Date of Award


Degree Name

Master of Science


Biological Sciences

First Advisor

Dr. John Jellies

Second Advisor

Dr. John Spitsbergen

Third Advisor

Dr. Christine Byrd-Jacobs

Access Setting

Masters Thesis-Open Access


The leech, Hirudo, has two efferents that converge upon the heart tube (HT) muscle; the segmentally iterated heart excitor motor neurons (HE), and the modulatory heart accessory neurons (HA). Using intracellular dye injections and antibody labeling, we were able to visualize and distinguish the morphologies of these two efferents. We found that HA(5) provides dense coverage of the anterior segments of heart tube muscle and extends along the HT into the posterior segments 6 and 7, while HA(6) projects centrally for several segments before extending into the periphery. HA(5) and HA(6) homologs show little or no overlap on HT segments, consistent with mutual avoidance by HA processes. This contrasts the pattern of iterated HEs which each extend on the HT about one segment anterior and posterior and overlap extensively with their segmental homologs. Together the HA and HE efferents generate an elaborate plexus. All HA varicosities appear to co-label with peptide, yet the HE possesses varicosities that are either peptide negative or positive. The junction of the LaV branch of the HT has a high concentration of FMRF positive varicosities belonging to both HE and HA. In contrast, the junctions of the LdV and LIV have sparse HA terminals while being heavily innervated with HE varicosities. Furthermore, the HE varicosities at these locations are predominantly FMRF negative.

Included in

Biology Commons