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Biomedical subjects

A Negi

Publications and source records attributed to A Negi.

At least 91 records · Page 5Linked to original sources
PubMed1988

The developmental changes of ERGs on spontaneous retinal degeneration of Celestial goldfish.

The Celestial goldfish, which belongs to the family of telescope-eye goldfish, displays unique spontaneous retinal degeneration associated with developmental anterodorsal protrusion of the eyeball. We observed concurrent changes in the electroretinogram. At the age of 75 days, the retinal layer was developed fully and the electroretinogram exhibited b-wave dominance similar to that of adult common goldfish. At the age of 105 days, when the eyeball began to protrude laterally, the b-wave amplitude decreased to 52% of its earlier developmental stage, with a prolonged peak time. Histologic change was observed in the retinal pigment epithelium and photoreceptor layers. At the age of 135 days, when the eyeball protruded further anterodorsally, the histologic changes extended to all retinal layers and the ERG b-wave was extinguished. Electrophysiologic and histologic changes in the Celestial goldfish eye were found to be proportional to the grade of eye protrusion. Since similar goldfish do not show these changes, however, the Celestial goldfish may be a new model of hereditary retinal degeneration.

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PubMed1987

Electrophysiological studies of spontaneous retinal degeneration in celestial goldfish (chotengan).

Spontaneous retinal degeneration of Celestial goldfish was studied histologically and electrophysiologically. Retinal degeneration was divided into three stages. Until the age of 75 days (Stage 0) the retina showed normal histological development and the electroretinograms (ERGs) exhibited dominant b-waves similar to those of adult common goldfish. By the age of 105 days (Stage 1), when the eyeballs began to protrude laterally, histological changes were first observed in the retinal pigment epithelium and photoreceptor layer. The b-wave amplitude decreased to 52% of that of Stage 0 with a prolongation of the peak latency. By the age of 135 days (Stage 2), when eyeballs protruded further anterodorsally, the retinal degeneration extended to the entire retinal layers and no b-waves were detected. The deterioration of the b-wave amplitude was closely correlated to the histological findings of retinal degeneration. The Celestial goldfish is considered to be a new model of hereditary retinal degeneration.

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PubMed1987

Effects of intraocular pressure and other factors on subretinal fluid resorption.

We observed the effects of intraocular pressure (IOP), vitreous pressure and gravity on the resorption of small retinal detachments (blebs) made with Hanks' solution or autologous serum. Raising the IOP decreased the absorption time moderately and lowering the IOP increased it. These effects were greater when the RPE had been damaged by sodium iodate or laser burns, but we conclude that IOP makes only a small, limited contribution to normal subretinal fluid absorption. Neither liquefaction of the vitreous nor retinal weight had a significant influence on fluid absorption.

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PubMed1986

Pharmacologic modification of subretinal fluid absorption in the rabbit eye.

We studied in the rabbit the effects of pharmacologic agents on the absorption of Hanks' solution from the subretinal space of experimental nonrhegmatogenous detachments. Intravenous acetazolamide had no effect at a clinical dose (15 mg/kg) but increased the rate of fluid absorption significantly at high doses (50 mg/kg). Acetazolamide causes systemic pH to fall, while PCO2 and PO2 increase; however, duplicating some of these effects by artificial respiration or breathing 95% O2 plus 5% CO2 did not alter the rate of fluid absorption. Adding cyclic AMP and related agents to the vitreous and subretinal space slowed down fluid absorption by 25%, whereas cyclic GMP analogues increased the rate of absorption by 33%.

Absorption↗
PubMed1986

Mechanisms of subretinal fluid resorption in the cat eye.

Small, non-rhegmatogenous retinal detachments (blebs) were made in cat eyes by injecting fluid into the subretinal space, and the time course of fluid resorption was monitored. Blebs made with Hanks' solution over the pigmented RPE resorbed 22% faster than those over the tapetum. Blebs made with a non-ionic solution (isotonic sucrose) took 43% longer to resorb than those made with Hanks' solution, and blebs containing 3 X 10(-3) M sodium cyanide took 32% longer than controls. These results suggest that active ionic transport is involved in the absorption of subretinal fluid in the cat, as it is in the rabbit. Oncotic pressure in the choroid may also contribute to resorption, because blebs made with autologous serum took roughly 3 times longer to resorb than those made with non-proteinaceous Hanks' solution. The retinal vascular system does not appear to contribute, since the resorption time was similar for Hanks' blebs made under normal retina and those made under ischemic retina (produced by occluding retinal branch arteries with argon laser photocoagulation or endodiathermy).

