Student Theses and Dissertations

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

RU Laboratory

Bargmann Laboratory


Animals must vary their behavior in response to changes in their environment, but behavior also remains consistent over time. This thesis focuses on a single interneuron, RIM, and a single behavior, the reversal, to better understand how the circuits driving motor outputs accomplish the seemingly contradictory tasks of generating appropriate and variable behaviors. In the compact and well-defined nervous system of C. elegans, the interneuron RIM is an important part of the reversal behavior circuit that contributes to sensory integration, behavioral variability, generation of behavioral states, and learning. RIM releases both glutamate and the biogenic amine tyramine (~noradrenaline) and forms gap junctions with neurons that govern various aspects of C. elegans locomotion. RIM is the major source of tyramine in C. elegans, and this output is known to extend reversal length of spontaneous and evoked reversals and to sharpen turns during escape response. However, the roles of RIM glutamate and RIM gap junctions in organizing reversal behavior have remained nebulous. I combine cell-specific genetic manipulations, behavioral analyses, and both manipulations and observations of neural activity to dissect the diverse synaptic outputs of the interneuron RIM. I reveal a role for RIM glutamate in spontaneous reversal behavior and show that RIM glutamate and RIM tyramine differentially regulate spontaneous reversals. Through comparative analysis of the exo- and endocytosis dynamics of RIM glutamate and tyramine, I provide evidence that they released from RIM under the same conditions and with similar dynamics, and that tyramine may also be released from a distinct, slower vesicle class. I also find that both RIM chemical synapses and electrical synapses are bidirectional regulators of C. elegans locomotion, stabilizing both the forward state and reversal state. I conclude that RIM is a dual-function neuron, able to both promote and inhibit reversal behavior.


A Thesis Presented to the Faculty of The Rockefeller University in Partial Fulfillment of the Requirements for the degree of Doctor of Philosophy

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