Biomedical subjects

L P Kok

Publications and source records attributed to L P Kok.

At least 19 recordsLinked to original sources

PubMed1992

A model for quantitative follow-up studies of cervical lesions.

A model for follow-up studies of cervical lesions is described in which the specimen were taken in a noninvasive way using Cytobrushes and in which automatic measurement of the abnormal nuclei in the sampled epithelial fragments was possible because 2-microns thin Feulgen-stained plastic sections were prepared. The planimetric parameters AREA, PERIMETER, FORM PE, and FORM ELL, and the densitometric parameters optical density (OD) and integrated optical density (IOD) were assessed. The mean total volume and the mean total DNA were calculated using stereological methods. The moderate dysplasias differed from the carcinoma in situs for all the densitometric parameters except for OD, and from the invasive carcinomas for IOD and 5cER. In the moderate-dysplasia group, there were three types of DNA histograms: a highly abnormal type resembling the histograms of the carcinoma group, a normal type, and an intermediate type. Changes in DNA histograms can be established during follow-up studies of dysplasias without having disturbed the lesion due to the efficient and elegant noninvasive sampling method that was not used in earlier quantitative studies.

Carcinoma in Situ↗

PubMed1992

Microwave irradiation and cross-linking of collagen.

In a multifactorial experiment, dermal sheep collagen was treated in diluted glutaraldehyde solutions, 70% ethyl alcohol, Cialit 1:5000, and distilled water for 1, 3 and 5 min, respectively, in combination with microwave irradiation at different temperature settings. The shrinkage temperature indicating the degree of cross-linking achieved was then determined. Treatment in 0.65% glutaraldehyde with microwave irradiation setting for 60 degrees C resulted in the maximum shrinkage temperature within 1 min, whilst at the lower setting of 50 degrees C, the maximum shrinkage temperature for both glutaraldehyde solutions is only reached after 5 min. Neither microwave irradiation by itself, Cialit or ethyl alcohol induce cross-linking of collagen fibres. These findings are relevant for implant studies.

Animals↗

PubMed1992

Psychiatric disorders associated with burns.

A study was made of burns patients who were referred for psychiatric problems. There were a total of 69 subjects, divided into three groups. The first group comprised thirty-four cases who attempted suicide by burning themselves--there were more women than men, the majority were less than forty years, and Indians were overrepresented. The majority of these were suffering from schizophrenia or a major depressive disorder. The second group of twenty-three patients were those who had a non-psychotic psychological reaction to their burns. The majority were also less than 40 years of age, and the main reactions were anxiety neurosis or reactive depression. The third group of twelve patients were suffering from delirium. All were pyrexic and in eleven, infective agents were cultured. Some of them also had electrolyte abnormalities and two had respiratory burns.

Adjustment Disorders↗

PubMed1992

A survey of sexual behaviour of Singaporeans.

In order to plan education programmes against sexually transmitted diseases (STDs) and HIV infection, a population-based survey on partner relations was conducted on 2,115 Singaporean men and women aged between 15 and 49 years. Of the 605 (60.1%) sexually experienced men and 647 (58.3%) sexually experienced women, 510 (84.3%) men and 644 (99.5%) women were married. Of the marrieds, 465 (76.9%) men and 638 (98.6%) women had their first sexual encounter with the person who was or later became their spouse. Of the sexually experienced men, 97 (16%) engaged in casual sex in the previous year, of which 76 (78.4%) were encounters with commercial sex workers. Of these encounters 55 (72.4%) were unprotected or partially protected by condoms. A history of casual sex in the previous four weeks was given by 18 men, of whom 14 (77.8%) were married. Nine (64.3%) of these married men had sex concurrently with both their wives and commercial workers. Persons at high risk were those who started sexual activity early, unmarried, sexually active men with no or low education, and persons who travelled. Of the sexually experienced respondents, 1,242 (99.2%) had heard about condoms, and 431 (34.4%) were currently using them as contraceptive devices. Attitudes towards condoms and willingness to use them to prevent STDs and HIV infection were favourable. Men were more permissive in their attitudes towards sex. The level of permissiveness in men and women was not corroborated by their reported behaviour, an indication of either under-reporting and/or a disparity between attitude and practice.

Adolescent↗

PubMed1991

ELISA incubation times can be reduced by 2.45-GHz microwaves.

