Intravenous Injection Of Sodium Iodate Research Articles

Use of an alternating current amplifier when recording the ERG c-wave to evaluate the function of retinal pigment epithelial cells in rats.

We studied the conditions under which c-waves of the electroretinogram (ERG), that represent retinal pigment epithelium (RPE) function, were detectable using an alternating current (AC) amplifier and whether the c-wave recorded using an AC amplifier was useful for evaluating RPE function. We recorded ERG responses in rats to 5s stimuli under the conditions in which the low-cut frequency and the stimulus luminance were varied. In addition, changes in ERGs were studied after intravenous injection of sodium iodate (SI) to induce RPE degeneration. The c-wave was detected clearly when the frequency of the low-cut filter was set at 0.01Hz and light stimulus luminances were ≥ - 1.0 log cd/m2. The c-wave was attenuated earlier than other waves (e.g., a-wave and b-wave) after SI administration. The c-wave was easily detectable using an AC amplifier with the low-cut filter set at 0.01Hz. Using the AC amplifier may allow easier c-wave recording, compared with the conventional use of a direct current (DC) amplifier, and could be useful for evaluating RPE function.

Irreversible Photoreceptors and RPE Cells Damage by Intravenous Sodium Iodate in Mice Is Related to Macrophage Accumulation.

To determine the mechanism causing degeneration of the retinal pigment epithelium (RPE) and photoreceptors in mice after an intravenous injection of sodium iodate (NaIO3). The time-dependent changes in NaIO3-induced retinal degeneration were determined by analyzing the retinal morphology by optical coherence tomographic (OCT) images, histological sections of the retina, physiology of the retina by electroretinography (ERG), and retinal blood flow by laser speckle flowgraphy. In addition, the expression of the genes associated with age-related macular degeneration in humans was assessed in the NaIO3-treated mice by RT-PCR. We also investigated whether macrophages were involved in the NaIO3-induced retinal degeneration. The intravenous injection of 20 mg/kg NaIO3 altered the morphology of the RPE cells and the ERGs transiently. With 40 mg/kg of NaIO3, the degeneration of the RPE cells was still present at 28 days. Aggregated melanin granules were surrounded by zonula occludens protein 1 (ZO-1)-positive cells. In addition, 40 mg/kg of NaIO3 led to a reduction in the amplitudes of the a- and b-waves of the dark-adapted ERGs. Histological studies showed that macrophages had infiltrated the retina and were present around the altered RPE cells. Depletion of the macrophages by a prior injection of clodronate liposomes prevented the damage of the outer retina after the NaIO3 injection but not the RPE. The NaIO3-induced retinal damage was reversible at low concentrations but permanent at high concentrations of NaIO3. The accumulation of macrophages around the RPE cells caused the photoreceptor cell death.

Assessing Sodium Iodate–Induced Outer Retinal Changes in Rats Using Confocal Scanning Laser Ophthalmoscopy and Optical Coherence Tomography

Sodium iodate induces RPE atrophy and photoreceptor degeneration, as seen in the pathogenesis of many retinal diseases. We investigated a new approach of analyzing retinal images using confocal scanning laser ophthalmoscopy (cSLO) that allows longitudinal assessment of sodium iodate-induced lesions in the retina of living rats. A single dose of sodium iodate (25-75 mg/kg) was given intravenously to adult Sprague-Dawley rats. Control animals were given normal saline or sodium iodide. The retina was examined by cSLO and optical coherence tomography (OCT) in living rats, which were then killed for histologic assessments. Confocal scanning laser ophthalmoscopy revealed the appearance of dark patchy blots in planar images of the retina 7 days after intravenous injection of sodium iodate (25-75 mg/kg). This finding coincided with the observations of degenerative changes in the outer retinal layers in OCT images and in histology of the retina. Further analyses showed a concomitant localization of degenerative profiles in histologic preparations of this retina, suggesting that the blots corresponded to the deteriorating photopigments and outer nuclear layer (ONL). In histologic sections, these degenerative profiles appeared as irregular folds or rosettes in the ONL. Quantitative analyses showed that the changes in blot number were dose dependent, which again coincided with results showing a dose-dependent lesion in the photopigment layer and ONL in histologic sections of the retina. Sodium iodate-induced degenerative changes can be assessed quantitatively and reliably by in vivo retinal imaging using cSLO in adult rats, allowing efficient evaluation of lesions in a large area of retina in longitudinal studies.

