426
While canal neuromasts play a role in feeding in some species, superfi cial neuromasts appear to mediate rheotaxis behavior in a variety of fi shes. In a classic study
by Montgomery et al. ( 1997 ), chemical ablation of the entire lateral line system
signifi cantly decreased rheotaxis, such that signifi cantly higher fl ow velocities were
necessary to elicit orienting behavior. CN ablation with gentamicin did not alter
rheotaxis, suggesting that only SN are necessary for responding to low velocity
fl ow. Consistent with this fi nding, Buck et al. ( 2012 ) and Suli et al. ( 2012 ) demonstrated that in larval zebrafi sh, which only have SN, chemical ablation of the lateral
line resulted in decreased rheotaxis (defi ned as an increase in the angle of the fi sh’s
head relative to current direction) and fl ow-mediated startle responses. These data
are consistent with the presumed function of SN as low frequency, direct current
detectors and CN as accelerometers that subserve fl ow sensing at higher velocities
(Coombs et al. 1989 , 2014 ).
One long-standing question is the relative contribution of the lateral line to sound
reception. Higgs and Radford ( 2013 ) measured auditory evoked potentials (AEPs)
in goldfi sh after streptomycin ablation of the lateral line and found increased thresholds (reduced sensitivity) to low frequency sound stimuli (100–200 Hz). Physical
SN ablation had no effect on thresholds, suggesting that CN specifi cally contribute
to the AEP response. Coffi n et al. ( 2014a ) examined the role for the lateral line in
sound source localization in plainfi n midshipman fi sh ( Porichthys notatus ), a soniferous species for which directional hearing and source localization is critical for
reproductive success. Female midshipman showed no changes in the proportion of
animals that localized the source after lateral line ablation, although changes in
bearing angle during the fi nal approach to the target speaker suggest that the lateral
line may help fi ne-tune the approach, similar to what is seen in feeding studies.
Collectively, these data support the hypothesis that many fi sh behaviors are driven
by the multisensory integration of visual, mechanosensory, and other sensory information (Braun and Coombs 2000 ; Webb et al. 2008 ; Schwalbe and Webb 2014 ).
4 Biomedical Applications
Fish inner ear and lateral line hair cells are homologous to hair cells in the mammalian inner ear and share a number of properties, including susceptibility to ototoxic
drugs (reviewed in Coffi n et al. 2004 , 2010 ). This latter feature makes fi shes choice
models for biomedical studies of drug-induced hair cell death and protection. Unlike
mammals, however, fi sh can fully regenerate lost hair cells, opening up a range of
studies exploring the cellular mechanisms underlying hair cell regeneration (Brignull
et al. 2009 ). Chemical ototoxins are effective tools for regeneration studies, as they
are usually employed to kill hair cells and trigger the regenerative process. In this
section we briefl y survey some of the cellular and molecular research on hair cell
death, protection, and regeneration using the fi sh inner ear and lateral line as a model
system. More comprehensive reviews are available in Brignull et al. ( 2009 ), Coffi n
et al. ( 2010 , 2014b ), and Esterberg et al. ( 2012 ).
A.B. Coffi n and J. Ramcharitar
While canal neuromasts play a role in feeding in some species, superfi cial neuromasts appear to mediate rheotaxis behavior in a variety of fi shes. In a classic study
by Montgomery et al. ( 1997 ), chemical ablation of the entire lateral line system
signifi cantly decreased rheotaxis, such that signifi cantly higher fl ow velocities were
necessary to elicit orienting behavior. CN ablation with gentamicin did not alter
rheotaxis, suggesting that only SN are necessary for responding to low velocity
fl ow. Consistent with this fi nding, Buck et al. ( 2012 ) and Suli et al. ( 2012 ) demonstrated that in larval zebrafi sh, which only have SN, chemical ablation of the lateral
line resulted in decreased rheotaxis (defi ned as an increase in the angle of the fi sh’s
head relative to current direction) and fl ow-mediated startle responses. These data
are consistent with the presumed function of SN as low frequency, direct current
detectors and CN as accelerometers that subserve fl ow sensing at higher velocities
(Coombs et al. 1989 , 2014 ).
One long-standing question is the relative contribution of the lateral line to sound
reception. Higgs and Radford ( 2013 ) measured auditory evoked potentials (AEPs)
in goldfi sh after streptomycin ablation of the lateral line and found increased thresholds (reduced sensitivity) to low frequency sound stimuli (100–200 Hz). Physical
SN ablation had no effect on thresholds, suggesting that CN specifi cally contribute
to the AEP response. Coffi n et al. ( 2014a ) examined the role for the lateral line in
sound source localization in plainfi n midshipman fi sh ( Porichthys notatus ), a soniferous species for which directional hearing and source localization is critical for
reproductive success. Female midshipman showed no changes in the proportion of
animals that localized the source after lateral line ablation, although changes in
bearing angle during the fi nal approach to the target speaker suggest that the lateral
line may help fi ne-tune the approach, similar to what is seen in feeding studies.
Collectively, these data support the hypothesis that many fi sh behaviors are driven
by the multisensory integration of visual, mechanosensory, and other sensory information (Braun and Coombs 2000 ; Webb et al. 2008 ; Schwalbe and Webb 2014 ).
4 Biomedical Applications
Fish inner ear and lateral line hair cells are homologous to hair cells in the mammalian inner ear and share a number of properties, including susceptibility to ototoxic
drugs (reviewed in Coffi n et al. 2004 , 2010 ). This latter feature makes fi shes choice
models for biomedical studies of drug-induced hair cell death and protection. Unlike
mammals, however, fi sh can fully regenerate lost hair cells, opening up a range of
studies exploring the cellular mechanisms underlying hair cell regeneration (Brignull
et al. 2009 ). Chemical ototoxins are effective tools for regeneration studies, as they
are usually employed to kill hair cells and trigger the regenerative process. In this
section we briefl y survey some of the cellular and molecular research on hair cell
death, protection, and regeneration using the fi sh inner ear and lateral line as a model
system. More comprehensive reviews are available in Brignull et al. ( 2009 ), Coffi n
et al. ( 2010 , 2014b ), and Esterberg et al. ( 2012 ).
A.B. Coffi n and J. Ramcharitar