RETINAL NEURONS SPECIFIC FOR CENTRIFUGAL MODULATION OF VISION

THE avian retina receives centrifugal projections from a midbrain nucl eus, the isthmo-optic nucleus. We labelled target cells for the isthmo -optic fibres by intracellular injections of Lucifer Yellow in fixed r etinal slices. The isthmo-optic recipient (IOR) cells had no major den drites extending into the inner plexiform layer, but had a thin axon-l ike process running horizontally in the junction between the inner nuc lear layer and the inner plexiform layer. The IOR cells were morpholog ically similar to the association amacrine cells of Cajal. Immunohisto chemical localization of aspartate and glutamate in the IOR cells sugg ested that they may use these excitatory amino acids as neurotransmitt ers.