The ELISA (Enzyme Linked Immuno Sorbent Assay) technique is widely applied in the field of immunology. The use of this technique implies several incubation periods, often requiring more than one hour each. Microwave irradiation is known to be very useful in accelerating different kinds of processes. This knowledge has led to the present study in which it is proved that 2.45-GHz microwaves are able to reduce ELISA incubation times. This time reduction of 50% or more concerns each of the four incubation steps of the specific indirect ELISA which is used to determine the amount of antibodies in NF90-hybridoma cell culture supernatants. These incubation steps involve the coating of the microtiter plate, the incubation with BSA against non-specific binding, and the incubations with the first and second antibody. Combinations of more microwave-influenced steps in one ELISA save a considerable amount of time. When in addition air is blown through the incubation fluid during microwaving, the extinction values are almost the same as those of conventionally performed ELISAs. Thus, a good match of power setting and irradiation time results in a total incubation time reduction from 5.5 hours to 2 hours in this particular ELISA. Carefully monitoring the temperature of the incubation fluids during irradiation with the use of a fiberoptic thermometer appeared to be of crucial importance in the development of an optimal procedure.

Enzyme-Linked Immunosorbent Assay↗

PubMed1991

Formalin is deleterious to cytoskeleton proteins: do we need to replace it by formalin-free Kryofix?

Formalin is hazardous for the environment and for the laboratory personnel and deleterious to cytoskeleton proteins. The pathology and anatomy laboratory can be formalin-free when Kryofix is used as a substitute fixative. In four years experience with Kryofix, we learned that immunostaining on paraffin sections is reproducible and of excellent quality. The current study concerns the comparison of interfilament staining on paraffin sections made from formalin or from Kryofix-treated tumors. For both keratin and vimentin there were false-negative findings in the formalin-fixed tumors. Of these two, vimentin was het most susceptible to formalin fixation. Three of the ten adenocarcinomas were positive for both keratin and vimentin, indicating that this double staining pattern is not uncommon. Postfixation of Kryofix-treated tissue with formalin results in false-negative immunostaining.

Adenocarcinoma↗

PubMed1991

Profile of a homosexual in Singapore.

A study was done on 40 homosexual subjects and 47 controls between the ages of 18-19 years, matched for race and age. There was no significant difference in the educational level, and family background of the 2 groups. But homosexuals had a significantly more unhappy childhood than the controls, were more often reprimanded than physically punished and were often teased by their classmates and called names. They were not overprotected or infantilized by their parents and there was no overclose relationship with their mothers. The majority mixed with effeminate boys, admired a senior person in school and about a third had a physical relationship with this person. Almost half had been molested when they were young. Less than a fifth had girlfriends. About three-quarters knew of AIDS and of these less than a fifth felt they would give up their sexual practices because of fear of AIDS. The main problems faced by the subjects were confusion about their identity, their desire to find the right partner, relationship problems and difficulties in controlling their impulses.

Adolescent↗

PubMed1991

Morphometry, densitometry and pattern analysis of plastic-embedded histologic material from urothelial cell carcinoma of the bladder.

An image analysis method of grading histologic sections of bladder carcinoma was tested. The method was new in four respects. First, for fixation of the biopsies a coagulant fixative was used. Second, 2-microns plastic sections were used to ensure the reproducibility of nuclear imaging. Third, a new stereologic approach was used for calculation of the nuclear volume and DNA content. Fourth, for the classification rule the morphometric, densitometric and texture features were used in concert. The IBAS 2000 instrument was used for the measurements. Texture analysis of the chromatin patterns was performed using Markovian texture features. Using discriminant analysis, of 22 parameters, 2 morphometric, 2 densitometric and 3 texture features were selected for the classification rule. With them, 89% of the bladder carcinomas were correctly classified into the three grades. All grade III tumors were classified correctly. Among the features tested, the densitometry of the DNA had the highest F values. All of the grade III tumors and 45% of the grade II tumor group had DNA histograms indicating aneuploidy. This study showed that plastic-embedded material is well suited to morphometry and densitometry and can be used for quantitative grading of bladder carcinoma.

Carcinoma, Transitional Cell↗

PubMed1990

Immunocytochemistry on free-floating sections of rat brain using microwave irradiation during the incubation in the primary antiserum: light and electron microscopy.

