Ultrastructural survey of the spinal cord of young tuatara (Sphenodon punctatus) with emphasis on the glia

Abstract

The caudal spinal cord of three 3-month old Sphenodon were examined by light and electron microscopy. The normal spinal cord shows white matter being invaded by dark cells of a seemingly oligodendrocyte type, which appear to be forming myelin sheaths. The presence of large numbers of filaments (7–10 nm in diameter) between the standard organelles, including microtubules of 20–24 nm diameter, is unusual for oligodendrocytes, but quite typical for astrocytes. A single oligodendrocyte-like cell can envelope many axons in order to delimit specific areas of white matter. In 3-month old tuatara it is difficult to discriminate between oligodendrocytes, astrocytes, and various neural elements in the dorsal region of the spinal cord because they are still insufficiently differentiated. Motoneurons, however, are well developed. Ependymal cells resemble oligodendrocyte-like cells, but have retained an epithelial position with desmosomes in order to delimit the central canal. These cells possess intermediate to low electron-density, and contain many filaments of 7–10 nm width and some typical microtubules. The spinal cord is covered by an elastic leptomeninx.

Keywords:

• Central nervous system
• spinal cord
• glial cells
• ultrastructure
• tuatara
• Sphenodon punctatus