, 1986). In particular, electron microscopy showed that the cholinergic motor neurons have long undifferentiated processes that extend along the nerve cord without making synapses. In the B-type motor neurons, for example, these long asynaptic processes extend farther posteriorly than do their neuromuscular junctions ( Figure 1C) ( White et al., 1986). These asynaptic processes were hypothesized to represent specialized proprioceptive sensors. If this is the case,

proprioceptive information might be expected to travel from posterior to anterior in the B-type motor neurons. A putative mechanosensory channel, UNC-8, is also expressed Selleckchem RG7204 in motor neurons ( Tavernarakis et al., 1997). However, whether any motor neuron is capable of proprioception, or how proprioception is used by the motor circuit, has Bleomycin concentration not been demonstrated. Biomechanical evidence also implies a role for proprioception in C. elegans locomotion as its gait adapts to the mechanical load imposed by

the environment ( Berri et al., 2009; Boyle et al., 2012; Fang-Yen et al., 2010). When worms swim in low-load environments, such as water, the bending wave has a long wavelength (∼1.5 body length L). When crawling or swimming in high-load environments ∼10,000-fold more viscous than water, the bending wave has a short wavelength (∼0.65 L), but whether or how proprioception might be related to gait adaptation has not been determined. Here, we examined whether the worm motor circuit has proprioceptive properties and how these properties are connected to undulatory dynamics. We apply microfluidic devices and in vivo optical neurophysiology Pregnenolone to show that proprioceptive

coupling between adjacent body segments constitutes the trigger that drives bending wave propagation from head to tail. We found that posterior body regions are compelled to bend in the same direction and shortly after the bending of the neighboring anterior region. We localize this form of proprioceptive coupling to the B-type cholinergic motor neurons. We quantify the spatial and temporal dynamics of this proprioceptive coupling, and use our biophysical measurements to calculate its role in undulatory dynamics. Proprioception in the C. elegans motor circuit, beyond simply explaining the propagation of an undulatory wave from head to tail, also provides a quantitative explanation for gait adaptation to external load. C. elegans moves forward on its side by propagating dorsal-ventral body bending waves from head to tail. The detailed kinematics of bending waves can be quantified by measuring curvature κ at each point along the body centerline over time ( Figure 2A). To measure κ, we first calculate R, the radius of curvature at each point along the centerline (κ = 1/R).