The Cellular and Molecular Basis of Direction Selectivity of Aδ-LTMRs

Abstract

Summary The perception of touch, including the direction of stimulus movement across the skin, begins with activation of low-threshold mechanosensory neurons (LTMRs) that innervate the skin. Here, we show that murine Aδ-LTMRs are preferentially tuned to deflection of body hairs in the caudal-to-rostral direction. This tuning property is explained by the finding that Aδ-LTMR lanceolate endings around hair follicles are polarized; they are concentrated on the caudal (downward) side of each hair follicle. The neurotrophic factor BDNF is synthesized in epithelial cells on the caudal, but not rostral, side of hair follicles, in close proximity to Aδ-LTMR lanceolate endings, which express TrkB. Moreover, ablation of BDNF in hair follicle epithelial cells disrupts polarization of Aδ-LTMR lanceolate endings and results in randomization of Aδ-LTMR responses to hair deflection. Thus, BDNF-TrkB signaling directs polarization of Aδ-LTMR lanceolate endings, which underlies direction-selective responsiveness of Aδ-LTMRs to hair deflection.

Cell-Type-Specific Splicing of Piezo2 Regulates Mechanotransduction

“…Sensory afferents have highly specialized endings that are likely important for mechanosensation (Bai et al, 2015; Rutlin et al, 2014). In mammals, other forms of mechanosensory specialization have been observed.…”

KCNQ Potassium Channels Modulate Sensitivity of Skin Down-hair (D-hair) Mechanoreceptors

“…Similar to KCNQ4, which localizes to circular and lanceolate endings of rapidly adapting mechanoreceptors (23), KCNQ3 is strategically localized to lanceolate endings of D-hairs where it can directly influence sensitivity by shunting depolarizing receptor currents upstream of action potential generation. The overall impact of KCNQ2/3 on D-hair sensitivity was modest and did not result in any obvious behavioral phenotype, but a larger effect might be seen with a complete loss of KCNQ2 in D-hairs or with more physiological stimuli (62). Furthermore, we cannot exclude that D-hairs adapted to the loss of KCNQ channel subunits in our constitutive knock-out mouse model.…”

Functional role of airflow-sensing hairs on the bat wing

“…Hence, we cannot exclude any of these factors. Rutlin et al (2014) presented evidence that a subset of mouse lanceolate afferents displays directional selectivity that is the result of their polarized morphology on one side of the hair. We observe both polarized lanceolate endings that localize to one side of hairs (Marshall et al 2015) and nonpolarized lanceolate endings that encircled bat-wing hairs (Fig.…”

“…Interestingly, in mice, primary follicles (guard hairs) are associated with Merkel cells and have lanceolates that surround the entire hair. Awl/auchene hairs also have direction-selective A␦ low-threshold mechanoreceptor (LTMR) neurons, i.e., polarized LTMR lanceolate endings, which show the strongest response when the hair is deflected caudorostrally (Rutlin et al 2014). Of course, the guard hairs of mice are large compared with the microscopic wing hairs of bats that have been developed to monitor boundary-layer airflow (Dickinson 2010).…”