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Biomedical subjects

R Dyck

Publications and source records attributed to R Dyck.

12 recordsLinked to original sources
PubMed2001

A preliminary examination of organizational capacity for heart health promotion in Alberta's regional health authorities.

The province of Alberta is located in western Canada, bordering the eastern slopes of the Rocky Mountains (see O'Loughlin et al., Figure 1). The population of 2.7 million is mostly located in two cities (Calgary and Edmonton) with the balance dispersed in smaller rural centres throughout the province. Principal industries include agriculture, forestry, telecommunications, oil and gas. These industries have helped create a strong provincial economy.

Alberta↗
PubMed2000

[Basic micro-electrophysiologic techniques used in neurobiology].

Problems of application of microelectrophysiological techniques in neurobiology are addressed. Authors focused on five basic recording techniques: micro-EEG, multi unit activity, single unit activity, intracellular recording and patch clamp techniques.

Action Potentials↗
PubMed1995

Inorganic components of drinking water and microalbuminuria.

Relatively little is known of the chronic effects attributable to the ingestion of inorganic components such as uranium and silicon. Although ingestion of large amounts of U can cause acute renal damage through a chemical effect, studies on humans have typically considered inhalation the route of exposure. We investigated the association between drinking water concentration levels of U and Si, and microalbuminuria, a sensitive biological indicator of renal dysfunction. Linear regression analysis revealed a statistically significant association between U cumulative exposure index and albumin per mmol creatinine (P = 0.03). No such significant relationship appeared for Si, although a positive trend was witnessed. Since normal but increasing levels of microalbuminuria were observed at U concentration levels below the Canadian Maximum Allowable Concentration (MAC), it is suggested that further study be undertaken.

Adolescent↗
PubMed1995

Lack of early acute rejection does not predict safe tapering of immunosuppression.

In an effort to reduce long-term complications of immunosuppressive medications, some investigators have devised protocols of reduced dosage [Kupin et al. 1988, Kelly et al. 1989, Reinsmoen et al. 1993] which are intended to maintain the stability of the transplant and at the same time prevent or retard immunosuppressive medication side effects. Implicit in this plan is the assumption that there has been the development of some degree of graft acceptance [Koene 1989] and/or tolerance [Goulmy et al. 1985, Muluk et al. 1991], yet it is also true that drug non-compliance is a common cause of late acute rejection and graft loss in stable kidney recipients [Rao et al. 1988, Didlake et al. 1988, Rao et al. 1989, Hricik et al. 1991]. The latter fact is a warning that immunosuppression should be cautiously and gradually reduced. Patients who reject grafts early tend to require more immunosuppression. It is not known, however, whether patients who do not reject early require less immunosuppression. Herein, we present a case of late acute cellular and vascular rejection that occurred 9 years after stable renal graft function, in the absence of early acute rejection episodes. This case provides evidence to support the notion that lack of early acute rejection may not predict safe reduction of immunosuppression therapy.

Acute Disease↗
PubMed1994

The correlation between cortical neuron maturation and neurofilament phosphorylation: a developmental study of phosphorylated 200 kDa neurofilament protein in cat visual cortex.

Neurofilament proteins are major constituents of the neuronal cytoskeleton. When phosphorylated, neurofilament proteins are thought to be involved in slowing down the slower component of axonal transport, thereby increasing neurofilament stability and conferring resistance to proteolysis. In order to investigate the correlation between phosphorylated neurofilament and plasticity of the cat visual cortex, we applied a monoclonal antibody, which recognizes only the phosphorylated form of neurofilament protein, to kitten visual cortex. This antibody appeared to recognize only axons. There was a progressive increase of phosphorylated neurofilament-immunoreactive axons in the cortical layers and white matter during development. In the visual cortex of young kittens, phosphorylated neurofilament immunoreactive processes were mostly long, fine, and continuous axons. However, in kittens older than 2 months of age, phosphorylated neurofilament immunoreactivity was characterized by short, punctae-like staining. The immunoreactive axons were most dense in deep cortical layers V and VI initially, followed at later ages by layers IVa and IVb, and finally in layer IVc and in the superficial cortical layers of adult animals. This developmental laminar pattern of distribution was not affected by early input restriction and coincides with electrophysiological evidence of early neuronal maturation. In addition, the phosphorylated neurofilament immunoreactivity can also be found in the dendrites and perikaya of degenerating neurons. These results suggest that phosphorylated neurofilament can be used as an index of functional maturity in the kitten visual cortex and also as a marker for neurodegeneration.

