Characterization of retinal function and glial cell response in a mouse model of oxygen-induced retinopathy.

Retinal neovascularization, such as that occurring in proliferative diabetic retinopathy and retinopathy of prematurity, can have serious effects on visual function. By using a mouse model of neovascularization, oxygen-induced retinopathy (OIR), the interplay among angiogenesis, neuronal function, and the macro- and micro-glial response was explored. OIR was induced by exposure of mice to 75% oxygen from postnatal day 7 (P7) to P11 and then room air until P18. Controls were reared in room air. Blood vessel development was assessed by using fluorescence histochemistry. Aberrant intravitreal neovascularization was present across all eccentricities of retina in mice with OIR, whereas the number of vessels present in the deep plexus was reduced in the central regions. Neuronal function of both the rod and cone pathways, assessed by using the electroretinogram, was found to be significantly reduced in OIR. This may in part be explained by an alteration in photoreceptor outer segment morphology and also a loss of neurons and their synapses in the inner nuclear and plexiform layers of the central retina. In addition, there was an increase in the number of gliotic Müller cells and microglia in mice with OIR and the increase in the number of these cells correlated with the absence of the deep plexus. This indicates that the activity of both macro- and microglia is altered in regions where the deep plexus blood supply is deficient. Treatments or genetic manipulations directed toward amelioration of proliferative retinopathy need to address not only the vascular changes but also the alterations in neuronal and macro- and microglial function.

Vessey KA ，Wilkinson-Berka JL ，Fletcher EL 《-》

The vasoneuronal effects of AT1 receptor blockade in a rat model of retinopathy of prematurity.

Retinal angiogenesis, neural dysfunction, and microglial activation occur in both humans with retinopathy of prematurity and in animal models of the disease. The aim of this study was to assess whether blockade of the renin-angiotensin system ameliorated these effects in rats with oxygen induced retinopathy (OIR). Sprague-Dawley rats were treated with 80% oxygen from birth to postnatal day (P)11 and were then placed in normal air until experimentation at P18, while control animals remained in normal air. Control and OIR rats were treated with the angiotensin II type 1 receptor (AT1 receptor) antagonist, valsartan (4, 10, or 40 mg/kg daily, intraperitoneally). Retinal function was assessed using the twin-flash electroretinogram and immunocytochemistry was used to evaluate vascular change and microglial activation. Oxygen-induced retinopathy was associated with growth of blood vessels into the vitreous in the peripheral retina, increased microglial number, and activation and a reduction in both rod and cone pathway function. Although treatment with valsartan reduced growth of vessels into the vitreous, it also reduced the formation of the deep vascular plexus. Valsartan treatment reduced microglial number and activation; however, it did not ameliorate neural dysfunction. At the highest dose examined, valsartan treatment reduced photoreceptor and inner retinal function in both the control and OIR animals. Valsartan was effective in reducing physiological and pathological angiogenesis and the microglial inflammatory response, indicating a role for the AT1 receptor in these processes, but it did not prevent retinal dysfunction. More work is needed to better understand the mechanisms underlying neuronal dysfunction in oxygen-induced retinopathy.

Hatzopoulos KM ，Vessey KA ，Wilkinson-Berka JL ，Fletcher EL ... -  《-》

Neuronal and glial cell changes are determined by retinal vascularization in retinopathy of prematurity.

We have characterized the vascular, neuronal, and glial changes in oxygen-induced retinopathy, a model of retinopathy of prematurity (ROP). Newborn Sprague-Dawley rats were exposed to either 80% +/- 2% oxygen to postnatal day P11 and then room air until P18 (ROP) or room air for the entire duration (controls). Retinal structure was examined under the light microscope and following postembedding immunocytochemistry in central, midperipheral, and peripheral regions. Müller cells were evaluated immunocytochemically with glial fibrillary acidic protein. The extent of vascularization was established histologically. ROP caused significant thinning of the inner cellular and plexiform layers, which became more pronounced in the peripheral inner nuclear layer of ROP animals (11.3% loss vs. 25.4% loss). Amacrine cell amino acid levels were particularly vulnerable in the peripheral retina; bipolar cells showed similar but less prominent changes. Müller cells had elevated glutamine levels and were most gliotic in the periphery. The vasculature extended to peripheral retinal regions at P18 in controls but not in ROP rats. The most striking pattern of change was evident in the midperipheral "transition zone" of ROP animals. Areas close to blood vessels showed neurochemical properties that were similar to those of the central retina, indicating a local protective effect of the inner retinal blood supply. We find that ROP produces complex vascular, neural, and glial changes that relate to the proximity of inner retinal blood vessels.

Downie LE ，Pianta MJ ，Vingrys AJ ，Wilkinson-Berka JL ，Fletcher EL ... -  《JOURNAL OF COMPARATIVE NEUROLOGY》

Effects of sustained hyperoxia on revascularization in experimental retinopathy of prematurity.

Gu X ，Samuel S ，El-Shabrawey M ，Caldwell RB ，Bartoli M ，Marcus DM ，Brooks SE ... -  《INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE》

Visual cycle modulation in neurovascular retinopathy.

Rats with oxygen-induced retinopathy (OIR) model the pediatric retinal disease retinopathy of prematurity (ROP). Recent findings in OIR rats imply a causal role for the rods in the ROP disease process, although only experimental manipulation of rod function can establish this role conclusively. Accordingly, a visual cycle modulator (VCM) - with no known direct effect on retinal vasculature - was administered to "50/10 model" OIR Sprague-Dawley rats to test the hypotheses that it would 1) alter rod function and 2) consequently alter vascular outcome. Four litters of pups (N=46) were studied. For two weeks, beginning on postnatal day (P) 7, the first and fourth litters were administered 6 mg kg(-1) N-retinylacetamide (the VCM) intraperitoneally; the second and third litters received vehicle (DMSO) alone. Following a longitudinal design, retinal function was assessed by electroretinography (ERG) and the status of the retinal vessels was monitored using computerized fundus photograph analysis. Rod photoreceptor and post-receptor response amplitudes were significantly higher in VCM-treated than in vehicle-treated rats; deactivation of phototransduction was also significantly more rapid. Notably, the arterioles of VCM-treated rats showed significantly greater recovery from OIR. Presuming that the VCM did not directly affect the retinal vessels, a causal role for the neural retina - particularly the rod photoreceptors - in OIR was confirmed. There was no evidence of negative alteration of photoreceptor function consequent to VCM treatment. This finding implicates the rods as a possible therapeutic target in neurovascular diseases such as ROP.

Akula JD ，Hansen RM ，Tzekov R ，Favazza TL ，Vyhovsky TC ，Benador IY ，Mocko JA ，McGee D ，Kubota R ，Fulton AB ... -  《-》