Tone and call responses of units in the auditory nerve and dorsal medullary nucleus of Xenopus laevis

Abstract

The clawed frog Xenopus laevis produces vocalizations consisting of distinct patterns of clicks.This study provides the first description of spontaneous, pure-tone and communication-signal evoked discharge properties of auditory nerve (n.VIII) fibers and dorsal medullary nucleus (DMN) cells in an obligatorily aquatic anuran. Responses of 297 n.VIII and 253 DMN units are analyzed for spontaneous rates (SR), frequency tuning, rate-intensity functions, and firing rate adaptation, with a view to how these basic characteristics shape responses to recorded call stimuli. Response properties generally resemble those in partially terrestrial anurans. Broad tuning exists across characteristic frequencies (CFs). Threshold minima are −101 dB re 1 mm/s at 675 Hz; −87 dB at 1,600 Hz; and −61 dB at 3,000 Hz (−90, −77, and −44 dB re 1 Pa, respectively), paralleling the peak frequency of vocalizations at 1.2-1.6 kHz with ~500 Hz in 3 dB bandwidth. SRs range from 0 to 80 (n.VIII) and 0 to 73 spikes/s (DMN). Nerve and DMN units of all CFs follow click rates in natural calls, ≤67 clicks/s and faster. Units encode clicks with a single spike, double spikes, or bursts. Spike times correlate closely with click envelopes. No temporal filtering for communicative click rates occurs in either n.VIII or the DMN.

Assessing stimulus and subject influences on auditory evoked potentials and their relation to peripheral physiology in green treefrogs (Hyla cinerea)

“…We detected no effect of subject size on thresholds, consistent with invasive recordings from the VIIIth nerve of frogs, which have not previously demonstrated an effect of subject size on average thresholds of fibers (Elliott et al, 2007; Frishkopf et al, 1968; Zakon and Wilczynski, 1988). Females generally had lower thresholds than males, an effect that was more pronounced for low and mid-frequencies.…”

“…However, effect sizes indicated that the effect of sex plays a relatively minor role in determining thresholds relative to the effect of frequency. For many frog species, the frequency to which the BP is most sensitive is lower in females than males (Narins and Capranica, 1976; Wilczynski et al, 1992; Zakon and Wilczynski, 1988; but see Elliott et al, 2007). However, consistent with previous studies in green treefrogs (Miranda and Wilczynski, 2009b; Penna et al, 1992), we did not see any evidence for a difference in the frequencies to which males and females were most sensitive.…”

“…Because these frogs are aquatic, it may be more relevant to consider responses to broadcasts or simulation of waterborne sound, such as those used by to generate behavioral and midbrain neurophysiological audiograms (e.g. Elepfandt et al, 2000; Elliott et al, 2007). Audiograms generated using these methods have distinct peaks in sensitivity at frequencies of 0.6 kHz and in the range of 1.6 to 2.0 kHz, the latter of which does overlap the dominant frequencies in Xenopus advertisement calls.…”

Specialization for underwater hearing by the tympanic middle ear of the turtle,Trachemys scripta elegans

“…Nevertheless, the peak disc velocity of 0.3 mm s 21 Pa 21 measured in the present study is comparable to that of Xenopus, ranging from 0.05 to 0.25 mm s 21 Pa 21 [26]. Therefore, the sensitivity of the turtle to underwater sound is broadly comparable to the sensitivity of both Xenopus [24] and otophysine fish [25], allowing for differences in experimental design and the generally higher thresholds in ABR experiments (see below).…”

“…The pointed tip of a vibration probe was connected to a B&K 4810 vibration exciter and glued to the disc using a drop of tissue glue (Vetbond, WPI). The vibration of the probe was calibrated using a small accelerometer (B&K 4500-A) connected to a B&K 2635 charge amplifier (see further details of the stimulation in Elliott et al [24]). The red line shows model data of fish swimbladder vibrations in a sound field [19] for 0.5 ml volume.…”