Transneuronal labeling in the pigeon visual system

Abstract

Two, four or six weeks after intraocular injections of mCi-amounts of [ 3H]proline or of a mixture of [ 3H]fucose and [ 3H]proline transneuronal labeling was observed in several areas of the pigeon brain, including the telencephalon and the cerebellum. The known primary retinal projections contralateral to the injected eye were most heavily labeled. Nuclei receiving projections from the labeled tectum had a much higher density of silver grains than the high background. Labeling in the retinotecto-rotundo-ectostriatal pathway was achieved in a chain involving at least three neurons. Transneuronal labeling was also found in the retino-thalamo-hyperstriatal pathway. The pathway from the retina to the nucleus ectomamillaris and to the nucleus lentiformis mesencephali and further on to the cerebellum was also labeled. These results confirm in the pigeon that injections of relatively large amounts of radioactivity labeled proline into the eye makes it possible to study not only primary visual pathways, but also several secondary connections and one tertiary projection.