Influential factors of thresholds for electrically evoked potentials elicited by intraorbital electrical stimulation of the optic nerve in rabbit eyes

Influential factors of electrical thresholds for electrically evoked potentials elicited by intraorbital stimulation of the optic nerve, including stimulation positions of the optic nerve, stimulating electrodes, frequency and duration of electrical pulses and pathological status of the optic nerve, were evaluated in 48 pigmented rabbit eyes. Intravenous injection of sodium iodate was used to induce transneuronal degeneration of the retinal ganglion layer subsequent to photoreceptor death. Two equations were derived to predict electrical thresholds needed to elicit cortical responses.

A procedure for recording electroretinogram (ERG) with a contact lens-type electrode, and effect of sodium iodate on ERG in rats

A procedure for recording the electroretinogram (ERG) in rats with a contact lens-type electrode was developed in order to examine visual toxicity overtime. Rats received a single intravenous injection of sodium iodate (SI), a retinotoxic compound, via the tail vein at a dose of 12.5, 20, 25 or 50 mg/kg, and the ERG was recorded for 10 days after dosing. Histopathologic examination of the retinas was then conducted. 1. The rats were anesthetized with ketamine hydrochloride (50 mg/kg, i.m.) after 90 to 120 min of dark-adaptation. Thirty-two responses to repetitive 1.2 joule light stimuli at 0.5 Hz interstimulus intervals were averaged by a microcomputer. Under these conditions, stable ERG a-wave, b-wave and oscillatory potentials could be recorded for 10 days. 2. At 12.5 mg/kg of SI, no treatment-related abnormalities were observed on the ERG. Doses of 20 mg/kg or more of SI caused depression of the amplitudes of the ERG a-wave and oscillatory potentials 2 hrs or 1 day after dosing. Following these changes, the amplitude of the ERG b-wave decreased 1 or 2 days after dosing. 3. Upon histopathologic examination of the retina, folding of the outer nuclear layer, disarrangement of the rods and cones and swelling and decrease of the pigment epithelial cells were observed at 20 mg/kg or more. The severity of the retinal lesions correlated well with the changes in the ERG. 4. Using this recording technique, it was confirmed that a stable ERG could be recorded repeatedly in rats, and the effects of SI on the ERG could be detected. Furthermore, histopathologic examination revealed that the severity of the retinal lesions correlated well with the changes in the ERG. These results indicate that the ERG recording technique employed in this study is useful for evaluating retinal toxicity in rats.

Biochemical changes in rabbit sclera following destruction of pigment epithelium

The long-term effect of destruction of the pigment epithelium by sodium iodate on the biochemistry of rabbit sclera was studied in one group with intravenous injection of sodium iodate, and in a second group with injection of sodium iodate into the right eye. Intravenous treatment produced a non-significant increase in the uronic acid concentration. In the second group the untreated fellow eye was microscopically intact, but was shown (as the treated eye) to alter the concentration of uronic acid in different parts of the sclera. All eyes from treated animals exhibited changes in the relative content of the various glycosaminoglycans and in the content of hydroxyproline, hydroxylysine and proline. This work indicates that the pigment epithelium may play a key role in the control mechanism of the scleral connective tissue, and this again has major implications in terms of a possible medical treatment of axial myopia.

Pericyte response during choriocapillaris atrophy in the rabbit.

