Fig. 2

Effects of elevations in the strength of electrical stimulation to the vagus nerve on esophageal striated muscle contractility in the rat esophagus. a Representative tracings of vagally mediated contractions in the intact and capsaicin (Cap)-treated rat esophagi, respectively, are shown. Electrical stimulations were applied to the vagus nerve using single pulses (pulse duration 100 μs; between-pulse interval 1 min) at intensities ranging from 1 to 80 V. Filled circles points of application of the single-pulse electrical stimulation (intensities 1, 4, 20, and 80 V). Open circles points of application of the single-pulse electrical stimulation(intensities 2, 8, and 40 V). b Intensity–response curves (maximal contraction 100 %) of the intact (open circle) and the Cap-treated (filled triangle) rat esophagi. Each data point represents the mean ± standard deviation (SD) (n = 4). c Electrical stimulations were applied to the vagus nerve using single 80-V pulses (pulse duration 10–100 μs; between-pulse interval 1 min). Duration–response curves (maximal contraction 100 %) of the intact (open circle) and the Cap-treated (filled triangle) rat esophagi are shown. Each data point represents the mean ± SD (intact n = 5, Cap-treated n = 4). d Representative tracings of contractions when electrical stimulations were applied to the vagus nerve using multiple 80-V pulses (pulse duration 100 μs) at a frequency of 1–50 Hz for 5 s in the intact and Cap-treated rat esophagi are shown. Increases in the frequency of pulses in the electrical stimulation evoked tetanic contractions