The Neuroprotective Effect of alpha-phenyl-N-tert-butyl-nitrone (PBN) in the Argon Laser Induced Retinal Ischemia

PURPOSE: We examined the ability of alpha-phenyl-tert-butyl-nitrone (PBN), an electron spin trapper, to determine the neuroprotective effect in the argon laser induced ischemic rat retina model. METHODS: After ischemic condition of rat retina was induced by argon green laser, PBN was given intraperitoneally at 50 or 100 mg/kg and normal saline was injected to control group. After 24 hours, 48 hours, and 7 days, the neuroprotective effect of PBN was examined by electroretinogram (ERG) and after 7 days, the enucleation of eyes was performed and histologic findings were compared by light microscopy and transmission electron microscopy. RESULTS: We found relatively reduced amplitude of ERG wave in the PBN injected group but not so greatly reduced as in normal saline control group. The retinal ganglion cell (RGC) layer and the number of RGCs were affected by acute ischemic changes but in the group of PBN treatment, the cell membrane was well preserved and vecuoles formation, cytoplasmic destructions, nuclear chromatin condensation were reduced. CONCLUSIONS: Systemic administration of PBN can ameliorate an argon laser induced retinal ischemia. Further investigations are necessary to decide effective dose without toxicity and to find more convenient methods of administrations.

The Changes of the Retinal Ganglional Cells in the Pressure-induced Ischemic Rabbit Retina

PURPOSE: There were many studies on the distributions of the retinal ganglion cells(RGC) in the experimental model of the retinal ischemia. RGC was known to be more sensitive to the ischemic injury than the other types of the retinal cells. So, we would identify the changes of the retinal ganglion cell morphologies and distribution after the iatrogenic retinal ischemia induced by intraocular pressure(IOP) elevation. METHODS: Eight pigmented and six white rabbits were used and retinal ischemia was induced by increasing IOP higher than 120 mmHg for 60 minutes. Electroretinogram were recorded at 6 days or 13 days, and histologic findings were observed at 7 or 14 days. RESULTS: After 7 days, RGC densities decreased, cytoplasmic staining disappeared, and the intranuclear hyperpigmentation was noted. RGC densities decreased significantly at 14 days. In the vertical retinal section, some flattening of retinal ganglion cell layer and inner plexiform layer was observed. Changes in the cellular morphologies were prominent. CONCLUSIONS: It may be more appropriate to examine both the retinal whole-mount and the vertical tissue section for the estimatation of the changes of retinal ganglion cell layer in the pressure-induced retinal ischemia.

The Effect of Antiproliferative Drugs on the Collagen Matrix Cultured with Retinal Pigment Epithelial Cell and Choroidal Fibroblast

PURPOSE: Epiretinal membrane in proliferative vitreoretinopathy (PVR) may cause tractional retinal detachment after vitreoretinal surgery. It has been thought that the proliferative membrane is mainly composed of choroidal fibroblasts and retinal pigment epithelial cells. Inspite of the technical advances, the treatment of PVR is still difficult. Therefore, the need for phamarcologic treatment of proliferative vitreoretinopathy is increasing. METHODS: In vitro models of proliferative vitreoretinopathy allow to identify the factors which may inhibit proliferation and contraction of collagen matrix by choroidal fibroblast and retinal pigment epithelial cells. Cultured choroidal fibroblasts and the RPE cells were plated to the collagen matrix and antiproliferative drugs was tested. RESULTS: Each antiproliferative drug showed the inhibition of collagen matrix contraction at following concentration: colchicine(0.1 microgram/ml), puromycin(1~10 microgram/ml), cytochalasin B(0.05 microgram/ml). Transmission electron micrograph of collagen matrices showed dense collagen fibers surrounding choroidal fibroblast and fine collagen fibers surrounding RPE cell. Scanning electron micrograph of collagen matrices contaning colchicine, puromycin, or cytochalasin B showed that collagen fibers were well preserved without distortion. All collagen matrices containing RPE cells showed more fine collagen fibers than those containing choroidal fibroblasts. CONCLUSION: Colchicine, puromycin, cytochalasin B showed inhibitory effect on cell mediated contraction in addition to potent antiproliferative effect. Retinal pigment epithelial cell played less significant role in causing PVR than choroidal fibroblast.

The Neuroprotective Effect of Intravitreal Melatonin Injection in Pressure-induced Retinal Ischemia

PURPOSE: The authors sought to determine the neuroprotective effect of melatonin in a model of ischemic injury in rabbit retina. METHODS: Ischemia was induced by high intraocualr pressure. A dose of 100 microgram of melatonin or dimethyl sulfoxide(DMSO) alone was injected intravitreally just after the induction of ischemia. After 7 and 14 days, the neuroprotective effect of melatonin on ischemic retina was examined with light microscope and transmission electron microscope. RESULTS: The authors found reduction of cytoplasm of retinal ganglion cell(RGC), vacuole formation, chromatin condensation and rupture of nuclear membrane in ischemia-injured eyes treated with DMSO alone. But in melatonin treated eyes, we found that RGC layer's thickness and number of RGC reduced and destruction of cytoplasmic organells and nuclear damage were minimal. The partial recovery of wave is noted in melatonin-treated eyes after ischemia induction. CONCLUSIONS: The melatonin(100 microgram) protected the rabbit retina from high intraocular pressure-induced ischemic injury when administered intravitreally. Melatonin may be useful to decrease neuronal damage in the retina as a result of ischemic injury. But further investigations are neccesary to decide effective concentration, route and time of administration.

The Toxic Effects of Diclofenac Sodium on Cultured Rabbit Corneal Epithelium

Diclofenac sodium is a widely used drug for reducing inflammation and pain after cataract, surgery or excirner laser photorefractive keratectomy. However,we could find epithelial defect while using this drug postoperatively. To investigate the toxic effects of diclofenac sodium, we cultured corneal epithelial cells and tissues, then exposed them to various concentratiotration of drugs and measured the cell number and expanding area from. the original corneal tissue. In cases of cell culture, the cell number was counted at 24, 48, and 72 hours` exposure to l2.5, 25, 50, and 100 ug/ml solution of diclofenac sodium and at. 5 days after two minute exposure to 0. I and 0.2% solution. The cell number was reduced significantly at 50ug/ml (72 hrs later) , 100ug/ml(48 or 72 hrs later) and 0.1, 0.2% of solution than that of the control group. In tissue culture, we exposed the epithelial tissue to the same condition of cell culture. In long duration exposure conditions, the size of the epithelium grown from the tissues was smaller than that in the control group, especially at the dosage of 50 and 100ug/ml. In short duratio(2 minutes) exposure conditions, no significant difference from the control group was found. In conclusion, diclofenac sodium has some suppressive effects on the growth and migration of the rabbit corneal epithelium and its postoperative high dose or frequent instillation might injure the corneal epithelial cells.