Amacrine cells are the most diverse group of neurons in the mammalian retina with more than 30 classes having been identified in the inner nuclear and ganglion cell layers. However, with a few notable exceptions, our understanding of the roles played by these neurons in visual processing is still rudimentary. The present lack of information about their functional properties is primarily due to past difficulties associated with making patch-clamp recordings from these neurons in the intact retina. These difficulties have now been overcome and the overall objective of the proposed research program is to obtain fundamental information essential to the eventual understanding of the role that these neurons play in visual processing. This will be achieved by making patch-clamp recordings from morphologically classified intact amacrine cells displaced to the ganglion cell layer (DACs). Recent evidence in both rabbit amacrine cells suggests that the somatic membrane properties of these neurons may play an important role in the processing of visual information. For the first specific aim, the investigators will make current-clamp recordings to assess the intrinsic membrane properties of different displaced amacrine cell classes. Secondly, to fully understand the mechanisms that govern the functional diversity of these neurons they will use specific ion channel blockers, ion substitution, and differences in activation and inactivation properties to examine the voltage-gated and calcium-activated potassium currents expressed by DACS. Finally, by recording the light-evoked response properties of DACs , they aim to establish the similarities and differences among neurons in terms of their light-evoked response properties, and relate any functional diversity to the different morphological classes. The results of this research program will significantly enhance our understanding of the roles played by distinct morphological classes of mammalian amacrine cell in the processing of visual information.
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