L. M. Franco

Comparison of electrically evoked cortical potential thresholds generated with subretinal or suprachoroidal placement of a microelectrode array in the rabbit

The aim of the study was to directly compare the threshold electrical charge density of the retina (retinal threshold) in rabbits for the generation of electrical evoked potentials (EEP) by delivering electrical stimulation with a custom-made microelectrode array (MEA) implanted into either the subretinal or suprachoroidal space. Nine eyes of seven Dutch-belted rabbits were studied. The electroretinogram (ERG), visual evoked potentials (VEP) and EEP were recorded. Electrodes for the VEP and EEP were placed on the dura mater overlying the visual cortex. The EEP was recorded following electrical stimulation of the MEA placed either subretinally beneath the visual streak of the retina or in the suprachoroidal space in the rabbit eye. An ab externo approach was used for placement of the MEA. Liquid perfluorodecaline (PFCL; 0.4 ml) was placed within the vitreous cavity to flatten the neurosensory retina on the MEA after subretinal implantation. The retinal threshold for generation of an EEP was determined for each MEA placement by three consecutive measurements consisting of 100 computer-averaged recordings. Animals were sacrificed at the conclusion of the experiment and the eyes were enucleated for histological examination. The retinal threshold to generate an EEP was 9 +/- 7 nC (0.023 +/- 0.016 mC cm(-2)) within the subretinal space and 150 +/- 122 nC (0.375 +/- 0.306 mC cm(-2)) within the suprachoroidal space. Histology showed disruption of the outer retina with subretinal but not suprachoroidal placement. The retinal threshold to elicit an EEP is significantly lower with subretinal placement of the MEA compared to suprachoroidal placement (P < 0.05). The retinal threshold charge density with a subretinal MEA is well below the published charge limit of 1 mC cm(-2), which is the level below which chronic stimulation of the retina is considered necessary to avoid tissue damage (Shannon 1992 IEEE Trans. Biomed. Eng. 39 424-6).

Decreased Visual Function after Patchy Loss of Retinal Pigment Epithelium Induced by Low-Dose Sodium Iodate

PURPOSE To correlate damage to the retinal pigment epithelium (RPE) with decreased visual function after the systemic administration of sodium iodate (NaIO(3)). METHODS Damage was produced in mice by injection of 15, 25, or 35 mg/kg NaIO(3). Visual function was assessed with the cued water maze (WM) behavioral test and the optokinetic reflex (OKR) measurement at different times after injection. Autofluorescence in whole eye flatmounts was quantified, and hematoxylin and eosin staining of paraffin sections was performed to assess changes in the outer retina. RESULTS After 15 mg/kg NaIO(3), cued WM test results were normal, whereas OKR measurements were significantly decreased at all times. Focal RPE loss began on day 21, but no significant damage to the outer nuclear layer was observed. After 25 mg/kg NaIO(3), the cued WM test was transitionally reduced and the OKR measurement again decreased at all times. Large areas of RPE loss occurred on day 14 with a reduced outer nuclear layer on the same day. With 35 mg/kg NaIO(3), the cued WM test was reduced beginning on day 14 with complete obliteration of the OKR beginning on day 3, large areas of RPE loss on the same day, and a reduced outer nuclear layer on day 7. CONCLUSIONS Stable, patchy RPE loss was observed with a low concentration of NaIO(3). The OKR measurement showed changes in visual function earlier than the cued WM test and before histologic findings were observed.

Long-term cellular and regional specificity of the photoreceptor toxin, iodoacetic acid (IAA), in the rabbit retina.

This study investigated the anatomical consequences of a photoreceptor toxin, iodoacetic acid (IAA), in the rabbit retina. Retinae were examined 2 weeks, 1, 3, and 6 months after systemic IAA injection. The retinae were processed using standard histological methods to assess the gross morphology and topographical distribution of damage, and by immunohistochemistry to examine specific cell populations in the retina. Degeneration was restricted to the photoreceptors and was most common in the ventral retina and visual streak. In damaged regions, the outer nuclear layer was reduced in thickness or eliminated entirely, with a concomitant loss of immunoreactivity for rhodopsin. However, the magnitude of the effect varied between animals with the same IAA dose and survival time, suggesting individual differences in the bioavailability of the toxin. In all eyes, the inner retina remained intact, as judged by the thickness of the inner nuclear layer, and by the pattern of immunoreactivity for protein kinase C-alpha (rod bipolar cells) and calbindin D-28 (horizontal cells). Müller cell stalks became immunoreactive for glial fibrillary acidic protein (GFAP) even in IAA-treated retinae that had no signs of cell loss, indicating a response of the retina to the toxin. However, no marked hypertrophy or proliferation of Müller cells was observed with either GFAP or vimentin immunohistochemistry. Thus the selective, long lasting damage to the photoreceptors produced by this toxin did not lead to a reorganization of the surviving cells, at least with survival as long as 6 months, in contrast to the remodeling of the inner retina that is observed in inherited retinal degenerations such as retinitis pigmentosa and retinal injuries such as retinal detachment.

Iodoacetic acid, but not sodium iodate, creates an inducible swine model of photoreceptor damage

Our purpose was to find a method to create a large animal model of inducible photoreceptor damage. To this end, we tested in domestic swine the efficacy of two chemical toxins, known to create photoreceptor damage in other species: Iodoacetic Acid (IAA) and Sodium Iodate (NaIO(3)). Intravenous (IV) administration of NaIO(3) up to 90 mg/kg had no effect on retinal function and 110 mg/kg was lethal. IV administration of IAA (5-20 mg/kg) produced concentration-dependent changes in visual function as measured by full-field and multi-focal electroretinograms (ffERG and mfERG), and 30 mg/kg IAA was lethal. The IAA-induced effects measured at two weeks were stable through eight weeks post-injection, the last time point investigated. IAA at 7.5, 10, and 12 mg/kg produce a concentration-dependent reduction in both ffERG b-wave and mfERG N1-P1 amplitudes compared to baseline at all post-injection times. Comparisons of dark- and light-adapted ffERG b-wave amplitudes show a more significant loss of rod relative to cone function. The fundus of swine treated with ≥10 mg/kg IAA was abnormal with thinner retinal vessels and pale optic discs, and we found no evidence of bone spicule formation. Histological evaluations show concentration-dependent outer retinal damage that correlates with functional changes. We conclude that NaIO(3,) is not an effective toxin in swine. In contrast, IAA can be used to create a rapidly inducible, selective, stable and concentration-dependent model of photoreceptor damage in swine retina. Because of these attributes this large animal model of controlled photoreceptor damage should be useful in the investigation of treatments to replace damaged photoreceptors.

Hepatitis C mixed cryoglobulinemia with undetectable viral load: A case series

DAA: direct-acting antiretrovirals HCV: hepatitis C virus LCV: leukocytoclastic vasculitis INTRODUCTION Mixed cryoglobulinemic vasculitis is caused by circulating cold-precipitable immunoglobulins, or cryoglobulins, composed of monoclonal (type II) or polyclonal (type III) IgM directed against a polyclonal IgG. It causes palpable purpura and has long been associated with hepatitis C virus (HCV) infection. The initial theory regarding the new antiviral medications, which have been so successful in treating hepatitis C, was that once the HCV was treated, the mixed cryoglobulinemic vasculitis would also resolve. Although initial studies confirmed this theory, later studies found that the vasculitis is persistent in some patients despite successful HCV treatment. Vasculitis occurred within months after treatment of HCV infection in most cases in the literature, but we present 3 cases of mixed cryoglobulinemic vasculitis months to years after successful HCV treatment and negative viral load and a review of the current literature.