Several types of mechanoreceptors have been identified anatomically in rodent whisker hair follicles, but their functional properties have not been fully studied. Here we developed a pressure-clamped single-fiber recording technique to record impulses on mouse whisker hair follicle afferent nerves following displacements of whisker hair follicles. On the basis of the patterns of impulses evoked by the mechanical stimulation, three functional types of mechanoreceptors were identified, including rapidly adapting (RA), slowly adapting type 1 (SA1), and slowly adapting type 2 (SA2) mechanoreceptors. Impulses of all these mechanoreceptors were almost completely abolished by 30 nM TTX, and were largely suppressed by cooling temperatures at 15°C. Tested at different displacement distances as different stimulation intensity, RA mechanoreceptors showed a limited capacity for stimulation intensity encoding, but both SA1 and SA2 mechanoreceptors displayed linear increases of impulse numbers with increased stimulation intensity. Tested with different ramp speed of displacements, RA impulses were only evoked by rapid ramp stimulation but SA1 and SA2 impulses could be evoked by both rapid and slow ramp stimulation. Tested with different stimulation frequency, all three types of mechanoreceptors well followed the stimulation at 10-100 Hz. Taken together, this study revealed some important functional properties of RA, SA1 and SA2 mechanoreceptors, which helps better understand the encoding of tactile information by different types of low-threshold mechanoreceptors.
