468
Like TPp neurons which provide the majority of far-reaching DA projections in
teleosts, the LC contributes the majority of NA projections throughout the brain and
TH-ir LC neurons show robust cFos-ir response to conspecifi c vocalizations in male
midshipman (Fig. 13d–f ). In addition, there were signifi cant positive correlations
between percent colocalization of cFos in TH-ir LC neurons and numbers of cFos-ir
at all levels of the auditory system we investigated (Fig. 14a–e ) which may refl ect
LC connectivity to those areas (Petersen et al. 2013 ). In songbirds, LC function is
necessary for song-induced IEG expression in auditory forebrain and normal
response to conspecifi c song (Appeltants et al. 2002 ; Lynch and Ball 2008 ; Pawlisch
et al. 2011 ; Velho et al. 2012 ). Therefore, activation of CA neurons in TPp and LC
may serve to coordinate appropriate behavioral responses to male competitors such
as an increase in motivated vocal courtship (Petersen et al. 2013 ). In addition, TPp
(and LC) activation may increase signal to noise at multiple levels of the central and
peripheral auditory system as well as modulate reafferent suppression via OE
control during calling behavior (Weeg et al. 2005 ).
6 Conclusions and Future Directions
Overall, these studies support a role for catecholamines in seasonal auditory plasticity
and auditory-driven social behavior in midshipman fi sh and have provided new
anatomical insights on catecholamines, and DA in particular, as important neuromodulators of auditory function in fi shes. Based on our current knowledge, below
are a list of important questions worthy of future investigations that will require
neurophysiological, behavioral, gene expression, and further anatomical approaches
to uncover function and mechanisms of CA action on audition and behavior in
fi shes. There remain a number of important questions that should be addressed in
future work, several of which are briefl y detailed below:
1. Where and via what receptors is dopamine acting in the midshipman saccule?
2. Does dopamine increase saccular hair cell sensitivity (lower threshold at higher
frequencies)?
3. Does dopamine increase signal to noise processing at the level of the auditory
primary afferents or hair cells?
4. Is catecholaminergic signaling important for female phonotaxis, motivation or
ability to localize sound in noisy acoustic environments where midshipman court
and breed?
Acknowledgements In terms of producing numerous foundational studies of fi sh auditory end
organs at the morphological and functional level, Art Popper is truly a pioneer and set the groundwork for many of us interested in fi sh hearing. Work from Art’s lab is inspirational in terms of
scope and diversity of species that have been studied. PMF had the pleasure of getting to know
Dick Fay personally during a summer spent at the Marine Biological Laboratory in Woods Hole,
MA while collaborating with him and JAS. Dick’s insights and contributions into the physiology,
anatomy and behavior of hearing in fi shes cannot be overstated. It was an honor to work with and
learn from him on a daily basis as Dick is exemplary in his patience, kindness, and generosity on
a s cientifi c and personal level.
P.M. Forlano and J.A. Sisneros
Like TPp neurons which provide the majority of far-reaching DA projections in
teleosts, the LC contributes the majority of NA projections throughout the brain and
TH-ir LC neurons show robust cFos-ir response to conspecifi c vocalizations in male
midshipman (Fig. 13d–f ). In addition, there were signifi cant positive correlations
between percent colocalization of cFos in TH-ir LC neurons and numbers of cFos-ir
at all levels of the auditory system we investigated (Fig. 14a–e ) which may refl ect
LC connectivity to those areas (Petersen et al. 2013 ). In songbirds, LC function is
necessary for song-induced IEG expression in auditory forebrain and normal
response to conspecifi c song (Appeltants et al. 2002 ; Lynch and Ball 2008 ; Pawlisch
et al. 2011 ; Velho et al. 2012 ). Therefore, activation of CA neurons in TPp and LC
may serve to coordinate appropriate behavioral responses to male competitors such
as an increase in motivated vocal courtship (Petersen et al. 2013 ). In addition, TPp
(and LC) activation may increase signal to noise at multiple levels of the central and
peripheral auditory system as well as modulate reafferent suppression via OE
control during calling behavior (Weeg et al. 2005 ).
6 Conclusions and Future Directions
Overall, these studies support a role for catecholamines in seasonal auditory plasticity
and auditory-driven social behavior in midshipman fi sh and have provided new
anatomical insights on catecholamines, and DA in particular, as important neuromodulators of auditory function in fi shes. Based on our current knowledge, below
are a list of important questions worthy of future investigations that will require
neurophysiological, behavioral, gene expression, and further anatomical approaches
to uncover function and mechanisms of CA action on audition and behavior in
fi shes. There remain a number of important questions that should be addressed in
future work, several of which are briefl y detailed below:
1. Where and via what receptors is dopamine acting in the midshipman saccule?
2. Does dopamine increase saccular hair cell sensitivity (lower threshold at higher
frequencies)?
3. Does dopamine increase signal to noise processing at the level of the auditory
primary afferents or hair cells?
4. Is catecholaminergic signaling important for female phonotaxis, motivation or
ability to localize sound in noisy acoustic environments where midshipman court
and breed?
Acknowledgements In terms of producing numerous foundational studies of fi sh auditory end
organs at the morphological and functional level, Art Popper is truly a pioneer and set the groundwork for many of us interested in fi sh hearing. Work from Art’s lab is inspirational in terms of
scope and diversity of species that have been studied. PMF had the pleasure of getting to know
Dick Fay personally during a summer spent at the Marine Biological Laboratory in Woods Hole,
MA while collaborating with him and JAS. Dick’s insights and contributions into the physiology,
anatomy and behavior of hearing in fi shes cannot be overstated. It was an honor to work with and
learn from him on a daily basis as Dick is exemplary in his patience, kindness, and generosity on
a s cientifi c and personal level.
P.M. Forlano and J.A. Sisneros