Conduction in myelinated, unmyelinated, and demyelinated fibers

Conduction in demyelinated axons is characterized by decreased conduction velocity, temporal dispersion of impulses, and conduction failure. It is not possible to infer the electrical properties of the bared internodal axon membrane in demyelinated fibers from observations of decreased conduction velocity or conduction failure. Cytochemical evidence indicates that there are, in fact, distinct structural differences between nodal and internodal regions of the normal axon membrane. This conclusion is confirmed by freeze-fracture and pharmacological studies. A number of approaches to the development of effective symptomatic therapy in the demyelinating diseases are suggested by recent experimental findings: determination of the membrane properties necessary for conduction across focally demyelinated regions and the identification of agents that would encourage the development of these properties; alterations in the external milieu of demyelinated fibers; and the development of agents that might promote remyelination.     

Cervical angiofollicular lymph node hyperplasia (lymphoid hamartoma)

A case of the hyaline vascular type of angiofollicular lymph node hyperplasia (lymphoid hamartoma) in the neck of a 25-year-old Hindu male is reported. A brief review of the literature is presented and relevant clinical, pathological and therapeutic aspects of this lesion are discussed.     

Genetics, ethics, and Alzheimer disease

This article considers the emerging research on Alzheimer disease (AD) genetics in relation to ethical questions surrounding presymptomatic and prenatal genetic testing. Given the rapid advance in AD genetics over the past 8 years, it is likely that the attention of clinicians and ethicists will increasingly turn to genetic issues. After a survey of current genetic knowledge, this article addresses 3 areas of likely ethical concern. While AD genetic screening programs are currently rare and restricted to specific pedigrees, they will become more common in the future. It is, therefore, imperative that society and clinicians begin to consider the ethical issues this raises.     

Effect of the A and B variants of both alpha s1- and kappa-casein on bovine casein micelle solvation and kappa-casein content

Casein micelle solvation, a micelle characteristic that is sensitive to many factors, has been measured by a centrifugation technique at 30 degrees C for a series of uncooled fresh skim milks at pH 6.3, 6.6, 6.9 and 7.1. The relative alpha s-(alpha s1-plus alpha s2-), beta- and kappa-casein contents of all centrifuge pellets and supernatants were determined by a standardized electrophoretic method. The calcium and phosphate contents of a number of the pellets and milk samples were also determined. Solvation of micelles from milks with various genetic variants of beta-lactoglobulin (A and B), alpha s1-casein (A and B) and kappa-casein (A and B) was often found to be lower for milks containing either the B variant of alpha s1-casein or the A variant of kappa-casein. It was also found that these two variant caseins were associated with a lower kappa-casein. It was also found that these two variant caseins were associated with a lower kappa-casein content of the milks and the micelles, which is consistent with the lower solvation as kappa-casein is associated with smaller micelle size and greater solvation. The solvations also seemed to increase during the lactation period. It is possible that some of the other features of milk and its products that have been ascribed to the differences in functional character between the A and B variants of alpha s1-casein may be partly caused by the increased level of kappa-casein. The reason for the association of the A variant of alpha s1-casein with higher concentrations of kappa-casein (and micelle solvation) is not obvious but possibly the haplotype alpha s1-casein A, beta-casein A1, kappa-casein A contains a controlling sequence in the chromosomal DNA that enhances expression of the kappa-casein gene.