Abstract
Abstract: :
Purpose:Endothelin–1 (ET–1) has been localized in the eye and its expression is increased in several optic neuropathies. Intraocular injections of ET–1 similarly causes the death of retinal ganglion cells (RGCs). Ciliary Derived Neurotrophic Factor (CNTF) has been shown to enhance the survival of RGCs and promote regeneration of their axons. In the present study we examined the effect of CNTF treatment on the survival of RGCs after intraocular injection of ET–1. Methods:RGCs were retrogradely labeled by injecting fluorogold (FG) into the superior colliculus (SC) of adult rats 2 days prior to treatments. 5 µl ET–1 (500 µM) was injected into the vitreous chamber of the eye. Two days later, 5 µl CNTF (17.4 µM) or PBS was injected into the vitreous. Pupil constriction velocity, optic nerve cross sectional area, and RGC density was determined 7, 14, and 21 days postinjection (n=5 for each time point). Pupil velocity was determined by exposing each dark adapted eye to a 10000 lux light stimulus until the pupil fully constricted. Animals were then fixed by transcardial perfusion with 4% formaldehyde followed by removal of the intracranial optic nerves (ONs) and isolation of the retinas. ON area was determined from semithin sections cut perpendicular to the nerve. RGC density was determined from confocal micrographs taken from the mid–peripheral retina after anti–FG immunohistochemistry. Results:ET–1/PBS injection reduced the normal density of RGC somas (2600 cells/mm2) by 15%, 23%, and 35% at 7, 14 and 21 days respectively. The density of RGCs in ET–1/CNTF treated retinas was reduced by 0%, 4%, and 19% at these time points. Pupil velocity was slowed from 0.35 mm/s to less than 0.25 mm/s after ET–1/PBS treatment within 7days, and remained unchanged for 21 days. ET–1/CNTF treatment did not improve the pupillary response at any time point. The area of the ON was decreased by 32% 21 days after both ET–1/PBS and ET–1/CNTF treatments. This reflects the equivalent loss of RGC axons in both treatment groups. Conclusions:These results demonstrate that CNTF treatment results in a 20% increase in RGC soma density 3 wks after ET–1 injection. In contrast, CNTF did not improve the pupillary response or the preservation of RGC axons in the ON. These findings suggest that intraocular injections of CNTF enhance the survival of RGC somas, but not the integrity of their axons.
Keywords: growth factors/growth factor receptors • ganglion cells • neuroprotection