Abstract

The hypothesis on transmitter specific, retrograde labeling of neuronal pathways and observations relevant to this hypothesis are discussed. After injection of (3H)-glycine into the pigeon optic tectum fast labeling of intrinsic elements in a restricted part of the subtectal n. isthmi, pars parvocellularis (Ipc), is found - strongly suggesting a rapid retrograde migration of radioactivity in neurons of the glycinergic Ipc-tectal pathway. Labeling of neuronal perikarya in the substantia nigra, in cell groups A8 and A10 and in the n. raphé dorsalis after (3H)-dopamine- and (3H)-serotonin-injection, however in the cortex and in the thalamus after (3H)-D-aspartate-injection into the rat caudoputamen and in the n. raphé dorsalis after (3H)-serotonin-injection but in the caudoputamen after (3H)-GABA-injection into the substantia nigra - all these patterns indicate a retrograde labeling with a certain - partly transmitter specific - selectivity in the pathways concerned. Transmitter related, retrograde transport may become a useful neuro-anatomical method. The cell biology and a possible biological function of the phenomenon remain to be investigated.