, Volume 152, Issue 1, pp 51-67

An ultrastructural analysis of myelin in the central nervous system of an amphibian

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Summary

An ultrastructural analysis of myelin in the ventral habenular and in the interpeduncular nuclei of the adult frog Rana esculenta has been carried out. In the ventral habenular nuclei, in addition to normally myelinated fibres, some myelin irregularities have been observed. They consist of myelin enwrapping the perikarya of some neurons and of isolated flaps of collapsed myelin. In the interpeduncular nucleus numerous myelinated fibres occur but few redundant myelin irregularities have been noticed.

The morphological data suggest that myelination of fibres in these sites is due to the spiral wrapping mechanism from a glial cell process while the myelin irregularities described in the ventral habenular nuclei are probably due to membrane synthesis within the cytoplasm of the myelinated neurons and of the oligodendrocytes which are sometimes observed in contact with the ensheathed neurons. In the interpeduncular nucleus myelinated fibres indenting astrocytes and oligodendrocytes have been observed.

The autor would like to express appreciation to Dr. R. Martin of Stazione Zoologica, Naples, for his constant support and to Mr. G. Dafnis for his assistance at the electron microscope.