Animals↗
PubMed1993

Histochemical localization of synaptic zinc in the developing cat visual cortex.

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 microns in diameter, with a centre-to-centre spacing of approximately 900 microns. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex.

Animals↗
PubMed1992

Enrichment of glutamate in zinc-containing terminals of the cat visual cortex.

The presence of glutamate and GABA was examined in zinc-containing terminals of the cat visual cortex using a post-embedding immunogold method. The surface density of immunogold-labelling was also evaluated in morphologically defined ultrastructural elements, namely terminals having round synaptic vesicles and making asymmetrical synapses (RA boutons), terminals with flat vesicles and symmetrical synapses (FS) and glial cell processes. Glutamate immunoreactivity was highest in RA terminals and in zinc-containing boutons. It was lower in FS terminals and lowest in glial cell processes. GABA immunoreactivity was highest in FS terminals and low in all other ultrastructural elements analysed, including zinc-containing terminals. Therefore, zinc-containing terminals show an enrichment of glutamate and they are likely to use this amino acid as their neurotransmitter. Moreover, the fact that many RA terminals that are negative for zinc show an enrichment of immunoreactive glutamate suggests that zinc-containing fibres represent a subpopulation of the glutamate axonal network.

Animals↗
PubMed1991

Sparing of two types of hippocampal rhythmical slow activity (RSA, theta) in adult rats decorticated neonatally.

The electroencephalographic (EEG) activity of the hippocampus was examined in adult freely moving rats that had had all of the neocortex, including the cingulate cortex and cingulum, removed at birth. Both the cholinergic and serotonergic forms of rhythmical slow activity (RSA or theta) were present in the dorsal hippocampus and retained their normal relation to behavior. The results show that following decortication, inputs to and connections within the hippocampus apparently retain the ability to produce normal EEG. Since adult decortications abolish serotonergic RSA, the results also suggest that following neonatal injury there is reorganization within remaining serotonergic projections to the hippocampus that spare this form of RSA.

Animals↗
PubMed1984

Comparative potency of tactile, auditory, and visual stimulus repetition in eliciting activated forebrain EEG in the rabbit.

The experiments addressed the question of whether certain modalities of stimulation are more effective in eliciting immobility-related, atropine-sensitive neocortical low-voltage fast activity and hippocampal rhythmical slow activity from the rabbit. More pronounced activation and less pronounced habituation followed tactile than auditory and visual stimulation. On the basis of these results, and other studies, it is suggested that atropine-sensitive electroencephalographic activity may be importantly involved in the central programming, initiation, and guidance of movement.

Animals↗
PubMed1979

Subclavian cannula for temporary hemodialysis.

A new silastic and teflon cannula has been developed for temporary hemodialysis access. It is introduced through the subclavian vein by the Seldinger technique. The cannula which is quick and easy to insert, can be used repeatedly for weeks or months without limiting the patient's mobility and without the need for repeated vessel punctures. Complications are few and largely preventable. Since introduction of the subclavian hemodialysis cannula at the Toronto Western Hospital in September 1977 no patient with end-stage renal failure has required insertion of a silastic-teflon shunt or temporary peritoneal dialysis, nor has hemodialysis had to be postponed because of lack of an arteriovenous fistula.

Bacterial Infections↗
PubMed1973

Auxin inhibition of ripening in bartlett pears.

The effect of indoleacetic acid and 2,4-dichlorophenoxyacetic acid on the ripening of intact mature-green pears (Pyrus communis var. Bartlett) was investigated using a vacuum infiltration technique.The effects of indoleacetic acid and 2,4-dichlorophenoxyacetic acid at concentrations of 0.01, 0.1, and 1.0 mm each were studied on softening, degreening, and on ethylene and CO(2) evolution. Softening and degreening were inhibited increasingly in response to increased concentrations of indoleacetic acid. This inhibitory property was amplified by 2,4-dichlorophenoxyacetic acid at concentrations comparable to those of indoleacetic acid. Application of the auxins also prevented the climacteric rise in respiration, but stimulated ethylene synthesis. Despite the presence of elevated ethylene levels, the inhibitory auxin effect was predominant.It is proposed that endogenous auxins in fruit represent a resistance factor in ripening and must be inactivated before ripening can occur.

Journal Article↗