A study of the centrifugal projections to the pigeon retina using two fluorescent markers

The centrifugal projection to the retina of the adult pigeon was studied by the retrograde transport of Diamidino yellow and Fast blue. On the contralateral side in the nucleus isthmo-opticus 8400-10,900 cells were stained while in the surrounding area 1500-2800 marked ectopic cells were counted. Up to 94 neurones, which are nearly all ectopic, project to the ipsilateral eye. Using double-labelling we concluded that there are no cells projecting to both eyes. This study shows that in the adult pigeon there exist more ectopic cells projecting to the retina than previously reported in horseradish peroxidase experiments.