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Biomedical subjects

J P Leung

Publications and source records attributed to J P Leung.

At least 19 recordsLinked to original sources
PubMed2001

Complications of intraarticular calcaneal fractures.

The treatment of intraarticular calcaneal fractures remains a controversy in orthopaedics because of the associated complications. The authors present a systematic review of complications associated with calcaneal fractures. A MEDLINE search was conducted to review the results of operative and nonoperative treatment of calcaneal fractures to determine the most common complications reported. The following were reported to be the most common complications: swelling and fracture blisters, compartment syndrome, wound dehiscence and infection, neurovascular injury, tendon injury, heel pad pain and heel exostosis, malunion, and arthritis. Each complication was reviewed as to etiology, incidence, diagnosis, prevention, and treatment. Increased awareness of these complications and their prevention will aid the practitioner in decision-making and result in better treatment outcomes for this fracture.

Arthralgia↗
PubMed1998

Recognition of facial expressions of emotion by children with attention-deficit hyperactivity disorder.

Fifty children and adolescents were tested for their ability to recognize the 6 basic facial expressions of emotion depicted in Ekman and Friesen's normed photographs. Subjects were presented with sets of 6 photographs of faces, each portraying a different basic emotion, and stories portraying those emotions were read to them. After each story, the subject was asked to point to the photograph in the set that depicted the emotion described. Overall, the children correctly identified the emotions on 74% of the presentations. The highest level of accuracy in recognition was for happiness, followed by sadness, with fear being the emotional expression that was mistaken most often. When compared to studies of children in the general population, children with ADHD have deficits in their ability to accurately recognize facial expressions of emotion. These findings have important implications for the remediation of social skill deficits commonly seen in children with ADHD.

Adolescent↗
PubMed1998

Recognition of facial expressions of emotion by Chinese adults with mental retardation.

We compared the ability of Chinese adults with mental retardation and nonhandicapped Chinese children to recognize the six basic facial expressions of emotion. Each subject was told a story identifying an emotion, presented with an array of six photographs of basic facial expressions of emotion, and asked to point to the photograph that depicted the story's emotion. Results showed that the children were more accurate than the adults in recognizing facial expressions of emotion except happiness on which both groups achieved 100% accuracy. Surprise, fear, anger, and disgust were confused most often by both groups. Recognition proficiency was not significantly correlated with age in the children or with IQ in the adults. Our results partially replicated those reported in earlier studies with non-Chinese individuals with mental retardation and raised the possibility that there may be cultural influences on a person's ability to recognize facial expressions of emotion.

Adolescent↗
PubMed1997

Teaching receptive naming of Chinese characters to children with autism by incorporating echolalia.

The facilitative effect of incorporating echolalia on teaching receptive naming of Chinese characters to children with autism was assessed. In Experiment 1, echoing the requested character name prior to the receptive naming task facilitated matching a character to its name. In addition, task performance was consistently maintained only when echolalia preceded the receptive manual response. Positive results from generalization tests suggested that learned responses occurred across various novel conditions. In Experiment 2, we examined the relation between task difficulty and speed of acquisition. All 3 participants achieved 100% correct responding in training, but learning less discriminable characters took more trials than learning more discriminable characters. These results provide support for incorporating echolalia as an educational tool within language instruction for some children with autism.

Autistic Disorder↗
PubMed1993

Psychological distance to reward: Segmentation of aperiodic schedules of reinforcement.

College students responded for monetary rewards in two experiments on choice between differentially segmented aperiodic schedules of reinforcement. On a microcomputer, the concurrent chains were simulated as an air-defense video game in which subjects used two radars for detecting and destroying enemy aircraft. To earn more cash-exchangeable points, subjects had to shoot down as many planes as possible within a given period of time. For both experiments, access to one of two radar systems (terminal link) was controlled by a pair of independent concurrent variable-interval 60-s schedules (initial link) with a 4-s changeover delay always in effect. In Experiment 1, the appearance of an enemy aircraft in the terminal link was determined by a variable-interval (15 s or 60 s) schedule or a two-component chained variable-interval schedule of equal duration. Experiment 2 was similar to Experiment 1 except for the segmented schedule, which had three components. Subjects preferred the unsegmented schedule over its segmented counterpart in the conditions with variable-interval 60 s, and preference tended to be more pronounced with more components in the segmented schedule. These findings are compatible with those from previous studies of periodic and aperiodic schedules with pigeons or humans as subjects.

