The inner retina is the site of complex interactions between bipolar cells, amacrine cells and ganglion cells. But the organization of the retina is not chaotic: although there are many amacrine cell types, most adhere to a relatively constant morphology and they are distributed across the retina in non-random mosaics. Furthermore, each cell type ramifies at a specific depth in the inner plexiform layer and makes a stereotyped set of synaptic connections. These repeating units of neural circuitry are the building blocks of retinal function. The goal of this proposal is to identify the neurons and neurotransmitters of some local circuits in the mammalian retina. The PI proposes to study neuronal circuitry by: 1) Measuring ACh release from cholinergic amacrine cells in the rabbit retina. This is a well established method which will provide data on the two types of starburst amacrine cells and the circuitry responsible for directional selectivity. 2) Identification of amacrine cell types by morphology and neurotransmitter. This will be accomplished for single cells by the intracellular injection of Lucifer Yellow or neurobiotin and autoradiography with 3H-glycine or 3H-muscimol. In addition, for some cell types, such as AII amacrine dells, the whole population may be stained,then studied, or subtracted to focus on the remaining cells by image analysis. 3) Dye coupling revealed by the intracellular injection of neurobiotin. The influence of dopamine on dye coupling in the inner and outer retina will be evaluated. Dopamine may control the merging of rod and cone pathways through the gap junctions between the rod amacrine cell (AII) and cone bipolar cells. 4) Intracellular recording from identified cell types. Starburst amacrine cells and AII amacrine cells may be stained selectively with DAPI, observed with fluorescence microscopy and impaled under visual control. Preliminary data indicates that physiological responses to light can be obtained after fluorescence illumination. Pharmacological agents will be applied to test certain specific pieces of circuitry.
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