Atypical tuning and amplification mechanisms in gecko auditory hair cells

Abstract

Significance Geckos are lizards capable of vocalization and can detect frequencies up to 5 kHz, but the mechanism of frequency discrimination is incompletely understood. The gecko’s auditory papilla has a unique arrangement over the high-frequency zone, with rows of mechanically sensitive hair bundles covered with gelatinous sallets. Lower-frequency hair cells are tuned by an electrical resonance employing Ca 2+ -activated K + channels, but hair cells tuned above 1 kHz probably rely on a mechanical resonance of the sallets. The resonance may be boosted by an electromotile force from hair bundles found to be evoked by changes in hair cell membrane potential. This unusual mechanism operates independently of mechanotransduction and differs from mammals which amplify the mechanical input using the motor protein prestin.

Cochlear tonotopy from proteins to perception

“…Characterize the hair cells in the chicken auditory papillaregenerated after destruction with ototoxic agents by examining hair bundle morphology to determine whether the original map is reproduced. 4. Re-investigate tonotopic morphogens in the mouse cochlea, focusing on the lateral region of the organ of Corti that includes the outer hair cells and Deiters cells.…”

“…[ 10 ] ) (D) Gekkonid lizard, auditory nerve fibers, blue circles [ 31 ] ; hair cells, black circles. [ 4 ] All position measurements normalized to mean length of cochlea: cat, 25 mm; gerbil ( Meriones unguiculatus ), 12 mm; bat ( Pteronotus parnelli ); 14 mm; chicken 4 mm; geckos, 1.5 mm (hair cell, crested gecko Correlophus ciliatus ), 2.0 mm (nerve fibers, Tokay gecko, Gekko gecko ).…”

“…Another type of abnormality is present in Gekkonid lizards, such as the Tokay gecko ( Gekko gecko ) [ 31 ] the crested gecko ( Correlophus ciliatus ) and the mourning gecko ( Lepidodactylus lugubris ). [ 4 ] Even though there exists a continuous tonotopic map, the orientation of the map in geckos is of opposite polarity to that of mammals and birds, with neurons tuned to high‐CFs located toward the apex of the basilar papilla and low‐CFs toward the base (Figure 2D). The Gekkonid basilar papilla also has an unusual structure.…”

Signatures of cochlear processing in neuronal coding of auditory information

“…The hair cells of the turtle (Crawford and Fettiplace, 1981) and the chicken (Fuchs et al, 1988) cochleae as well as those from the bullfrog's sacculus (Lewis, 1988) or the gecko auditory papilla (Beurg et al, 2022) all display a phenomenon of electrical resonance. Using patchclamp, current steps cause a dampened oscillation of the transmembrane potential.…”

Otoacoustic Emissions in Non-Mammals

“…There is clear evidence that in turtles, 1 kHz is the upper frequency limit of all hair cells and is based on electrical tuning [ 15 ], and the hair-cell format resembles that of the unidirectional areas in lizards. There is some evidence for electrical tuning in lizard hair cells, but it is currently not clear where it is found and what its upper frequency limit is (e.g., [ 16 , 17 ]). It is of course possible that during the many millions of years of evolution, frequency tuning mechanisms have differentially evolved, which will make the clarification of this concept difficult.…”