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Biomedical subjects

R F Mayer

Publications and source records attributed to R F Mayer.

At least 55 records · Page 3Linked to original sources
PubMed1983

Contractile properties of rat fast-twitch skeletal muscle during reinnervation: effects of testosterone and castration.

The isometric contractile properties of skeletal muscle were examined after nerve crush to establish the temporal sequence of recovery during reinnervation of normal, castrated, and testosterone-treated rats. Extensor digitorum longus muscles of male rats were studied in vivo 8 to 21 days after crushing the peroneal nerve 1 cm from the muscle. The earliest signs of functional reinnervation in normal animals were observed 8 to 9 days after nerve crush when faint muscle twitches with markedly prolonged twitch contraction times were recorded. By days 10 and 11, twitch tension was 9 to 20% of control, twitch contraction time was 149 to 183% of control, and tetanic tension was 4 to 9% of control values. The optimal frequency of stimulation was 58 to 64 Hz, the twitch:tetanus ratio was three times control values, and little or no posttetanic potentiation of twitch tension was observed. During the next 9 days there was a gradual return of all experimentally measured contractile properties toward control values; the relative rate of return was twitch tension greater than twitch contraction time greater than twitch:tetanus ratio greater than tetanic tension greater than optimal frequency of stimulation greater than posttetanic potentiation. Neither testosterone nor castration significantly altered either the rate or extent of functional reinnervation 8 to 21 days after nerve crush (P greater than 0.05). During this period the twitch:tetanus ratio for any given animal was highly correlated (r = 0.83, P less than 0.001) with the extent of functional recovery of neurally evoked muscle tension and was determined to be the most reliable index of the degree of muscle reinnervation. These data provide valuable baseline information for future studies of reinnervation of skeletal muscle.

Animals↗
PubMed1982

Physiological alterations of motor units in hemiplegia.

Isometric contractions of single motor units in the first dorsal interosseous muscle were recorded with an intramuscular microstimulation technique in patients with short- or long-term hemiplegia and compared with controls. In the hemiplegic patients motor units could be classified as in controls, utilizing twitch contraction time and fatigue sensitivity, as FF (fast fatigable), FR (fast fatigue resistant) and S (slow fatigable). The mean twitch contraction time of fast-twitch but not slow-twitch units was slightly prolonged in patients with spastic hemiplegia and motor units, especially type S, tended to generate larger twitch tensions. A fourth type of motor unit, characterized by slow-twitch contraction times and increased fatigability (SF units), was recorded in long-term hemiplegia. The data demonstrate that during long-term spastic hemiplegia in man some motor units develop increased fatigability and prolonged-twitch contraction times, reflecting the dynamic properties of muscle.

Adult↗
PubMed1982

Neuromuscular transmission in single motor units in myasthenia gravis.

Forty-eight single motor units (MUs) were recorded in the first dorsal interosseous muscle in 10 patients with generalized myasthenia gravis (MG) using the technique of intramuscular microstimulation. The data were compared statistically with 126 MUs recorded from 19 controls. Motor units were characterized as fast-twitch fatigable (FF), fast-twitch fatique resistant (FR), and slow-twitch (S). There was a preponderance of fast-twitch MUs in the MG sample. Decremental action potentials greater than 10% were recorded in both fast- and slow-twitch units in MG, but the mean percent decrement was greater in F than in S units. Mean twitch contraction and half-relaxation times were faster in MG MUs than in controls. No significant change in mean twitch tension was recorded in either F or S units. The study shows that the defect in neuromuscular transmission in MG is not selective for one MU type.

Adult↗
PubMed1981

Neural regulation of glucose 6-phosphate dehydrogenase in rat muscle: effect of denervation and reinnervation.

We tested the hypothesis that glucose 6-phosphate dehydrogenase (G6PD) in rat extensor digitorum longus (EDL) muscle is under neural control by studying changes in G6PD activity in EDL muscles following nerve crush-induced denervation and reinnervation. Changes in G6PD were correlated with choline acetyltransferase activity, as well as with neurological function, muscle weights, and muscle isometric twitch tension. The data show a dramatic increase in G6PD following denervation. The gradual recovery of enzyme activity toward normal levels correlates with the return of functional synaptogenesis manifested by the return of neurological function, choline acetyltransferase, and muscle twitch tension. We conclude, therefore, that muscle G6PD is under neural control. G6PD activity provides a facial biochemical indicator of muscle reinnervation.

