Retinal neurones specific for centrifugal modulation of vision.

The avian retina receives centrifugal projections from a midbrain nucleus, the isthmo-optic nucleus. We labelled target cells for the isthmo-optic fibres by intracellular injections of Lucifer Yellow in fixed retinal slices. The isthmo-optic recipient (IOR) cells had no major dendrites extending into the inner plexiform layer, but had a thin axon-like process running horizontally in the junction between the inner nuclear layer and the inner plexiform layer. The IOR cells were morphologically similar to the association amacrine cells of Cajal. Immunohistochemical localization of aspartate and glutamate in the IOR cells suggested that they may use these excitatory amino acids as neurotransmitters.