Spectra of G ratio, myelin sheath thickness, and axon and fiber diameter in the guinea pig optic nerve

John Guy, E. Ann Ellis, Kay Kelley, G. Marion Hope

Research output: Contribution to journalArticlepeer-review

71 Scopus citations


The spectra of fiber and axon diameter, myelin sheath thickness, fiber density, and g ratio of the optic nerve were analyzed for the strain-13 guinea pig, an animal extensively utilized in the investigation of experimental disorders of demyelination. Our detailed analytical study of the normal guinea pig optic nerve provides the basis for comparison to disease states and the morphology of other species. As in the rat, mouse, and chipmunk, fiber diameters in the guinea pig were unimodal, but dissimilar to the trimodal fiber spectra of the cat and primate. The predominance of medium-sized fibers (0.80-2.00 μm), common to most species, contributed to the larger mean fiber diameter (1.45 μm) of the guinea pig optic nerve, in which small fibers (0.50 μm or less) were infrequent and fibers larger than 5.00 μm in diameter, seen in the cat and primate, were absent. While myelin sheath thickness increased with axon diameter in the guinea pig, as in other species, a g ratio of 0.81 in the guinea pig was greater than in most mammals. Since conduction velocity is dependent on axon size, as well as myelin properties, the relatively larger mean axon diameter of the guinea pig optic nerve (1.18 μm) may compensate for the decrease in its myelination.

Original languageEnglish (US)
Pages (from-to)446-454
Number of pages9
JournalJournal of Comparative Neurology
Issue number4
StatePublished - Sep 22 1989
Externally publishedYes


  • conduction
  • electron microscopy
  • morphometric analysis

ASJC Scopus subject areas

  • Neuroscience(all)


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