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M C Prestige

Publications and source records attributed to M C Prestige.

11 recordsLinked to original sources
PubMed1980

Growth of a limb spinal nerve: an ultrastructural study.

A quantitative study of the delivery of nerve fibres to the developing limb has been made. Electron microscope (EM) sections of SN 9 in Xenopus were taken at close intervals between dorsal root ganglion and limb-bud. Numbers and types of axons in each section were counted. Counts declined steadily with distance from the ganglion towards the base of the limb. This is large due to some axons not having grown the full distance at the time of fixation. The slope corresponded with an outgrowth velocity of 0.5 mm a day, without branching. Distally, at stages 50 and 51, but not at stages 49 and 54, the decline was reversed, and a peak of axon number was found. This is strong evidence for axon branching in this region. Since this took place at least one stage before SN 9 bifurcated, and since the bifurcation was distal to the branching when it did appear, it is suggested that axon branching at a nerve bifurcation might be part of a trial-and-error mechanism for pathway selection. Observations were made on the sheath surrounding the nerve, and on its assembly. Initially, axons grow out naked and not parallel; Schwann cells migrate after the growing front. Processes of these cells collect individual axons, and transfer them inwards to form the primitive parallel fibre bundle, enclosed by a family of Schwann cells. Myelination later occurs in a similar manner: Schwann-cell processes extend into a bundle of naked axons and eventually encircle a single transitional axon, with one Schwann cell eventually containing many such axons. Finally comes the stage of promyelin, in which a single Schwann cell encircles a single axon. Myelin whorls are then formed from this complex.

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PubMed1976

Evidence that at least some of the motor nerve cells that die during development have first made peripheral connections.

The paper sets out to determine whether the spinal motoneurons that die during the normal development of Xenopus tadpoles have been peripherally connected before death. The numbers of cells in the control ventral horns were compared with the numbers remaining after early (stage 50 or 52/53) amputation of the limb bud. Up to stage 52, there was no difference between the two sides, but thereafter the numbers on the amputated side fell away until at stage 57 none were left. Thus, as neurons mature, they become dependent for survival on contacting the limb. During this time, there was no difference between amputees and controls in the numbers of mitoses in that part of the ventricular layer that gives rise to ventral horn cells, indicating no change in proliferation. Thus, the numbers of ventral horn cells remaining after early amputation is a measure of the numbers of cells in the normal animal that are still independent of the limb (Phase I cells) and hence by subtraction, the other cells (post-Phase I cells) are those that only survive by virtue of having contacted the limn. A graph of numbers of post-Phase I cells shows a peak at stage 54 and thereafter declines as metamorphosis approaches. This is interpreted to indicate that a number of cells that survive at stage 54 by reason of peripheral contacts or connections in the limb subsequently themselves die, that is, that al least some of the cells that die during normal development have previously made contacts within the limb.

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