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Swarupa Kancherla, Kevin Chan; Microstructural and physiological alterations in hypoxic-ischemic-injured visual system. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4896.
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Neonatal cerebral hypoxia-ischemia (HI) and carotid artery occlusion from HI can lead to chronic retinal and optic nerve (ON) degeneration and visual impairments. We explored the use of diffusion tensor MR imaging (DTI), gadolinium-enhanced MRI (Gd-MRI), manganese-enhanced MRI (Mn-MRI), and chromium-enhanced MRI (Cr-MRI) at 7 Tesla to determine the consequences of neonatal HI in the visual system.
Sprague-Dawley rats (12-16 g, N=8) underwent unilateral ligation of left (L) common carotid artery at postnatal day 7 followed by hypoxia for 2 hrs. 1 year after HI insults, DTI and dynamic Gd-MRI after systemic Gd injection were performed to all animals. 1 month after DTI and Gd-MRI, Mn-MRI was performed to 4 animals and Cr-MRI on the other 4 after intravitreal Mn(II) or Cr(VI) injection into both eyes.
DTI showed 56% lower fractional anisotropy (FA) in ipsilesional L-ON than contralesional right (R) ON (p<0.001). In addition, 26% lower FA was observed in R anterior optic tract (OT) compared to L-OT (p<0.05). The anterior vitreous chamber (AVC) showed more Gd enhancement in L eye compared to R eye at 50-60 mins after Gd injection (p<0.05). There was more Gd enhancement in L-AVC compared to L posterior vitreous chamber (PVC) at 40-60 mins after Gd injection (p<0.01). Cr-MRI showed 16% weaker enhancement in L retina than R retina (p<0.05). Mn-MRI showed 14% lower signal intensity in L-ON than R-ON, and R superior colliculus (SC) possessed 23% lower signal intensity than L-SC (p<0.01).
DTI showed more disorganization of anterior visual pathway projected from ipsilesional L eye (L-ON and R anterior OT) compared to contralesional R eye. This may explain the less anterograde axonal transport of Mn2+ ions along the visual pathway projected from L eye and stronger Mn enhancement in L-SC. Gd-MRI showed significantly more Gd enhancement in L-AVC compared to L-PVC or R-AVC. These suggested neonatal HI led to compromise of permeability at the blood-aqueous barrier and/or aqueous-vitreous junction. Because of potential linkage between Cr MR contrast and lipid metabolism, the less Cr enhancement in L retina than R retina may suggest altered lipid oxidation or decreased cellular densities in HI-injured retina. These results provide important evidence for understanding the chronic pathophysiological changes in the visual system after neonatal HI and improving strategies for vision preservation.
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