Retrograde and anterograde axonal transport demonstrated by intracerebral injection of a labeled protein-acylating agent.

Following injection of the tritium-labeled protein-acylating agent, N-succinimidyl propionate, into the neostriatum in rats, retrograde labeling of nigrostriatal cells in the pars compacta of the subtantia nigra and anterograde labeling of the striatonigral terminal field in the nigral pars reticulata were demonstrated by autoradiography, at 18 hr survival. Labeling of the corticopontine terminal field and of corticothalamic cell bodies in cortical layer 6 were also seen, deriving from corticofugal fibers of passage through the striatal injection site. In comparison, neostriatal injection of horseradish peroxidase was found to yield nigral cell and terminal field labeling, but the corticopontine terminal field was not labeled, and very few cortical cells in layer 6 were labeled. These results show that the retrograde and anterograde axonal transport of endogenous proteins can be profitably studied by this in vivo protein-acylating technique, and suggest that the method may prove useful as a connection-tracing technique, especially because of the novel attribute of labeling terminal fields by anterograde axonal transport following injections into white matter axonal bundles, with concomitant labeling od the cell bodies of origin of these axons.