Effect of Isoprostanes on Retinal Transmitter Release

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DESCRIPTION (provided by applicant): Isoprostanes (IsoP's) are a series of prostaglandin-like compounds that are formed in abundance in vivo by a non-enzymatic, free radical catalyzed peroxidation of arachidonic acid independent of cyclooxygenase. In addition to providing a reliable measure of in vivo and in vitro oxidative stress, IsoP's can exert pharmacological effects in some tissues. A review of literature revealed that very few studies have addressed the effects of IsoP's on neurotransmitter release from central or peripheral tissues. Although IsoP's have been reported to modulate sympathetic neurotransmission from anterior uveal tissues, no studies have investigated the potential regulatory effects of these compounds on neurotransmission in the retina. In the present study, we will test the hypothesis that IsoP's can modulate glutamate, gamma-aminobutyric acid (GABA) and dopaminergic transmission in the retina both in vitro and in vivo. The overall objective of the present study is to examine the effect of different series of IsoP's (A1, E1, E2, F1, F2 and F3) on glutamate, GABA and dopamine release from retinae both in vitro and in vivo. Experiments in this project have, therefore, been designed to answer the following questions: (i) do different IsoP's alter the release and/or availability of glutamate, GABA and dopamine in vitro and in vivo? (ii) are the effects produced by IsoP's comparable to those of other arachidonic acid metabolites (prostaglandins and thromboxanes)? (iii) what is the role of presynaptic IsoP heteroreceptors in the effects caused by these compounds on glutamate, GABA and dopamine in vitro and in vivo? We anticipate that the results of the present study will improve our understanding of the basic mechanisms involved in the effects of IsoP's on retinal glutaminergic, GABAergic and dopaminergic transmission. Furthermore, these studies may reveal pharmacologically/toxicologically accessible sites for the action of IsoP's in the retina. We hope that observations made in this project will be applicable to diseases of the retina associated with the generation of free radicals and oxidative damage such as ischemia, glaucoma, diabetic retinopathy and age-related macular degeneration.