Exp. Brain Res. 13, 127-134 (1971) ©by Springer-Verlag 1971 Axonal Transport of Macromolecules I. Protein Migration in the Central Nervous System STEPHEN c. BONDY Division of Neurology, University of Colorado Medical Center, Denver (USA) Received January 8, 1971 Summary. The avian visual system has been used to study the transport of proteins and their precursors along the optic tract. Various labeled compounds were injected into a single eye of new hatched chicks. The radioactivity of com- ponents in the optic lobe that was contralateral to, and innervated by, the injected eye was compared to radioactivity in the ipsilateral lobe, not innervated by the treated eye. Proteins migrating from the ganglion cells of the retina to the optic tectum seemed to be relatively stable and may be rich in praline and glycine. Microtubular protein migrated at a rate similar to nonmicrotubule soluble protein, and slower than particulate protein. With the exception of y-aminobutyric acid, transport of free amino acids occurred to only a minor extent. Following monocu- lar injection of tritiated fucose, a rapid asymmetry in the specific activities of protein from contralateral and ipsilateral lobes, was established. Thus the more rapidly migrating proteins may be attached to glycosidic residues. The carbohy- drate moeity of these glycoproteins is attached in the nerve cell body, prior to their axonal transport to the optic tectum. There was no evidence for transneuronal transfer of protein as in no cai;e was a differential in specific activity observed in labeled protein from paired cerebral hemispheres. Key Words: Axon flow - nerve Protein migration - Avain visual system - Optic Introduction The movement of materials along neuronal axons was first established by Weiss and Hiscoe (1948) and has since been well documented. More recently interest has focused especially on the axonal transport of proteins (Karlson and Sjostrand, 1968; McEwen and Grafstein, 1968; Kidwai and Ochs, 1969). A convenient model for such studies is the avian visual system where the optic nerves are totally decussated (Cowan, Adamson and Powell, 1961). Each optic tract of the bird supplies solely the contralateral optic lobe. Thus, after injection of radioactive precursor into a single eye, isotopically labeled compounds may migrate to the contralateral lobe. Any radioactivity appearing within the ipsi- lateral optic lobe must be due to blood-borne or diffused radioactive materials. Increased specific activity of the contralateral optic lobe over the paired ipsilateral lobe within a single animal must be attributed to a specific migratory process. (Taylor and Weiss, 1965; Elam and Agranoff, 1970). The ipsilateral lobe thus 9 Exp. Brain Res. Vol. 13