424
and extrastriolar regions, with fl ask-shaped type I hair cells present in the striolar
region and cylindrical type II hair cells in extrastriolar areas (Wersäll 1956 , 1960 ).
Data from early transmission electron microscopy (TEM) studies suggested that the
sensory hair cells of anamniotes were exclusively type II (Wersäll 1961 ). However,
more recent TEM investigations have demonstrated that the sensory epithelia of the
lagena and utricle have two distinct populations of hair cells, one within a striolar
region, which contains larger hair cells and a distinct line of hair bundle polarity
reversal, and the other in an extrastriolar zone (Saidel et al. 1990 ; Chang et al.
1992 ).
In the mammalian ear, striolar hair cells are particularly susceptible to aminoglycoside toxicity (Forge and Li 2000 ; see Wu et al. 2002 ; Salvi et al. 2008 ). Similarly,
striolar hair cells in fi shes are preferentially ablated by gentamicin, while extrastriolar hair cells remain relatively unaffected (Yan et al. 1991 ; Chang et al. 1992 ;
Lanford et al. 2000 ). Regional differences in gentamicin-induced hair cell loss have
also been demonstrated in the goldfi sh saccule along with shifts in auditory thresholds (Ramcharitar and Brack 2010 ; Ramcharitar and Selckmann 2010 ), suggesting
that hair cell heterogeneity is present in all three otolith end organs. Collectively,
these data demonstrate similarities in hair cell morphology and associated ototoxin
sensitivity across vertebrates, suggesting that inner ear hair cell heterogeneity arose
early in vertebrate evolution.
In contrast, there are confl icting data on the differential susceptibility of superfi -
cial versus canal neuromast hair cells to ototoxic damage. Initial studies using SEM
to assess hair cell damage suggested that CN hair cells were preferentially damaged
by ototoxic treatment, while SN remained intact, suggesting a possible parallel
between CN hair cells and the type I hair cells of the inner ear (Song et al. 1995 ;
Coombs et al. 2001 ). However, a recent study by Van Trump et al. ( 2010 ) used
fl uorescence- based assays to determine that gentamicin signifi cantly reduced hair
cell survival in both superfi cial and canal neuromasts in zebrafi sh and Mexican
blind cavefi sh ( Astyanax mexicanus ). Future studies are needed to resolve these
confl icting data and clarify the pharmacologic heterogeneity of lateral line hair
cells. Nonetheless, as a whole, the data strongly suggest that hair cell heterogeneity
arose very early in the evolution of vertebrates (Popper 2000 ).
3 Perception and Behavior
Ototoxic compounds, most often aminoglycoside antibiotics and cobalt chloride,
have long been used to disable the lateral line system so as to study the effects of
mechanosensory depravation on fi sh behavior. These studies have investigated
behaviors such as rheotaxis (orientation to water current) and feeding, and the relative contribution of the lateral line to sound reception. This body of work underscores the dynamic use of the lateral line system for a variety of behaviors, depending
on species, feeding modality, and availability of additional sensory information.
Wersäll and Flock ( 1964 ) were the fi rst to report aminoglycoside sensitivity in the
A.B. Coffi n and J. Ramcharitar
and extrastriolar regions, with fl ask-shaped type I hair cells present in the striolar
region and cylindrical type II hair cells in extrastriolar areas (Wersäll 1956 , 1960 ).
Data from early transmission electron microscopy (TEM) studies suggested that the
sensory hair cells of anamniotes were exclusively type II (Wersäll 1961 ). However,
more recent TEM investigations have demonstrated that the sensory epithelia of the
lagena and utricle have two distinct populations of hair cells, one within a striolar
region, which contains larger hair cells and a distinct line of hair bundle polarity
reversal, and the other in an extrastriolar zone (Saidel et al. 1990 ; Chang et al.
1992 ).
In the mammalian ear, striolar hair cells are particularly susceptible to aminoglycoside toxicity (Forge and Li 2000 ; see Wu et al. 2002 ; Salvi et al. 2008 ). Similarly,
striolar hair cells in fi shes are preferentially ablated by gentamicin, while extrastriolar hair cells remain relatively unaffected (Yan et al. 1991 ; Chang et al. 1992 ;
Lanford et al. 2000 ). Regional differences in gentamicin-induced hair cell loss have
also been demonstrated in the goldfi sh saccule along with shifts in auditory thresholds (Ramcharitar and Brack 2010 ; Ramcharitar and Selckmann 2010 ), suggesting
that hair cell heterogeneity is present in all three otolith end organs. Collectively,
these data demonstrate similarities in hair cell morphology and associated ototoxin
sensitivity across vertebrates, suggesting that inner ear hair cell heterogeneity arose
early in vertebrate evolution.
In contrast, there are confl icting data on the differential susceptibility of superfi -
cial versus canal neuromast hair cells to ototoxic damage. Initial studies using SEM
to assess hair cell damage suggested that CN hair cells were preferentially damaged
by ototoxic treatment, while SN remained intact, suggesting a possible parallel
between CN hair cells and the type I hair cells of the inner ear (Song et al. 1995 ;
Coombs et al. 2001 ). However, a recent study by Van Trump et al. ( 2010 ) used
fl uorescence- based assays to determine that gentamicin signifi cantly reduced hair
cell survival in both superfi cial and canal neuromasts in zebrafi sh and Mexican
blind cavefi sh ( Astyanax mexicanus ). Future studies are needed to resolve these
confl icting data and clarify the pharmacologic heterogeneity of lateral line hair
cells. Nonetheless, as a whole, the data strongly suggest that hair cell heterogeneity
arose very early in the evolution of vertebrates (Popper 2000 ).
3 Perception and Behavior
Ototoxic compounds, most often aminoglycoside antibiotics and cobalt chloride,
have long been used to disable the lateral line system so as to study the effects of
mechanosensory depravation on fi sh behavior. These studies have investigated
behaviors such as rheotaxis (orientation to water current) and feeding, and the relative contribution of the lateral line to sound reception. This body of work underscores the dynamic use of the lateral line system for a variety of behaviors, depending
on species, feeding modality, and availability of additional sensory information.
Wersäll and Flock ( 1964 ) were the fi rst to report aminoglycoside sensitivity in the
A.B. Coffi n and J. Ramcharitar