Identification of locally synthesized proteins in proximal stump axons of the neurotomized hypoglossal nerve.

Analysis of radioactively labeled proteins was carried out on microsamples of myelin-free axons isolated from neurotomized and normal hypoglossal nerves of the rabbit after in vitro incubation with [3H]leucine. Major radioactive peaks in axonal endings of the proximal stump 18 h after neurotomy, identified by autoradiography of microelectrophoregrams, had apparent molecular weights of 52,000d, 41,000d and 18,000d. This autoradiographic pattern differed from that of axons of untransected nerve in: (1) not having a prominent 100,000d component present in the latter; and (2) having a novel 41,000d component not present in the latter. Labeling of axonal proteins in the proximal stump in vivo resulted in no apparent retrograde transport during the 5 h studied. Autoradiographic analysis of labeled proteins released by nerves into the medium during in vitro incubation revealed a major radioactive peak with an apparent molecular weight of 77,000d. Attempts to demonstrate uptake of the 77,000d component by unlabeled axons in vitro and in vivo were unsuccessful. The hypothesis was advanced that the 52,000d protein may be neurofilament protein, and the possible significance of the 41,000d component was discussed in the contexts of the pathology of the traumatized proximal stump, and of the antecedent events leading to axonal outgrowth.