Myelin from human peripheral nerves. Quantitative and qualitative studies in two age groups.

Myelin in femoral nerve segments obtained at autopsy was isolated quantitatively by a series of discontinuous and continuous flotation procedures. The total amount of myelin isolated from these nerves was expressed as the sum of cholesterol, glycolipid, phospholipid, and protein and averaged 2.6+/-0.4 mg/g in a group aged 60-77 yr compared with 10.8+/-1.9 mg/g of nerve in a group aged 35-58 yr. The lower value in the older group remained apparent whether the myelin content was related to the whole nerve segment, its unit length or weight. This indicates that the decrease is an absolute one, not related to a change with aging in the nonmyelin content of nerve. No qualitative differences in myelin lipids were found between the two groups. Protein content was, however, significantly higher in the older group (34 and 28.7% of the total myelin weight, respectively). The decrease in myelin content with aging, observed by direct measurement in this study, may be the structural counterpart to age related alterations in peripheral nerve function-decreased conduction velocity, and impaired appreciation of vibration.

The characterization of type I and type III collagens from human peripheral nerve.

The normal chemical features of peripheral nerve collagens were determined on postmortem, histologically normal adult human femoral nerve. 1. Genetically distinct type I, [alpha1(I)2]alpha2, and type III, [alpha1(III)]3, were isolated by differential salt precipitation and the component subunit chains, alphal(I), alpha2 and alphal(III) were obtained by ion-exchange chromatography and gel filtration. 2. The molecular weight of alphal(I) and alpha2 of type I collagen was 95 000 and that for type III was 280 000. Reduction of type III with dithiothreitol yielded expected alpha1(III) chains of 95 000 molecular weight. 3. The amino acid composition of the three collagen chains, alpha1(I), alpha2, and alpha1(III), was the same as previously reported values for the corresponding chains from human skin except for slightly elevated hydroxylysine content. 4. Peripheral nerve collagen was found to contain 81% type I collagen and 19% type III. These results indicate that peripheral nerve collagen characteristics closely simulate that of human skin and differ from that of human aorta and other parenchymal organs. These data will permit a chemical analysis for possible abnormalities of peripheral nerve collagen in various neurogenic disorders.

Why can't you achieve adequate regional anesthesia in the presence of infection?

Observed in this study were morphologic changes in inflamed nerves, along with biochemical changes, which appear to act concurrently to deactivate or prevent activation of the local anesthetic solution. Morphologic changes were observed along the nerve fiber distant from the inflammatory site. These neuro-degenerative changes were seen at the axon and myelin sheaths level. The biochemical data support the presence in the inflamed nerve of amino acids which may be the product of lysosomal rupture and proteolytic enzyme release. These inflammatory mediators may affect either the local anesthetic or the environment of the nerve fiber. The precise mechanism of action of these catalytic products cannot be determined from this study.