Transplantation of Adult Neural Stem Cells into Healthy and Acute Ischemic Rat Eyes: A Functional and Morphological Analysis

Abstract

Abstract: : Purpose: To functionally and morphologically characterize the rat retina and optic nerve after neural stem cell (NSC) transplants to healthy rat eyes and eyes damaged with acute elevation of intraocular pressure (IOP). Methods: Acute ocular ischemia was induced in rat eyes by elevating IOP to 110 mmHg for 60 min. GFP-expressing adult rat NSCs derived from the hippocampus were transplanted by intraocular injection 10 days after surgery (15 rats received NSCs, 6 rats received non-viable NSCs). An additional 10 healthy rat eyes received NSC transplants. Direct and indirect pupil light reflexes (PLR) were recorded from the unoperated eye, and electroretinograms (ERGs) were recorded from the operated and control eyes. Eyes were subsequently prepared for immunohistochemical analysis. Results: Transplanted NSCs were detected in 5 of 10 healthy rat eyes 30 days after transplant. Monitoring of PLR amplitudes revealed no significant difference between preoperative and postoperative values. Analysis of ERG amplitudes revealed no significant difference between transplanted and non-transplanted (control) eyes. However, latency time of a-waves was significantly prolonged in transplanted eyes compared to control eyes (p=0.04, Paired t-test). Transplanted NSCs were found in 8 of 15 acute ischemic eyes 8 weeks after surgery. Analysis of PLR function revealed no significant difference between acute ischemic eyes which received NSCs and those eyes which received non-viable cells at all time points (35d postop, p>0.1; 42d, p>0.1; 60d, p>0.1 Student’s t-test). ERG analysis of the a- and b-wave amplitudes and latency times also revealed no significant difference between acute ischemic eyes which received NSCs and those that received non-viable cells 60 days post transplant. Morphological analysis revealed that transplanted NSCs survived and differentiated in both normal and injured retinal environments. Morphological integration occurred primarily within the inner retinal layers and was commonly observed in the ischemic retinas while integration into normal retinas occurred only in damaged regions. Conclusions: Based on ERG and PLR analysis, and under the conditions used in the present study, no evidence for protection or recovery of function to damaged retinas and optic nerves was observed after transplantation of adult neural stem cells. Future studies are designed to determine if a critical period exists for functional integration of NSCs.

Keywords: neuro-ophthalmology: optic nerve • transplantation • ischemia