Maintenance and degradation of proteins in intact and severed axons: Implications for the mechanism of long-term survival of anucleate crayfish axons (original) (raw)
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Neuroscience Letters, 1991
Glial nuclei have been reported to be incorporated into the axoplasm of surviving distal stumps (anucleate axons) weeks to months after lesioning abdominal motor axons in rock lobsters. We have not observed this phenomenon in crayfish medial giant axons (MGAs) which also survive for weeks to months after lesioning. Glial nuclei were not observed within MGAs perfused with a physiological intracellular saline. However, incorporation of glial nuclei was observed after MGAs were perfused with intracellular salines containing Fast green. From these and previously published data, we confirm that glial incorporation into axoplasm can occur, but we suggest that is is not a common mechanism used by crustaceans to provide for long-term survival of anucleate axons.
Effect of temperature on long-term survival of anucleate giant axons in crayfish and goldfish
The Journal of Comparative Neurology, 1990
The effect of temperature on the electrophysiology and morphology of anucleate axons was examined following severance of crayfish medial giant axons and goldfish Mauthner axons from their respective cell bodies. Although anucleate segments of each giant axon exhibited long-term survival for weeks to months at 5-25 degrees C in crayfish and 10-30 degrees C in goldfish, the two axons differed in their survival characteristics. All measures of long-term survival in crayfish medial giant axons were independent of animal holding temperature, whereas all measures in Mauthner axons were dependent on holding temperature. Medial giant axons survived for at least 90 days in crayfish maintained at 5-25 degrees C in this and previous studies. Mauthner axons survived for over 5 months in goldfish maintained at 10 degrees C but survived for 1 month at 30 degrees C. Postoperative time had different effects on many single measures of long-term survival (axonal diameter, amplitude of action or resting potentials) in medial giant axons compared to Mauthner axons. For example, resting and action potentials in crayfish medial giant axons remained remarkably constant at all holding temperatures for 0-90 postoperative days. In contrast, resting and action potentials in goldfish Mauthner axons declined abruptly in the first 10-20 postoperative days followed by a slower decline at each holding temperature. We suggest that the mechanism of long-term survival is not necessarily the same in all anucleate axons.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1996
Cellular mechanisms that might affect the degradation of neurofilament proteins (NFPs) were examined in the distal segments of severed goldfish Mauthner axons (M-axons), which do not degenerate for more than 2 months after severance. Calpain levels, as determined by reactivity to a polyclonal antibody, remained constant for 80 d postseverance in distal segments of M-axons and then declined from 80 to 85 d postseverance. Calpain activity in rat brain, as determined by a spectrophotometric assay, was much higher than calpain activity in control and severed goldfish brain, spinal cord, muscle, or M-axons. Calpain activity was extremely low in M-axons compared with that in all other tissues and remained low for up to 80 d postseverance in distal segments of M-axons. Phosphorylated NFPs, as determined by Stains-All treatment of SDS gels, were maintained for up to 72 d postseverance and then decreased noticeably at 75 d postseverance when NFP breakdown products appeared on silver-stained ...
Axoplasmic Transport in the Crayfish Nerve Cord
Proceedings of the National Academy of Sciences, 1969
Axoplasmic proteins in the crayfish nerve cord were labeled by the incorporation of high specific activity 3 H-leucine that was injected into one of the abdominal ganglia. The labeled proteins moved caudad as a sharply defined peak at 1.1 mm/day. The level of radioactivity in the cord decreased slowly as the peak approached the tail. From the sharpness of the peak and the low decrement of label with distance it is deduced that the axoplasm is probably a gel, and some of it is not consumed as it is transported along the axon but reaches the terminal and, perhaps, the synaptic regions.