We studied the effects of microwave irradiation during the incubation of free-floating brain sections with primary antibodies against gamma-aminobutyric acid (GABA), enkephalin and vasopressin. Vibratome sections of perfusion-fixed rat brain were incubated: (a) overnight at room temperature (20-22 degrees C), (b) during various periods of time under microwave irradiation, such that the induced temperatures did not exceed 10 degrees C, (c) same as (b) but with induced temperatures not exceeding 40 degrees C, (d) without microwave irradiation, at 4-10 degrees C (temperature control for (b)), (e) same as (d) but at 40 degrees C (temperature control for (c)). During the incubation-irradiation we continuously monitored the temperature and controlled it by cooling and by manipulating the energy output of the magnetron. The peroxidase immunocytochemical procedure was completed using for all sections the same incubation parameters. Selected GABA-immunoreacted sections were examined in the electron microscope. Incubation at 10 degrees C in the primary antiserum as short as 30 min, with or without microwave irradiation, already results in (weak) binding of the antibodies to immunoreactive structures. One or 2 h of incubation in the primary antiserum in the microwave oven at 40 degrees C or at the same temperature outside the microwave oven results in excellent staining of GABA-immunoreactive structures and of good staining of enkephalin- or vasopressin-immunoreactive structures. The ultrastructural details were much better preserved in incubated-irradiated sections than in sections incubated overnight and only slightly less preserved than in the other control sections. There is no improved penetration of the antibodies into the sections. We conclude that by using microwave technology or by raising the temperature of the incubation medium, the time of incubation, at least in these antisera, can be shortened drastically, whereas the ultrastructural details remain well preserved.

Animals↗

PubMed1990

Microwaves for microscopy.

Sample preparation for microscopy is based on physical and chemical processes. These processes can be influenced by microwave irradiation. The prerequisite for the development of good microwave procedures is knowledge of histochemistry combined with understanding of the physics of microwave irradiation. Examples of superior results of fixation, processing, and (immuno) staining performed in the microwave oven are presented, both for light- and electron microscopy.

Animals↗

PubMed1990

Microwave-stimulated brain enzyme incubations are possible at the unphysiological condition of 50 degrees C.

Microwave-stimulated enzyme incubations for acetylcholinesterase, 5'-nucleotidase, alkaline phosphatase, lactate dehydrogenase, malate dehydrogenase, succinic dehydrogenase and isocitric dehydrogenase were studied, and compared with incubations in a waterbath. Temperature settings of 37 degrees C and 50 degrees C were used, and the incubation times were varied from 30 seconds to 30 minutes. The desired temperature of the incubation solution was reached in the microwave oven within 1 minute, whilst in the waterbath it took 10 to 25 minutes. The microscopic results for alkaline phosphatase and succinic dehydrogenase at a temperature setting of 50 degrees C were superior in the microwave method for incubation times less than 15 minutes. It is postulated that the increased reaction product of alkaline phosphatase and succinic dehydrogenase is due to a temperature effect, which has to be large enough to be of practical value. For the other enzymes studied, microwave-stimulated incubations were no better than the conventional incubations at corresponding temperatures. For 5'-nucleotidase there were aspecific lead deposits in the microwave method. All enzymes performed at the elevated, unphysiological temperature of 50 degrees C proved to have advantages, except for 5'-nucleotidase, whilst for malate dehydrogenase there was an aspecific reduction of the colour developer at this temperature.

Animals↗

PubMed1990

A psychosocial study of high risk subjects for AIDS.

A psychosocial study of 5 high risk groups for AIDS (50 homosexuals, 50 drug addicts, 23 male to female transsexuals, 45 male patients at a sexually transmitted disease clinic, and 43 female prostitutes) and 5 matched control groups showed that the majority of the subjects were mostly single, with a secondary level of education and lived with family members. Although all had a high risk of AIDS, condom use was not prevalent. The subjects were less knowledgeable about AIDS than controls, were more anxious about getting AIDS and had a more hopeless and pessimistic outlook to life; however they appeared to be as altruistic and responsible as the controls.

Acquired Immunodeficiency Syndrome↗

PubMed1989

Human papillomavirus (HPV)-associated male and female genital carcinomas in a Hindu population. The male as vector and victim.

