Secondary retinal ganglion cell death and the neuroprotective effects of the calcium channel blocker lomerizine.
OBJECTIVE
After partial optic nerve (ON) injury, intact retinal ganglion cells (RGCs) undergo secondary death, but the topographic distribution of this death is unknown, and it is unclear which cell death pathways are involved. Although the calcium channel blocker lomerizine reduces RGC death after partial ON injury, it is unknown whether this drug alleviates necrotic or apoptotic death.


METHODS
The dorsal ON was transected in adult Piebald-Virol-Glaxo (PVG) rats, and the site of secondary RGC death was determined using anterograde and retrograde DiI tracing. RGC death was assessed at 2 and 3 weeks. Retrograde tracing with fluorogold injected into the superior colliculus 3 days before euthanatization was used to identify RGCs undergoing secondary death. Overall cell loss was quantified using betaIII-tubulin immunohistochemistry. Lomerizine (30 mg/kg, oral) or vehicle was given twice daily, and retinal wholemounts were analyzed for necrotic morphology (nucleic acid stain) or anticleaved caspase-3 expression at 2 and 3 weeks.


RESULTS
Ventral retina was identified as the site of secondary RGC death, and central and dorsal retinae were defined as sites of both primary and secondary death. Overall RGC loss occurred by 2 weeks in central and ventral retina (P < 0.05) and by 3 weeks in dorsal retina (P < 0.05). Secondary RGC death was characterized mainly by necrotic morphology, with caspase-3 expression in some RGCs. Lomerizine reduced secondary necrosis at 2 weeks and secondary caspase-3 expression at 3 weeks.


CONCLUSIONS
Lomerizine had differential effects on necrotic and apoptotic death with time, but its inability to completely prevent secondary death suggests that full neuroprotection will require combinatorial treatments.
Fitzgerald
Melinda
M
Experimental and Regenerative Neurosciences, School of Animal Biology and Western Australian Institute of Medical Research, University of Western Australia, Crawley, WA, Australia. melfitz1@cyllene.uwa.edu.au
Payne
Sophie C
SC
Bartlett
Carole A
CA
Evill
Lauren
L
Harvey
Alan R
AR
Dunlop
Sarah A
SA
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002232:Carbocyanines; D053148:Caspase 3 / Q000378:metabolism; D002452:Cell Count; D016923:Cell Death / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005456:Fluorescent Dyes; D018696:Neuroprotective Agents / Q000494:pharmacology*; D020221:Optic Nerve Injuries / Q000150:complications; D010879:Piperazines / Q000494:pharmacology*; D051381:Rats; D012164:Retinal Diseases / Q000209:etiology / Q000473:pathology / Q000517:prevention & control*; D012165:Retinal Ganglion Cells / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology*; D014404:Tubulin / Q000378:metabolism
D002121:Calcium Channel Blockers; D002232:Carbocyanines; D005456:Fluorescent Dyes; D018696:Neuroprotective Agents; D010879:Piperazines; C488416:Tubb3 protein, rat; D014404:Tubulin; C024286:3,3'-dioctadecylindocarbocyanine; C052424:lomerizine; D053148:Caspase 3