Ultrastructural changes at gap junctions between lesioned crayfish axons
Cell and Tissue Research, 1980
In crayfish, the severed distal segment of single lateral giant axon (SLGA) often survives for at least 10 months after lesioning if this segme;t retains a septal region of apposition with an adjacent, intact SLGA. In control (unsevered) SLGAs, this septal usually contains gap junctions and 50-60 nm vesicles near the axolemma of both SLGAs. From 1-14 days after lesioning, the distal segment of a severed SLGA undergoes obvious ultrastructural changes in mitochondria and neurotubular organization compared to control SLGAs or to adjacent, intact SLGAs in the same animal. Gap junctions are very difficult to locate in severed SLGAs within 24 h after lesioning. From two weeks to ten months after lesioning, the surviving stumps of severed SLGAs often appear remarkably normal except that structures normally associated with the presence of gap junctions remain very difficult to find. These and other data suggest that SLGA distal segments receive trophic support from adjacent, intact SLGAs. The mechanism of this support probably could not be via diffusion across gap junctions between intact and severed SLGAs since gap junctions largely disappear after lesioning. However, trophic maintenance could occur via the exocytotic - pinocytotic action of 50-60 nm vesicles which are always present on both sides of the septum between an intact SLGA and a severed SLGA distal segment.
Calcium-activated proteolysis of neurofilament proteins in goldfish Mauthner axons
Journal of Neurobiology, 1995
We have examined the proteolytic breakdown of neurofilament proteins (NFPs) in isolated Mauthner axoplasm (M-axoplasm). Documentation of proteolytic breakdown of NFPs in M-axoplasm is important because NFPs are not degraded in distal segments of severed Mauthner axons (M-axons) maintained in vivo for up to 62 days at 20°C. By incubating M-axoplasm with 2 mM calcium in vitro, we have demonstrated that M-axoplasm contains an endogenous calcium-activated neutral protease that degrades NFPs. This calcium-activated proteolysis of M-axoplasm NFPs produced novel bands on silver-stained gels. These novel bands were presumed to be NFP breakdown products because they reacted with antibodies to the α-intermediate filament antigen (anti-IFA) on immunoblots from these gels. Incubations of M-axoplasm with 2 mM calcium plus exogenous calpain produced novel bands similar to those observed for M-axoplasm incubated with 2 mM calcium. Incubations of M-axoplasm with 2m M calcium plus calpain inhibitors did not produce these novel bands. These in vitro data indicate that M-axoplasm contains calpain that degrades NFPs and produces novel bands similar to those observed from distal segments of severed M-axons maintained in vivo longer than 62 days postseverance. Factors that affect the activity of calpain or affect the ability of calpain to degrade NFPs could account for the delayed degradation of NFPs in distal segments of severed M-axons maintained in vivo. © 1995 John Wiley & Sons, Inc.
Changes in axonally transported proteins during axon regeneration in toad retinal ganglion cells
Journal of Cell Biology, 1981
In an effort to understand the regulation of the transition of a mature neuron to the growth, or regenerating, state we have analyzed the composition of the axonally transported proteins in the retinal ganglion cells of the toad Bufo marinus after inducing axon regeneration by crushing the optic nerve. At increasing intervals after axotomy, we labeled the retinal ganglion cells with [35 S] methionine and subsequently analyzed the labeled transported polypeptides in the crushed optic nerve by means of one-and two-dimensional electrophoretic techniques . The most significant conclusion from these experiments is that, while the transition from the mature to the regenerating state does not require a gross qualitative alteration in the composition of axonally transported proteins, the relative labeling of a small subset of rapidly transported proteins is altered dramatically (changes of more than 20-fold) and reproducibly (more than 30 animals) by axotomy. One of these growth-associated proteins (GAPS) was soluble in an aqueous buffer, while three were associated with a crude membrane fraction . The labeling of all three of the membrane-associated GAPS increased during the first 8 d after axotomy, and they continued to be labeled for at least 4 wk . The modulation of these proteins after axotomy is consistent with the possibility that they are involved in growth-specific functions and that the altered expression of a small number of genes is a crucial regulatory event in the transition of a mature neuron to a growth state.
Ultrastructural correlates of motor nerve regeneration in crayfish
Cell and Tissue Research, 1974
Identified motor neurons innervating distal limb muscles in the crayfish claw have been examined by light and electron microscopy after surgical interruption. The functionally competent distal segments of such axons, a few weeks after the operation, show enlarged glial sheaths that contain occasional small satellite axonal profiles (cf. Nordlander and Singer, 1972); evidence is presented that such profiles can arise