Connecting morphology to physiology in the mouse tactile sensory system

The sensation of touch is constructed from multiple types of unique sensory receptors acting in parallel. How the structure of different mechanoreceptors in the hair and skin relates to the functional output of their accompanying neurons remains poorly understood. One challenge in studying this problem is being able to provide natural stimuli to awake, behaving animals while also being able to experimentally isolate these different sensory receptors. We describe how the gene NetrinG-1 is selectively expressed in two specific sensory receptors in the mouse whisker follicle: club-like and lanceolate endings. We then selectively recorded from primary sensory afferents with club-like and lanceolate endings in vivo by photo-identifying them and recorded their activities during behavior. We found that both ending types were rapidly adapting to touch. Most were extremely direction selective, and displayed rapid responses to contact. Their patterns of activity could be well described by modeling the forces at the base of the whisker follicle, and were best explained by firing in response to a combination of lateral, axial, and dynamic forces. This study for the first time definitively links two morphological subtypes of mechanosensory receptors with their electrophysiological responses.