Abstract
Purpose:
Bipolar cells relay the signals from photoreceptors to ganglion cells, which are the output elements of the retina. Depending on the size, morphology and stratification depth of their axon terminals or dendritic trees many different bipolar and ganglion cell types can be distinguished. We are interested, whether ganglion cell dendrites sample their bipolar cell input homogenously from all bipolar cell axons stratifying in the same stratum, or whether the ganglion cell dendrites are selectively contacted by certain types of bipolar cells only.
Methods:
We used two transgenic mouse lines (GFP-O and JamB), immunohistochemistry and confocal imaging, to visualize several ganglion cell types in combination with markers for ribbon synapses (CtBP2) and type 2 (Syt2) bipolar cells in retinal flat mount preparations. We analyzed for several ganglion cell types the proportion of synaptic input from type 2 bipolar cells relative to their total bipolar cell input.
Results:
The following ganglion cell types, which all stratify in sublamina 1 were investigated: C6, B1, B3-Off and C2-Off ganglion cells (Sun et al. 2002, J Comp Neurol 451:115-126). C6 ganglion cells receive only minor input from type 2 bipolar cells (21.6 %; n = 14 cells). Type 1 and 4 bipolar cells also stratify in S1 of the IPL, and could provide the remaining 78.4 % of bipolar cell input. Preliminary experiments revealed that type 1 bipolar cells provide the majority (75 %) of input to C6 cells, whereas less than 5 % are provided by type 4 bipolar cells, suggesting a selective connectivity of type 1 bipolar cells with C6 ganglion cells. In contrast to C6 cells, B1, B3-Off and C2-Off ganglion cells receive a larger proportion of their input from type 2 bipolar cells (B1: 42.5 %; B3-Off: 42.2 %; C2-Off: 44.4 %) than C6 cells, indicating that they sample more homogeneously from different bipolar cell types.
Conclusions:
Our data indicate that some ganglion cell types, as shown here for C6 cells, receive synaptic input preferentially from certain bipolar cell types, while others receive input from different varieties of bipolar cells. Such differences may correlate with distinct physiological roles of these ganglion cells, requiring input from bipolar cells, which transfer specific features of the light signal.
Keywords: 691 retina: proximal (bipolar, amacrine, and ganglion cells) •
531 ganglion cells •
554 immunohistochemistry