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Biomedical subjects

V Navaratnam

Publications and source records attributed to V Navaratnam.

At least 73 records · Page 4Linked to original sources
PubMed1986

Ultrastructure of the ventricular myocardium of the bat Eidolon helvum.

Ultrastructural studies, including a preliminary morphometric analysis, of the right ventricular myocardium in the West African bat Eidolon helvum show that the myocytes contain a wider T-tubule system and a higher proportion of mitochondria and lipid droplets than in typical terrestrial mammals such as the rat; these features in the bat are even mor pronounced than in hibernating species such as the golden hamster. In addition to having coupling arrangements with T-tubules and surface sarcolemma, cisterns of junctional sarcoplasmic reticulum are closely apposed to mitochondria and lipid droplets.

Animals↗
PubMed1986

Differentiation of the myocardial rudiment of mouse embryos: an ultrastructural study including freeze-fracture replication.

The differentiation of the myocardial rudiment was examined in mouse embryos, isolated between the afternoons of the eighth and ninth days of gestation, by means of transmission electron microscopy of ultrathin sections and of freeze-fracture replicas; some of the material used for sectioning was labelled with ruthenium red. Formation of the presumptive pericardial cavity commences during the late presomite stage (afternoon of the eighth day) and the myocardial rudiment originates in situ as a thickening of the splanchnic pericardial lining. Initially, the myocardium comprises an epithelium or plate directly exposed to the pericardial lumen and overlying a separate layer of endocardial elements. As the heart tube bulges into the pericardial coelom, it becomes surrounded by a sleeve of myocardium which thickens and stratifies during the ninth day and subsequently (on the tenth day) acquires an epicardial covering of flattened cells. The myocardium commences pulsations at or about the 3-4 somite stage (morning of the ninth day) by which time the myoblasts already contain striated myofibrillae and specialised cell junctions. From its earliest appearance, the myocardial plate contains tight junctions and desmosomes between the lateral borders of the apical parts of the myoblasts. Gap junctions soon appear in the same regions and they increase in number and extent, as the myoblasts elongate and divide, thus establishing contact in various planes; they are supplemented by the formation of fasciae adherentes and of more desmosomes. On the other hand, tight junctions decline in extent and are eventually confined to the epicardium. Other features such as caveolae and T-tubules are not established by the end of the ninth day and coupling arrangements of the sarcoplasmic reticulum are only in the rudimentary stages of formation.

Animals↗
PubMed1986

Variations in the structure of nexuses in the myocardium of the golden hamster Mesocricetus auratus.

The structure of nexuses in the atrioventricular node of the golden hamster was studied with the transmission electron microscope, using thin sections and freeze-fracture replicas, and was compared with that of nexuses in the working myocardium of the right ventricular wall. Whereas ventricular myocardium contained macular nexuses only, nodal tissue contained annular and linear configurations as well as maculae of varying size. The significance of such variations in nexus pattern is not clear although several hypotheses are discussed in the literature. Measurements made on electron micrographs, after allowing for tilt of the specimen, yielded a particle diameter of 10.59 nm for nodal myocardium and 10.95 nm for ventricular myocardium, both measurements being substantially higher than figures generally cited in the literature. In each area the measurements had a normal distribution suggesting a single type of particle. The small but significant difference in particle size between the two areas is more likely to be caused by dissimilarities in packing arrangement rather than by differences in intrinsic structure or in functional state.

Animals↗
PubMed1981

Differentiation of alpha-adrenergic responsiveness in the neonatal rat iris after decentralization or extirpation of the superior cervical ganglion.

