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Biomedical subjects

C K Tan

Publications and source records attributed to C K Tan.

At least 127 records · Page 7Linked to original sources
PubMed1981

Ultrastructural changes after intracisternal injection of 6-hydroxydopamine in the intermediolateral nucleus of the monkey (Macaca fascicularis).

The ultrastructural changes following a single intracisternal injection of 6-OHDA were studied in the intermediolateral nucleus of the monkey spinal cord. Post-operative survival periods ranged from 20 hours to 14 days. At all stages, only boutons containing clear, round vesicles (R-boutons) and those containing dense-cored vesicles (DCV-boutons) underwent degeneration. Boutons containing flattened vesicles (F-boutons) appeared to be unaffected. Changes were seen even at 20 hours after injection and these were confined to R-boutons only. The changes included an initial swelling and crowding of the vesicles, followed by an increase in the electron density of the axoplasm. The latter change was most marked on the second post-operative day and by the third day, most of the electron-dense profiles were glia-engulfed. By the third day, also, many unmyelinated and, occasionally, myelinated axons showed accumulations of mitochondria, membrane-bound tubular profiles and electron-dense bodies. Many astrocytic processes also showed accumulation of tubular profiles. From the fifth day onwards, few degenerating R-boutons were encountered but DCV-boutons containing swollen vesicles, with or without their dense cores, were obvious. Unmyelinated and, occasionally, myelinated axons and astrocytic processes containing tubular elements still continued to be seen. By the fourteenth post-operative day, degenerating profiles were rarely observed. The probable significance of these findings has been discussed in the light of recent anatomical and biochemical studies.

Animals↗
PubMed1980

Purification of deoxyribonucleic acid polymerase delta from calf thymus: partial characterization of physical properties.

Deoxyribonucleic acid (DNA) polymerase delta has been purified 7800-fold from calf thymus, to a specific activity of 28 000 units/mg of protein. Similar to DNA polymerase delta from bone marrow [Byrnes, J.J., Downey, K. M., Black, V. L., & So, A. G. (1976) Biochemistry 15, 2817], the calf thymus enzyme is associated with 3'- to 5'-exonuclease activity. Both DNA polymerase and 3'- to 5'-exonuclease activities copurify on hydroxylapatite, DNA-cellulose, and molecular sieve chromatography. The ratio of exonuclease activity to polymerase activity is approximately 1:12. When the most highly purified fraction is subjected to polyacrylamide gel electrophoresis under nondenaturing conditions, both DNA polymerase and exonuclease activities have the same mobility at several acrylamide gel concentrations. Isoelectric focusing experiments have shown that both activities have the same pI. These data suggest that 3'- to 5'-exonuclease activity is an intrinsic property of DNA polymerase delta. The molecular weight of the enzyme, as estimated from measurements of Stokes radius and sedimentation coefficient, is 152 000.

Animals↗
PubMed1980

Experimental degeneration of motor and sensory cortical terminals in the cuneate nucleus of the monkey (Macaca fascicularis).

A total of nine monkeys (Macaca fascicularis) of both sexes was used for the present study. Eight monkeys were used for either motor or sensory cortical lesions, and were allowed to survive for 1--7 days post-operatively. No degenerating nerve terminals were observed 1 day following either motor or sensory cortical lesions. After a motor cortical lesion, most degenerating terminals were seen on the third and only a few on the fifth day. Following a sensory cortical lesion, most degenerating terminals were seen on the fifth and fewer on the third and seventh days. Two types of degenerative changes were observed: granular and electron-dense. Granular change was more evident after the shorter survival periods, while the electron-dense type of degeneration was more commonly seen in animals which were allowed to survive longer after operation. The cortical axon terminals were small and contained either round or flattened synaptic vesicles. Most of those axons containing flattened vesicles originated from the sensory cortex, but a few came from the motor cortex. Vice versa, most of those axons containing round vesicles appeared to arise from the motor cortex and only a few from the sensory cortex. Cortical axon terminals containing round synaptic vesicles formed asymmetrical synapses with small to medium-sized dendrites poor in organelles. In a few instances such cortical terminals were observed to be postsynaptic to other axon terminals containing flattened vesicles. No cortical axon terminal was observed to terminate presynaptically on another axon terminal. Cortical terminals containing flattened vesicles formed symmetrical synapses with dendritic profiles of varying diameters, some of which were the proximal dendrites of Group II neurons. No cortical axon terminals containing flattened vesicles have been observed to form axo-axonal synapses in the cuneate neuropil.

Animals↗
PubMed1980

The fine structure of the intermediolateral nucleus of the spinal cord of the monkey (Macaca fascicularis).

