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Biomedical subjects

M R Wood

Publications and source records attributed to M R Wood.

12 recordsLinked to original sources
PubMed1992

Plasmalemmal insertion and modification of sodium channels at the nerve growth cone.

We have characterized voltage-dependent sodium channels in growth cones (GCPs) isolated from fetal rat brain using saxitoxin and TTX binding as well as recordings from channels reconstituted into lipid bilayer membranes. Both high- and low-affinity binding sites are present in GCP membranes. However, the two binding sites are segregated largely or completely, with the high-affinity binding sites in the plasmalemma, and the low-affinity sites in an internal membrane compartment. Plasmalemmal insertion of these internal sites can be triggered by high-potassium depolarization and depends on a metalloendoprotease-requiring mechanism. These observations indicate that a precursor-product relationship exists between the internal and external sodium channels of the growth cone, and therefore suggest that channel externalization causes conversion of low-affinity to high-affinity saxitoxin receptors. This conversion may represent a step of channel capacitation.

Animals↗
PubMed1987

The value of stump split skin grafting following amputation for trauma in adult upper and lower limb amputees.

One hundred and twenty adult patients were reviewed in whom split skin grafts were applied to the stump following traumatic amputation of the upper limb (44 amputees) or lower limb (76 amputees). The average follow-up period was seven and a half years after initial amputation. There was delay in prosthetic fitting in all patients. Approximately one third of patients complained of occasional minor ulceration, controlled by removing the prosthesis for a few days or modification of the prosthesis. Further revision surgery, including excision of the grafted skin often combined with proximal bone resection, but not removal of the proximal joint, was necessary in 29% of below-elbow amputees and approximately 50% of below and above-knee amputees. At the above-elbow level, use of skin grafts allowed prosthetic fitting because of preservation of sufficient length of the stump. Despite the fact that revision surgery may often be necessary, split skin grafting has a definite place in the early management of the stump following traumatic limb amputation in the adult. Preservation of stump length with the knee or elbow joint allows easier rehabilitation and lower energy expenditure when using the prosthesis. Partial foot amputation, when combined with skin grafting usually requires subsequent revision to a more proximal level to obtain a satisfactory result.

Amputation Stumps↗
PubMed1987

The value of revision surgery after initial amputation of an upper or lower limb.

The value of revision surgery when carried out more than six weeks after initial amputation of the upper or lower limb was assessed. When performed for stump and/or phantom limb pain alone, only 33/95 (35%) obtained satisfactory results after one revision; 25/95 (26%) of the patients required four or more surgical procedures without relief of pain. However, when carried out for local specific pathology, the results of surgical revision were 100% successful, even if the procedure had to be repeated once in 15% (28/189) of this group of patients. Transcutaneous nerve stimulation appeared to offer no long lasting relief of pain following amputation surgery.

Adult↗
PubMed1986

Electrophysiological and morphological correlates of axotomy-induced deafferentation of the goldfish Mauthner cell.

Axotomy-induced changes in afferent synapses to the goldfish Mauthner cell have been analyzed with intracellular recordings and with electron microscopy. The studies encompassed 7-208 days after cervical spinal cord transection. The physiological findings suggest a persistent and specific reduction in excitatory chemical inputs to the soma and proximal lateral dendrite, with no changes in somatic inhibition or in the electrotonic and chemical inputs to the more distal regions of the lateral dendrite. Corroborative morphological evidence includes swelling of the M-cell soma, as indicated by a 35% increase in the length of its minor diameter, an increased spacing and a quantitatively lower density of terminals on the soma, and the appearance of astrocytic processes partially or completely engulfing the terminals in that region. Similar changes were observed on the inferior dendrites projecting from the ventral surface of the soma, although these dendrites do not exhibit the chromatolytic changes observed at the soma. In contrast, there are no noticeable changes in either the synaptic investment of the lateral dendrite or its ultrastructure. Quantitative and qualitative data support the conclusion that there is a restricted and specific reduction in the proximal excitatory inputs to the M-cell. The evidence also suggests that electrotonic junctions between afferents and the M-cell remain intact, functionally and structurally.

Afferent Pathways↗
PubMed1979

Synaptic regeneration in identified neurons of the lamprey spinal cords.

Identified reticulospinal neurons whose giant axons were severed after spinal cord transection were filled with horseradish peroxidase. Whole mounts and serial-section light and electron micrographs show axon regeneration across the spinal lesion and the formation of new synapses. Normal swimming activity returns in the spinally transected animals, although the regenerated synapses are in atypical regions of the spinal cord.

Animals↗
PubMed1977

Two types of presynaptic configurations in insect central synapses: an ultrastructural analysis.

Two structurally distinct types of synapses have been identified in the cockroach metathoracic ganglion. The two synaptic types are distinguished on the basis of (a) the shape and position of the presynaptic density seen by serial thin sectioning and (b) the arrangement and location of vesicle attachment sites (VAS) on the presynaptic membrane obtained from replicas of aldehyde-fixed, freeze-fractured neuropile. Bar-type synapses in thin sections possess a long presynaptic density located in a trough or groove opposite the extracellular space between two contiguous postsynaptic processes. In freeze-fracture, this trough is flanked by two rows of vesicle attachment sites. The second synaptic conformation consists of rows of discrete dense projections located on the convexities of the presynaptic membrane, i.e., directly opposite a single postsynaptic process. This conformation has been correlated with groups of VAS linearly arranged also on the convexities of the presynaptic membrane. These structurally different synapses may represent functionally different contacts within the insect ganglion.

Animals↗
PubMedDate not supplied

Rapidly-frozen, cultured, human endothelial cells: an ultrastructural and morphometric comparison between freshly-frozen and glutaraldehyde prefixed cells.

Cultured, human endothelial cells from the iliac vein were divided into two groups for rapid-freezing using liquid helium in a Heuser-type cryopress freezing machine. The first group of cells was prefixed in buffered 2% glutaraldehyde solution whereas the second group was freshly-frozen. Following freeze substitution and embedding, morphometric analysis was carried out on thin sections of groups of endothelial cells. Measurements showed that glutaraldehyde prefixation significantly increases the numerical and volume densities of the vesicles compared to those of the freshly-frozen cells. However, the fact that no significant increase was demonstrated either in the numerical or volume densities of the caveolae, and that no significant change was observed in the ratio of the cell perimeter to area, suggests that the membrane source for these extra vesicles is internally generated. Studies are currently under way to identify the source of this membrane.

Cells, Cultured↗