and 12 +/- 1%, respectively. Conversely, force and shortening velocity decreased by 12 +/- 1% (n = 13) and 22 +/- 2% when normal Ringer was replaced by 1.22R hypertonic solution. These changes doubled when the tonicity was altered from normal Ringer to 0.62R and 1.44R, respectively.4. Changes in fibre cross-sectional area equivalent to those obtained in the 0.81R and 1.22R solutions (+11% and -13%, respectively) were produced by varying the sarcomere length within the range 2.0-2.5 mum in the normal Ringer solution. Maximum velocity of shortening remained very nearly constant under these conditions, indicating that the shortening velocity, like the isometric force, is not critically dependent on changes in myofilament lattice width over the range considered.5. The results support the view that both shortening velocity and active force are modulated by changes of the intracellular ionic strength above and below the level that normally exists in the intact muscle fibre.

Animals↗
PubMed1976

Interaction between lanthanum and calcium in isolated guinea-pig heart.

The effect of lanthanum ion on the contraction of the perfused guinea-pig heart has been investigated. Lanthanum caused inhibition of the contractile force. The dose-response curves suggest that there is more than one site with which lanthanum may interact. The high affinity interaction is antagonised by high external calcium. The possibility that a low concentration of lanthanum may block calcium entry into the myocardium is discussed.

Animals↗