Biomedical subjects
Publications and source records attributed to J Cooke.
The flexor tendons of the middle toes of chickens were divided and the flexor profundus repaired after varying intervals up to 6 weeks. The best results were obtained with repairs within a few hours, the next best with repairs any time after the 10th day and the worst with repairs between the 4th and 7th days.
Tectal polarity for retinal connections remains reversible long after the anatomical pattern of neural structures has been determined. Cells in the diencephalon seem to control this polarity. Following certain embryonic operations, the diencephalon developed behind the tectum. In such cases, the polarity of the retino-tectal projection was reversed.
During Xenopus embryogenesis and early growth, somite number stays close to a species-typical value for each morphological stage. This remains true even after operations on blastulae which lead to the development of abnormally small but otherwise complete early embryos, involving reduction in number of cells assigned to each somite. Evidence presented suggests that a body-position gradient may be involved, but in rather different ways at different stages, in controlling total somite number.
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The time-course of the remaining gastrulation movements has been investigated after removal of the dorsal lip, the presumptive foregut endoderm and the anterior mid-dorsal mesoderm as a plug-shaped mass of cells from beginning gastrulae of Xenopus laevis and Bombina orientalis. This embryonic region has been previously studied in its role as an organizer, when grafted into a host gastrula marginal zone. There is usually no effect of the removal of these cells, the first morphogenetically active ones, either upon rate of subsequent completion of the external aspects of gastrulation, or upon the internal evolution of the presumptive mesodermal mantle. This finding is discussed in connexion with results of a previous paper on pattern formation in early Xenopus development, since it may help to distinguish between possible types of explanation for those results.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
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Following radiation treatment, ablative surgery, and surgical flap reconstruction in cases of oral cancer, postoperative follow-up for oral cancer recurrence presents a difficult task. Computed tomography (CT) remains the most accessible method of postoperative assessment; however, it has yet to be conclusively shown to provide an advantage over an adequate history and physical examination. Twenty-four consecutive patients who had undergone flap reconstruction of the oral cavity for advanced or radiorecurrent disease were studied over an 18-month period. Eight patients showed no evidence of recurrent tumor either clinically or by CT scan. Eleven patients had evidence of recurrent disease clinically, which was confirmed by CT. In four patients, clinically unsuspected regional recurrent tumor was revealed by CT. One false negative scan was encountered. CT proved to be a sensitive modality for detecting clinically unsuspected recurrences, particularly regional recurrences.
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The amphibian nervous system has long been thought to arise from within a large (greater than 10(3) population of dorsal ectodermal cells, that would otherwise differentiate only as epidermis, as a result of inductive signals from underlying dorsal mesoderm at gastrulation. It has recently been claimed, however, that small cell groups are set aside much earlier in amphibian development, as the sole founders of particular portions or 'compartments' of the body plan. This would imply a dramatic re-interpretation of classical experiments where a second dorsal blastoporal lip, grafted to the ventral side of a gastrula containing 10,000 or more cells, causes there the development of a second central nervous system (CNS) in host tissue. We show that such surgically induced second nervous systems are made by host cells which have lineages separate from those that contribute to the original CNS from the 32-cell stage. Thus neural induction can occur as traditionally supposed, by assignment of ectodermal cell fate in relation to dorsal mesoderm during gastrulation. We discuss the implications of this for the recent proposals about early compartmentation in vertebrate development.
The formation of a body plan from an initially radially symmetrical egg during animal development is presumed to involve a 'positional system'and a subsequent mechanism of local response to position values provided by this system. Early gene products intimately connected with the latter response mechanism have been identified in Drosophila, and because these share conserved sequences with possible counterparts in vertebrates , there is renewed interest in understanding the physiological nature of the positional system itself in a vertebrate embryo. In the frog Xenopus, body position value appears to be specified in outline across much of the egg material by stages comprising a few cells, after only approximately 2h of development. This is already suggestive of a structural or mechanical recording system rather than a diffusion-controlled gradient. I describe here an experiment aimed at perturbing the positional system by causing gravity-driven rearrangements within eggs which conflict with their own, self-organizing rearrangements near the time of the first cleavage. The system appears to retain its full regulatory properties during only a brief time interval, so that records of positional profiles disturbed at the close of that interval are permanent, and give rise to systematically abnormal body patterns in otherwise healthy larvae. The results are inconsistent with the notion that Xenopus primary pattern results from a set of determinant 'plasms' in the egg, or from a mechanism dominated by long-range diffusion of molecules.