The rabbit and rat choriocapillaris atrophies in response to experimental destruction of the retinal pigment epithelium by intravenous injection of sodium iodate. This provides a convenient model of capillary atrophy. We have observed that pericytes are spared during this process; the atrophy is due to loss of endothelium only. Extensive examination of thin sections obtained 1 day to 11 weeks after administration of iodate showed that pericytes retained their normal relationship to the remnant capillary basement membrane left behind as the endothelial tube atrophied. This was most conspicuously manifested in their retention of processes longitudinally disposed along the sleeves of remnant basement membrane. The processes retained bundles of actin filaments that had dense regions along them and inserted into subplasmalemmal densities at basement membrane attachment sites, i.e. they had the characteristics of stress fibers. The pericytes did not phagocytose the debris of endothelial necrosis, in spite of their known phagocytic abilities. Necrotic endothelial cells were eliminated by sloughing into the capillary lumen. The observations support the idea that the function of pericytes in the choriocapillaris, the major source of nutrition for the retinal photoreceptors, resides in their contractility, and that pericytes do not remove necrotic endothelium during capillary atrophy.

Combined effects of DL-?-aminoadipic acid with sodium iodate, ethyl alcohol, or light stimulation on the ERG c-wave and on the standing potential of albino rabbit eyes

Albino rabbits were treated with intravitreal injections of DL-alpha-aminoadipic acid (alpha-AAA) into one eye (0.1 ml of a 0.15 M solution) and 0.1 ml of saline into the contralateral eye. Thirteen to fourteen hours later the DC electroretinogram (ERG) and/or the standing potential (SP) were recorded. (1) In eight of nine animals the c-wave amplitude of alpha-AAA injected eyes was increased compared with that of control eyes. Following intravenous injection of Sodium Iodate (40 mg/kg in 2% solution) the c-waves of both eyes were rapidly replaced by negative potentials. In 8 of 9 animals the amplitude reduction was more marked in alpha-AAA-treated eyes than in control eyes, but the final amplitude was higher in the former than in the latter. The SP was reduced with difference in curve form but not significantly in amplitude between the eyes. (2) In nine other rabbits iv.-injected ethyl alcohol (0.4 g/kg in 20% solution) provoked a transient increase of SP level and c-wave amplitude in control eyes and smaller but similar changes in alpha-AAA injected eyes. (3) In another five animals the SP was recorded following a step from darkness to continuous light stimulation. The light peak was less pronounced in alpha-AAA treated eyes than in control eyes.

CHANGES IN THE JUXTAPAPILLARY RETINAL PIGMENT EPITHELIUM FOLLOWING INTRAVENOUS INJECTION OF SODIUM IODATE

The effect of an intravenous injection of sodium iodate on the retinal pigment epithelium immediately surrounding the optic nerve head has been investigated using horseradish peroxidase as a morphological tracer. A sodium iodate injection leads to a necrotic reaction of practically the complete retinal pigment epithelium. The juxtapapillary pigment epithelium, however, showed only attenuation and depigmentation without any necrotic reaction 4 and 12 days after the injection. Twenty‐six days following the injection the epithelium had almost normalized. The result of this study thus demonstrates a noteworthy resistance of the juxtapapillary retinal pigment epithelium against the sodium iodate effect. At no stage was there a clear indication of a breakdown of the permeability barrier constituted by the juxtapapillary retinal pigment epithelium. Horseradish peroxidase moved into the peripapillary sensory retina by lateral diffusion from the surrounding retina and diffused into the optic nerve head proper, confirming the presence of a diffusional pathway through the Kuhnt intermediary tissue.

