Date of Award:

5-1-1996

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Dana K. Vaughan

Committee

Dana K. Vaughan

Committee

Nabil N. Youssef

Committee

Stanley D. Allen

Abstract

The hypothesis that prompted my study on the leech (Hirudo medicinalis) stated that sensory affernents from the prostomial lip, via the cephalic nerves, make synaptic contact with Rezius cells in the subesophageal ganglion ("the brain") as part of the circuit that triggers feeding behavior in this animal. Several neuronal tracing substances of different colors were used to study sensory and central neuron morphology. First, cephalic nerves D1, D2, V1, and V2 were backfilled using dextran conjugates, and the resulting patterns of labeled cell bodies and neurites were mapped. Second, a Retzius cell body in the third rostral segment (R3) of the subesophageal ganglion was injected with a greenish-yellow fluorescent dye, Lucifer Yellow, and the resulting pattern of dye-filled cell body and neurites was mapped. The greenish-yellow pattern thus revealed the proposed central nervous system target of the sensory afferent cells. Finally, Texas Red conjugated dextran and Lucifer Yellow procedures were combined to directly view overlap in the subesophageal ganglion between red neurites from the D1 cephalic nerve and greenish-yellow projections from the ipsilateral R3 Retzius cell. When viewed through a confocal microscope, the red and greenish-yellow dye overlap occurred within an optical plane of a few microns, which represents opportunity for direct synaptic contact between the two. These data support my hypothesis that sensory afferents from the prostomial lip synapse directly onto Retzius cells in the subesophageal ganglion of the medicinal leech.

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