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 o f mammalian retinae. In this report, it is shown that commercially availabl e antibodies to the calcium binding protein calretinin may be used to label the population of AII amacrine cells selectively. Calretinin-positive amac rine cells had the morphological attributes of AII amacrine cells. Double-l abeling procedures showed that calretinin-positive somata were surrounded b y 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 bip olar 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 i s indicative of synaptic connections, as well described for rod bipolar inp ut to AII amacrine cells. AII amacrine cells also were double-labeled for c alretinin and parvalbumin; however, a scattergram analysis of red versus gr een intensity showed that the parvalbumin antibody stained additional unide ntified amacrine cells. In conclusion, at the appropriate dilution, calreti nin antibodies are a useful marker for AII amacrine cells in the rabbit ret ina. (C) 1999 Wiley-Liss, Inc.