Angiotensin Type-1 Receptor Inhibition Is Neuroprotective to Amacrine Cells in a Rat Model of Retinopathy of Prematurity

Abstract

Purpose: : Retinopathy of Prematurity (ROP) is a retinal vascular disease associated with deficits in the scotopic vision. The aim of this study was to characterize in detail the neuronal deficits that occur in a rat model of ROP, and whether the angiotensin II type-1 receptor (AT₁R) inhibitor, valsartan, alters retinal neurochemistry and cell survival.

Methods: : Newborn Sprague-Dawley rats were exposed either to 80%:21% O₂ (22:2 hours/day) until postnatal day 11 (P11), then 7 days room air, or room air for the entire experimental period. Valsartan (40 mg/kg/day) was administered from P12-P18. Retinae were aldehyde fixed and either resin embedded, sectioned at 180nm and processed for serial section post-embedding IMCC (primary antisera: glutamate, GABA, glycine, aspartate, glutamine, taurine; kindly donated by Prof RE Marc), or sectioned at 12µM on a cryostat. Cell death was assessed by quantification of TUNEL positive cells. Amacrine cell changes were detected by analysis using antisera directed against tyrosine hydroxylase (TH), protein kinase C (PKC), parvalbumin (PV), and angiotensin receptor 2 (AT₂R)

Results: : Amino acid immunocytochemistry revealed widespread changes in virtually all classes of neurons, and especially amacrine cells. Pattern recognition analysis showed a reduction in amacrine cell classes including one that includes AII amacrine cells, the main interneurons of the rod pathway. There was a decrease in the density of amacrine cells in retinae with ROP; glycine and not GABA immunoreactive amacrine cells density was reduced. Neuronal loss was confirmed by a reduction in thickness of the INL and IPL and a significant increase in TUNEL labelling from P11-P13. Further evaluation of the change in amacrine cells during ROP revealed a significant reduction in PV-immunoreactive, AII amacrine cell density. There were no changes in the density of other amacrine cell types including TH, PKC , or AT₂R amacrine cells. Treatment with valsartan, prevented the loss of AII amacrine cells and partially ameliorated neurochemical changes.

Conclusions: : This study shows that neurons within inner retina especially AII amacrine cells are particularly affected by ROP, and that treatment with an AT₁ receptor antagonist, is partially protective. The effect on AII amacrine cells could explain the deficits in scotopic vision previously reported.

Keywords: retina • retinopathy of prematurity • amacrine cells