Crayfish CNS: Minimal degenerative‐regenerative changes after lesioning

Abstract

Removal of an abdominal ganglion or a segment of a connective of the ventral nerve cord in crayfish (Procambarus simulans) resulted in little regenerative outgrowth from cut ends of CNS axons and no replacement of ablated cell bodies, even after 9–12 months. A few small‐diameter interneurons, but no giant axons, showed physiological and/or morphological evidence for regeneration across the lesion site. No behavioral, physiological or morphological evidence for degeneration of severed axonal segments of any interneuron (except for a few damaged segments of the septate lateral giant axons) was seen 2–3 weeks after lesioning and survival of isolated segments of medial giant axons was associated with hypertrophy of their glial‐connective tissue sheaths. Very little morphological degeneration of severed CNS interneurons was seen even 9–12 months after lesioning, except for isolated distal stumps of medial giant axons.Physiological evidence for degenerative changes was obtained after 9–12 months for CNS synapses posterior to the lesion site in that these synapses rapidly fatigued with repeated stimulation whereas synapses anteror to the lesion continued to function normally. This difference in synaptic efficacy might be explained by an interruption of a rostral‐caudal transport of axoplasmic proteins in these ventral nerve cords (Fernandez et al., '70, '71). A rostral‐caudal flow of trophic substances might also account for the 9–12 month survival of some anterior segments of lateral giant axons which were disconnected from their original cell bodies but which remained in contact with rostral cell bodies via septate junctions.