Increased myelination related enzymatic activities in neuron-glial heterokarya

Co-culture study of rat neuron-glial interaction: evidence of neuronal influence on myelination

Organotypic cultures of newborn rat brains were exposed to the neurotoxin kainic acid or the DNA synthesis inhibitor arabinoside C. The cultures were subsequently co-cultured and the myelination-related enzymatic activities, such as 2',3'-cyclic nucleotide phosphohydrolase and uridine diphosphate-galactose-ceramide galactosyl transferase, were determined under various culture conditions. The newly formed myelin basic protein in the cultured brain tissue was determined by the radioimmunoprecipitation method. The myelination-related enzymatic activities and the synthesis and accumulation of myelin basic protein in the co-cultured brain tissue were found compatible to the control cultures which were not exposed to either drug. The cultures which had been treated with either drug, but not subsequently co-cultured, were found to have decreased enzymatic activities and myelin basic protein synthesis. The experimental data suggest that myelinogenesis requires an interaction between functional neurons and oligodendroglial cells and further supports the hypothesis that the neuron exerts a regulatory effect on the glial myelination mechanism.

Lipids of nervous tissue: composition and metabolism

As indicated in the Introduction, the many significant developments in the recent past in our knowledge of the lipids of the nervous system have been collated in this article. That there is a sustained interest in this field is evident from the rather long bibliography which is itself selective. Obviously, it is not possible to summarize a review in which the chemistry, distribution and metabolism of a great variety of lipids have been discussed. However, from the progress of research, some general conclusions may be drawn. The period of discovery of new lipids in the nervous system appears to be over. All the major lipid components have been discovered and a great deal is now known about their structure and metabolism. Analytical data on the lipid composition of the CNS are available for a number of species and such data on the major areas of the brain are also at hand but information on the various subregions is meagre. Such investigations may yet provide clues to the role of lipids in brain function. Compared to CNS, information on PNS is less adequate. Further research on PNS would be worthwhile as it is amenable for experimental manipulation and complex mechanisms such as myelination can be investigated in this tissue. There are reports correlating lipid constituents with the increased complexity in the organization of the nervous system during evolution. This line of investigation may prove useful. The basic aim of research on the lipids of the nervous tissue is to unravel their functional significance. Most of the hydrophobic moieties of the nervous tissue lipids are comprised of very long chain, highly unsaturated and in some cases hydroxylated residues, and recent studies have shown that each lipid class contains characteristic molecular species. Their contribution to the properties of neural membranes such as excitability remains to be elucidated. Similarly, a large proportion of the phospholipid molecules in the myelin membrane are ethanolamine plasmalogens and their importance in this membrane is not known. It is firmly established that phosphatidylinositol and possibly polyphosphoinositides are involved with events at the synapse during impulse propagation, but their precise role in molecular terms is not clear. Gangliosides, with their structural complexity and amphipathic nature, have been implicated in a number of biological events which include cellular recognition and acting as adjuncts at receptor sites. More recently, growth promoting and neuritogenic functions have been ascribed to gangliosides. These interesting properties of gangliosides wIll undoubtedly attract greater attention in the future.(ABSTRACT TRUNCATED AT 400 WORDS)

mRNA-directed cell-free myelin basic protein synthesis: no evidence of neuronal control

The specific mRNA of myelin basic protein (MBP) was isolated from active myelinating rat brains. The isolated mRNA was able to direct the synthesis of immunochemically detectable MBP in a wheat-germ cell free protein synthesis system. There was, however, no evidence of neuronal translational control of the in vitro MBP synthesis kinetics found within the experimental parameters. The possibility of neuronal control of MBP gene expression is therefore postulated likely to be at the transcriptional level.