The retinal pigment epithelium diffusion barrier in the rabbit eye after sodium iodate injection. A light and electron microscopic study using horseradish peroxidase as a tracer

The breakdown and repair of the retinal pigment epithelium diffusion barrier after intravenous injection of sodium iodate was investigated using horseradish peroxidase as a morphological tracer. Four days after the injection of sodium iodate, histological examination revealed a widespread destruction of the pigment epithelium, confirmed by tracer studies showing a marked breakdown of the diffusion barrier. Horseradish peroxidase penetrated freely from a preretinal depot to the choroid, and also from the choroid, following intravenous injection, into the sensory retina. During the next weeks the retinal pigment epithelium was gradually replaced by a heterogenous cell layer. Approximately 4 weeks after the injection of sodium iodate this cell layer was well established and showed tortuous intercellular spaces and, in some places, junction-like appositions between adjacent cells. In spite of this, horseradish peroxidase was still able to penetrate this cell layer in both direction, indicating that the diffusion barrier was not re-established. In the early 4-day stage, and also in the late stage, the penetration of the tracer in the retinochoroidal direction was clearly more extensive than in the chorioretinal direction. It is suggested that this finding is due to a bulk flow of fluid out of the eye through the retina and choroid.

Interrelationships between the retinal pigment epithelium and the neurosensory retina.

The role of the retinal pigment epithelium in regulating transport between the choriocapillariss and sensory retina was studied by examining the diffusion fluorescent across the intact rabbit retinal pigment epithelium and the retinal pigment epithelium damaged by intravenous injection of sodium iodate. Destruction of the tight junctions of the retinal pigment epithelium allowed free diffusion of fluorescein from the choroid into the retina. The electrical characteristics of the cat retinal pigment epithelium which play an important role in governing transport of substances across the retinal pigment epithelium were studied. The apical membrane of the cat retinal pigment epithelium resembled that of the frog in having high sensitivity to apical K+, greater sensitivity to apical Na+, and less sensitivity to apical HCO3-. The apical membrane was sensitive to oubain which produced a rapid fall in the transepithelial potential. Previous studies of the electrical properties of the retinal epithelium in cold blooded preparations are summarized with emphasis on the important interactions between the retinal pigment epithelium and sensory retina and the implications that these studies have with regard to the regulation of photoreceptor function.

Amino acid transport across blood-aqueous barrier of mammalian species

The concentration of free amino acids in the plasma, aqueous and vitreous humors of sheep was determined by ion exchange chromatography. With the possible exception of methionine and glycine, the concentration of every amino acid in the aqueous humors of posterior and anterior chamber was found to be significantly higher than in the corresponding plasma while the vitreous humor was deficient in all amino acids with respect to these fluids. The most pronounced concentration gradients between aqueous humors and plasma were noted for aspartic acid and glutamic acid, which were found to be 9–13 times higher in the aqueous humors. Cystine and lysine, which were least concentrated in the aqueous humors, were approximately 1·7 times that in the corresponding plasma; for all other compounds the aqueous/plasma ratios were greater than 2. These observations lead to the conclusion that most of the amino acids are transported across the ciliary epithelium by an active process. While the concentration gradients between the anterior aqueous and plasma were similar to those existing between the aqueous of posterior chamber and plasma for all amino acids, the relative concentration of arginine, aspartic acid, glutamic acid, histidine, serine and threonine in the anterior chamber with respect to plasma appeared to be higher than in the posterior chamber, suggesting the possibility that there may also be active transport across the iris. The role of vitreous humor in regulating the amino acid levels in the aqueous humors was investigated in rats by abolishing the vitreous/plasma gradient. Following a single intravenous injection of sodium iodate the steady state concentration of [ 14C]cycloleucine in the vitreous increased from 34% of plasma to 90% of plasma value while that in the anterior aqueous increased from 80 to 120% of plasma level. The results suggest that cycloleucine and possibly other amino acids are actively transported across the blood-aqueous barrier of these animals. It is concluded that the deficiency of amino acids observed in the aqueous humors of certain species may be due to the “sink effect” of the vitreous humor and that active transport of amino acids across the blood-queous barrier may be involved in all mammalian species.