Abstract
Purpose::
In the rod - AII pathway, rod signals pass from AII amacrine cells to ON cone bipolar cells (ONCB) via gap junctions. Recent evidence has suggested that some ganglion cells do not receive rod signals via this pathway (Volgyi et al. 2005. J. Neurosci. 24:11182-92). It follows that the ONCBs that excite this population of ganglion cells must not receive rod inputs via the rod-AII pathway. It has also been shown that AIIs and ONCBs remain coupled in light adapted conditions (Xin and Bloomfield, Vis Neurosci. 1999 Jul-Aug;16(4):653-65; Veruki and Hartveit, J Neurosci. 2002 Dec 15;22(24):10558-66), but whether all ONCBs remain coupled is unknown. Therefore, we sought to determine if there are any ONCBs that are not coupled to AII amacrine cells in light and dark adapted conditions.
Methods::
We prepared flat mount rabbit retina in both dark and light adapted conditions. Fixation of dark adapted tissue occurred in the dark since light adaptation could have occurred during the time required for cross-linking. We immunostained with antibodies to Glycine, Galpha0 and PKCalpha. Galpha0 labels all depolarizing bipolar cells and PKCalpha labels all rod bipolar cells. Glycine labels glycinergic amacrine cells as well as ONCBs that are coupled to AIIs. We used "glycine coupling" as a measure of functional gap junction coupling between ONCBs and AII amacrine cells.
Results::
We expect that all ONCBs that are coupled to AIIs will contain glycine. Any cells that do not have glycine are presumed to be uncoupled from the AII-ON cone bipolar network. ON cone bipolars were marked as Galpha0 positive / PKCalpha negative. Our data show that there is a population of Galpha0 + / PKCalpha - cells that do not stain for glycine. The fraction of ONCBs that do no contain glycine is higher in light adapted conditions than in dark adapted conditions.
Conclusions::
It appears that, in dark adapted tissue, there is a population of ON cone bipolar cells that are not glycine coupled to AII amacrine cells, and therefore, they and the ganglion cells they excite would not receive input via the rod-AII pathway. There also appears to be a greater number of uncoupled ONCBs under light adapted conditions than under dark adapted conditions, suggesting that light adaptation modulates the coupling between AIIs and ONCBs.
Keywords: bipolar cells • amacrine cells • gap junctions/coupling