Biomedical subjects
M Sparks
Publications and source records attributed to M Sparks.
Helping the parents after a baby's death.
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Peripheral axotomy induces neurofilament decrease, atrophy, demyelination and degeneration of root and fasciculus gracilis fibers.
We have recently shown that peripheral axotomy by hindlimb amputation in adult cats sequentially results in neurofilament and microtubule decrease and axonal atrophy, myelin wrinkling, myelin remodeling (de- and remyelination), more atrophy and axonal degeneration in proximal sciatic and L7 segmental nerve fibers. The neuropathologic, morphometric and teased fiber alterations in the myelinated fibers (MF) of roots and sampled levels of fasciculus gracilis in groups of adult cats 24 months after hindlimb amputation have now been studied. We found: a severe decrease of neurofilaments, axonal atrophy, myelin wrinkling, de- and remyelination and axonal loss in posterior root axons; that these morphologic abnormalities extended up the fasciculus gracilis in the appropriate territories established from degenerative studies; that the retrograde effect was less severe in ventral root fibers, although atrophy and sprouting were demonstrated here, and that the cellular sequence of retrograde atrophic degeneration of ascending axons was similar to that observed in proximal stump axons. These findings confirm that primary afferent neurons are more vulnerable to axotomy than lower motor neurons and may provide an additional explanation for the poorer functional restoration of sensory than of motor deficit after root compression and in delayed nerve reconnection. Our observations also have important implications for interpretation of neuropathologic alterations in roots and fasciculus gracilis, since the observed features may be secondary to axotomy of peripheral nerve fibers induced by disease and not evidence of a primary derangement.
Minimal pathologic expression of a mutant gene for hereditary motor and sensory neuropathy.
Transverse sections of the sural nerve of a 46-year-old woman without neuropathic symptoms or abnormalities on nerve conduction, electromyography, or computer-assisted sensory examination contained minute regions with large onion bulbs intermingled with normal-appearing myelinated fibers and surrounded by fields of normal myelinated fibers. This woman's 19-year-old daughter had long-standing hypertrophic neuropathy with diffusely distributed large onion bulbs. Computer-imaging reconstruction of myelinated fibers and teased myelinated fiber studies of fascicles containing focal regions with onion bulbs of the mother's nerve provided evidence that onion bulbs surrounded atrophic axons with short internodes and demyelination. This is the least expression for inherited neuropathy which has been reported. These findings therefore suggest that an inherited neuropathy may be minimally expressed by a pathologic alteration of only selected neurons (axons).
The morphometric composition of myelinated fibres by nerve, level and species related to nerve microenvironment and ischaemia.
An extensive morphometric evaluation of the number, density and diameter distribution of myelinated fibres (MFs) of different nerves, of different proximal-distal levels of nerves, and of different species is reported. The methodology used provides reliable estimates of number and size because of the use of optimal histological techniques, semi-thin sections, careful systematic sampling, nonsubjective evaluation of transverse MF profiles using computerized imaging and evaluation of large numbers of MFs and nerves. The non-MF percentage of endoneurial area was also measured as an index of the amount of nerve microenvironment. We have confirmed that the MF composition is quite variable between nerves, between levels of nerves, and between species. In general the density of MFs is lower in the nerves of man than in the nerves of other animals evaluated, in distal than in proximal levels, in old age and in disease. Although increased endoneurial fluid may play a role in resistance to ischaemic block it appears that the intrinsic metabolic properties of the neural tissue itself are most important.
Permanent axotomy, a model of axonal atrophy and secondary segmental demyelination and remyelination.
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