The structural and functional differentiation of hair cells in a lizard's basilar papilla suggests an operational principle of amniote cochleas.
The hair cells in the mammalian cochlea are of two distinct types. Inner hair cells are responsible for transducing mechanical stimuli into electrical responses, which they forward to the brain through a copious afferent innervation. Outer hair cells, which are thought to mediate the active process that sensitizes and tunes the cochlea, possess a negligible afferent innervation. For every inner hair cell, there are approximately three outer hair cells, so only one-quarter of the hair cells directly deliver information to the CNS. Although this is a surprising feature for a sensory system, the occurrence of a similar innervation pattern in birds and crocodilians suggests that the arrangement has an adaptive value. Using a lizard with highly developed hearing, the tokay gecko, we demonstrate in the present study that the same principle operates in a third major group of terrestrial animals. We propose that the differentiation of hair cells into signaling and amplifying classes reflects incompatible strategies for the optimization of mechanoelectrical transduction and of an active process based on active hair-bundle motility.
Chiappe
M Eugenia
ME
Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York 10065-6399, USA.
Kozlov
Andrei S
AS
Hudspeth
A J
AJ
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002454:Cell Differentiation / Q000502:physiology* / Q000528:radiation effects*; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D004307:Dose-Response Relationship, Radiation; D004560:Electricity; D006198:Hair Cells, Auditory / Q000502:physiology* / Q000648:ultrastructure; D066298:In Vitro Techniques; D008116:Lizards / Q000033:anatomy & histology*; D008564:Membrane Potentials / Q000502:physiology / Q000528:radiation effects; D008854:Microscopy, Electron; D009434:Neural Pathways / Q000502:physiology / Q000528:radiation effects; D016900:Neurofilament Proteins / Q000378:metabolism; D009925:Organ of Corti / Q000166:cytology*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology
D002120:Calcium Channel Agonists; D016900:Neurofilament Proteins; D010455:Peptides; C051774:neurofilament protein H; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C064719:iberiotoxin