Fast axonal transport in central nervous system and peripheral nervous system axons following axotomy

Abstract

After axotomy, changes in the composition of fast axonally transported proteins (FTP) within the peripheral nervous system (PNS) axons have been reported. The most significant and reproducible changes involved polypeptides found within the molecular weight range of 31.0 to 14.5 kilodaltons (Bisby, 1980). We wished to determine whether similar changes following axotomy occur in axons of the central nervous system (CNS). Intracranial axotomy of the left optic tract was performed stereotaxically in rats. Six days post axotomy 50 μCi ³⁵[S]-methionine was injected into the vitreous body of both eyes. FTP were isolated within the optic nerves 2 h after isotope injection. The nerve segments were processed for SDS-PAGE, fluorography, and compared to similarly prepared fluorographs of normal and eight day postaxotomy sciatic nerve segments. The labelling of 5 major polypeptide bands (S₁, MW ≃ 28,000; S_2a, MW ≃ 25,000; S_2b, MW ≃ 23,000; T₁, MW ≃ 20,200; and T₂, MW ≃ 17,000) was studied by laser densitometry. Band S_2b showed a highly significant (p < 0.001) increase in concentration, while bands S₁ and T₁ demonstrated highly significant decreases in concentration following axotomy of the sciatic nerve. In contrast, after axotomy of the retinal ganglion cell axons the only significant change was a decrease (p < 0.05) in T₁. We suggest that failure of CNS axons to respond similarly to PNS axons following axotomy may be related to the failure of CNS axons to regenerate.