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Biomedical subjects

J G Scott

Publications and source records attributed to J G Scott.

At least 109 records · Page 6Linked to original sources
PubMed1979

Molecular heterogeneity of Hageman trait (factor XII deficiency): evidence that two of 49 subjects are cross-reacting material positive (CRM+).

We have studied plasmas of 49 individuals with homozygous Hageman trait from 42 kindreds, all of which contained less than 1% of the Hageman factor (factor XII) clotting activity of pooled normal plasmas. Forty-seven plasmas contained less than 1% of Hageman factor antigen. In two other, unrelated individuals with Hageman trait, nonfunctional material immunologically indistinguishable from normal Hageman factor was detected in plasma by radioimmunoassay at concentrations of 39% and 80%, respectively. These plasmas did not contain circulating anticoagulants against Hageman factor and, as in ordinary Hageman trait, displayed impaired surface-mediated plasma reactions such as fibrinolysis and kinin generation. Upon immunodiffusion against anti-Hageman factor serum, these plasmas formed a single precipitin line of complete identity with normal plasma or purified Hageman factor. Upon immunoelectrophoresis, the precipitin line had the same mobility as normal Hageman factor. Nonfunctional Hageman factor and normal Hageman factor behaved identically on a Sephadex G-150 column (apparent MW = 100,000) and on sucrose density-gradient centrifugation (4.5S). Nonfunctional Hageman factor was adsorbed to kaolin as readily as normal Hageman factor, suggesting that the binding site to negatively charged surfaces is different from functional sites. Antiserum raised against Hageman factor-like material in a CRM+ Hageman trait plasma specifically inactivated Hageman factor activity in normal plasma. The plasmas of three heterozygotes in these families contained approximately twice as much Hageman factor antigen as Hageman factor activity, whereas those of 16 heterozygotes in ordinary (CRM-) Hageman trait families contained approximately equal amounts of activity and antigen. The present study indicates that rarely homozygous Hageman trait may be CRM+ and that this defect is genetically determined.

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PubMed1976

Alterations of synapses on axotomized motoneurones.

1. Properties of medial gastrocnemius motoneurones in cats were examined with intracellular electrodes 1-77 days after partial transection of the medial gastrocnemius muscle nerve. 2. Three sequential stages of reaction were defined: (i) firstly, conduction velocity of axotomized motoneurones fell, but e.p.s.p. properties and Ia-motoneurone connectivity were normal; (ii) secondly, e.p.s.p.s became characterized by prolonged rise times and half-widths and by diminished amplitudes; (iii) finally, failures of connectivity were also seen, that is, Ia spindle afferent fibres connected with fewer axotomized than normal homonymous motoneurones. 3. The reason for the change of e.p.s.p. properties cannot be stated with certainty: among the factors may be (i) a change of motoneurone membrane properties and morphology; (ii) partial detachment of synaptic boutons before their total disconnexion, and (iii) detachment of Ia afferent branches terminating on the motoneurone soma before those on the dendrites. 4. The previous conclusion that alteration of e.p.s.p. profiles following motoneurone axotomy was due to total disconnexion of those Ia fibres making synapses on the soma and proximal dendrites ("somatic stripping") must be modified to account for the findings that e.p.s.p. changes are seen before connectivity changes.

Animals↗
PubMed1976

Individual EPSPs produced by single triceps surae Ia afferent fibers in homonymous and heteronymous motoneurons.

1. The individual EPSPs evoked by the action of single Ia fibers from cat triceps surae (MG, LG, SOL) were recorded in homonymous and heteronymous motoneurons innervating these same three muscles. 2. In general, Ia fibers projected to a greater percentage of homonymous than heteronymous motoneurons. One class of Ia afferent evoked EPSPs in virtually all homonymous motoneurons; the other had a substantially lower projection frequency. Possible difficulties introduced by the limited resolution of the averaging technique are discussed. 3. Individual EPSPs were larger on the average if evoked a) in SOL rather than in MG or LG motoneurons, b) by LG rather than by MG or SOL afferent fibers, or c) in homonymous rather than in heteronymous motoneurons. The mean EPSP was larger in homonymous than in heteronymous motoneurons because the largest EPSPs (greater than 150 muV) were found mainly in homonymous motoneurons. 4. Rise times of EPSPs were only slightly shorter in homonymous than in heteronymous motoneurons, suggesting that other factors besides relative location of Ia terminals account for the observed EPSP amplitude differences. Rise times in SOL motoneurons were longer than those in MG or LG. 5. LG afferent fibers tended to produce larger EPSPs in rostral than in caudal LG motoneurons, and MG afferents produced larger EPSPs in caudal than in rostral MG motoneurons. These spatial effects were in accord with the more rostral entry of LG than MG Ia afferents into the spinal cord. The differential projection of SOL afferents to MG and SOL motoneurons which overlap spatially in the spinal cord suggests a species specificity in addition to a location specificity.

Animals↗
PubMed1975

The effect of peripheral nerve cross-union on connections of single Ia fibers to motoneurons.

The distribution of Ia terminals to alpha-motoneurons has been investigated under conditions where a) the Ia fiber innervates a foreign muscle and b) the motor axon innervates a foreign muscle. This distribution has been assessed by examining which motoneurons develop an EPSP in response to stimulation of a single Ia afferent fiber. Cross-union of the medial gastrocnemius and lateral gastrocnemius-soleus nerves has been performed in 5--8 day old kittens and the effect of this procedure on Ia connections to alpha-motoneurons has been investigated in the adult about one year later. No rearrangement of synaptic connections has been observed under these conditions. The connections from self-unioned Ia afferents and to self-unioned motoneurons are also normal. The individual EPSP's in these motoneurons with regenerated axons have normal rise times. The findings of normal Ia connections as well as normal EPSP rise times in alpha-motoneurons with regenerated motor axons indicates reversibility of the changes seen in axotomized motoneurons.

Animals↗