Nerve terminal proteins of the rabbit visual relay nuclei identified by axonal transport and two-dimensional gel electrophoresis.

The proteins in nerve terminals can be uniquely identified by two-dimensional gel electrophoresis of proteins labeled during synthesis in the cell body and then transported intra-axonally to the terminals. We have explored the potential of the identification procedure by comparing the proteins which are transported from the retina to the lateral geniculate nucleus (LGN) and the superior colliculus (SC) of the rabbit. We have been able to identify between 150 and 200 proteins which ate common to both LGN and SC nerve terminals, very few of which are present at significantly different concentrations in one nucleus relative to the other. The similarity between proteins sent from the retina along two neural pathways subserving different functions illustrates the subtlety of biochemical changes that must underlie physiological differences. Only a small fraction of the labeled proteins are major proteins of the relay nuclei as judged by Coomassie-staining, and some of these arise from in situ nonspecific labeling with blood-borne radioactivity, rather than by transport to the terminals. We have shown that about 5 times more proteins are transported at fast than at intermediate transport rates. More than 50% of the fast proteins turn over rapidly and are gone in 24 h. Few intermediate proteins turn over rapidly. Since only 6% of the proteins in the relay nuclei (at 36 h) could not be detected in the optic tract at that time, transsynaptic labeling by breakdown and resynthesis must be small, if it occurs at all.