The effects of stimulating alpha-adrenergic receptors in the iris of neonatal rats (up to 30 days of age) whose superior cervical ganglion (SCG) has been decentralized or extirpated 3 days after birth were investigated by measuring changes in pupil diameter. The responses of these experimental animals were compared with those of normal animals of similar age. Alpha-adrenergic stimulation was effected by topical application of noradrenaline (NA) after blockade of beta-adrenoceptors with dichlorisoproterenol and cholinoceptors with atropine. The results reveal that although decentralization of the SCG depletes the NA content of the ipsilateral iris as demonstrated by radio-chemical assay and formaldehyde-induced fluorescence, it does not affect the development of alpha-adrenoceptor responsiveness. Even the more severe disruption of the innervation caused by extirpation of the SCG did not affect the responsiveness of the ipsilateral iris.

Aging↗
PubMed1981

Ultrastructural changes in atrial myocardium of the ageing rat.

Ageing changes in the fine structure of atrial myocardial cells were studied in rats ranging from 2-32 months in age. The most striking change observed was the increasingly frequent appearance, from about 6 months onwards, of helically aggregated strands containing filaments which in respects other than arrangement bore resemblance to thick myofilaments. Other ageing changes included the accumulation of dense bodies and various types of mitochondrial degradation.

Aging↗
PubMed1981

The ultrastructure of myocardial cells in the golden hamster Cricetus auratus.

Electron microscope studies of the myocardium of the golden hamster revealed that the primary T-tubules in ventricular and atrial myocytes are substantially wider than their counterparts in most other mammalian species. Another feature is the presence of numerous lipid bodies but these are not as closely apposed to mitochondria as in seal myocardial cells. General atrial myocardial cells in the hamster contain numerous electron-dense spherical granules but these are absent from cells of the nodal and conducting system; in regard to these latter features in hamster resembles most other mammals.

Animals↗
PubMed1981

Early differentiation of the heart in mouse embryos.

The differentiation of the heart was examined in mouse embryos, isolated between the afternoons of the eighth and ninth day of gestation, by means of scanning electron microscopy as well as by light microscopy of standard histological material and thin plastic sections. Cavitation within the presumptive pericardial mesoderm commences during the late presomite stage (afternoon of eighth day) and myocardial rudiments are established by thickening of the pericardial lining adjacent to the endoderm near the base of the foregut pocket. At first the thickening lies on the ventral aspect of the pericardial cavity but, as the foregut pocket deepens and the trunk region of the embryo moves en masse caudally and ventrally, it comes to lie on the dorsal wall. A separate layer of cells comprising the primitive endocardium differentiates deep to the myocardial thickening, between the latter and the endoderm. Cavitation of the endocardial tissue occurs bilaterally about the 1-2 somite stage so as to establish bilateral endocardial tubes. These endocardial tubes become enclosed within the myocardial mantle which bulges into the pericardial cavity. A layer of acellular material (the cardiac jelly) appears between the endocardium and myocardium at about this time. At about the 4-somite stage, the endocardial tubes coalesce across the mid-line to establish a single median cardiac tube, and the entire heart rudiment is suspended in the mid-line by a wide dorsal mesocardium. Our observations indicate that, contrary to previous views, at no time during cardiogenesis in the mouse are two distinct heart primordia present which subsequently fuse to form a single median entity. The principal similarities and differences between cardiogenesis in the mouse, and mammals in general, and avians are discussed.

Animals↗
PubMed1980

Social background and attitudes towards drugs as predictors of drug use among Malaysian students.

Those Malaysian secondary schoolchildren who have ever used an illicit drug do not differ significantly in terms of social class background, ethnicity or rural/urban location, from the majority of their contemporaries who have not used drugs. The cross-sectional data show a rapid secular trend towards the sexes being equally involved in drug use. Significant differences between ever and never users are, however, found in their attitudes towards drug taking and their beliefs about the properties of drugs, although both groups share the same rather negative image of the typical drug user. Thus, drug users have accepted some of the attitudes towards drug issues which are normative in the non-user group, whilst developing other attitudes which are consistent with their continuing use. It is argued that adolescent drug abuse in Malaysia is not to be linked specifically with social deprivation, but should be seen as being part of the life style of particular groups in all strata of society.

