Axons of the pyramidal tract do not increase their transport of growth-associated proteins after axotomy.

We compared the effects of axotomy on the composition of fast axonally transported proteins in rat sciatic sensory axons and pyramidal tract axons, 7 days after axotomy. L-[35S]methionine was administered to dorsal root ganglia or sensorimotor cortex and after 6 or 4 h, respectively, labelled proteins were obtained from sciatic nerve or pyramidal tract. Transported proteins were characterized by one- and two-dimensional electrophoresis, followed by fluorography. As previously reported, sciatic axotomy produced changes in the labelling of fast-transported proteins, notably, increased labelling of a spot designated GAP43. In contrast axotomy of pyramidal axons produced no increased labelling of GAP43, although it could be identified in both normal and axotomized samples. Autoradiography of spinal cord distal to the lesion confirmed that our procedures did indeed label axons and that the axotomy did interrupt these axons. Our finding that axotomy does not stimulate changes in composition of fast-transported proteins in the corticospinal tract agrees with previous studies on mammalian retinal ganglion cell axons and leads us to conclude that this failure to respond to axotomy is a general feature of non-regenerating CNS axons.