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Biomedical subjects

A Zorn

Publications and source records attributed to A Zorn.

9 recordsLinked to original sources
PubMed1999

Single cells can sense their position in a morphogen gradient.

Xenopus blastula cells show a morphogen-like response to activin by expressing different genes according to the concentration of activin to which they are exposed. To understand how cells recognize their position in a concentration gradient, it is essential to know whether each cell responds individually to activin concentration. An alternative idea, proposed by previous work, is that cells need to interact with their neighbours to generate a concentration-related response. To distinguish between these ideas, we have cultured blastula cells under conditions which provide different degrees of contact with other cells, allowing nil to maximum communication with their neighbours. The cultures include cells attached to fibronectin and cells resting unattached on an agarose base. The cultures also include cells that have no contact with any cell except their clonal progeny, cells that have lateral contact to neighbouring cells, and cells that are completely enveloped by other cells in a reaggregate. We have used RNase protection and in situ hybridization to assay the expression of the activin-responsive Xenopus genes Xbra, Xgsc, Xeomes, Xapod, Xchordin, Mix1, Xlim1 and Cerberus. We find no difference in gene expression between cells attached to fibronectin and those unattached on agarose. Most importantly, we find that cells respond to activin in a concentration-related way irrespective of their degree of contact with other cells. Therefore interaction among cells is not required for the interpretation of morphogen concentration, at least in the case of the early genes studied here. We conclude that isolated blastula cells can sense and respond individually to activin by expressing genes in a concentration-dependent way.

Activins↗
PubMed1995

Prevention of clinical trichostrongylidosis in calves by strategic feeding with the predacious fungus Duddingtonia flagrans.

The present investigation showed that strategic feeding of first-season calves with the microfungus Duddingtonia flagrans through the initial 3 months of the grazing season could prevent severe clinical trichostrongylidosis in the late summer. The successful prevention of disease was particularly noteworthy in view of the high stocking rate practiced on this permanent pasture, which was widely contaminated with a range of gastrointestinal nematodes. The results showed that larval populations of Ostertagia and Cooperia were significantly reduced on the pasture grazed by the fungus-treated calves. Numbers of Nematodirus seemed less affected. The present paper discusses the complexity of fungus-nematode interactions in dung pats under natural conditions.

Animals↗
PubMed1995

Biological control of trichostrongyles in calves by the fungus Duddingtonia flagrans fed to animals under natural grazing conditions.

The present study was conducted in the 1993 grazing season with yearling calves exposed to a pasture with a natural mixed trichostrongyle larval infection. It was shown that daily feeding with the microfungus Duddingtonia flagrans during the first 2 months of the season led to a lowered herbage infectivity and a reduced acquisition of Ostertagia sp. and Cooperia sp. later in the season. In addition, the procedure delayed the onset of clinical disease. This was due to the nematode-destroying effects of the fungi in the dung excreted by the fungus-treated calves, as evidenced by results from a parallel in vitro assay on faecal larval cultures. The paper discusses future research needs before practical biological control can be implemented.

Animal Feed↗
PubMed1995

Predacious activity of the nematode-trapping fungus Duddingtonia flagrans against cyathostome larvae in faeces after passage through the gastrointestinal tract of horses.

This study was undertaken to examine the potential of the nematode-trapping microfungus Duddingtonia flagrans to survive passage through the gastrointestinal tract of horses and subsequently to destroy free-living stages of cyathostomes in faecal cultures. Three different oral dose levels were tested, two horses being used for each level. Faeces were collected twice daily and the numbers of parasite eggs per gram of faeces were determined. The numbers of infective third stage larvae which developed in faecal cultures were determined after the cultures had been incubated for 2 weeks at 24 degrees C. Results showed a positive relationship between dose level and reduction in the number of infective larvae. Fungi were recovered in faeces at times which corresponded to high larval reduction.

Animal Feed↗
PubMed1994

Rapid-sequence orotracheal intubation with rocuronium: a randomized double-blind comparison with suxamethonium--preliminary communication.

Eighty ASA I-III patients were randomly assigned to four groups. Group I patients received rocuronium 0.6 mg kg-1 immediately prior to thiopentone, while patients in group II received the same dose immediately after the induction agent. In groups III and IV a priming dose of rocuronium 0.04 mg kg-1 was administered prior to induction. Group III patients received rocuronium immediately prior to thiopentone. In group IV, suxamethonium 1.5 mg kg-1 was administered immediately after thiopentone. Intubation conditions were scored by a blinded investigator. An intubation time of > 60 s was defined as a failure. All patients could be intubated within 60 s. Priming with rocuronium did not improve intubation conditions. Total intubation scores > 6 occurred significantly more often in group II (P < 0.01 vs. all other groups). A single bolus dose of rocuronium 0.6 mg kg-1 (2 x ED95) administered immediately prior to thiopentone 6 mg kg-1 offers the same intubation conditions as suxamethonium 1.5 mg kg-1.

Adult↗
PubMed1993

Gene activation in response to neural induction.

In order to study the molecular processes involved in the final steps of neural induction, we are investigating the transcriptional regulation of the Xenopus laevis neural cell adhesion molecule (NCAM) gene. NCAM is expressed very early during neural development and its expression is dependent on neural induction signals. Using microinjection of reporter gene constructions into fertilized frog eggs, we have shown that cloned copies of the NCAM promoter respond appropriately to neural induction signals. Examination of the Xenopus NCAM promoter reveals a number of potential regulatory elements. We have directed our attention to a small region of the promoter that is highly conserved over large evolutionary distances. This region contains an enhancer, the OZ element, and also a silencer element, the N-box. We have purified DNA DNA proteins that interact specifically with both the OZ enhancer and the N-box silencer sequences. A model suggesting a role for these regulatory factors during neural induction is presented.

Animals↗
PubMed1989

New data confirming a circannual rhythm in spermatogenesis.

Our study demonstrates a circannual rhythm in spermatogenesis by 2697 spermiograms of healthy probands and subfertile patients. This rhythmicity is valid both for fertile as well as for subfertile men. In both groups, the lowest values of sperm count occurred in the summer while the peak values occurred in the winter and spring. For basal diagnostic purposes in male hypofertility, spermiograms should be obtained before or after the summer months. In oligospermia seasonal fluctuation in sperm density should be taken into account in in vitro fertilization and in artificial insemination, homologous.

Adolescent↗