Author

Crowley

Date of Award

4-2000

Degree Name

Master of Science

Department

Biological Sciences

First Advisor

Dr. John Jellies

Second Advisor

Dr. Christine Byrd-Jacobs

Third Advisor

Dr. John Spitsbergen

Access Setting

Masters Thesis-Open Access

Abstract

The neural circuit that controls rhythmic contraction of the hearts in the medicinal leech, Hirudo medicinalis, provides an amenable model to investigate pathfinding and target selection. The bilaterally paired heart tubes (HT) in leech are eventually innervated by the heart excitor motomeuron (HE) following a period of remodeling that requires the presence of the HT. To begin characterizing possible HT-derived cues, co-cultures of CNS with innervated HT have been used. Previous work demonstrated that young, but not adult, HT was able to support profuse general outgrowth, but the HE extended few projections onto HT of any age. Current studies show that the inability of the HE to extend onto its target in vitro is not due to an influence of innervation state of the muscle nor is the result limited to living tissue. These results, when taken in conjunction with HE development in vivo, support the hypothesis that the HE is responding to a specific, target-derived signal that stops or slows extension on the target. These results suggest that the HT target tissue constituitively expresses a signal specific for the HE. Furthermore, the selective signal, as well as general growth-permissive substrates, survives in the matrix despite the loss of intact, viable muscle cells.

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