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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 muCi 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 post-axotomy sciatic nerve segments. The labelling of 5 major polypeptide bands (S1, MW congruent to 28,000; S2a , MW congruent to 25,000; S2b , MW congruent to 23,000; T1, MW congruent to 20,200; and T2, MW congruent to 17,000) was studied by laser densitometry. Band S2b showed a highly significant (p less than 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 less than 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.

The composition of proteins conveyed by fast axonal transport in growing or regenerating axons is different from that of intact, mature axons. Consistent alterations have been observed in several different types of neurons, but adult peripheral axons (rabbit hypoglossal motoneurons) seemed to be exceptions because during their regeneration there was no increased labelling of a 23 kilodalton (kD) protein associated with the growth state. We examined the composition of fast-transported proteins, labelled by application of [35S]methionine to the hypoglossal nuclei, in intact and regenerating hypoglossal nerves of the rat. Using one- and two-dimensional electrophoresis we detected both increases and decreases in the labelling of specific polypeptides during regeneration. In particular, there was increased labelling of a 23 kD polypeptide. Changes were maximal 7 days after axotomy and subsided thereafter, coincident with reinnervation of the tongue. We conclude that hypoglossal axons show the same changes in transported protein composition which are characteristic of the growth state in other axons. Thus, we have strengthened the correlation between the growth state and changes in synthesis of a set of polypeptides of unknown function.