Journal Article↗
PubMed1989

Immunohistochemical analysis of pulmonary and pleural tumors with the monoclonal antibody HYB-612 directed against the multidrug resistance (MDR-1) gene product, P-glycoprotein.

In this study, 212 untreated primary pulmonary and pleural neoplasms were studied immunohistochemically with the monoclonal antibody HYB-612 which detects the multidrug resistance (MDR)-related P-glycoprotein (gp180). A tumor was considered positive for the expression of the MDR phenotype, even if a single rare positive cell was detected. Using this criterion, all of the various histologic subtypes were found to express MDR to varying degrees. The frequency of expression of this phenotype was found to be notably higher in non-small-cell carcinomas than in small-cell carcinomas. These findings are consistent with the known clinical responses of these neoplasms. The detection of gp180 in untreated lung neoplasms may be predictive of the responsiveness of neoplasms to chemotherapeutic agents. In addition, its presence or absence might be useful in determining the appropriate treatment protocol for given patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1989

Psychological distance to reward: A human replication.

Choice behavior in college students was examined in two experiments using the concurrent-chains procedure. In both experiments, the concurrent chains were presented on a microcomputer in the form of an air-defense game in which subjects used two radar systems to detect and subsequently destroy enemy aircraft. Access to one of two radar systems was controlled by a pair of independent concurrent variable-interval 60-s schedules with a 4-s changeover delay always in effect. In the terminal link, the appearance of an enemy aircraft was determined by a pair of differentially segmented fixed-time schedules (Experiment 1) or fixed-interval schedules (Experiment 2) of equal overall duration. In Experiment 1, the terminal-link duration was either 20 s or 40 s, and subjects preferred the unsegmented to the segmented intervals. In Experiment 2, the duration was either 10 s or 60 s, and the reinforcement contingencies required responding during the terminal link. Prior to the reinstatement of the initial link, subjects estimated the duration of the terminal-link schedule. Segmentation affected choice in the 60-s conditions but not in the 10-s ones. Preference for the unsegmented schedule was correlated with an overestimation of the durations for the segmented schedules. These results replicated those found in animal experiments and support the notion of increasing the psychological distance to reward by segmenting a time-based schedule of reinforcement.

Journal Article↗
PubMed1988

Smoking cessation through cigarette-fading, self-recording, and contracting: treatment, maintenance and long-term followup.

Seven adult subjects, all with extensive smoking histories, participated in a smoking cessation program. Intervention procedures included cigarette-fading, self-recording, and contracting. A changing-criterion analysis showed that six of the seven subjects were able to abstain from smoking within two months of intervention. The seventh subject was able to meet two changes in criterion, but dropped out of the treatment programme during the third. Of the sex remaining subjects, five were able to abstain from smoking during the six-month maintenance period. The sixth subject resumed smoking in the fourth month of maintenance and preferred to continue smoking thereafter. Followup data, collected every three months for two years, showed that the five remaining subjects were able to abstain from smoking for two years following the cessation of the maintenance programme.

Adult↗
PubMed1988

Behavioral vision training for myopia: stimulus specificity of training effects.

The present study assessed transfer of visual training effects for myopia using two different training stimuli and a single subject A-B-C-A design. A male student volunteer, with lens prescription of -3.0 D (left) and -2.0 D (right), served as the subject. During baseline (10 sessions), visual acuity was assessed by two behavioral acuity tests. One test consisted of 50 line drawings of common objects as testing stimuli and the other test had 50 Chinese characters. A procedure including stimulus fading and reinforcement (positive verbal feedback) was used to train the subject to identify either pictorial stimuli or Chinese characters presented from a distance. Training was effective in improving performance on both behavioral acuity tests during the training phases and follow-up but the change was more pronounced on the specific stimuli being used for training. Refractive errors assessed on a weekly basis showed no change in the physiology of both eyes. These results suggest that effects of visual training only partially transferred to untrained stimuli.

Adult↗
PubMed1988

Preference for simple interval schedules of reinforcement in concurrent chains: Effects of segmentation ratio.

