Target cells for the isthmo-optic fibers in the retina of the Japanese quail.

The isthmo-optic nucleus (ION) is the major origin of the centrifugal fibers projecting to the avian retina. The retinopetal fibers from the ION were labeled with biocytin and examined light- and electron-microscopically in the Japanese quail. The terminals were seen on cell bodies in the inner part of the inner nuclear layer. These neurons innervated with the isthmo-optic fibers appear to constitute a separate population different from the 'ordinary' amacrine cells.