The proenkephalin A-derived neuropeptides (the enkephalins), and specific receptor sites for these peptides have been reported in retinas of several species, with a localization which supports a role for these peptides as amacrine cell neurotransmitters. The nature of the role of these neuropeptides in retinal function is not clear, due in great part to current uncertainty regarding the specific molecular forms of these peptides endogenous to and active in the mammalian retina. It is particularly difficult to resolve and unambiguously identify all the closely related proenkephalin-derived peptides (the enkephalins, dynorphins and neoendorphins). This project will utilize biochemical and morphological studies to identify neuroactive peptides in mammalian retina, and to determine the presence of the proenkephalin B-derived peptides, the dynorphins/neoendorphins, in the retina. The proenkephalin-derived peptides in mammalian retina will be directly identified and assayed by high performance liquid chromatography (HPLC) and subsequent radioimmune and radioreceptor assays. This complements and extends the PI's earlier immunocytochemical and chromatographic identification of met- and leu-enkephalin in the guinea pig retina. These neuropeptides are known to coexist with the classical neurotransmitters in complex synapses, and to interact in what are still poorly understood ways. Only after the endogenous neuropeptides are unambiguously identified can their role in visual function, and the nature of their complex synaptic interactions with other transmitters, be effectively studied. It is anticipated that this analytical chemical approach will lead to the identification of the endogenous opiate ligands in the retina. Identification of the dynorphins and neoendorphins in retina will resolve the discrepancies between the known presence of opiate receptors in several mammalian species, and the inability so far to identify endogenous ligands for these receptors. The further identification and characterization of the opioid neuropeptides in the retina is required for future studies of their role in retinal visual processing.