A concurrent-chains procedure was used to examine pigeons' preferences between segmented and unsegmented terminal-link schedules of reinforcement. During the initial link, a pair of independent, concurrent variable-interval 60-s schedules was in effect. In the terminal link, reinforcement was provided by a chain fixed-interval fixed-interval schedule on one key and by a simple fixed-interval schedule with an equal interreinforcement interval in the other. The relative duration between the first and second components (segmentation ratio) in the terminal-link chained schedule was systematically varied while the terminal-link duration was kept constant at either 15 s or 30 s in two sets of conditions. With few exceptions, the simple schedule was preferred to the chained schedule. Furthermore, this preference was inversely related to the size of the segmentation ratio in the segmented schedule. When the segmentation ratio was smaller than 1:1, preference was more extreme for a 30-s condition than for a 15-s condition. However, preference decreased more rapidly in conditions with the longer terminal-link duration when the ratio increased. Taken together, these results were consistent with previous findings concerning the effect of the terminal-link duration on choice between segmented and unsegmented schedules. In addition, the data suggested that segmentation ratio in a segmented schedule constitutes another potent factor influencing preference for the unsegmented schedule.

Journal Article↗
PubMed1986

Monoclonal antibodies as reversible equilibrium carriers of radiopharmaceuticals.

We have prepared monoclonal antibodies (MoAbs) with the specific ability to bind metal chelates such as 111In benzyl EDTA. One, 10, 50 and 100 micrograms MoAb CHA255 Kb = 4 X 10E9 was complexed with 111In BLEDTA II, BLEDTA IV, and benzyl EDTA and injected i.v. in Balb/c mice with KHJJ tumor. The biological half-life by whole body counting was profoundly altered for all three compounds; from minutes to hours with 10 micrograms; to days with 100 micrograms. Tumor uptake increased 50 fold at 24 h with increasing MoAb but satisfactory tumor concentrations (3% per g) and tumor/blood ratios (1.8:1) were obtained with an amount equivalent to 7 mg for a human. Blood level and whole body activity were decreased 30-50% within 3 h or i.v. injection of a "flushing" dose of unlabeled indium benzyl EDTA, increasing tumor/blood ratios to 50:1.

Animals↗
PubMed1986

Preference for less segmented fixed-time components in concurrent-chain schedules of reinforcement.

A concurrent-chain procedure was used to examine choice between segmented and less segmented response-independent schedules of reinforcement. A pair of independent, concurrent variable-interval 60-s schedules were presented in the initial link, along with a 1.5-s changeover delay. A chained fixed-interval fixed-time and its corresponding tandem schedule constituted the terminal links. The length of the fixed-interval schedule in the terminal link was varied between 5 s and 30 s while that of the fixed-time schedule was kept at 5 s over conditions. The first components of both terminal-link schedules were accompanied by the same stimulus. Except in the baseline condition, the onset of the second component of the terminal-link chained schedule was accompanied by either a localized (key color) or a nonlocalized (dark houselight) stimulus change. Stimulus conditions were constant during the terminal-link tandem schedule. With three exceptions, pigeons demonstrated a slight preference for the tandem over the chained schedule in the terminal link. Furthermore, this preference varied inversely with the length of the first component. In general, these results are consistent with previous studies that reported an adverse effect on choice by segmenting an interval schedule into two or more components, but they are inconsistent with studies that reported preference for signaled over unsignaled delay of reinforcement.

Journal Article↗
PubMed1985

Preference for unsegmented interreinforcement intervals in concurrent chains.

Five pigeons were trained under concurrent-chain schedules in which a pair of independent, concurrent variable-interval 60-s schedules were presented in the initial link and either both variable-interval or both fixed-interval schedules were presented in the terminal link. Except for the baseline, one of the terminal-link schedules was always a two-component chained schedule and the other was either a simple or a tandem schedule of equal mean interreinforcement interval. The values of the fixed-interval schedules were either 15 s or 60 s; that of the variable-interval schedules was always 60 s. A 1.5-s changeover delay operated during the initial link in some conditions. The pigeons preferred a simple or a tandem schedule to a chain. For the fixed-interval schedules, this preference was greater when the fixed interval was 60 s than when it was 15 s. For the variable-interval schedules, the preferences were less pronounced and occurred only when the changeover delay was in effect. For a given type of schedule and interreinforcement interval, similar preferences were obtained whether the nonchained schedule was a tandem or simple schedule. The changeover delay generally inflated preference and lowered the changeover rate, especially when the terminal-link schedules were either short (15 s) or aperiodic (variable-interval). The results were consistent with the notion that segmenting the interreinforcement interval of a schedule into a chain lowers the preference for it.

