Abstract
Purpose :
Recently, it has been shown that mouse OFF-Alpha transient (OFF-α T) retinal ganglion cells (RGCs) in the dorsal mouse retina generate different responses to light stimulation than those in the ventral retina; these variations were correlated to differences in the organization of the presynaptic network. Here, we examine the postsynaptic properties of these cells to see if these also contribute to the differential responses.
Methods :
Whole cell patch recordings were obtained from OFF-α T RGCs from the dorsal and ventral mouse retina (n=16). Spiking responses were measured at varying levels of injected current. Subsequently, we filled cells (n=8), stained for streptavidin, ChAT and AnkyrinG and did confocal microscopy to capture morphology. Unequivocal cell type identification was made from light responses and from dendritic stratification in the inner plexiform layer. AIS length was determined by measuring the length of co-aligned regions of RGC axons and AnkyrinG.
Results :
RGCs responded with regular spiking at low current amplitudes but stopped sustained spiking, i.e. spiking throughout the duration of the current injection, at larger current injections. These failure thresholds were significantly higher in dorsal than in ventral OFF-α T RGCs (763 ± 106 pA vs. 425 ± 128 pA; p=0.0001). Furthermore, spiking output at a given amplitude that was below the failure threshold was more sustained in dorsal than in ventral cells. AIS length was significantly longer in dorsal than in ventral RGCs (28.5 ± 3.5 μm vs. 13.1 ± 2.2 μm; p=0.0003). Consistent with previous reports, dendritic field diameter of dorsal RGCs tended to be larger than ventral cells (390 ± 29 μm vs. 286 ± 24 μm; p=0.0032) whereas dendritic architecture was similar in the two groups.
Conclusions :
Our results indicate that OFF-α T RGCs that receive higher levels of synaptic input are functionally different from cells that receive lower levels, e.g. they can generate regular spiking patterns in response to much higher levels of current. AIS differences between the two groups of cells suggest the identification of an anatomical substrate that underlies the functional differences.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.