Massimo Vergassola

Massimo Vergassola, UCSD

Symmetry and adaptation in C. elegans touch response

Interactions with the physical world are deeply rooted in our sense of touch and depend on ensembles of somatosensory neurons that invade and innervate the skin. Somatosensory neurons convert the mechanical energy delivered in each touch into excitatory membrane currents carried by mechanoelectrical transduction (MeT) channels. Pacinian corpuscles in mammals and touch receptor neurons (TRNs) in Caenorhabditis elegans nematodes have low thresholds for activation, respond symmetrically and adapt rapidly to the application and the removal of mechanical loads. Recordings from Pacinian corpuscles in the 1960s showed that sinusoidal stimulation resulted in frequency doubling within a sensitive frequency band, suggesting that these receptors function as frequency-tuned vibration sensors. At the time, the surrounding lamellar capsule was proposed to generate these response dynamics by acting as a mechanical filter. However, similar response dynamics have since been seen in many other mechanoreceptors, leading to controversy over the specificity of this hypothesis. Using a combination of in vivo electrophysiology, feedback-controlled mechanical stimulation, and physical modeling, we resolve this controversy in favor of a mechanical model which is generic and independent of specific embedding structures.