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Biomedical subjects

M J Cullen

Publications and source records attributed to M J Cullen.

At least 109 records · Page 6Linked to original sources
PubMed1980

The prevention of coronary heart disease in general practice.

Four hundred and eighty-one (75 per cent) of the male patients between 35 and 55 years of age in a health centre group practice were screened for risk factors for coronary heart disease. An attempt was made to alter these factors and the effectiveness of the intervention was later assessed. We consider that where there is an attached health visitor a screening programme can be carried out as part of general practice without too great an increase in work-load for the general practitioner. The continued surveillance of those at risk and the alteration of the risk factors is more arduous. We think the assistance of the other health care professionals such as the area health education officer and dietician is essential in such a programme.

Adult↗
PubMed1979

Remodelling of optic nerve myelin sheaths and axons during metamorphosis in Xenopus laevis.

Whole mounts and transverse sections of Xenopus optic nerves were examined with the light and electron microscopes before, during, and after metamorphosis. In stage 52--58 tadpoles, almost all myelin sheaths were circular in transverse sections. Early in metamorphosis (stages 60--61) large redundant myelin loops surrounded many large axons in central regions of the nerve. The loops subsequently were broken down into ovoids and lamellar segments that remained mostly within oligodendrocytes. These myelin changes were not observed in the chiasm or next to the eye. They were not associated with significant axonal degeneration and were no longer apparent in optic nerves of young frogs. Xenopus optic nerves also became shorter during metamorphosis. We therefore suggest that myelin sheaths with redundant loops which degenerate and disappear are being remodelled as the nerve decreases in length.

Animals↗
PubMed1979

Node-like areas of intramembraneous particles in the unensheathed axons of dystrophic mice.

The unensheathed axons in the spinal roots of adult dystrophic mice were examined by freeze-fracture electron microscopy. In most areas of these abnormal fibers the distribution of intramembraneous particles was similar to that of the internodal segments of normal axons with many more particles on the PF (internal) leaflets of these axonal surface membranes than on their EF (external) leaflets. However, patches of axonal membranes were also observed in which the distribution of intramembraneous particles resembled that seen in nodes of Ranvier.

Animals↗
PubMed1979

High thyroid radiation dose associated with 131-I-19-iodocholesterol adrenal scanning.

We have examined two patients undergoing 131I-19-iodocholesterol adrenal scans in order to assess thyroidal radiation dose. Thyroid uptakes of 3--5% of the administered 2 mCi dose were found despite prior administration of Lugol's iodine. Analysis of serum samples over a ten day period after iodocholesterol injection indicated that less than 10% of the radioactivity was free iodide. Kinetic results showed a high value for the thyroid/plasma 131I ratio indicating thyroid retention of 131I. This was substantiated by thyroid scintigrams. The thyroid radiation dose was estimated to be 200--250 rad for the two patients. The associated carcinogenic risk is of sufficient magnitude, in our opinion, to warrant regular follow-up of all patients who have undergone 131I-19-iodocholesterol adrenal scanning.

19-Iodocholesterol↗
PubMed1979

The value of a tracer dose in predicting the kinetics of therapeutic doses of 131I in thyrotoxicosis.

The kinetics of tracer doses of 131I, assessed by measuring uptake and effective half-life, correlate well with the kinetics of therapy doses. The effective half-life was measured using thermoluminescent discs fixed to the patients' anterior neck surface. This method gives results comparable with those obtained using an uptake probe, and met with a good response by the patients. Using the kinetics of the tracer dose to assist prescription of radioiodine therapy would considerably reduce the spread of absorbed doses to the glands of a group of patients. The case for attempting more exact dosimetry in this field is reviewed.

Half-Life↗
PubMed1978

An experimental analysis of interlamellar tight junctions in amphibian and mammalian C.N.S. myelin.

The distribution of interlamellar tight junctions was examined in myelin sheaths of Xenopus tadpole optic nerve and rabbit epiretinal tissue fixed with aldehydes, postfixed with osmium ferrocyanide and embedded in a water-soluble medium, Durcupan. Intramyelinic zonulae occludentes were clearly formed by fusion of adjacent intraperiod lines which corresponded to the external leaflets of oligodendrocytes. These occurred in register with other tight junctions present within successive lamellae and appeared as a series of radial lines extending either partially or totally across the thickness of the myelin sheath. This distribution of zonulae occludentes corresponded with that of tight junctional particle strands observed in freeze-fracture replicas. Analysis of intramyelinic vacuolation induced by hexachlorophene (HCP) intoxication indicated that lamellar splitting was frequently limited by the tight junctions. The intramyelinic zonulae occludentes also restricted the diffusion of colloidal lanthanum which had penetrated the myelin intraperiod gap following in vivo perineural injection. The results of this study provide evidence favouring a correspondence between interlamellar tight junctions and the 'radial component' of myelin described earlier by other investigators. Furthermore, observations of swollen myelin sheaths, resulting from HCP intoxication, suggest that these junctions may play a major role in maintaining myelin sheath integrity and limiting the extent of breakdown during certain pathological conditions.

Animals↗
PubMed1978

Experimental (-) emetine myopathy. Ultrastructural and morphometric observations.

