Varicosities of intraretinal ganglion cell axons in human and nonhuman primates.
OBJECTIVE
To describe varicosities of intraretinal ganglion cell axons in the nerve fiber layer of human and nonhuman primate retinas.


METHODS
Intraretinal ganglion cell axons of seven human donors (1-85 years old) and two nonhuman primates (Macaca mulatta, 15 and 17 years old) were immunohistochemically stained with an antibody of neurofilament on flatmounted retinas and examined with light microscopy. In addition, the axons within the retinal nerve fiber layer were examined with transmission electron microscopy in one human and one nonhuman retina. The variations of diameters of single axons were measured on transverse- and parallel-cut sections, and the frequency distributions of the diameters were statistically evaluated.


RESULTS
Varicosities of the intraretinal ganglion cell axons were found throughout the retinas in both nonhuman primate and human eyes of all ages examined. The varicosities were rich in mitochondria and had desmosome- and hemidesmosome-like junctions with other axons and retinal glial cells. Measured on parallel-cut axons, the mean diameter (+/-SD) of varicosities was 2.7 +/- 0.9 micro m, whereas the mean diameter of intervaricosity regions was 0.7 +/- 0.3 micro m. The diameter distribution for transverse-cut axons was also bimodal, but the two peaks were much closer because the peak of the larger-diameter group decreased.


CONCLUSIONS
The results demonstrated that intraretinal ganglion cell axons are predominantly varicose fibers in both human and nonhuman primates. Size variations exist within a single axon's diameter and thereby affect the patterns of diameter distribution seen in transverse-cut preparations. The mitochondria-rich varicosities and the presence of intercellular junctions suggest that the varicosities may be functional sites that serve local high-energy demands of unmyelinated fibers and signal transmission.
Wang
Lin
L
Discoveries in Sight, Devers Eye Institute, 1225 NE 2nd Avenue, Portland, OR 97232, USA.
Dong
Jin
J
Cull
Grant
G
Fortune
Brad
B
Cioffi
George A
GA
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001369:Axons / Q000378:metabolism / Q000648:ultrastructure*; D048429:Cell Size; D002675:Child, Preschool; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007223:Infant; D008253:Macaca mulatta; D036421:Nerve Fibers, Unmyelinated / Q000378:metabolism / Q000648:ultrastructure*; D016900:Neurofilament Proteins / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure*
D016900:Neurofilament Proteins; C051774:neurofilament protein H