Tracer coupling of neurons in the rat retina inner nuclear layer labeled by Fluorogold

A subpopulation of neurons in the inner nuclear layer (INL) of the rat retina were labeled 9-13 weeks after application of Fluorogold (FG) to the superior colliculus. Neurobiotin injection of FG-labeled cells in the INL of flatmounted living retina revealed that these cells consisted of both displaced ganglion cells and a subset of amacrine cells. Fluorogold-labeled amacrine cells in the INL showed tracer coupling to other presumptive amacrine cells in the INL, but there was no evidence of coupling to neurons in the ganglion cell layer (GCL). As the labeling of amacrine cells by FG may be due to gap junction coupling between ganglion and amacrine cells, these data add to the evidence that tracer coupling between these cells can be unidirectional. Some of the FG-labeled displaced ganglion cells in the INL injected with Neurobiotin also showed tracer coupling to neurons in the INL or GCL.