5 research outputs found
Structural and functional consequences of oxygen induced retinopathy
Retinopathy of prematurity (ROP) is a potentially blinding retinal disorder, which results from the exposure of the premature infant to hyperoxia. The diagnosis and the assessment of severity of ROP are based on the degree of retinal vascular abnormalities (such as avascular peripheral retina and neovascularisation), which are observed upon fundus examination. However, even if the vascular consequences of ROP are resolved, functional sequels such as high myopia, anisometropia and strabismus, may persist through adulthood. In severe cases, even more dramatic consequences, namely retinal detachment and blindness, may also occur. In oxygen-induced retinopathy (OIR), the animal model of ROP, hyperoxia-induced vasoobliteration and neovascularisation have been studied extensively in mice, rats, cats and dogs. However, the functional and ultrastructural changes that might result from the exposure to hyperoxia have not yet been examined in details. In this study, we report functional, as assessed with the electroretinogram (ERG), and structural, determined with histological sections of the retina, consequences of postnatal hyperoxia which took place during a period of intense retinal maturation, that is, the first 14 days of life of Sprague Dawley rats.Our results indicate that there is a sigmoidal dose-response correlation between the increasingly longer duration of oxygen exposure, and the decrease in the postreceptoral retinal activity, as revealed by the gradual reduction in the amplitudes of rod and cone dominated b-waves and oscillatory potentials. Furthermore, the cone function appeared to be slightly more affected than that of the rod. Also, of all the ERG components the oscillatory potentials, especially the short latency ones, appeared to be the most sensitive to the hyperoxia. The gradual thinning of the outer plexiform layer (OPL) is also correlated with the duration of oxygen exposure, while the reduction in the number of horizontal cells is not.Secondly, our experimental approach has allowed us to evidence a period of higher oxygen susceptibility (a window), which takes place during the second week of life of the newborn rats, more specifically around postnatal day 10. Several oxygen exposures of short duration, which included this period, were shown to be more detrimental to the rod and cone function than longer exposures taking place prior to or after this window. This would suggest that during the normal maturation process, the immature retina is not equally sensitive to the hyperoxic insult, presumably because specific retinal structures (synapses in OPL) are targeted by oxygen.Finally, Trolox C, a potent water-soluble antioxidant, partially prevents the functional and structural consequences of OIR. The prophylactic effect appears to benefit more the rod function than that of the cone.To conclude, we believe that this new knowledge will help us understand the pathophysiological processes at the origin of oxygen toxicity in the immature retina, thus, significantly increasing our insights on the human form of this disease, namely ROP, which as a result, will be instrumental in devising new therapeutic avenues to help fight this potentially debilitating retinal disorder
Evidence against the Regulation of Grain Set by Spikelet Abscisic Acid Levels in Water-Stressed Wheat
A possible role of abscisic acid (ABA) in the regulation of grain set in water-stressed wheat (Triticum aestivum L.) was investigated using a split root system to dry half the roots while the remainder were kept watered. Water uptake by the wet roots maintained the leaf water potential at the normal level, whereas the ABA produced in the dry roots was transported to the spike. This caused the spikelet ABA level to increase to the same extent as when the entire root system was stressed to permit a drop in the leaf water potential. In spite of this, the former treatment did not induce a reduction in grain set, whereas the latter did. Thus, contrary to previous reports, water stress-induced changes in spikelet ABA level alone do not appear to regulate grain set
Evidence against the Regulation of Grain Set by Spikelet Abscisic Acid Levels in Water-Stressed Wheat
Electrocatalytic properties of manganese and cobalt polyporphine films toward oxygen reduction reaction
International audienceNovel member of polymetalloporphines, namely manganese polymetalloporphine of type I (pMnP-I) obtained by ion exchange from magnesium polyporphine of type I (pMgP-I) is reported for the first time and compared to its cobalt analogue (pCoP-I). Both polymer films have been obtained via two-step procedure: demetaladon of the pMgP-I electrode film via its exposure to trifluoroacetic acid solution, resulting in formation of the metal-free polyporphine of type I (pH(2)P-I) followed by electrochemically induced incorporation of Co or Mn ions from the acetonitrile solution of cobalt and manganese perchlorates. A further oxidative transformation of pCoP-I, polymer films has led to the corresponding polyporphines of type II, pCoP-II and pMnP-II, possessing such unique features as condensed polymer structure with a very high density of active sites and high electronic conductivity within a very broad potential range including the one corresponding to the neutral (uncharged) state of the polymer matrix. Both polymers of type II also exhibit interesting electrocatalytic activity toward oxygen electroreduction in aqueous neutral (pH 6.7) and alkaline (pH 13) media which was evaluated under cyclic voltammetric and steady-state conditions. The results demonstrate that the efficiency (regardless of the electrolyte) of both polymetalloporphines is comparable to bare platinum electrode. The effect of annealing of polymer-modified electrodes on their catalytic properties has also been considered