Animals↗
PubMed1981

Recent advances in the molecular mechanisms of human and animal models of myasthenia gravis.

The receptor-channel molecule is a dynamic system which exists in multiple conformations and that is the way we should think of it when we study antibody interaction with the molecule. The results presented here suggest that some antibodies may affect receptor function by occupying sites other than the receptor site. Some of these sites may by exposed only in certain conformations, and occupation of some site by antibodies may effect conformational changes. These small but perhaps important differences in cholinergic channel properties of the myasthenic muscle from the normal one are revealed by studying the effect of myasthenic sera on drug interactions with the channel sites. The sera of myasthenics are able to react with certain channel conformations and are able to affect the interaction of channel antagonists such as H12HTX and QNB. The sera appear to act preferentially with the open conformation of the channel. As a consequence of such an effect, important conformational changes of the channel may fail to occur upon activation.

Acetylcholine↗
PubMed1981

Freeze fracture studies of human neuromuscular junctions. Membrane alterations observed in myasthenia gravis.

Freeze fracture replicas of neuromuscular junctions from normal human patients and those with facioscapulohumeral and limb girdle muscular dystrophies, progressive muscular atrophy, and myasthenia gravis were examined by stereoscopic electron microscopy. Endplates from most human patients closely resemble those of normal adult rats fixed by intravascular perfusion. However, endplates from patients with myasthenia gravis have clinically relevant alterations in postsynaptic membrane infrastructure, including decreased number of P-face particles and increased number of E-face particles in the crests of the junctional folds. Other junctional fold crests are narrowed or obliterated and are replaced by incompletely sealed membrane vesicles rich in intramembrane particles. Similar alterations are not produced in rat endplates by immersion fixation, exposure to low pH, brief hypoxia, prolonged or extreme hypothermia, prolonged or high frequency nerve stimulation, or by prolonged nerve quiescence. Rather, the destructive alterations observed in junctional fold membranes in myasthenia gravis endplates are correlated with decreased acetylcholine sensitivity and to removal of endplate acetylcholine receptors by immunologic processes.

Animals↗
PubMed1980

Malignant fibrous histiocytoma of the kidney.

We report on a 33-year-old woman with malignant fibrous histiocytoma of the kidney. This malignant mesenchymal tumor is indistinguishable clinically and radiologically from a renal cell carcinoma. In our patient the tumor recurred locally following nephrectomy and metastasized to the lung. Post-nephrectomy radiation and chemotherapy may not alter the poor prognosis.

Adult↗
PubMed1978

Structure and function of the motor unit. Effects of immobilization, monoparesis or paraplegia.

Single motor units have been studied in the medial gastrocnemius muscle in cat following acute or chronic unilateral hind limb immobilization or antero-lateral spinal cord section. Immobilization produces muscle atrophy by 5 weeks and in the chronic phase (4-6 months) is characterized functionally by reduced twitch and tetanus tensions and structurally by fiber atrophy without type grouping or preponderance. Antero-lateral cord section with minimal motor dysfunction does not produce muscle atrophy or change in tension but in the chronic animals there is a slight decrease in twitch-tetanus ratios. Changes in the functional properties of motor units reflect changes in structure and both may result from secondary effects (i.e., type and amount of muscle activity, muscle length, pain, etc.) of a neuromuscular disease on muscle.

Animals↗
PubMed1977

Assessment of cellular and humoral immunity of myasthenics.

A close association of autoimmune diseases or autoimmune phenomena in myasthenia gravis is well known. A comprehensive immunological study of 22 patients with myasthenia gravis showed that changes in the immune system mainly involve the thymus-derived lymphocytes (T cells). Anti-thymus antibody was present in 90% of the patients, and it paralleled the frequency of thymic abnormality in myasthenia gravis. It is postulated that in myasthenia gravis the altered T cell functions caused by anti-thymus antibody result in the formation of an array of autoantibodies including the factor which blocks the neuromuscular transmission.

Adolescent↗