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Biomedical subjects

K Frederiksen

Publications and source records attributed to K Frederiksen.

29 records · Page 2Linked to original sources
PubMed1988

Proliferation and differentiation of rat neuroepithelial precursor cells in vivo.

Important features of adult neuronal number, location, and type are a consequence of early embryonic events that occur before neurons have differentiated. We have measured cell number during embryogenesis of the rat CNS. Markers that are expressed in the proliferating neuronal precursor are required to study the mechanisms controlling their proliferation and differentiation. By applying immunohistochemistry, fluorescence-activated cell sorting, and 3H-thymidine auto-radiography to dissociated rat CNS cells, we show that the monoclonal antibody Rat 401 recognizes a cell population with proliferative, temporal, and quantitative features expected of neuronal precursors.

Animals↗
PubMed1987

Allotransplantation of human teeth. A retrospective study of 73 transplantations over a period of 28 years.

An assessment was made of the postoperative fate of 73 allotransplanted human teeth carried out by 3 surgeons between 1956 and 1980 to determine the clinical and radiographical course of immunogenetically unmatched allotransplanted human teeth. The mean ages of recipients and donors were 34.1 and 15.2 years, respectively; 47 of the grafts had incomplete root-formation at time of transplantation. Mean observation period was 7.8 years with a maximum of 28 years. The study was terminated December 1985. The mean functional time of the grafts (function of graft without symptoms) was 6.8 years (max. 28.5 years). No signs of pulpal survival were found in any graft. Root resorption was found in 91.6% of grafts within a mean of 8.8 months after transplantation, causing a high frequency of graft loss within the first 2 years (34.1%). Recipients older than 45 years of age retained the grafts significantly longer than young patients. The major causes of graft loss were replacement (60.3%) and inflammatory resorption (24.4%). Graft loss due to marginal periodontitis was minor (2.7%). Inflammatory resorption, which was found more frequent in young recipients (P = 0.02), usually caused rapid rejection, whereas the survival time after ankylosis was significantly longer. In conclusion, no clinical or radiographical evidence of long-term survival of the pulpal or periodontal tissues of the unmatched allografts were found. However, despite a progressing replacement resorption frequently present, the allografts seem to function clinically sufficient, symptomless and often with clinically normal gingival condition for many years. Increasing age of the recipient at time of transplantation significantly increased the function time of the graft. Younger recipients showed more inflammatory resorption of the grafts.

Adolescent↗
PubMed1983

Surface molecules identify groups of growing axons.

Studies on vertebrate and invertebrate species have established that, during development, axons have the ability to choose particular paths over others. The chemical basis of this pathfinding is not clear but biochemical differences between neurons have long been postulated to account for the specificity of neuronal connections. Such subtle molecular differences between different cells in a single tissue are difficult to study with standard biochemical techniques but hybridoma technology has offered a potential solution to this type of problem. This technique has made possible the production of monoclonal antibodies for identifying and characterizing a family of glycoproteins which are expressed on the surface of specific axon bundles during the development of the leech nervous system. The results show that groups of growing axons do indeed carry chemically distinct surface molecules.

Animals↗
PubMed1982

Ability of the xid gene to prevent autoimmunity in (NZB X NZW)F1 mice during the course of their natural history, after polyclonal stimulation, or following immunization with DNA.

F1 hybrid offspring of New Zealand Black mothers and New Zealand White fathers [(NZB X NZW)F1] female mice develop antibodies to single-stranded (ss) and native DNA, immune complex glomerulonephritis, massive proteinuria, and premature death with renal failure. By a series of matings, congenic (NZB X NZW)F1 . xid/xid mice were prepared. These mice were different from (NZB X NZW)F1 mice in having the X chromosome-linked immune deficiency gene, xid, in homozygous form. Such congenic (NZB X NZW)F1 . xid/xid females failed to develop antibodies to single-stranded or native DNA. They also failed to develop fatal renal disease as measured by proteinuria, glomerular histology, glomerular immunofluorescence, and survival. To control for unknown genetic factors, studies were performed with littermates that were derived by mating NZB . xid/+ females with NZW . xid/Y males such that the resulting offspring were either (NZB X NZW)F1 . xid/xid (and therefore "defective") or (NZB X NZW)F1 . xid/+ [phenotypically like (NZB X NZW)F1]. In these and in additional studies, mice were housed in the same cages and identified by ear tagging so as to avoid possible environmental variations from cage to cage. In these studies, xid/xid mice failed to develop the characteristic signs of autoimmunity, whereas the controls did. Similar results were also obtained with (NZW X NZB)F1 xid/xid mice compared with (NZW X NZB)F1 xid/+ mice. The effect of xid/xid upon (NZB X NZW)F1 mice was further investigated by assessing responses to immunization and polyclonal B cell activation in vivo. The xid/xid mice failed to produce anti-ssDNA following immunization with ssDNA complexed to a protein carrier in fluid form or even emulsified in adjuvant. Finally, the xid/xid mice failed to produce antiDNA in response to multiple injections of the polyclonal activator, bacterial lipopolysaccharide (LPS), or the polyclonal activator, polyribose inosinic acid . polyribose cytidylic acid. However, the xid/xid mice were neither generally hyporesponsive nor unable to recognize LPS because they made normal antibody responses following immunization with LPS to which multiple trinitrophenyl groups were chemically attached. We conclude from these studies that xid/xid, which is known to cause the deletion of a B cell subset, has a profound affect upon (NZB X NZW)F1 mice, rendering them insusceptible to the naturally occurring autoimmune disease characteristic of (NZB X NZW)F1 mice, and preventing them from producing antibodies to DNA despite purposeful immunization and polyclonal B cell activation. These results force a reevaluation of previous concepts regarding the mechanisms by which xid/xid might interfere with the development of autoimmunity, and a consideration of therapeutic implications.

