Title: Decoding the Worm Brain: Toward a Complete Biophysical Atlas of the C. elegans Nervous System

Speaker: Qiang Liu, Research Assistant Professor, Rockefeller University

Time: 15:00-16:00, April 25, 2019

Location: Room 411, Life Science Building


C. elegans, with its compact nervous system, complete wiring diagram and sophisticated yet tractable behaviors, is a powerful model organism for understanding how a brain functions at the molecular, cellular, and system levels. However, scarcity of accurate assessment of the biophysical properties of individual cell types in the C. elegans nervous system has hindered the development of a comprehensive model of the whole worm brain. A compelling example is that, for over 30 years, the scientific community has incorrectly assumed that C. elegans and other nematodes lack neuronal action potentials and are incapable of utilizing spike-coding strategies for information processing. 
Our recent work identified calcium-mediated action potentials and spike-coding schemes in a defined neuron, the olfactory neuron AWA. Through ion substitution, pharmacology, mutant analysis and modeling, we determined the ionic basis and mechanisms underlying the characteristic firing features of AWA action potentials. Simultaneous patch-clamp recording and calcium imaging in AWA revealed that action potentials may encode features of natural odor stimuli with both rate and temporal coding schemes. The characterization of AWA action potentials marks a shift in our conception of information processing in the C. elegans nervous system and calls for an analysis of all neuronal cell types to inform future modeling. 
We thus embarked on a systematic electrophysiological analysis of each neuron class in C. elegans. Here I report that among the 23 neuron classes examined to date, three additional spiking neurons were identified: an interneuron AIA, and the GABAergic enteric motor neurons AVL and DVB. Action potentials in these neurons possess characteristic firing features and waveforms that are distinct from AWA action potentials and each other, suggesting different underlying biophysical mechanisms and physiological functions. Behavioral and calcium imaging experiments are currently underway to determine the functional implications of these newly discovered action potentials. 
An encouraging picture that emerges from these results is that instead of being the outlier animal that does not use neuronal action potentials, C. elegans possess a plethora of diverse spiking neurons to implement specific functions. Thus, C. elegans is now poised to be the ideal model system to understand how animals choose one form of coding strategy over the other for neuronal computational and behavioral tasks. In the long run, a complete biophysical atlas with comprehensive electrophysiological characterization of every neuronal class of the entire organism will be critical for obtaining a rigorous model for C. elegans brain function.