Development and regeneration of the escape reflex in the earthworm, Eisenia foetida

Studies of earth medial (MGF) and lateral (LGF) giant fiber regeneration were made following single transection, grafting, or transplantation of the ventral nerve cord (VNC). In addition, the effects of food deprivation on giant fiber development were examined. Following VNC transection, recovery of giant fiber spike through-conduction occurred as early as 20 h, but usually within 38-48 h. Recovery of LGF and MGF through-conduction in grafted animals occurred by 65 h (+OR-) 26 SD (n = 13) and by 7-14 days (n = 6), respectively. Conduction of giant fiber spikes in transected and grafted groups was initially intermittent with relatively long conduction times across the lesion. These properties were correlated with the presence of small diameter (5-8 (mu)m) sprouts, which arose from the cut ends of the giant fibers and joined one another across the lesion. Physiological and anatomical evidence indicated that MGF and LGF reconnections were cell-specific;In transplantation studies, lengths of VNC were removed from segments 10-22 or 75-87 of one worm and transplanted into centrally denervated regions of segments 10-22 or 75-87 in a recipient animal. By 4-10 days after surgery, both ends of the transplanted VNC were joined to the ends of the recipient VNC. These junctions involved an apparent cell-specific union of the giant nerve fibers. By 4-5 weeks, giant fibers within the transplanted VNC (but not in the junctional region) had formed numerous branch-like extensions; however, the extensions were less abundant by 9-10 months. Despite these morphological changes there were no accompanying changes in giant fiber conduction velocity. Touch sensitivity of the giant fibers in the transplant region was restored by two weeks after transplantation, while restoration of MGF-mediated motor neuron and muscle potentials occurred by 3-4 weeks. In all cases, functional properties of the restored sensory and motor pathways in the transplant region reflected the origin of the donor VNC;To examine the effects of food deprivation on the postembryonic development of the giant fibers, newly hatched animals were reared from 56 days in media containing different levels of food. Giant fiber development (as indexed by conduction velocity and diameter) was unaffected at most levels whereas somatic development (as indexed by body weight) was stunted by these same levels