PT - JOURNAL ARTICLE AU - Akihiro Yamada AU - Hidemasa Furue AU - Jianguo G Gu TI - Angular tuning properties of low threshold mechanoreceptors in isolated rat whisker hair follicles AID - 10.1523/ENEURO.0175-22.2022 DP - 2022 Nov 11 TA - eneuro PG - ENEURO.0175-22.2022 4099 - http://www.eneuro.org/content/early/2022/11/11/ENEURO.0175-22.2022.short 4100 - http://www.eneuro.org/content/early/2022/11/11/ENEURO.0175-22.2022.full AB - Angular tuning is preferential sensory response to a directional stimulus and is observed in the whisker tactile system. In whisker hair follicles, there are at least three types of low threshold mechanoreceptors (LTMRs): rapidly adapting (RA), slowly adapting type 1 (SA1), and slowly adapting type 2 (SA2). These LTMRs display angular tuning but their properties remain incompletely studied. Here we used isolated rat whisker hair follicles and pressure-clamped single-fiber recordings to study angular tuning of these LTMRs. Angular tuning was determined with impulses elicited by ramp-and-hold deflection of whisker hair in 24 directions each at 15° for a total of 360°. We show that RA display impulses during ramp-up, both ramp-up and ramp-down, or ramp-down dynamic phases. Both SA1 and SA2 respond to angular stimuli with slowly adapting impulses in most angles. However, SA1 and SA2 show rapidly adapting responses in other angles. All the three types of LTMRs display strong angular tuning, and there is no significant difference in angular tuning index among them. Population wise, the majority of SA1 are tuned in the caudal direction, a large part of SA2 are tuned in the rostral direction, and RA are tuned in multiple directions. In the angles showing strong tuning, the three LTMRs respond to increased stimulation amplitudes with increased impulse numbers in a hyperbola relationship, and the responsiveness based on impulse numbers is SA2 > SA1 > RA. Our findings provide new information on angular tuning properties of LTMRs in whisker hair follicles and help to understand directional encoding.Significance StatementAngular tuning in the whisker tactile system is essential in life of rodents. Here we studied angular tuning of three types of low threshold mechanoreceptors (LTMRs) in whisker hair follicles: rapidly adapting (RA), slowly adapting type 1 (SA1), and slowly adapting type 2 (SA2). All three types of LTMRs display strong angular tuning in response to whisker hair deflection. Population wise, SA1 are largely tuned to the caudal direction, SA2 are tuned mainly to the rostral direction, and RA are tuned to multiple directions. The three LTMRs respond to increased whisker hair deflection amplitudes with increased impulse numbers, and the responsiveness is SA2 > SA1 > RA. Our findings provide new insights into directional encoding by whisker hair follicle LTMRs.