Embryonic and postembryonic neurogenesis in the ventral nerve cord of the freshwater crayfishCherax destructor (original) (raw)
2001, Journal of Experimental Zoology
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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.
Journal of Neurobiology, 2002
in the olfactory pathway of many decapod crustaceans. However, the relationships between precursor cells and the temporal characteristics of mitotic events in these midbrain regions have not been examined. We have conducted studies aimed at characterizing the sequence of proliferative events that leads to the production of new deutocerebral projection neurons in embryos of the American lobster, Homarus americanus. In vivo bromodeoxyuridine (BrdU) labeling patterns show that three distinct cell types are involved in neurogenesis in this region. Quantitative and temporal analyses suggest that the clearing time for BrdU is 2-3 days in lobster embryos, and that the sequence of proliferative events in the midbrain is significantly different from the stereotypical pattern for the generation of neurons in the ventral nerve cord ganglia of insects and crustaceans. The unusual pattern of proliferation in the crustacean midbrain may be related to the persistence of neurogenesis throughout life in these regions.
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