397
VIIA . This mutant exhibits morphological and functional defects similar to those of
mouse mutants with inner ear defects (Ernest et al. 2000 ) and to humans with nonsyndromic deafness caused by myosin VIIA mutations (Liu et al. 1997 ). Also, Foxi1
(aka FKh10) expressed in the otic precursor cells is necessary for normal inner ear
development in both mice (Hulander et al. 2003 ) and zebrafi sh (Solomon et al. 2003 ).
The fact that similar genes are important for auditory and vestibular function in both
mammals and fi shes support the hypothesis that vertebrate hair cells and the sense of
hearing fi rst evolved in early fi shes (Popper and Fay 1999 ; Coffi n et al. 2004 ). Since
there is considerable conserved synteny between zebrafi sh and human genes, roles
for human genes can potentially be understood from zebrafi sh mutations (Barbazuk
et al. 2000 ). Thus, fi shes may provide insight into human hereditary deafness and
into the pathways of hair cell death and regeneration.
Many zebrafi sh mutations that affect the inner ear and lateral line also affect other
critical physiological systems and are lethal during early development, thus standard
psychophysical or physiological hearing tests have not been reported for fi sh with
such mutations. Instead, loss of auditory and vestibular function in zebrafi sh is
assumed when abnormal development of auditory or lateral line structures is evident,
or crudely measured from behavioral acoustic startle response assays (Bang et al.
2000 , 2002 ). As the startle response is mediated by Mauthner cells, large reticulospinal neurons that innervate contralateral spinal motor neurons and receive signals from
ipsilateral sensory afferents (Weiss et al. 2006 ), excitatory post- synaptic currents
(EPSCs) have been recorded from these cells as a correlate of auditory function (Han
et al. 2011 ). More recently, assays have been developed to better quantify hearing
sensitivities across different frequencies in zebrafi sh larvae (Zeddies and Fay 2005 ;
Cervi et al. 2012 ; Bhandiwad et al. 2013 ). These novel techniques should allow for
more detailed assessment of potential hearing defi cits in fi sh mutants in the future.
4 Acquired Hearing Loss
Acquired hearing loss in humans can result from aging, ear infections, diseases,
acoustic trauma, and ototoxic medications (ASHA 2014 ). No studies have examined the effect of aging or disease on hearing in fi shes, although the zebrafi sh has
been used as a model for aging research (Gerhard 2003 ). However, hearing loss in
fi shes following exposure to intense sound stimulation and ototoxins has been
extensively documented.
4.1 Sound-Induced Hearing Loss
The fi rst study to report hearing loss in a fi sh was done by Popper and Clarke ( 1976 ).
They exposed goldfi sh ( Carassius auratus ) to intense pure tones of either 300, 500,
800, or 1000 Hz at approximately 149 dB re 1 μPa for 4 h and then measured
Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes
VIIA . This mutant exhibits morphological and functional defects similar to those of
mouse mutants with inner ear defects (Ernest et al. 2000 ) and to humans with nonsyndromic deafness caused by myosin VIIA mutations (Liu et al. 1997 ). Also, Foxi1
(aka FKh10) expressed in the otic precursor cells is necessary for normal inner ear
development in both mice (Hulander et al. 2003 ) and zebrafi sh (Solomon et al. 2003 ).
The fact that similar genes are important for auditory and vestibular function in both
mammals and fi shes support the hypothesis that vertebrate hair cells and the sense of
hearing fi rst evolved in early fi shes (Popper and Fay 1999 ; Coffi n et al. 2004 ). Since
there is considerable conserved synteny between zebrafi sh and human genes, roles
for human genes can potentially be understood from zebrafi sh mutations (Barbazuk
et al. 2000 ). Thus, fi shes may provide insight into human hereditary deafness and
into the pathways of hair cell death and regeneration.
Many zebrafi sh mutations that affect the inner ear and lateral line also affect other
critical physiological systems and are lethal during early development, thus standard
psychophysical or physiological hearing tests have not been reported for fi sh with
such mutations. Instead, loss of auditory and vestibular function in zebrafi sh is
assumed when abnormal development of auditory or lateral line structures is evident,
or crudely measured from behavioral acoustic startle response assays (Bang et al.
2000 , 2002 ). As the startle response is mediated by Mauthner cells, large reticulospinal neurons that innervate contralateral spinal motor neurons and receive signals from
ipsilateral sensory afferents (Weiss et al. 2006 ), excitatory post- synaptic currents
(EPSCs) have been recorded from these cells as a correlate of auditory function (Han
et al. 2011 ). More recently, assays have been developed to better quantify hearing
sensitivities across different frequencies in zebrafi sh larvae (Zeddies and Fay 2005 ;
Cervi et al. 2012 ; Bhandiwad et al. 2013 ). These novel techniques should allow for
more detailed assessment of potential hearing defi cits in fi sh mutants in the future.
4 Acquired Hearing Loss
Acquired hearing loss in humans can result from aging, ear infections, diseases,
acoustic trauma, and ototoxic medications (ASHA 2014 ). No studies have examined the effect of aging or disease on hearing in fi shes, although the zebrafi sh has
been used as a model for aging research (Gerhard 2003 ). However, hearing loss in
fi shes following exposure to intense sound stimulation and ototoxins has been
extensively documented.
4.1 Sound-Induced Hearing Loss
The fi rst study to report hearing loss in a fi sh was done by Popper and Clarke ( 1976 ).
They exposed goldfi sh ( Carassius auratus ) to intense pure tones of either 300, 500,
800, or 1000 Hz at approximately 149 dB re 1 μPa for 4 h and then measured
Causes and Consequences of Sensory Hair Cell Damage and Recovery in Fishes