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Biomedical subjects

Y M Cheung

Publications and source records attributed to Y M Cheung.

34 records · Page 2Linked to original sources
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↗
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↗
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↗
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↗
PubMed1975

Developmental effects of neonatal sex hormones on spatial and activity skills in the white rat.

The purpose of this experiment is to extend these experiments by using varying neonatal hormonal differentiation processes and to examine the effects of these different methods of neonatal feminization on changes in spatial and activity skills. The experiment involved three neonatally feminized groups of male rats: 'castration alone', 'estrogen alone', and 'estrogen injected castrates' together with one female sample, 'testosterone injected castrates', while treated and untreated male and female controls were also used. The data provide partial support for the major hypotheses that neonatal gonadectomy and opposite sex hormones administered to male and female castrated rats (together and independently for males) would reverse the normal sex-associated abilities of the white rate (higher male spatial learning and higher female activity). However, the feminization effect for the male 'estrogen alone' and 'castration alone' experimental groups was much greater than for the male estrogen injected castrates. The masculinized females, testosterone injected castrates, also had higher spatial learning and lower activity levels, while the feminized male's spatial and activity skills were also reversed. This confirmed in part the extent to which neonatal gonadal sex hormones are effective at critical periods of development in programming the brain in terms of sex-associated spatial and activity skills. Adult hormonal replacement therapy was also administered at 12 months and supported the hypothesis that sex hormones in adults would be mainly activational and have less marked effects than the significant directional changes obtained by these neonatal sex hormones and castration techniques.

Age Factors↗
PubMedDate not supplied

The effects of different types of neonatal feminization and environmental stimulation on changes in sex-associated activity/spatial learning skills.

This research programme commenced in West Africa, where it was found that individuals with kwashiorkor gynaecomastia were feminized. This was also reinforced by the interacting dominant maternal socialization practices (Dawson, 1966). This was confirmed with feminized responses for adult male rats, on the Tolman-Maze (Dawson, 1972), while as well confirmed neonatally, for both feminized male and female rats (Dawson, Cheung and Lau, 1973, 1975). The present experiment tests the interacting effects of various levels of environmental stimulation, high, normal and low (Levitsky and Barnes, 1972), using feminized male rats. Thus castration, oestrogen and castration, and oestrogen feminized males, were contrasted with male and female controls. The results confirmed the physiological growth curves and other anatomical differences. As well, the activity data confirmed the hypothesis, for the combined samples (where high Ns mean more reliability) and also the environmental stimulation (F ratio: d.f. 18 and 57, 11.37, p less than 0.001; low Ns here mean lower reliability). However, for the symmetrical maze, the results for the combined samples, were not as convincing as in Dawson et al. (1973, 1975), although the environmental stimulation produced significant results in many cases, including a significant interaction for the analysis of variance (F ratio: d.f. 18 and 57, 3.12 p less than 0.001).

Adolescent↗
PubMedDate not supplied

Crossed sacculo-ocular pathway via the Deiters' nucleus in cats.

Single unit recordings were made in the Deiters' nucleus of cats in response to electrical stimulation of the superior area of the contralateral saccule and the ipsilateral oculomotor (IIIrd) nuclear complex. Correct placements of the stimulating and recording electrodes were identified by upward movements of the eyeballs associated with characteristic field potentials in the Deiters' nucleus. Stimulation of the contralateral saccule induced a negative N wave followed by positive P1 and P2 potentials. One hundred twenty-two units responded to contralateral saccular stimulation with a mean latency of 2.48 +/- 0.06 msec (SEM). Of these, only the responses of 31 cells could be made to collide with antidromic spikes evoked from ipsilateral IIIrd nuclear stimulation. This implies that the crossed sacculo-ocular pathway would involve at least four neurons with one commissural cell interposing between the bilateral vestibular nuclei.

Afferent Pathways↗
PubMedDate not supplied

Adaptive rival penalized competitive learning and combined linear predictor model for financial forecast and investment.

We propose a prediction model called Rival Penalized Competitive Learning (RPCL) and Combined Linear Predictor method (CLP), which involves a set of local linear predictors such that a prediction is made by the combination of some activated predictors through a gating network (Xu et al., 1994). Furthermore, we present its improved variant named Adaptive RPCL-CLP that includes an adaptive learning mechanism as well as a data pre-and-post processing scheme. We compare them with some existing models by demonstrating their performance on two real-world financial time series--a China stock price and an exchange-rate series of US Dollar (USD) versus Deutschmark (DEM). Experiments have shown that Adaptive RPCL-CLP not only outperforms the other approaches with the smallest prediction error and training costs, but also brings in considerable high profits in the trading simulation of foreign exchange market.

Algorithms↗
PubMedDate not supplied

Isolation of the uterotonic principle from Leonurus artemisia, the Chinese motherwort.

A search in ancient Chinese medicinal literature and modern phytochemical references indicates that the therapeutic value of Leonurus artemisia (I-mu ts'ao, the Chinese motherwort) might reside in a uterotonic principle present in leaves. Leonurine (4-guanidino-n-butyl syringate) was isolated from fresh and dry leaves of Leonurus artemisia. The uterotonic effect of leonurine was demonstrated in rat uterus in vitro. Results from this study suggest that functional phytochemistry based on ethnobotanical experience could lead to development of new and effective drugs from Chinese medicine.

China↗