Adolescent↗
PubMed1980

Social attitudes, self-description and perceived reasons for using drugs: a survey of the secondary school population in Malaysia.

The present paper is the third and concluding part of a study of the secondary school population of two of Malaysia's thirteen states, Penang and Selangor. Since completion of the two earlier papers, the research team has investigated the pattern and nature of drug use among the equivalent population in a third state, Kelantan, and has again found essentially the same pattern of results: youthful drug use is most clearly related to precocious self-assertion, and a set of beliefs and attitudes about drugs and drug taking, and is largely unrelated to indicators of social deprivation or personal problems. The significance of this repeated finding in Kelantan is that, in this much more rural and traditional state, adult and established patterns of drug use had historically differed considerably from those found in the two more urban and cosmopolitan states of Penang and Selangor. Our findings indicate that the new pattern of drug use by youth has transcended the older cultural differences between the states, and is in turn explained by a more universally familiar set of characteristics in adolescent development.

Achievement↗
PubMed1980

Patterns of drug use amongst Malaysian secondary schoolchildren.

A representative sampling of the secondary school population of two states of Malaysia (sample size 16166) indicated that 11% of students had had experience of drug use. Use of a single drug was the common pattern, with cannabis reported most often by older students, and sedatives most often by younger students. A quarter of those who had used drugs reported experience with four or more substances and were likely to have progressed rapidly to heroin. This progression may be facilitated by the ready availability of heroin and the local tradition of smoking or inhaling rather than injecting opiates. Descriptions of drug migration patterns based on Western samples are not fully appropriate worldwide, because the youthful abuser is much influenced both by local market forces and by cultural traditions, even though the epidemic of youthful drug abuse is itself worldwide.

Adolescent↗
PubMed1980

Legal sanctions and information about drugs as influences upon the decision by adolescents whether to use illicit drugs.

Although those Malaysian secondary schoolchildren who have never used drugs are consistent in their support for legal and social sanctions against drug use, it is argued that such sanctions are a relatively unimportant factor in the decision whether or not to use drugs. Non-drug users inhabit a social world separated from their drug-using contemporaries; they rely on information from public rather than direct social sources, and claim to have been little interested in information received. However, there is evidence that, for a minority of the drug-using sub-sample, public information campaigns have made them more rather than less interested in experimenting with drug substances.

Adolescent↗
PubMed1980

Traditional therapies and the treatment of drug dependence in Southeast Asia.

Many countries in Southeast Asia have the experience of traditional treatments of drug dependence, or have healers who are extending traditional methods to meet contemporary needs. Some treatments, for example those used in some Buddhist monasteries in Thailand and clinics in Japan, rely upon the philosophical and religious traditions of the country; others come closer to faith healing and magic in their practices; and many use herbal preparations during detoxification and afterwards, as well as offering spiritual or secular therapy. This paper argues that careful evaluation be made of the methods and outcome of these traditional treatments of drug dependence and summarizes some of the evidence so far published.

Acupuncture Therapy↗
PubMed1978

The T-tubule system in the specialized and general myocardium of the rat.

The T-tubule system in cardiac muscle cells has been investigated with the electron microscope in 10 adult rats after infiltration with horseradish peroxidase. All cardiac muscle cells possess a T-system, but its complexity varies according to the region of the heart. It is most extensive in the general ventricular myocardium where there are primary, secondary and tertiary transverse tubules as well as longitudinal elements, and there are numerous couplings between the T-system and the sarcoplasmic reticulum (SR). The T-system and associated SR couplings are less extensive in the atrium and in the atrioventricular conducting system. It is least well developed in the nodes, particularly in the sinuatrial node, where it is restricted to primary T-tubules. There are numerous SR couplings with the sarcolemma in all types of cardiac muscle cells. Where intercalated discs occur, SR couplings are associated with non-specialized parts of the disc. The possible significance of these ultrastructural features in regard to the speed of conduction by myocardial tissues, and in the excitation-contraction sequence is discussed.

Animals↗