Date of Defense

Spring 4-27-2010


Biological Sciences

First Advisor

John Jellies


The study of synapses is a relevant topic for all living organisms, as our bodies are coordinated by billions of successful nerve connections. Multiple cells often synapse onto one target cell, begging the question of how specific circuits then operate. What allows the target cell the ability to utilize both innervations? The leech, Hirudo verbana, is a useful model to study these questions. The heart tubes are innervated by two neurons, the heart excitatory and heart accessory neurons. Heart excitatory neurons originate at segments 3 through 18 within the leech, while heart accessory neurons originate at ganglia 5 and 6 and must therefore project axons intersegmentally. Studies have shown the synaptic locations of the heart excitatory neurons along the heart tubes and vessel junctions. Recent research has shown that while heart accessory neurons from ganglion 5 synapse onto the heart tubes in both anterior and posterior locations relative to segment 5, the propagation of heart accessory neuron 6 remains unknown. The heart accessory neurons from ganglion 6 have been followed to segment 10, but the target location is unidentified. This thesis is that the heart accessory neurons innervate the heart tubes at a very posterior region within the leech. Using a lipophilic dye (DiI) to locate the heart accessory neuron 6 projections, the author discovered that only heart excitatory neurons became dye-labeled from DiI application within the heart tubes. While the results did not allow the original hypothesis to be examined, other questions have been impacted. These results have led the author to suggest that the synapses of the heart accessory neurons differ from those of the heart excitatory neurons, which is contrary to what had been previously thought. These negative results, while unexpected, may have a very positive impact on projects within the lab.

Access Setting

Honors Thesis-Campus Only