The ultrastructural changes induced by (-) emetine hydrochloride were studied in two skeletal muscles of the rat. (-) Emetine was administered at a dose level of 2 mg/kg for periods ranging from one to four weeks. Changes were noted after the one week stage and were progressive with all muscle components appearing to be affected. Myofibrillar changes included Z line streaming, rod formation, myofilament loss and contraction clumping. Mitochondrial degeneration was detected, but the most striking feature of the induced myopathy was the extensive membrane proliferation. The membranes were considered to be involved in the isolation of sarcoplasmic constitutents in the production of autophagic vacuoles. Morphometry was carried out in order to quantify some of the changes in the fibre components.

Animals↗
PubMed1978

The influence of thyroid geometry on the response of LiF and CaSO4 thermoluminescent discs to 131I and 125I irradiation.

Recent work has demonstrated that LiF and CaSO4 thermoluminescent discs may be used to monitor the effective half-life of radioiodine in the thyroid in man. To provide a firm basis for this work, the radiation field presented by model thyroids to thermoluminescent discs on the surface of a neck phantom has been examined in detail. The influence of thyroid mass, depth and lobe separation, factors which in practice are highly variable, has also been determined. The results demonstrate that the method is sufficiently sensitive to measure less than 0.5 muCi of 131I or 125I in the human thyroid, and that effective half-life determinations should not be influenced by minor positioning errors which may be encountered when placing thermoluminescent discs on the neck surface.

Calcium↗
PubMed1977

The ultrastructure of the developing medial preoptic nucleus in the postnatal rat.

The postnatal maturation of the medial preoptic area (MPOA) of male and female rats was studied by means of light and electron microscopy. In Golgi-Kopsch preparations, bi- and multipolar cells were present at birth in both sexes; the perikarya of most of these cells, as seen with the electron microscope, exhibited an immature appearance characterized by a sparse organelle content. During the next 5-10 days, an increase in cell size and cytoplasmic differentiation occurred in each sex. By 10 days, many of the MPOA neurons displayed an increased organelle density with the most prominent change being a proliferation of rough endoplasmic reticulum. Further neuronal development was also evidenced by a greater frequency of dendritic spines than seen at either birth or 5 days. Lastly, the number of synapses per unit area increased rapidly in each sex during the first two weeks of postnatal life. Thus, a period of increasing cytological maturation and synaptic organization closely paralleled previously demonstrated stages of functional differentiation of gonadotrophin regulatory mechanisms in the rat brain.

Androgens↗
PubMed1977

The effects of low temperature on myelin formation in optic nerves of Xenopus tadpoles.

To test the effect of cold on CNS myelin formation, optic nerves of stages 52-55 Xenopus tadpoles were examined electron microscopically after maintenance at 15, 10, 7 and 4 degrees C for 1-7 days. Nerves from tadpoles maintained at 15 degrees C resembled 22 degrees C (room temperature) controls. After 3 days at 10, 7, or 4 degrees C, tongue processes and perikarya of many myelin forming oligodendrocytes were swollen and filled with vesicular membrane profiles. The number of axonal microtubules was decreased in affected fibers but the lamellar structure of their myelin sheaths remained normal. Astrocytes were hypertrophic and contained large aggregates of filaments. Longer exposure to 10 or 7 degrees C increased the number of affected fibers but the changes were not more severe or associated with degeneration. The delayed onset, lack of progression and reversibility of the changes indicated that cold has a direct metabolic effect on myelin forming oligodendrocytes. Alterations produced by nerve transection or exposure to mitotic inhibitors differed, suggesting that cold induced changes were not due primarily to either axonal degeneration or reduced axonal transport.

Animals↗
PubMed1977

Postnatal ultrastructural changes in the cat myocardium: a morphometric study.

In order to understand more clearly the basis for our previously observed postnatal age related changes in the mechanical performance of the cat myocardium we have carried out a quantitative ultrastructural analysis of right ventricular papillary muscles obtained from adult cats (1.8 to 2.3 kg), infant cats (16 days of age), and neonatal kittens (less than 72 hours old). Volume fractions were calculated for myofibrils, sarcoplasm, mitochondria, lipid, sarcoplasmic reticulum (SR), golgi, and nuclei. The myofibril content of neonatal fibres was significantly less than that of the infant or adult groups (P less than 0.05 and 0.005 respectively). In addition the infant fibres contained a smaller volume of myofibrils than the adult ones (P less than 0.001). The mitochondrial content of the neonatal fibres was also significantly less than that of either the infants' (P less than 0.005) or adults' (P less than 0.001). These data provide an anatomical basis for the progressive age related increase in mechanical performance of the cat myocardium, in postnatal life.

Animals↗
PubMed1976

Two mechanisms for hypothyroidism after 131I therapy.

It is proposed that the incidence of hypothyroidism after radioiodine therapy of thyrotoxicosis has two distinct mechanism. One operates in the first two years after therapy and depends on radiation dose. The other operates in later years, and is not, to any significant extent, dose dependent. Possible canidates for each mechanism are explored.

Dose-Response Relationship, Radiation↗