An electron microscopical study of the intermediolateral nucleus of the monkey has shown that the neurons could be classified into at least three main types. The perikarya and proximal dendrite of Types I and II neurons were almost completely covered with astrocytic processes. Both these types of neurons were characterized by prominent profiles of rough endoplasmic reticulum arranged in parallel stacks in Type I and in small aggregates in Type II. The Golgi apparatus was well developed in both types. In contrast, Type III neurons, which were consistently smaller than the other two types, were only partially covered by astrocytic processes, their meagre RER consisted of single short strands of ribosome-studded cisterns randomly dispersed in the cytoplasm and their Golgi apparatus was poorly dveloped. The nuclear outline of all three types of neuron was irregular, but that of Type III neurons was deeply indented. Axosomatic synapses were rarely observed in Types I and II neurons but were common in Type III neurons. Axon terminals in the intermediolateral nucleus could also be divided into three main classes according to their synpatic vesicular morphology. R-boutons contained round agranular vesicles, DCV-boutons contained a mixture of agranular and large dense-cored vesicles and F-boutons contained flattened or ellipsoidal vesicles. All three classes of axon terminals formed simple axodendritic synapses and also took part in the formation of glia-encapsulated glomerular synapses in which the most common arrangement was that of a central dendrite which was synaptically contacted by axon terminals. F-boutons formed axosomatic synapses with all three types of neurons, R-boutons synapsed commonly on Type III neurons and only occasionally on Type II neurons, while DCV-boutons were rarely seen to form axosomatic synapses. No axo-axonal synapses were observed.

Animals↗
PubMed1980

Innervation of the muscularis externa in the stomach of a coral fish, Chelmon rostratus Cuvier.

The muscularis externa of the stomach of the coral fish, Chelmon rostratus Cuvier, consists of four discrete layers - an outermost longitudinal layer followed by a circular, an oblique and an innermost layer. The muscle bundles of the oblique layer appear to be surrounded by thin prolongations of the innermost layer. In longitudinal sections of the innermost layer only rarely were small bundles of unmyelinated axons seen to course between the muscle cells. Vesiculated axon profiles within such nerve bundles occasionally came into apposition with the surface of muscle cells. The number of cross sectioned muscle fibres counted in the oblique, circular and longitudinal layers was 1365, 1408 and 745 respectively. The number of nerve bundles (single and multiple axon profiles) per 1000 muscle fibres was 62 (oblique layer), 30 (circular layer) and 28 (longitudinal layer). Single axon profiles comprised 51% (oblique layer), 36% (circular layer) and 10% (longitudinal layer). The number of axon profiles in the nerve bundles varied between 2 and 43. Nerve bundles containing 2-5 axon profiles formed 43% (oblique layer), 55% (circular layer) and 38% (longitudinal layer) of all nerve bundles. Vesiculated axon profiles within the nerve bundles made up approximatey 55% (oblique layer), 41% (circular layer) and 28% (longitudinal layer). Axon profiles containing round agranular vesicles (AGVs) comprised 35% (oblique layer), 30% (circular layer) and 10% (longitudinal layer). Axon profiles containing large granulated vesicles (LGVs) comprised 54% (oblique layer), 60% (circular layer) and 85% (longitudinal layer). Axon profiles containing flattened vesicles comprised 11% (oblique and circular layers) and 5% (longitudinal layer). The neuromuscular junctional gaps between vesiculated axon profiles and the surfaces of muscle cells varied between 11-270 nm (oblique layer), 11-290 nm (circular layer) and 31-110 nm (longitudinal layer). Gaps of 11-30 nm formed 48% and 22% in the oblique and circular layers, respectively. In the oblique layer such gaps were made up of 48% of AGVs, 50% of LGVs and 46% of FVs. The corresponding figures in the circular layer were 18%, 35% and 33%. The majority of vesiculated axon profiles contacted one muscle cell. Vesiculated axon profiles contacting two muscle cells comprised 31% (oblique layer) and 21% (circular layer). Vesiculated profiles contacting three muscle cells comprised 7% (oblique layer) and 21% (circular layer). Rarely, an axon profile contacted four muscle cells. An innervated muscle cell was usually contacted by a single axon profile but there were cases where two or even three axon profiles made contact with a single muscle cell.

Animals↗
PubMed1979

Experimental degeneration of primary afferent terminals in the cuneate nucleus of the monkey (Macaca fascicularis).

