Lam, Brian, Madruga, Blake, Carmona, Javier, Shrestha, Ahis, Jin, Suying, Mendoza, Steve, Thatcher, Joseph, Arisaka, Katsushi, Niaki, Shayan
[
International Worm Meeting,
2017]
Extensive advances have been made in understanding the behavior of C. elegans in two dimensional environments. However, they impose substantial constraints on the worm's motion and ultimately restrict the set of possible natural behavioral states it can demonstrate. Addressing limitations encountered by previous efforts in three dimensional imaging, we designed and built a microscope capable of tracking the motion of C. elegans via a set of motorized stages while navigating freely within a sample volume. The variation of gelatin concentration (1% - 4%) and the utilization of temporally controlled ultraviolet photo-stimulation (405 nm) were also incorporated into the system. The addition of a refractive index mismatch correction chamber and fluorescence detection enable novel opportunities for observation and categorization of motion. Preliminary data of photoavoidance response in three dimensions was acquired and demonstrates the added complexity present in an unconstrained response. A novel use of fluorescence enables the identification of C. elegans' absolute orientation with respect to the ventral nerve cord. A model of motion based on sinusoidal wave propagation was applied to C. elegans' forward locomotion, thereby categorizing a set of three dimensional body states inhabited. From this analysis, we have identified three distinct motional states: one of which is sinusoidal in the worm's ventrodorsal plane, another which is sinusoidal in their lateral plane, and a final state that is helical in shape. Fitting this parametric model allows the extraction of a variety of wave-based parameters including wavelength, frequency, wave speed and phase difference which may then be correlated with other dynamic quantities and gelatin concentrations. Namely, the phase difference acts as a direct indicator of the degree to which the worm's posture is planar or helical, allowing the ability to parameterize its general motional form with a single number. Furthermore, from pre-existing, established data of the C. elegans' connectome, we hypothesize a neuronal mechanism for rhythmic signal generation based on the SMD motor neurons which predicts the motional states observed.