Abstract
Purpose::
It was well documented that both the dendritic field (DF) and receptive field (RF) of retinal ganglion cells (RGCs) are developmentally regulated in postnatal mammalian retina. It is not clear, however, whether the developmental change of RGC RF correlates with the DF. The goal of this study is to determine the developmental profiles of mouse RGC DFs and RFs after eye opening.
Methods::
Thy1-YFP-expressing mice were used for the DF measurements and three-dimensional dendritic structures of RGCs were obtained from YFP-expressing RGCs using a confocal microscope. A multielectrode array system was used to record RGC action potentials of wild type mice evoked by a small white square (25µm×25µm), which flashing at different locations of a test field (1.5mm×1.5mm) at 1Hz upon black background. ON and OFF RFs were mapped based on the peak frequency of ON and OFF responses at each location, respectively.
Results::
The results were analyzed based on the ON, OFF and ON-OFF RGCs. The average sizes of both DFs and RFs increased with age after eye opening for all three groups of RGCs and the sizes of RFs were larger than that of DFs by 60% to 170% for different groups of RGC. Interestingly, the developmental changes in the sizes of DFs and RFs were not proportional for ON and OFF RGCs. For ON cells, the average size of DFs increased by 15% from P12 to P33 while the average size of RFs increased by 60% during the same time period. Therefore, the ratio of RF/DF of ON RGCs was increased from 1.7 to 2.3. In contrast, the average DFs of OFF RGCs increased by 78% but the average RFs only increased by 20% during this time period. This resulted in a decrease of RF/DF ration from 2.4 at P12-13 to 1.6 at P33. On the other hand, the DFs and RFs for both ON and OFF fields of ON-OFF RGCs increased more proportionally (16-27%) and, therefore, the RF/DF ratios were less significantly altered during postnatal development after eye opening (increased 0.07 for ON filed and decreased 0.07 for OFF field).
Conclusions::
We interpret these results as that both DF and RF of RGCs continuously develop after eye opening but different synaptic pathways seems to be regulated differently. With increase of age, ON RGCs and ON field of ON-OFF RGCs receive more converging synaptic inputs so the RFs increased more than DFs whereas the OFF RGCs and the OFF field of ON-OFF RGCs receive relatively less converging synaptic inputs so the DFs increased more than RFs.
Keywords: retina • retina: proximal (bipolar, amacrine, and ganglion cells) • retinal connections, networks, circuitry