Neuroscience Vol. 45, No. 1, pp. 221-225, 1991 Printed in Great Britain 0306-4522/91 $3.00 + 0.00 Perpmon Press plc 0 1991 IBRO zyxwvu PROSTAGLANDIN E, CHANGES IN THE RETINA AND OPTIC NERVE OF AN EYE WITH INJURED OPTIC NERVE A. BAR-ILAN,* N. NAvEH,*t C. WEISSMAN,* M. BELRIN* and M. SCHWARTZ$ *Maurice and Gabriela Goldschleger Eye Research Institute, Tel Aviv University, Sackler Faculty of Medicine, Chaim Sheba Medical Center, Tel Hashomer, Israel SDepartment of Neurobiology, Weizmann Institute of Science, Rehovot, Israel Ahstract4hanges in arachidonic acid metabolism were studied in the optic nerve, the choriomtina, and in the vitreous following crush injury to the optic nerve of rats. Crush injury led to: (i) a 3.9-fold increase in optic nerve prostaglandin type Er in vitro production which peaked on day 5 and was followed by a gradual decline, but was still significantly higher than baseline levels by day 12; (ii) a two-fold increase in the chorioretina prostaglandin type E, in vitro production which peaked on day 1, and resumed baseline levels by day 3; (iii) a 3.5-fold increase in vitreous prostaglandin type E, levels on day 1 which remained at 1.5-2 times higher than baseline levels for the rest of the study period (12 days). The findings indicate that the pattern of changes in prostaglandin type E, production by the optic nerve (consisting mostly of white matter) is different from that described for injured brain tissues. The prolonged accumulation of vitreal prostaglandin type E, in eyes with damaged optic nerve may lead to undesirable effects on the retina beyond those directly manifested in the retina by altered axonal flow in the injured optic nerve. Injury to the optic nerve, both direct and indirect, usually results in immediate total loss of vision. Both surgical optic nerve decompression and high dose corticosteroids have been used therapeutically, with varying degrees of success. The efficacy of these treatments is currently unknown, as no prospective controlled studies have been carried out comparing the two treatments with no treatment.22*27*32s3v Prostaglandins and other eicosanoids are syn- thesized through the cyclooxygenase pathway from arachidonic acid, which is released from cell mem- brane phospholipids whenever the cells are exposed to various stimuli, such as hypoxia or mechanical stimulation.38 Prostaglandins are also known for their mediatory role in the reaction to injury.v~24An im- proved neurological recovery was reported in animals suffering from spinal trauma or brain ischemia fol- lowing a combined drug treatment that included the cyclooxygenase inhibitor indomethacin.i4 There is only sparse information on the involvement of pros- taglandins in retinal pathophysiology: the retina ex- hibits cyclooxygenase activity,36 is directly affected by excessive prostaglandins as shown by electro-retin- ography,43 whereas an increased prostaglandin E2 (PGEJ production by the chorioretina was observed following retinal injury induced by laser ir- radiation.33*u We therefore decided to study the changes in arachidonic acid metabolism in injured optic nerve, and the corresponding changes in the retina as well tTo whom correspondence should be addressed. Abbreuiations: PGE,, prostaglandin type E,. as in the adjacent vitreous. Pharmacological manipu- lation of such biochemical changes may serve as a basis for medical therapy in cases of optic nerve injury. EXPERIMENTAL PRDCEDURRS Optic nerve crush injury was performed in male albino rats (Charles River, T.A.U. Animal Resources Unit), 0.24.3 kg, anesthetized with an intraneritoneal iniection of 40 mg/kgketamine HCl (Vetalar, Parke-Davis) and 8 mg/kg xylazine-HCl (Rompum, Bayer, Leverkusen). After incision of the conjunctiva and displacement of the ocular muscles the optic nerve was exposed and crushed for 3Os, 2 mm distal to the eyeball, using a reverse action capsule forceps modified to enable adjustment of compression power. The pressure applied was predetermined to cause an immediate disappearance of the compound action potential followed by its recovery 30min later to 200-5OOuV.’ The animals were divided into two groups: (i) crush’injury group; (ii) sham-operated group (animals that underwent injury as in group i, but without crushing the nerves). The rats were killed at zero time (immediately after surgery, nine rats/group), and one, three, five, and 12 days later (seven rats/group), by an overdose of pentobarbitone. The optic nerve was exposed, and detached from the eyeball following skull opening. This allowed dissection of the nerve at the chiasm, so that the whole length of the nerve could be obtained. Much care was taken to minimize trauma to the optic nerve during tissue detection, as this can greatly al&t eicosanoid production. ‘iJ6 The enucleated eyes were frozen in liquid nitrogen and dissected later. The anterior segment of the eye was removed, while the vitreous and the whole retina attached to the choroid were each carefully separated from the sclera, and placed in separate vials. Weighed optic nerve sections, vitreous, and chorioretina were each incu- bated separately in Krebs-Ringer-bicarbonate at 37°C for 30 and 10 min, respectively. In a few cases when retina tissue weight was too low (c 10 mg), tissues from two eyes were pooled and assayed together. Incubation media PGE, levels 221