Animals↗
PubMed1979

A simple and rapid whole-mount staining method with methyl green-pyronin G applied to a molluscan brain preparation.

Subesophageal ganglia of molluscs have been stained as whole mounts with methyl green-pyronin G to display the relative location of individual neurons. Nuclei appear blue, perikarya red. Expose the ganglion cells by dissection of the connective tissue in snail Ringer. Transfer the ganglion to a fixative of 2.5% glutaraldehyde in 0.1 M Na cacodylate pH 7.1 at 4 C for 12--24 hours, and wash in distilled water for 1 1/2 hours. Stain with methyl green-pyronin G for 1/2--1 hour and differentiate in 96% ethanol using many rapid changes. Transfer the ganglion to absolute ethanol for 2 1/2 hours and clear in xylene for 3 hours before embedding in Depex in a suitable dish. When the Depex has hardened, the preparation can be stored, and is readily available for subsequent examination. The method may be applicable to other invertebrate tissues, and may be useful in preparing objects for teaching purposes.

Animals↗
PubMedDate not supplied

Methods for assessment of future demand of medical doctors in Denmark.

BACKGROUND: Whereas supply prognoses is mainly a matter of establishing mathematical scenarios with ongoing adjustments of variables, reliable demand prognoses are more difficult and complex to establish. However, optimum use of human and educational resources and--on the other hand--sufficient supply of medical doctors calls for reliable supply as well as demand prognoses. METHODS: Based on a number of technical and political considerations the first demand prognosis was based on three different methods; 1. Changes in demand due to demographic changes. 2. An evaluation made by the owners of the hospitals. 3. An evaluation made by the scientific medical societies. RESULTS: The demand prognosis was found to be hampered by a number of limitations. Demographic changes beyond the next 10 years was found to be unreliable. Moreover, the demand observed during the last 20 years was only to a very limited extent explained by demographic changes. The owners of the hospitals could only prognosticate for an election period, i.e. for about 5 years,--and only in very general terms that were difficult to interpretate. From some counties the answers did only seem to be based on rather superficial analysis and gave very little information. Each of the Scientific Medical Societies claimed increasing demands for the next 25 years, despite marked expectations for diagnostic and therapeutic advantageous technological developments. The overall conclusion from the combined weighed analysis was an expected increase in the demand of medical doctors of about 1% per year in the short as well as in the long term (25 years). This should be compared to the observed development during the last 10 years, i.e. an annual increase of 1.7-1.8%.

Demography↗
PubMedDate not supplied

Dimensioning of the postgraduate educational training in Denmark.

BACKGROUND: Postgraduate medical training in Denmark consists of basic training, offered to all medical doctors, followed by specialist training. The National Board of Health is responsible for the overall frame of medical training in Denmark and determines the number of trainee positions for each of the 42 specialities available. The total number of positions and their distribution between specialities are based on demand, supply and demographic considerations. Approximately 85% of medical doctors finalise specialist training. METHODS: Denmark is divided into three educational regions: North, South and East. Each region consists of counties, with their own administration. The National Board of Health approves each position for postgraduate training. All new positions and changes of existing positions are evaluated before approval by The National Board of Health. An updated version of the list of educational positions is available on the internet. CONCLUSION: The Danish governmental authorities have an efficient tool to control the dimensioning of the postgraduate medical education and thereby the production of specialists. Medical doctors can easily get information about where to obtain trainee positions. The majority of hospital departments improve their recruitment potential by participating in medical training. A number of structural changes, for instance establishing of medical centres and corporations within larger entities across an extended geographic area, specialisation between hospitals and reduced number of hospitals, calls for decentralisation of the administration in order to improve flexibility in the organisation of postgraduate medical training. However, the National Board of Health will still co-ordinate at the national level.

Denmark↗