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PubMed1986

Quantitative estimation of metabolic transport of subretinal fluid.

A new technique to measure the ongoing rate of subretinal fluid resorption inside the living eye is described. Experimental non-rhegmatogenous detachments (blebs) were made in the posterior pole of rabbit eyes by injecting fluid directly into the subretinal space, and the height of these blebs was measured with a YAG laser focusing system utilizing dual He-Ne beams. The resorption rate for Hanks' balanced salt solution was relatively constant during the initial 2.5 hr, and averaged 0.12 +/- 0.04 microliter/mm2/hr. The resorption rate for blebs made with non-ionic solution (isotonic sucrose) was only 0.03 microliter/mm2/hr. The resorption rate for blebs made with Hanks' solution plus 1 mM DNP was 0.04 microliter/mm2/hr. These data support the concept that subretinal fluid is resorbed primarily across the retinal pigment epithelium, and suggests that 70% of this absorption is dependent upon active ionic transport. The remaining 30% is probably driven by the higher oncotic pressure of the choroid.

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PubMed1986

Acute changes in RPE apical morphology after retinal detachment in rabbit. A SEM study.

The morphology of the apical surface of rabbit retinal pigment epithelium was studied by scanning electron microscopy from the first minute to several hours after making small nonrhegmatogenous retinal detachments (blebs). From 0 to 5 min, there were only slight changes in the homogeneous, dense mat of filamentous microvilli. From 5 to 30 min, filamentous microvilli retracted exposing larger processes. From 30 to 60 min blunt processes became completely exposed and sheet-like processes disappeared. At about 60 min, cone sheaths were no longer identifiable in most specimens. Between 60 min and the time of retinal reapposition (several hours), the apical surface became highly rounded. Colchicine and cytochalasin-D had no effect on the time required for fluid resorption, but colchicine greatly accelerated and enhanced cell rounding, while cytochalasin-D produced prominent apical tufts.

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PubMed1985

Kinetics of macromolecules injected into the subretinal space.

Small, experimental, non-rhegmatogenous retinal detachments (blebs) in rabbit eyes resorbed 50% more slowly when filled with autologous serum than with Hanks' solution. To study the fate of large molecules in the subretinal space, carboxyfluorescein and several sizes of FITC-dextrans were injected into blebs and their movement followed by fluorophotometry. Carboxyfluorescein diffused quickly into the vitreous and was gone from the space after 8 hr. FITC-dextran 10-S (smaller than albumin) also diffused readily into the vitreous and took about 30 hr to be eliminated from the subretinal space. The diffusion of FITC-dextran 70-S and 150-S (both larger than albumin) was markedly slower, and roughly 80% of the 150-S was still present in the subretinal space after 3 days. Since the subretinal fluid in all of these blebs resorbed within 10 hr, the physiologic mechanisms for fluid resorption and elimination of large substances appear to be independent. Damaging the RPE barrier with sodium iodate allowed even the larger FITC-dextrans to exit from the subretinal space.

Absorption↗
PubMed1985

Some experimental data concerning the safety of vitrectomy.

Several reasons why vitrectomy does not compromise retinal functions are shown, based on closed and open-sky vitrectomy on the rabbit eye. We observed that ERG b- and c-waves were stable during and after open-sky vitrectomy. The c-wave disappeared when the retina was detached. Function of the retinal ganglion cells after vitrectomy was shown to be almost normal by electrophysiological studies and by measured amounts of axonally transported radioactive proteins.

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PubMed1984

Experimental serous retinal detachment and focal pigment epithelial damage.

We made small nonrhegmatogenous retinal detachments (blebs) in rabbits over regions of retinal pigment epithelium (RPE) that were damaged mechanically or by laser photocoagulation. Fluorescein diffused readily into blebs made over damaged RPE, but the subretinal fluid was resorbed more quickly than from blebs overlying normal RPE. Thus, focal damage appears to facilitate water movement from, rather than into, the subretinal space. We conclude from these data that central serous chorioretinopathy is not caused simply by a passive "leak" through the RPE barrier, and the effects of photocoagulation in this disease cannot be explained simply as sealing such a leak.

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PubMed1984

Healing of photocoagulation lesions affects the rate of subretinal fluid resorption.