Six monkeys (Macaca fascicularis) were used for the present study. In animals which survived for 2-6 days after section of C5 to T1 dorsal roots, at least four types of degenerating afferent terminal were observed - electron-dense, electron-lucent, neurofilamentous and flocculent. The electron-dense degeneration was the most common and was seen as early as 2 days after rhizotomy. The neurofilamentous type was the second commonest and was found predominantly in the 3 days' survival material. The electron-lucent and flocculent types were less commonly encountered. Since the profiles exhibiting neurofilamentous hyperplasia showed varying degrees of electron density it is suggested that this type of degeneration progresses to the electron-dense type with time. The present study also showed that the primary afferent terminals in the cuneate nucleus of the monkey are mostly large and that they contain round vesicles. They are commonly found within synaptic complexes in which they are presynaptic to dendrites of various sizes, and are themselves postsynaptic to smaller axon terminals containing flattened vesicles. Degenerating terminals forming isolated synapses were less commonly seen. No dorsal root axon terminals formed axosomatic synapses.

Animals↗
PubMed1978

The fine structural organization of the cuneate nucleus in the monkey (Macaca fascicularis).

The fine structure of the cuneate nucleus of the monkey (Macaca fascicularis) has been studied. The neurons were classified into three groups according to their nuclear morphology, the arrangement of the rough endoplasmic reticulum (RER) and the appearance of the Golgi complexes. Group I neurons had a regular nucleus and contained abundant cytoplasm in which were found well-developed RER and Golgi complexes. Group II neurons had a slightly irregular nucleus and a variable arrangement of the RER and Golgi complexes. Group III neurons were characterized by a deeply indented nucleus, and scanty cytoplasm in which the cytoplasmic organelles were poorly developed. Group II neurons were the most commonly encountered while Group I neurons were the rarest. Axon terminals contained either round of flattened vesicles. Axon terminals and dendrites commonly formed synaptic complexes. In one type the axon terminal, containing round vesicles, formed the central element, which is presynaptic to the dendrites surrounding it; in addition it is postsynaptic to axon terminals containing flattened vesicles. In another type a large dendrite formed the central element which is postsynaptic to axon terminals containing round or flattened vesicles.

Animals↗
PubMed1978

Fine structure of the myenteric and submucous plexuses in the stomach of a coral fish, Chelmon rostratus Cuvier.

The fine structure of the teleostean myenteric and submucous plexuses has been studied in the stomach of the coral fish, Chelmon rostratus Cuvier. The myenteric plexus is a prominent loose mesh containing nerve cells, myelinated and unmyelinated axon profiles, vesiculated axon profiles, Schwann cells, collagen and capillaries. Unmyelinated axons greatly outnumber the myelinated ones. Vesiculated axon profiles were uncommon, and synapses were rarely observed. Compared with the myenteric plexus, the submucous plexus was more modest in size; it was devoid of nerve cells and myelin sheaths were only occasionally seen.

Animals↗
PubMed1977

DNA synthesis during meiosis of eight-spored strains of Chlamydomonas reinhardi.

In strain 137F of Chlamydomonas reinhardi, the zygospores undergo one round of nuclear DNA replication followed by three divisions to produce octospores. The third division without replication has been interpreted by Sueoka et al. (1967, 1969) to mean that the gametes and vegetative cells have at least binemic chromosomes. We have repeated their experiments using the same strain. However, the meiotic products were inviable--unable to undergo postmeiotic vegetative growth, DNA replication or division. On the other hand, using a variant of strain 137C which also has three divisions during germination we have shown that meiosis is normal. Zygospores from this strain undergo two rounds of nuclear DNA replication prior to the formation of octospores. These meiotic products are viable and capable of postmeiotic vegetative growth, replication and division. Since the third division without DNA replication subsequent to the two meiotic divisions leads to inviable products, and the strain which has viable products after three divisions does not lack the additional replication, meiosis in Chlamydomonas reinhardi provides no evidence of a bineme chromosome structure.

Chlamydomonas↗
PubMed1976

Levels of circulating norepinephrine and epinephrine before, during, and after cardiopulmonary bypass in man.

Little information is available on the levels of circulating catecholamines during cardiac surgery. A study was undertaken to measure the serum levels of epinephrine and norepinephrine before, during, and after cardiopulmonary bypass in 16 patients. Sampling were drawn before induction, after intubation, before bypass, 2 and 8 minutes after initiation of the bypass, and 20 minutes after bypass. The findings of this study show that the initiation of cardiopulmonary bypass was associated with a significant but transient fall in mean blood pressure accompanied by an increased secretion of adrenal epinephrine and norepinephrine. The cause of the observed hypotension may be due to an initial hemodilution of the circulating catecholamines by the 2 L. pump-priming solution. The secretion of adrenal catecholamines appears to be a compensatory response to the lowered blood pressure as indicated by the rapid return of the blood pressure in the ensuing minutes. Twenty minutes after bypass, both the blood pressure and serum catecholamine levels were observed to have returned to preinduction levels.

Anesthesia, Inhalation↗