Ionic mechanisms of action potentials in retinal ganglion cells

The retina serves as an ideal model system for investigations that aim to bridge the gap between systems level descriptions and underlying mechanisms at cellular and molecular levels. The major aim of this project is to characterize and understand biophys ical mechanisms that generate action potentials in retinal ganglion cells (RGCs). RGCs are the output elements of the retina and translate signals based on a neural code using graded potentials in bipolar cells (and amacrine cells) into signals based on a spike code. Based on their morphological and visual response properties, RGCs can be divided into 10-20 different types and it is generally assumed that each type of RGC processes and transmits information about a particular feature of a complex visual s timulus (parallel processing). While there is strong evidence for a heterogeneity among RGCs with respect to intrinsic electrophysiological properties, including the expression of various types of time- and voltage-dependent ion currents, it has been very difficult to correlate such differences with the different types of RGCs. In addition, compared to several model systems elsewhere in the CNS, mammalian RGCs are not well characterized with respect to the biophysical mechanisms that generate action poten tials and we lack biophysically realistic models based on solid experimental evidence obtained from the RGCs themselves. These problems have also hampered attempts at developing realistic numerical models of action potential generation in RGCs. In this pr oject, we aim to perform detailed investigations of action potential generating mechanisms in RGCs, to study how such mechanisms might differ between different functional types of RGCs and to study how differences in time- and voltage-gated conductances m ight confer different coding properties.