Antibody to calretinin stains AII amacrine cells in the rabbit retina: Double-label and confocal analyses

The AII or rod amacrine cell is a critical interneuron in the rod pathway of mammalian retinae. In this report, it is shown that commercially available antibodies to the calcium binding protein calretinin may be used to label the population of AII amacrine cells selectively. Calretinin-positive amacrine cells had the morphological attributes of AII amacrine cells. Double-labeling procedures showed that calretinin-positive somata were surrounded by dopaminergic varicosities and that calretinin-positive dendrites enclosed rod bipolar terminals, both as previously described for AII amacrine cells. By analyzing the surrounding kernel for each labeled pixel in the rod bipolar image, it is shown here that AII processes are adjacent to rod bipolar terminals at a level that far exceeds the random overlap present in images in which one label was rotated out of phase. Such a spatial relationship is indicative of synaptic connections, as well described for rod bipolar input to AII amacrine cells. AII amacrine cells also were double-labeled for calretinin and parvalbumin; however, a scattergram analysis of red versus green intensity showed that the parvalbumin antibody stained additional unidentified amacrine cells. In conclusion, at the appropriate dilution, calretinin antibodies are a useful marker for AII amacrine cells in the rabbit retina.