The neurotoxic effects of hydrogen peroxide and copper in Retzius nerve cells of the leech Haemopis sanguisuga.

Oxidative stress and the generation of reactive oxygen species (ROS) play an important role in cellular damage. Electrophysiological analyses have shown that membrane transport proteins are susceptible to ROS. In the present study, oxidative stress was induced in Retzius nerve cells of the leechHaemopis sanguisugaby bath application of 1 mM of hydrogen peroxide (H2O2) and 0.02 mM of copper (Cu) for 20 min. The H2O2/Cu(II) produced considerable changes in the electrical properties of the Retzius nerve cells. Intracellular recording of the resting membrane potential revealed that the neuronal membrane was depolarized in the presence of H2O2/Cu(II). We found that the amplitude of action potentials decreased, while the duration augmented in a progressive way along the drug exposure time. The combined application of H2O2and Cu(II) caused an initial excitation followed by depression of the spontaneous electrical activity. Voltage-clamp recordings revealed a second effect of the oxidant, a powerful inhibition of the outward potassium channels responsible for the repolarization of action potentials. The neurotoxic effect of H2O2/Cu(II) on the spontaneous spike electrogenesis and outward K(+)current of Retzius nerve cells was reduced in the presence of hydroxyl radical scavengers, dimethylthiourea and dimethyl sulfoxide, but not mannitol. This study provides evidence for the oxidative modification of outward potassium channels in Retzius nerve cells. The oxidative mechanism of the H2O2/Cu(II) system action on the electrical properties of Retzius neurons proposed in this study might have a wider significance, referring not only to leeches but also to mammalian neurons.

Clinical aspects of posterior uveitis in ocular sarcoidosis.

Two clinical forms of the "white spot" syndrome in patients with posterior uveitis in definitive and presumable ocular sarcoidosis were analyzed. Group 1 was characterized by periphlebitis and discrete white spots around the vein of the retina, so-called "candle-wax", whereas group 2 showed yellow-orange solitary nodules located at the choroid, i.e. multifocal choroiditis. Visual acuity and the severity of clinical presentation were assessed in both groups. Visual acuity, Snellen equivalent was 0.52 +/- 0.36 in group 1 and 0.82 +/- 0.39 in group 2 with lesions at the level of choroid. One-way analysis of variance ANOVA showed a statistically significant between-group difference in visual acuity (p = 0.03). The mean severity of clinical presentation was 11.80 +/- 2.04 points in group 1 and 5.80 +/- 4.18 points in group 2. T-test for independent samples yielded a statistically significant difference between the groups (p = 0.02). A statistically significant difference in visual acuity was the result of vasculitis in the group with the "candle-wax" phenomenon, which is associated with retinal vasculitis and causes cystoid macular edema and reduction of visual acuity. Complications such as cataract, glaucoma and neovascularization, which also decrease visual acuity, were more frequent in group 1.