LONG-TERM SURVIVAL FOLLOWED BY DEGRADATION OF NEUROFILAMENT PROTEINS IN SEVERED MAUTHNER AXONS OF GOLDFISH

The morphology and protein composition of intact and severed Mauthner axons (M-axons) from goldfish were examined on electron micrographs, s odium dodecyl sulfate gels, and immunoblots. Neurofilaments were the m ost common cytoskeletal element on electron micrographs, and neurofila ment proteins (NFPs) were the most intensely silver-stained bands in M -axoplasm microdissected from control M-axons. NFPs at about 235, 145, 123, 105, 80, and 60 kD in M-axoplasm were identified with four monoc lonal and three polyclonal antibodies. Similar immunoblots of samples of the M-axon myelin sheath (M-sheath) showed no reactivity to antibod ies against NFPs. For up to 62 days following spinal cord severance in goldfish maintained at 15 degrees C, the ultrastructure, protein band ing pattern, and anti-NFP immunoreactivity of severed distal segments of M-axons did not change compared with control M-axons. At 62 to 81 d ays after severance, novel bands appeared in many silver-stained gels and anti-NFP immunoblots of distal M-axons. NFP bands completely disap peared from distal M-axon segments of some M-axons as early as 72 days after severance. However, NFP bands persisted in some distal segments for up to 81 days after severance. The degradation of NFPs occurred e qually along the entire length of a distal M-axon segment, that is, th ere was no indication of a proximal-to-distal or distal-to-proximal se quence of NPP degradation in distal segments of severed M-axons. These biochemical data were consistent with morphological data that showed little change in the diameter or ultrastructure of severed M-axons hel d at 15 degrees C for about 2 months followed by a rapid collapse of t he entire distal segment at 72 to 85 days postseverance. (C) 1994 John Wiley and Sons, Inc.