DOUBLE-STAINING OF HORIZONTAL AND AMACRINE CELLS BY INTRACELLULAR INJECTION WITH LUCIFER YELLOW AND BIOCYTIN IN CARP RETINA

Horizontal and amacrine cells in the isolated carp retina were impaled with micropipette electrode, identified by their characteristic light responses, and injected iontophoretically with markers for morphologi cal study. Both Lucifer Yellow CH and biocytin were injected simultane ously. Lucifer Yellow was seen by its own fluorescence while biocytin was visualized by binding with Texas Red-linked or horseradish peroxid ase-conjugated avidin. For cone-connected horizontal cells, biocytin-c oupled cells were found to be approximately five-times more numerous t han Lucifer Yellow-coupled cells. Coupling for both tracers was consis tently hampered by intravitreally applied dopamine. In untreated retin as, the injected Lucifer Yellow was restricted within one rod-connecte d horizontal cell, while biocytin revealed several coupled neighbors. Amacrine cells, labeled by the tracers, were morphologically grouped i nto eight types, based on our earlier classification.(29) Among them, amacrine cells, belonging to three types (Fnd, Pmb or Pma), were confi rmed to be Lucifer Yellow-coupled, and the number of biocytin-coupled cells was more numreous (about 2.5 times) than that of Lucifer Yellow- coupled cells. Most amacrine cells (i.e. Pwd, Fnb and Fna) showed bioc ytin-coupling with no Lucifer Yellow-coupling. A few classified (i.e. Pwb and Fwa) and unclassified cells did not show any coupling. Since t he tracer coupling takes place via gap junctions, the majority of amac rine cells, belonging to certain homologous types, appear to be functi onally coupled with each other in the inner plexiform layer. However, dopamine did not influence the range of tracer coupling between amacri ne cells in the carp retina under the present experimental conditions.