A model to study differences between primary and secondary degeneration of retinal ganglion cells in rats by partial optic nerve transection.
OBJECTIVE
To use a rat model of optic nerve injury to differentiate primary and secondary retinal ganglion cell (RGC) injury.


METHODS
Under general anesthesia, a modified diamond knife was used to transect the superior one third of the orbital optic nerve in albino Wistar rats. The number of surviving RGC was quantified by counting both the number of cells retrogradely filled with fluorescent gold dye injected into the superior colliculus 1 week before nerve injury and the number of axons in optic nerve cross sections. RGCs were counted in 56 rats, with 24 regions examined in each retinal wholemount. Rats were studied at 4 days, 8 days, 4 weeks, and 9 weeks after transection. The interocular difference in RGCs was also compared in five control rats that underwent no surgery and in five rats who underwent a unilateral sham operation. It was confirmed histologically that only the upper optic nerve had been directly injured.


RESULTS
At 4 and 8 days after injury, superior RGCs showed a mean difference from their fellow eyes of -30.3% and -62.8%, respectively (P = 0.02 and 0.001, t-test, n = 8 rats/group), whereas sham-operation eyes had no significant loss (mean difference between eyes = 1.7%, P = 0.74, t-test). At 8 days, inferior RGCs were unchanged from control, fellow eyes (mean interocular difference = -4.8%, P = 0.16, t-test). Nine weeks after transection, inferior RGC had 34.5% fewer RGCs than their fellow eyes, compared with 41.2% fewer RGCs in the superior zones of the injured eyes compared with fellow eyes. Detailed, serial section studies of the topography of RGC axons in the optic nerve showed an orderly arrangement of fibers that were segregated in relation to the position of their cell bodies in the retina.


CONCLUSIONS
A model of partial optic nerve transection in rats showed rapid loss of directly injured RGCs in the superior retina and delayed, but significant secondary loss of RGCs in the inferior retina, whose axons were not severed. The findings confirm similar results in monkey eyes and provide a rodent model in which pharmacologic interventions against secondary degeneration can be tested.
Levkovitch-Verbin
Hana
H
Department of Ophthalmology, Wilmer Institute, Johns Hopkins Hospital, Baltimore, Maryland, USA.
Quigley
Harry A
HA
Martin
Keith R G
KR
Zack
Donald J
DJ
Pease
Mary Ellen
ME
Valenta
Danielle F
DF
D000818:Animals; D001369:Axons / Q000473:pathology; D002452:Cell Count; D016923:Cell Death; D003911:Dextrans; D004195:Disease Models, Animal; D005456:Fluorescent Dyes; D009410:Nerve Degeneration / Q000209:etiology* / Q000473:pathology; D009412:Nerve Fibers / Q000473:pathology; D009900:Optic Nerve / Q000473:pathology / Q000601:surgery; D020221:Optic Nerve Injuries / Q000150:complications*; D051381:Rats; D017208:Rats, Wistar; D012162:Retinal Degeneration / Q000209:etiology* / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000473:pathology*; D012235:Rhodamines; D013266:Stilbamidines
C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D003911:Dextrans; D005456:Fluorescent Dyes; D012235:Rhodamines; D013266:Stilbamidines; C051311:rhodamine dextran