Fig. 1

Effects of norepinephrine and β2 receptor antagonist ICI 118,551 on Merkel disc mechanoreceptors and afferent neuron excitability. a Top panel, sample trace shows SA1 impulses recorded from a whisker afferent fiber following mechanical displacement of its whisker hair follicle. The displacement distance was 38 μm, made by a probe at the enlargement section of the whisker hair follicle. Bottom panel, sample trace recorded from the same whisker afferent fiber in a, but without mechanical stimulation, in the absence and presence of 5 mM NE. b Summary data (n = 9) show the NE did not directly elicit impulses in the whisker afferent fibers displaying SA1 impulses (Merkel disc mechanoreceptors). c Three sample traces show SA1 impulses in the absence (control, top), presence of 50 μM ICI 118,155 (middle), and wash out of the drug (bottom). d Summary data of the experiment illustrated in c to show that 50 μM ICI 118,155 inhibited SA1 impulses in both dynamic and static phases (n = 4). e Left panel, sample traces show voltage-activated currents recorded in a trigeminal ganglion neurons in the absence (control, solid black line), presence of 50 μM ICI 118,155 (red line), and wash out of the drug (dashed line). f Summary data (n = 7) of inward currents illustrated in E in the absence (control), presence of 50 μM ICI 118,155, and wash out of the drug. g Two sets of sample traces show membrane responses of trigeminal neurons to currents steps in the absence (control, top panel) and presence of 50 μM ICI 118,155 (bottom). h Summary data (n = 7) of the experiment illustrated in g showing action potentials with peak potentials over 0 mV in control and fail of firing action potentials with peak potential below 0 mV. i & j Similar to c and d except ICI 118,155 at 1 μM was applied, which did not affect SA1 impulses (n = 5). In all experiments, whisker hair follicles were harvested from adult mice, perfused with Krebs bath solution. Single fiber recordings were made with a fire-polished electrode (~ 5 μm in diameter). Norepinephrine was applied for 10 min in each test, and ICI 118,551 was applied for 30 min in each test. Data represent Mean ± SEM, ns, not significantly different, *p < 0.05, **p < 0.01, ***p < 0.001, paired student’s t-test