Abstracts Category : Other

Mapping Neuronal Morphology to Physiology in a Rhythmic Motor Circuit

by Adriane G Otopalik

A neurons unique physiological waveform arises from its palette of ion channels and receptors, as superimposed on its geometrical structure. The crustacean stomatogastric ganglion (STG), a small rhythmic motor circuit, exhibits fourteen identified neuron types with highly-conserved physiological waveforms and complex morphologies. In this thesis, I examine how morphology shapes neuronal physiology in the STG. Using high-resolution neuronal reconstructions and a suite of computational tools, I quantify numerous morphological features of four STG neuron types. This work revealed remarkable animal-to-animal variability in neuronal morphology. I also demonstrate that STG neurons do not adhere to current hypotheses regarding wiring optimization principles. I then studied the physiological consequences of animal-to-animal morphological variability in one neuron type, the Gastric Mill (GM) neuron. Utilizing focal photo-uncaging of glutamate in tandem with electrophysiological techniques, I characterize passive voltage signal propagation. I find that GM neurons, despite their complex structures, operate much like single compartments. Taken together, these studies suggest that relatively compact electrotonic structures may effectively compensate for the observed morphological variability observed across animals. A final study describes the development of photoactivatable peptides for probing the subcellular actions of endogenous neuromodulatory substances in individual STG neurons. This work culminates in the synthesis of two photoactivatable peptides endogenous to the STG: TNRNFLRF-NH2 and CabTRP1a. Although the compounds could be successfully photolyzed, they did not yield consistent responses when photoactivated in the biological preparation. The design process and preliminary experimental results are discussed. Altogether, this thesis serves as a case study of neuronal morphology and passive physiology in the STG and sheds light on our current conceptual framework for understanding how morphology maps to function in diverse nervous systems.