Fig. 2.

Expression patterns of mAChRs relative to the expression of α7 nAChRs. Confocal image stacks of projections of 5 optical sections (0.5 μm steps) of m1, m3, and m5 mAChRs relative to α7 nAChRs. Colocalization was assessed from single confocal optical sections and masked onto overlay images. Column 1, A and B: subsets of amacrine cells and ganglion cells (arrowheads) and subsets of bipolar cells (small arrowheads) were immunoreactive for both m1 mAChRs and α7 nAChRs. Other bipolar cells (arrows), amacrine cells (notched arrowheads), and ganglion cells (triangles) were m1 immunoreactive but not α7 immunoreactive. Muscarinic m1 and nicotinic α7 receptor IR were also colocalized in a band in the On sublamina of the IPL. Colocalization of IR throughout the rest of the IPL was limited. Column 2: ganglion cells and subsets of amacrine cells (triangles) were immunoreactive for the α7 nAChR subunit, whereas other amacrine cells were immunoreactive for m2 mAChRs (notched arrowheads). However, there was no apparent colocalization between m2 IR and α7 IR in cell bodies. m2 labeling in cell somas was very dim (notched arrowheads), even though IR was broadly distributed throughout the IPL, with intense labeling in a broad center band. There were double-labeled processes throughout the IPL, with strong masking at the boundary of GCL in the On sublamina of the IPL. Column 3: whereas a small number of bipolar cells were immunoreactive for both α7 nAChR subunits and m3 mAChRs (small arrowheads), the majority of immunoreactive bipolar cells was immunoreactive either for m3 mAChRs (small arrows) or α7 nAChRs (notched arrowheads), although there was a narrow band of colocalization in the OPL. Likewise, immunoreactive cells in the inner INL and GCL, presumptive amacrine and ganglion cells, displayed either α7 or m3 IR but not both. m3 IR was distributed primarily in 2 bands in the inner and outer IPL and sparsely colocalized with α7 IR. Column 4: cells in the GCL were m4 immunoreactive and α7 immunoreactive (arrowheads), whereas ganglion cells (triangles) and amacrine cells (notched arrowheads) were immunoreactive only to antibodies against α7 nAChR subunits. Dendritic stratification of α7-immunoreactive ganglion cells appeared to be in the On sublamina of the IPL, as colocalization through the rest of the IPL was minimal. Column 5: there was no apparent colocalization of m5 IR and α7 IR in ganglion cells (triangles) or amacrine cells (notched arrowheads), but bipolar cells with small cell bodies appeared to be immunoreactive for both m5 mAChR and α7 nAChR subunits (small arrowheads). Double-labeled processes were sparsely distributed throughout the IPL. Original scale bar, 50 μm. Bottom: boxed areas in detail; original scale bar, 10 μm.