Journal Article↗
PubMed1981

Characteristics of membrane and cytosol forms of the mammary tumor glycoprotein molecule MTGP in human breast carcinoma cell cultures and tumors.

The presence, concentration and selected molecular characteristics of the human mammary carcinoma glycoprotein molecule set MTGP, a trace and apparently tumor-specific molecule, were examined in fifteen cell cultures established from mammary carcinomas, tissue from seven mammary carcinomas and control cultures. Both cytosol and membrane-associated forms of MTGP were analyzed, and each was phenotyped by reference to isoelectric point and buoyant density. All cells or tissues of mammary carcinoma origin contained membrane MTGP, whereas cytosol MTGP was undetectable in cell cultures from half of the mammary carcinomas. Neither membrane nor cytosol MTGP were detectable in cells other than mammary carcinomas. Cytosol MTGP could be assigned to three groups by reference to presence, isoelectric point and buoyant density. Membrane MTGP also exhibited heterogeneity between different tumors and could be assigned to three groups by isoelectric point and buoyant density. Each form of MTGP was homogeneous for a given single tumor or cell culture and retained its phenotypic features with passage and cloning. Four general types of MTGP are proposed, through there may be additional fine heterogeneity that cannot be further resolved at this time. These data provide an initial characterization of the membrane form of MTGP and an integrated characterization that is consistent with the concept that tumor-specific antigens may possess both constant regions by reference to antigens recognized by the antisera and variable structure by reference to physicochemical characteristics.

Antigens, Neoplasm↗
PubMed1980

Radioimmunoassay for tissue distribution of a human mammary tumor-specific glycoprotein.

The candidate tumor-specific soluble mammary tumor glycoprotein with a molecular weight of approximately 20,000 (MTGP20) has been isolated from human breast carcinomas and characterized biochemically. Although with the use of xenoantisera this glycoprotein has previously been demonstrated only in breast carcinomas, analyses of body fluids and conclusions regarding putative tumor specificity have been limited by the sensitivity of assays. In the present study, a specific radioimmunoassay has been developed. With appropriate selection of buffer, the assay has a sensitivity threshold of less than 0.1 unit of MTGP20 per ml, equivalent to less than 250 pg type I MTGP20 per ml or less than 530 pg type II MTGP20 per ml, which is more than 200-fold more sensitive than previously described assays. MTGP20 type I, which contains tyrosine, was labeled with 125I and used as the immunochemical ligand in a double antibody competitive inhibition assay. A partial weak cross-reaction was observed with a mixture of placental glycoprotein (perchloric acid extract), but this reaction was abolished by absorption of antisera with placental glycoprotein. Normal tissue and tumors of other than breast origin were devoid of MTGP20-related antigens. MTGP20-related antigens were not detectable in sera or concentrated urine specimens from normal individuals or patients with metastatic breast carcinomas. The present studies further support the probable tumor specificity of this glycoprotein but indicate that it does not represent a circulating secretory product of the cancer cell and does not provide a serum marker for breast carcinoma.

Animals↗
PubMed1980

Subcellular localization of the sedimentable form of mammary tumor glycoprotein to the tumor cell plasmalemma.

A form of mammary tumor glycoprotein (MTGP) has been observed to be associated with the sedimentable fraction of homogenates of human carcinomas of the breast. A MTGP-containing breast carcinoma cell line, HS-578T (AY-726), containing both soluble and sedimentable forms of MTGP, was fractionated by differential ultracentrifugation, discontinuous sucrose gradient and on a polyethylene glycol-dextran gradient. The separated crude nuclei fraction, crude mitochondrial fraction, disrupted organelles, ribosomes and rough microsomes, smooth microsomes, and plasmalemma were characterized by electron microscopy and enzymatic markers which confirmed that each fraction was highly enriched in the respective subcellular constituents. Analysis of insoluble MTGP demonstrated significant coisolation with the plasmalemma. On the basis of the present data showing that the sedimentable form of MTGP is firmly associated with the plasmalemma and previous evidence showing the specificity of MTGP for breast carcinoma cells and the surface exposure of MTGP on viable cells, we conclude that sedimentable MTGP is an integral membrane glycoprotein that could have biological significance in the behavior or immunobiology of these tumors.

Breast Neoplasms↗