Nitric Oxide and Signal Loss in the "ROP Rat" Retina

Abstract

 

Purpose:

 

Investigate the role of the nitric oxide (NO) system and associated calcium-binding proteins in retinal signaling in the ROP rat.

 

Methods:

 

The Penn et al. (1994) "50/10" model of ROP (n=18) was studied; room-air-reared (RAR) rats served as controls (n=17). Rod and rod-driven signaling were assessed by ERG at P15-16 (antedating marked neovascularization). The log of the saturating amplitude of the rod photoreceptors’ response (Rm_P3) was subtracted from the log saturating amplitude of the second-order bipolar cells’ response (Rm_P2) for each ROP and RAR rat. In turn, log Rm_P2 was subtracted from the log saturating amplitude of the oscillatory potentials (Em^½), which originate largely in tertiary and higher cells (amacrines/ganglions). These two ratios were compared between ROP and RAR rats by two-factor (group×parameter) repeated measures ANOVA. On P16, following ERG, pups were sacrificed, eyes enucleated, fixed, and cryosectioned, and immunocytochemistry was used to localize calbindin, calretinin, and nNOS in the retina.

 

Results:

 

Rm_P3, Rm_P2, and Em^½ were significantly attenuated in ROP rats. The ratio of Rm_P3 to Rm_P2 did not differ between ROP and RAR rats, but the ratio of Rm_P2 to Em^½ was dramatically reduced (0.37 log units). Although the neuroprotective calbindin was detected in horizontal cells in both RAR and ROP retinas, fewer somata were labeled in the ROP rats and their labeling was weaker. There was increased calretinin in amacrine cells and three sublamina of the IPL in ROP rats. nNOS, which is upregulated in oxidative stress, was detected in more amacrine cells in the ROP rat retinae.

 

Conclusions:

 

There are increased numbers of nNOS labeled amacrine cells in ROP. These changes may be associated with signal loss in the inner retina, indicated by the loss of OP amplitude in ROP rat ERGs. Changes in IPL synapses may also be at play. Quantitative comparison of ERG parameters to histology will be needed to determine functional and molecular interrelations. Normalization of synaptic development in ROP may be feasible using NO inhibitors.  

 

Keywords: retinopathy of prematurity • nitric oxide • electroretinography: non-clinical