Epidemiologic, histologic and immunohistochemical data concerning male (penile) and female (cervical and vulvar/vaginal) genital carcinomas in a Hindu population are reported. The data are from Bali, an Indonesian Hindu island in a country with a predominantly Muslim population. In contrast to the surrounding Muslim population, circumcision is rare in the people of Bali, and the rate of phimosis in grown men is very high. The Balinese epidemiologic data of 1985 to 1986 were compared with 1986 data from The Netherlands. In Bali, cervical carcinoma was the most frequent carcinoma in women, and vulvar/vaginal carcinoma ranked seven. These carcinomas were much less frequent in The Netherlands. In Balinese men, penile carcinoma is the second most frequent carcinoma, whereas it is rarely diagnosed in The Netherlands. Penile carcinomas are found in Bali in younger age groups than in The Netherlands. Based on the immunohistochemical staining results, it is estimated that over 75% of the studied Balinese genital carcinomas contain human papillomavirus (HPV). The data presented in this paper may indicate that the cofactor of impeded postcoital hygiene can be of great importance for male and female HPV-associated genital carcinogenesis. It is clear that Balinese men, in particular men with extreme phimosis, are both vectors and victims of HPV. In The Netherlands the man is exclusively the vector of HPV.

Adult↗

PubMed1989

Microwave treatment of xenogeneic cartilage transplants.

Human rib cartilage was irradiated with microwaves according to six different methods and transplanted into rabbits. Untreated rib cartilage preserved in Cialit served as a control. After 12 and 40 wk of implantation, the microscopic appearance of these xenogeneic cartilage transplants was given a score in comparison with the transplants preserved in Cialit. The microwave treatment of the cartilage appeared to improve the results. The Cialit-preserved transplants showed progressive resorption by macrophages with central necrosis and fragmentation, which was not present in the microwave-treated grafts. Microwaves seem to stabilize the cartilage matrix and enhance the diffusion of fixatives. Irradiation in ethanol as an immersion fluid appeared to be the best method. The results of transplantation can benefit from the use of microwaves in the preservation of the cartilage. It is argued that, in addition, microwave irradiation might be used for inactivation of human immunodeficiency virus in human cartilage used for transplantation.

Animals↗

PubMed1989

Accelerated immunogold silver and immunoperoxidase staining of paraffin sections with the use of microwave irradiation. Factors influencing results.

With the use of microwave irradiation, incubation times for the immunotechniques used in immunomicroscopy can be shortened significantly. The authors found that factors influencing results are irradiation time, power output, and presence of gold label. Precise temperature control is essential, and techniques to achieve this are discussed. For beta-human chorionic gonadotropin (beta-HCG), the results with the immunoperoxidase technique were inferior to those of the conventional technique, and with the immunogold silver technique an enhancement of labeling results was achieved. Immunogold silver staining for beta-HCG on paraffin sections can be performed with the use of microwave irradiation within one hour.

Histological Techniques↗

PubMed1989

Cerebral tumours presenting with psychiatric symptoms.

Four cases of cerebral tumours presenting with psychiatric symptoms were referred to the psychiatrist for management. They displayed some degree of cognitive impairment, notably impaired memory for recent events, and nominal aphasia. Clinical neurological examinations were generally unremarkable with no evidence of focal signs or features of raised intracranial pressure. CT scan demonstrated parietal lobe lesions in all four patients with two showing involvement of the frontal lobe, one the temporal lobe and another the occipital lobe as well. Only one patient was operated, two died and the last continued treatment elsewhere. Factors contributing to the psychiatric symptomatology of cerebral tumours are raised intracranial pressure, location of the tumour, nature of the tumour and the individual constitution and response of the patient.

Brain Neoplasms↗

PubMed1989

Hypnotic susceptibility in kavadi carriers in Singapore.

A group of fourteen Hindu devotees, who participated in a religious ceremony involving piercing of tongue and body by metal skewers, and the carrying of 'kavadis' were examined to ascertain their hypnotisability, and to compare their experiences during hypnosis and a trance. They were found to have a low mean score of 3.85 on the Revised Stanford Profile Scales of Hypnotic Susceptibility. Those who have higher scores had experiences during the religious ritual which appeared to be similar to those in the hypnotic state.

Adolescent↗

PubMed1989

Diminished responsibility--a psychiatric viewpoint.

Diminished responsibility is based on the notion that mental disorder may make a person only partially accountable for his act in the killing of another person. For this plea to succeed it has to be shown that an accused has to be suffering from such an abnormality of mind that his responsibility for the action is substantially diminished. As these concepts of abnormality of mind and criminal responsibility do not fit easily into psychiatric classification of mental disorders, nine senior psychiatrists who regularly attend court as expert witnesses were surveyed and their viewpoints about mental abnormality and diminished responsibility were elected.

Attitude of Health Personnel↗