Evidence for an active process and a cochlear amplifier in nonmammals

Area of Science:

• Auditory Neuroscience
• Evolutionary Biology
• Cellular Biophysics

Background:

• Outer hair cells in mammals exhibit active shape changes, forming a cochlear amplifier that boosts hearing sensitivity and frequency selectivity.
• Evidence suggests active processes are present in non-mammalian sensory hair cells, prompting investigation into their evolutionary origins and commonality.

Purpose of the Study:

• To explore the evolutionary ancestry and commonality of active mechanisms in sensory hair cells.
• To determine the likely origin of active motor mechanisms in the earliest hair cells of the lateral line system.
• To investigate the location and function of active processes in non-mammalian auditory systems.

Main Methods:

• Review of existing evidence on active processes in mammalian and non-mammalian sensory hair cells.
• Comparative analysis of hair cell function across different vertebrate groups.
• Examination of auditory phenomena in terrestrial non-mammals.

Main Results:

• Active movements in hair cells are advantageous for signal detection near thermal noise levels and overcoming fluid viscosity.
• The earliest active motor mechanism is hypothesized to have been localized in the hair-cell bundle of fish lateral line systems.
• Auditory phenomena in terrestrial non-mammals indicate the presence of a cochlear amplifier, suggesting the mammalian ear is not unique in this regard.

Conclusions:

• Active processes in sensory hair cells likely evolved early, potentially in the lateral line system of fish.
• The active motor mechanism is proposed to have originated within the hair-cell bundle.
• Recent findings support the localization of active processes in non-mammalian hair-cell bundles, closely linked to the transduction process.