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Raymond C. Wong, Shaun L. Cloherty, Michael R. Ibbotson, Brendan J. O'Brien; Are Retinal Ganglion Cell Intrinsic Physiological Properties Conserved?. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4572.
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© ARVO (1962-2015); The Authors (2016-present)
Different aspects of the visual scene (e.g. form, colour, motion) are encoded in the retina in many parallel pathways. These features are extracted through the complex synaptic array of the more than 60 different retinal cell types. Ultimately, this information must be encoded into the spike trains of the 15-20 different retinal ganglion cell types whose axons reach a similar number of central brain nuclei.Previously, we have shown that the intrinsic physiological properties of RGCs vary widely. For example, cat alpha RGCs are capable of spiking in excess of 300Hz whereas the kappa cell can only sustain 40Hz (O’Brien et al., 2002). We have now completed a comprehensive study of rat RGCs intrinsic properties which has a diversity in their intrinsic physiological properties similar to that found in cats. We wondered, therefore, whether these intrinsic physiological properties are conserved among the two species.
Using whole cell patch clamp recording techniques combined with confocal reconstruction of recorded cells, we have characterized the intrinsic physiological properties of 130 rat RGCs. Morphological classification of individual RGCs was done according to Sun et al. (2002).
Using a hierarchical cluster analysis (SPSS v19) with 8 intrinsic properties (Resting potential, Input Resistance, Time Constant, Maximum Frequency, Spike width, Steady-State Frequency, Frequency Adaptation, Anomalous Rectification) ,approximately five different cell groups including many different morphological types were indicated. Specifically, our data suggest that while some cat RGC types have a single close relative in the rat retina: (e.g. cat/rat: alpha/A2, zeta/B4), others seem to be related to a handful of other types. Interestingly, cat beta cells remained isolated throughout most of the clustering algorithm, and eventually clustered with the alpha & A2 cells.
These data suggest that there are a few clearly homologous RGC types that exist in cat and rat retina based exclusively upon their intrinsic physiology. Cat Beta cells, however, do not appear to be present in rats and the data suggest they may have originally evolved from alpha cells. As the spiking output of RGCs ultimately limits what information they can carry, these data suggest that five different 'channels' may have evolved to support different forms of information transfer from the eye to the brain.
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