Mei Zhen

Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hosptital, Toronto, Canada

Title: Membrane excitability and neural control:  what we learn from the C. elegans nervous system

Abstract: Behaviors consist of distinct states and their seamless transitions. C. elegans spontaneously switches between two opposite states, forward and backward movement, a phenomenon long thought to reflect the reciprocal inhibitions between two interneurons that separately gate the forward and backward motor circuits. Combining experimental data and mathematical modeling, we show that instead of a strict antagonism, these neurons function in a master-slave configuration, with opposite functional polarity in different time-scales. Specifically, the interneuron that controls the backward movement, a less expressed motor state, maintains the animal’s overall spontaneous motility. The interneuron previously thought to specifically gate reversals not only phasically inhibit the interneuron that activates forward movement at a fast timescale, but also, maintains a tonic excitation of the forward-promoting interneuron at a longer timescale. It thus serves as the master neuron to ensure the animal to flexibility transit between two motor states without losing mobility. We further discovery that this tonic excitation results from the master neuron’s sustained depolarized membrane potential, which could not be inferred from either the connectome or behavioral output alone. We propose that a tonically active neuron breaks the symmetry between the motor circuits as an alternative to the long-assumed symmetrically configured mutual inhibition module.

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