Physiological and developmental gradients in Lumbriculus variegatus

Lesiuk, Nalena
Major Professor
Charles D. Drewes
Committee Member
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Theses & dissertations (Interdisciplinary)

Lumbriculus variegatus is known to have external morphological, microanatomical, physiological and behavioral gradients along its body axis. The advantages of using this worm include the possibility of performing behavioral assessment of unique responses, swimming and body reversal, and non-invasive electrophysiological recordings of the nerve conduction. The autotomy reflex in Lumbriculus is an active stereotyped, all-or-none response in which the body is clearly and quickly separated into two fragments. The response consists of formation of lateral fissure in the body just anterior to the compression site and became circumferential. After the autotomy, the exposed terminal surfaces of both anterior and posterior fragments rapidly close within 10 min. The duration of autotomy reflex is at least 65 ms. Nicotine is a dependable and powerful paralytic agent that also block autotomy responses enabling us to perform surgical manipulations of the ventral nerve cord in Lumbriculus. The regeneration of ventral nerve cord after the transection occurs during the first several hours. The first sign of the reconnection of the giant fibers occurred as early as 10 h. On the other hand, the non-giant fiber mediated behavioral responses recovered faster (8 h) and independently from giant fibers system. All the results show the rapidity and specificity of regeneration in central nervous system that mediates locomotor reflexes in Lumbriculus. By surgically removing more segments of ventral nerve cord (ablation) we found that the ventral nerve cord has the ability to regenerate and reconnect similar to the transection, only slower. Ectopic head regenerated from the ablation site in 30% of the worms. The ectopic-headed worms responded to touch stimuli by producing behavioral responses as two individual worms. The ectopic head also showed an influence on the rearrangement of MGF and LGF sensory fields. Finally, Lumbriculus is introduced for uses in classroom study of circulation system. A fast, simple and inexpensive materials and procedures for the observation of blood vessel pulsation is developed. In addition, two pharmacological agents, nicotine and caffeine, were shown to have effects on the pulsation rate of the dorsal blood vessel in Lumbriculus.