Long-term survival of severed crayfish giant axons is not associated with an incorporation of glial nuclei into axoplasm (original) (raw)
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Neuroscience Letters, 1989
Previous electrophysiological experiments have shown that in the abdominal extensor muscles of rock lobsters, axons which were cut in surviving animals do not degenerate peripherally for several months, but conduct action potentials and release transmitter quanta on stimulation closely distal to the scar. Electron micrographs from the axon distal to the scar (in a reliably conducting region) show invasion of the axoplasmic space by nucleated cells, probably glia. After several months, the cell membranes of the invaders have vanished and apparently functional multiple nuclei remain. We suggest that decentralized axons may survive for months with the help of 'donated' nuclei.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
Protein maintenance and degradation are examined in the severed distal (anucleate) portions of crayfish medial giant axons (MGAs), which remain viable for over 7 months following axotomy. On polyacrylamide gels, the silver-stained protein banding pattern of anucleate MGAs severed from their cell bodies for up to 4 months remains remarkably similar to that of intact MGAs. At 7 months postseverance, some (but not all) proteins are decreased in anucleate MGAs compared to intact MGAs. To determine the half-life of axonally transported proteins, we radiolabeled MGA cell bodies and monitored the degradation of newly synthesized transported proteins. Assuming exponential decay, proteins in the fast component of axonal transport have an average half-life of 14 d in anucleate MGAs and proteins in the slow component have an average half-life of 17 d. Such half-lives are very unlikely to account for the ability of anucleate MGAs to survive for over 7 months after axotomy.
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.
Degeneration and regeneration in crustacean peripheral nerves
Journal of Comparative Physiology, 1974
and physiological ( ) data from several crustacean species kept at 19-21~ show that isolated stumps of motor axons often survive intact for 150-250 days whereas sensory axonal segments usually degenerate within 20 days. Axonal segments of both motor and sensory axons that remain connected to their cell body generally remain functionally and morphologically normal after lesioning. No evidence was found for collatecal innervation of denervated muscles from intact motor neurons supplying nearby muscle masses, although the motor nerve terminals may not have completely degenerated. Evidence is presented that motor axons specifically re-innervate their original muscle mass if such re-innervation occurs within 90 days after lesioning. Regenerating sensory and motor fibers make appropriate CNS and peripheral connections so as to re-establish correctly a peripheral reflex found in intact animals .
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.
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
Ventral Nerve Cord Transection in Crayfish: A Study of Functional Anatomy
Journal of Crustacean Biology, 1998
In crayfish, neural degeneration and regeneration in the ventral nerve cord occur in one of two ways, depending on the injured fiber. Most fibers degenerate in 1 or 2 weeks, while giant fibers degenerate slowly. Although degenerative changes are similar in both cases, they do not seem to correlate with motor behavioral alterations. The aim of this work was to characterize the time course of behavioral and anatomical changes following ventral nerve cord (VNC) transection in crayfish. The behavioral analysis was focused on the righting reflex whose changes were correlated with morphological studies performed on longitudinal sections and analyzed with transmission (TEM) and scanning electron microscope (SEM). Latency for the righting reflex increased after VNC transection and then slowly decreased toward control values. Anatomically, degenerative changes began to appear 10 days after VNC transection. Disruption in membrane arrangement, subcellular organelles, and a strong increase in glia appeared in small fibers. To a lesser degree, similar changes could be detected in medial and lateral giant fibers. Glial growth reconnected the transected VNC where regeneration signs were detected in small fibers. Both stumps were reconnected at least by glial tissue 90 days after transection, while giant axons were still degenerating; at this time, the righting reflex returned to control values.
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.