Abstract
Purpose: :
Right at the first synapse in the mammalian retina, the stream of incoming visual information is split into multiple parallel information channels, preprocessed in the retinal network and relayed to the brain via different types of retinal ganglion cells (RGCs). About 20 different morphological RGC types have been described, with each RGC population tiling the retinal surface with its dendritic arbors. Here, we simultaneously record from all RGC types at one retinal location to obtain a complete sample of the information sent to the brain and to understand how the representation of spatio-temporal information in a local image patch is distributed across different RGC types. We aim to establish a more complete view of what visual information is preserved in the retina and how it is decomposed into the different channels.
Methods: :
Light-evoked Ca2+ activity is recorded at single-cell resolution from groups of RGCs loaded with synthetic Ca2+ indicator dyes in whole-mounted mouse retina using two-photon (2P) microscopy. In contrast to multi-electrode recordings, the imaged RGCs remain accessible to microelectrodes and, thus, can be easily dye-filled for morphological identification or targeted for patch-clamp recordings. We use a simple full-field light stimulus consisting of luminance changes and a temporal frequency chirp, and cluster responses into functionally defined classes using a simple k-means algorithm.
Results: :
Recording light responses from over 500 neighboring GCL cells in a single retinal patch revealed that over 80% of cells reliably responded to a full field stimulus modulated in time and intensity. Single cell activity patterns could be clustered into more than 15 functionally distinct types, yielding about 40% ON cells, 25% ON/OFF and 15% OFF cells, in agreement with previous reports. In addition, presentation of spatially modulated stimuli such as moving bars and spot-maps allow to quickly but reliably identify different types of DSGCs and to map spatial receptive fields. We now aim to establish a simple battery of stimuli that in combination will allow to functionally cluster all >20 morphologically described RGCs in the mouse retina.
Conclusions: :
We show that retinal ganglion cells can be clustered into functionally defined classes based on their Ca2+-responses to simple light stimuli. Our method allows us to create an inventory of all retinal ganglion cells present at a single retinal location. This local retinal "information fingerprint" should be very informative, not only for our understanding of neuronal computations in the healthy retina, but also as a research tool for evaluating specific functional deficiencies in diseased or degenerating retinae.
Keywords: ganglion cells • calcium • image processing