POSTNATAL HYPEROXIA: STRAIN COMPARISONS FROM THE RETINAL BLOOD VESSELS TO THE OPTIC NERVE

Abstract

Abstract: : Purpose: We have shown that the retina of newborn Long Evans (LE) rats reacted more than Sprague Dawley (SD) rats to postnatal hyperoxia. We examined whether other features of postnatal hyperoxia showed similar strain differences. Methods: SD (n=4 control, 28 exposed) and LE rats were exposed to hyperoxia (n=4 control, 4 exposed) as previously described (ARVO 2002). Photopic flash VEPs (intensity: 0.9 log cd.m^–2.sec; background: 30cd.m^–2) were recorded at postnatal day 30. Retinal flatmounts were also analyzed at P14. Results: fVEP measurements from SD and LE rats indicate that hyperoxia from P0–9 did not affect the peak time (PT) or the amplitude of early components (N₁= 60ms, P₁=70ms, N₂=95ms and P₂=130ms). In contrast, P₃ (PT=160ms) was delayed by 35ms and attenuated to 25% of control amplitude. The early components disappeared after exposure from P0–14, while the remnant of P₃ was further delayed by 50ms compared to control (PT=210ms). Hyperoxia also reduced retinal blood vessel coverage to 54.18%±4.37 and 22.68%±1.99 (P<.01) of control in SD and LE rats, respectively; SD rats, nevertheless, showed a more even distribution of vessels compared to LE rats. Conclusions: Both fVEPs and retinal flatmounts give further insight into the pathology created by OIR and complement our previous claims on ERGs and retinal histology. Vascular consequences of postnatal hyperoxia are more prominent in LE rats compared to SD rats. In addition, while the retinal structural anomaly in the SD model is limited to the OPL, it is more extensive in the LE model. Of particular interest in both strains is the fact that the VEP is already affected for the P0–6 exposure regimen, whereas the ERG and retinal structure remain unchanged. Whether this is due to a cortical amplification of an undetectable subclinical functional retinal anomaly or the concurrent effect of hyperoxia on cortical function remains to be elucidated. Funded by CIHR and Réseau Vision.

Keywords: retinopathy of prematurity • retina • electroretinography: non–clinical