We have measured the rate of subretinal fluid resorption in rabbits by monitoring the collapse of small experimental retinal detachments (blebs) filled with either Hanks' solution (non-proteinaceous) or autologous serum. Blebs filled with Hanks' solution resorbed much more rapidly over freshly lasered RPE than normal RPE, but the effect disappeared over 10 to 14 days. This time course corresponds with angiographic and histologic evidence of RPE repair. In contrast, blebs filled with serum resorbed at nearly the same rate regardless of whether the RPE had been lasered or not. We conclude that photocoagulation destroys the RPE barrier acutely, and until the barrier heals non-proteinaceous subretinal fluid will be drawn out rapidly by the oncotic pressure of the choroid. This acute effect of photocoagulation is of uncertain benefit in clinical conditions because of protein in the subretinal fluid, and it seems more likely that photocoagulation works in serous retinopathy by arresting an active source of fluid.

Absorption↗
PubMed1984

Validation of a model of non-rhegmatogenous retinal detachment.

To study the movement of subretinal fluid, we have injected fluid into the subretinal space through a glass micropipette and monitored its resorption. This technique has been criticized as a model of non-rhegmatogenous detachment because the small retinal hole made by the micropipette might allow efflux of subretinal fluid into the vitreous. The present experiments answer this criticism: we found that sealing the micropipette hole with cyanoacrylate, mucilage or an air bubble had no effect on the rate of subretinal fluid resorption, and detachments with two to five micropipette holes did not resorb faster than those with only one.

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PubMed1984

Effects of subretinal and systemic osmolality on the rate of subretinal fluid resorption.

Small norhegmatogenous retinal detachments (blebs) were made in Dutch rabbit eyes by injecting solution into the subretinal space. There was no difference in resorption time between blebs made with isotonic, hypertonic or hypotonic sodium chloride. However, blebs made with sucrose solution took longer to resorb than those made with Hanks' solution, regardless of whether the sucrose was hypotonic or hypertonic. Intravenous injection of hyperosmotic solution (mannitol) accelerated the resorption of Hanks'-filled blebs but the injection of hypoosmotic solution (water) had no clear effect. The authors conclude that osmotic differences between the subretinal space, and the vitreous and/or choroid, are rapidly equilibrated by the surrounding tissues; but the rate of bleb resorption will be affected by the size and membrane permeability of the molecules within the subretinal space. The effects of increased serum osmolality may involve not only osmotic pressure but an opening of the tight junctions of the RPE.

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PubMed1983

Mode of ion movements into vitreous. Equilibration after vitrectomy.

Ion movements into and out of the vitreous space after closed vitrectomy were the same as in open-sky vitrectomy in rabbits. Ion increase or decrease depended primarily on passive penetration, although active transport contributed to increases during the early phase in equilibration. Ions penetrated from the entire area of tissue in contact with the vitreous space; and the posterior wall, comprising the largest area of contact, was an important route. This feature was related to compromise of the blood-retinal barrier following vitrectomy.

Animals↗
PubMed1983

The resorption of subretinal fluid after diffuse damage to the retinal pigment epithelium.

We studied the role of the retinal pigment epithelium (RPE) in the resorption of different subretinal fluids from under small experimental retinal detachments (blebs) in the rabbit. Damaging the RPE with sodium iodate caused the resorption time, for blebs made with an ionic solution (Hanks'), to decrease from 2-6 hours to only about 30 minutes. Blebs made with sucrose also absorbed much more quickly after iodate. However, blebs made with autologous serum resorbed no faster after iodate. We conclude that iodate destroys the membrane barrier properties of the RPE, allowing subretinal fluid to cross freely according to oncotic pressure. We postulate that in the normal eye, where osmotic fluid movement is low because of the high resistance barrier, the RPE must transport fluid actively to keep the subretinal space dehydrated.

Absorption↗
PubMed1982

Importance of bicarbonate ion in the vitreous space.

Intraocular irrigating solutions used during vitrectomy must be safe for all tissues surrounding the vitreous space. Bicarbonate and glucose were essential to the maintenance of retinal function. In this study the optimum concentration of bicarbonate in the irrigating solution for the retina was determined electrophysiologically with the use of the in vitro eyecup of the rabbit. In 15 to 25 mmole/L of bicarbonate solutions, the electroretinographic (ERG) b wave was well maintained. Higher concentrations of bicarbonate (35 to 45 mmole/L), which have been considered to be advantageous for the integrity of the corneal endothelium, were shown to suppress the retinal activity. These results were also found in in vivo eyecup, as determined with ERG and visual evoked response. Properly performed open-sky vitrectomy, itself, does not cause severe damage to the normal retinal function.

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