Saccular hearing in anurans

Abstract

Acoustic sensing in anurans is mediated by several inner ear organs, including the amphibian papilla, basillar papilla, and lagena. The contribution of the saccule to hearing in adult ranids tends to be constrained to vibration sensitivity and gravity sensing, although there has been some evidence for low-frequency hearing sensitivity as well. The organs that mediate hearing in larval ranids are less well understood. Several studies have postulated a strong role for saccular-mediated hearing in tadpoles, operating by the sensing of particle motion mediated by direct kinetic effects on otolithic organs (the fenestral pathway). Physiological studies show that, in tadpoles, the medial and lateral vestibular nuclei are sensitive to particle motion stimulation, while the dorsal medullary nucleus is more sensitive to pressure stimulation. Anatomical tract tracing with lipophilic cyanocarbanine dyes placed in the saccular branch of the eighth nerve show projections to both auditory and vestibular medullary nuclei, suggesting that input from the saccule may play a role in both particle and pressure sensation.