A-C, Photomicrographs, depicting an isolated head of a Xenopus laevis tadpole before (A₁) and after opening of the dorsal cranium (A₂) and removal of the skin to disconnect the forebrain (FB, white dotted line in A₂) and to make the brainstem, otic capsule (OtC in A₁, B_1,2) and extraocular neuromuscular system (i.e. N.IV motor innervation of the SO eye muscle in C) accessible for extracellular single- and multiple-unit recordings and bath-application of drugs; further removal of the entire hindbrain (HB, white dashed line in B₁) yielded access to the peripheral part of the N.VIII for electrophysiological recordings of afferent fibers innervating the different vestibular sensory endorgans in the otic capsule (B₂). D,E, A computer-controlled turntable (D) allowed spatially specific application of sinusoidal rotational stimuli of semi-intact preparations in the horizontal (red arrows) and vertical planes (e.g. left AC - right PC, blue arrows in E). F,G, Typical multiple-unit discharge modulation, recorded from N.IV (trochlear nerve, F) and the anterior branch of N.VIII (vestibular nerve, G) during 5 cycles of rotation (0.5 Hz) in the AC - PC plane, illustrated in E. H, In vitro optical motion recording of the left eye (E) during 5 cycles of rotation in the horizontal plane (0.5 Hz). Scale bar is 1 mm in A_1,2 and 0.2 mm in B₁,C; calibration bar and positional excursion amplitude of the rotational stimulus in F also apply to G,H; AC, PC, anterior, posterior vertical semicircular canal; LR, MR, SR, lateral, medial, superior rectus eye muscle; SO, superior oblique eye muscle; OT, optic tectum, Tpos, table position.

A, Schematic of the experimental setting depicting the semi-intact preparation, horizontal sinusoidal turntable positional changes (Tpos; 0.5 Hz, ±10°) and video capture of eye motion. B,C, Single sweeps of co-aligned horizontal positional oscillations of the left (green) and right (red) eye, extracted from video sequences during turntable rotation (B) and average responses (± SEM, shaded areas; n = 8) over a single cycle (C); note that table and eye motion are oppositely directed in agreement with aVOR behavior. D-I, Effect of bath-applied pancuronium (0.12 mg/ml, D,G), benzocaine (0.05%, E,H) and MS-222 (0.05%, F,I) on single sweeps of horizontal sinusoidal turntable motion (Tpos)-evoked eye movements (D-F) and average response (± SEM, shaded areas; n = 8, respectively) over a single cycle (dashed line; G-I); recordings (same color code in G-I) were obtained before (Control, black traces), 5 min (orange traces) and 15 min (red traces) after onset of drug application as well as 1 hour (blue traces, D-F) and 3 hours after beginning of the wash-out (brown trace, F). J, Progression of pharmacological influence on eye motion gain (ratio of eye/table motion magnitude) after application/wash-out of pancuronium, benzocaine and MS-222. K, Dose-response curve of MS-222 impact on the gain of rotation-induced eye motion 5 and 15 min after drug application; the significance of difference in J,K is indicated: *, p≤0.01; **, p≤0.001; ***, p≤0.0001, with respect to control values. Calibration bars in D,G also apply to E,F and H,I, respectively.

A, Schematic of the experimental setting depicting the semi-intact preparation, roll-axis turntable positional changes (T_pos, 0.5 Hz, ±10°) and extracellular recordings of spontaneous and motion-evoked multiple-unit discharge of the superior oblique (SO) eye muscle-innervating trochlear nerve. B-D, Single sweeps of sinusoidal roll motion (Tpos)-evoked discharge modulation (B₁,C₁,D₂), spontaneous firing of the trochlear nerve (D₁) and average firing rate modulation (± SEM, shaded areas) over a single cycle (dashed line; B₂,C₂,D₃) before (Control, gray traces and plots), 5 min (orange traces and plots), 15 min (red traces and plots) and after wash-out (blue traces and plots) of bath-applied pancuronium (0.12 mg/ml, B), benzocaine (0.05%, C) and MS-222 (0.05%, D); inset in B₂ shows relative peak firing rates before (gray) and after pancuronium application (red); insets in D_1,3 show relative resting rates (D₁) and peak firing rates during roll motion stimulation (D₃) before and during drug application and after wash-out; number of experiments in parentheses in insets; while no significant change (n.s., p = 0.975) of the peak firing rate occurred after adding pancuronium to the bath (B), benzocaine (C) and MS-222 (D) blocked the motor responses entirely (***, p≤0.0001). E, Dose-response curve of benzocaine and MS-222 (n = 20, respectively) on spontaneous and motion-triggered peak modulation values of multiple-unit trochlear motor spike discharge.

A-B, Single sweeps of spontaneous (A), roll motion (Tpos)-evoked (B₁) multiple-unit discharge of the superior oblique (SO) eye muscle-innervating trochlear nerve and average firing rate modulation (± SEM, shaded areas; B₂) over a single cycle (dashed line; B₂) before (Control, gray traces and plot), 10 min after application of dimethylsulfoxide (Control w/DMSO, green traces and plot), 5 min (orange traces) and 15 min after application of benzocaine (0.05%; red traces) and four hours after wash-out (blue traces and plot); inset in A show relative resting rates before (gray), in the presence of DMSO (green), benzocaine (orange and red, complete block) and after wash-out (blue); number of experiments in parentheses; while no significant change (n.s., p = 0.880) of the peak firing rate occurred after adding DMSO to the bath, benzocaine (0.05%) blocked the motor responses entirely (***, p≤0.0001).

A, Schematic of the experimental setting depicting the semi-intact preparation, vibrational stimulation of lateral line neuromasts (10 Hz, ±150 µm) and extracellular recordings of the multiple-unit discharge of the peripheral portion of the posterior lateral line nerve (PLLN). B,C, Single sweeps of spontaneous (B₁) and vibration-evoked discharge modulation (C₁) in the PLLN before (Control, gray traces and plots), 5 min (orange traces and plots) and 15 min after bath-application (red traces and plots) and after wash-out (blue traces and plots) of MS-222 (0.05%); relative resting (B₂) and peak firing rates (C₂) before, during and after wash-out show the reversible drug effect; number of experiments in parentheses. D, Dose-response curve of MS-222 on multiple-unit spontaneous and sensory stimulus-evoked spike discharge modulation in mechanosensory (lateral line and vestibular) nerve fibers. E, Schematic of the experimental setting depicting the semi-intact preparation, roll-axis turntable positional changes (T_pos, 0.5 Hz, ±10°) and extracellular recordings of the multiple-unit discharge of the peripheral portion of N.VIII (vestibular). F,G, Single sweeps of spontaneous (F₁) and roll motion-evoked discharge modulation (G₁) of the N.VIII and average firing rate modulation (± SEM, shaded areas; n = 8, respectively) over a single cycle (dashed line; G₂) before (Control, gray traces and plots), 5 min (orange traces and plots) and 15 min after bath-application (red traces and plots) and after wash-out (blue traces and plots) of MS-222 (0.05%); ^#,^## in G_1,2 indicate activated responses in different nerve fibers by either direction of the sinusoidal roll motion; relative resting (F₂) and peak firing rates (G₃) before, during and after wash-out show a complete block and partially reversed drug effect; number of experiments in parentheses; ***, p≤0.0001; n.s., not significant.