Behavioral plasticity and central regeneration of locomotor reflexes in the freshwater oligochaete, Lumbriculus variegatus. II: Ablation studies

Abstract

After 8-1 0 segments of posterior ventral nerve cord were ablated in Lumbriculus variegatus, touch-evoked locomotor responses were evident both in segments anterior and posterior to the ablation site. However, responses in these two regions were independent and uncoupled. During recovery, four outcomes were observed at the ablation site: (Group 1) recovery of normal functions with no growth of new segments; (Group 2) formation of a laterally protruding, multi-segmented, ectopic head; (Group 3 ) formation of a laterally protruding, amorphous, and multi-segmented outgrowth; and (Group 4) segmental autotomy. i n Groups 1 and 2, touch-evoked swimming and body reversal were studied. in addition, sensory fields and conduction properties of giant nerve fibers were examined near the ablation site. i n some Group 1 worms, clear-cut behavioral and electrical signs of recovery and reconnection were seen by 3 d after ablation. By 8 d, all worms had recovered and exhibited response patterns comparable to those of normal worms. i n Group 2 worms, with an ectopic head, segments posterior to the ablation (together with those in the ectopic head), exhibited touch-evoked swimming and body reversal responses resembling those of a complete worm. Segments anterior to the ectopic head were independently capable of locomotor responses. Medial and lateral giant fiber sensory fields in worms with ectopic heads reflected a pattern expected for two worms. Thus, through apparent morphallactic reorganization, a medial giant fiber sensory field emerged which included the ectopic head and 10-1 5 adjacent posterior segments. In contrast, electrical recordings showed longitudinal through-conduction of giant fiber spikes, across the ablation site. Histological examination revealed that the giant nerve fibers in the ectopic head were complexly interconnected with those in the main body axis.Additional key words: giant axons, ectopic head, neural plasticity

Asexual Reproduction and Segmental Regeneration, but not Morphallaxis, are Inhibited by Boric Acid in Lumbriculus variegatus (Annelida: Clitellata: Lumbriculidae)

“…Whether or not these differences represent systematic disparity between architomy and paratomy remains to be determined. One common aspect of the regeneration of naidid (Drewes & Fourtner, 1991), lumbriculid (Lesiuk & Drewes, 2001b), and enchytraeid worms (Yoshida-Noro et al, 2000) is that the central nervous system likely plays a mechanistic role in this developmental process. The formation of a regeneration blastema often requires ongoing nerve fiber outgrowth in annelids (Dinsmore & Mescher, 1998).…”

“…Specifically, body segments isolated from posterior regions, which acquire a new, more anterior segmental position, exhibit transformations in touch sensory fields, giant fiber conduction velocity, axonal diameter, and other physiological properties appropriate for the fragment's new positional identity. Lesiuk & Drewes (2001b) demonstrated the formation of ectopic heads in L. variegatus as a result of ventral nerve cord ablation. Following ectopic head formation, morphallactic changes occur within the giant fiber system, but only in 10-15 segments posterior to the newly formed ectopic head.…”

Effects of nerve injury and segmental regeneration on the cellular correlates of neural morphallaxis

“…1a; Lesiuk and Drewes, 2001b); however, whether specific segmental damage involving nerve cord lesion is required for EH formation remains unknown. To address the requirement for nerve cord injury in EH formation, a population of worms had five segments of dorsal body wall excised, along with the underlying DBV and gut tissue (dorsal lesions lacking nerve cord damage, DL; Fig.…”

“…Neural morphallactic reorganization of giant fiber anatomy and physiology occurs in segments posterior to newly formed EHs (Lesiuk and Drewes, 2001b). That is, earlier to lesion and EH formation, posterior segments possess only LGF sensory fields and activate only tail shortening behavior (Lesiuk and Drewes, 2001b; Martinez et al, 2005).…”

Assessing the acute hazards of zinc oxide nanomaterials to Lumbriculus variegatus

“…A number of papers have used this behaviour of L. variegatus. Some authors have employed electro-physical techniques to test the conductivity of neural pathways (Rogge and Drewes 1993;Lesiuk and Drewes 2001;Sardo and Soares 2010), while others have used touch-evoked response techniques (Lesiuk and Drewes 2001;Ding et al 2001;O'Gara et al 2004O'Gara et al , 2006. This behavioural endpoint has not been used yet to assess toxicity of NMs and therefore it is important to evaluate its use in this context.…”