Journal of Comparative Physiology A

, Volume 177, Issue 5, pp 577–590 | Cite as

Postmetamorphic changes in auditory sensitivity of the bullfrog midbrain

  • S. S. Boatright-Horowitz
  • A. Megela Simmons
Original Paper


During metamorphosis, the lateral line system of ranid frogs (Rana catesbeiana) degenerates and an auditory system sensitive to airborne sounds develops. We examined the onset of function and developmental changes in the central auditory system by recording multi-unit activity from the principal nucleus of the torus semicircularis (TSp) of bullfrogs at different postmetamorphic stages in response to tympanically-presented auditory stimuli. No responses were recorded to stimuli of up to 95 dB SPL from latemetamorphic tadpoles, but auditory responses were recorded within 24 hours of completion of metamorphosis. Audiograms from froglets (SVL < 5.5 cm) were relatively flat in shape with high thresholds, and showed a decrease in most sensitive frequency (MSF) from about 2500 Hz to about 1500 Hz throughout the first 7–10 days after completion of metamorphosis. Audiograms from frogs larger than 5.5 cm showed continuous downward shifts in MSF and thresholds, and increases in sharpness around MSF until reaching adult-like values. Spontaneous activity in the TSp increased throughout postmetamorphic development. The torus increased in volume by approximately 50% throughout development and displayed changes in cell density and nuclear organization. These observations suggest that the onset of sensitivity to tympanically presented airborne sounds is limited by peripheral, rather than central, auditory maturation.

Key words

Metamorphosis Anuran Audiogram Development Midbrain 



characteristic frequency


most sensitive frequency


phasic burst


primary like




snout-vent length


torus semicircularis


laminar nucleus of TS


magnocellular nucleus of TS


principal nucleus of TS


tympanic width


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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • S. S. Boatright-Horowitz
    • 1
  • A. Megela Simmons
    • 1
    • 2
  1. 1.Department of NeuroscienceBrown UniversityProvidenceUSA
  2. 2.Department of PsychologyBrown UniversityProvidenceUSA

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