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1.1 Catecholamines as Good Candidates for Modulation
of Audition and Auditory-Driven Behaviors
Catecholamines are well documented as regulators of motivation, attention,
arousal, and reward as well as modulators of motor and sensory systems across
vertebrates (Berridge 2008 ; Berridge and Waterhouse 2003 ; Hurley et al. 2004 ;
Joshua et al. 2009 ; Kelly and Goodson 2015 ; Riters 2012 ). Importantly, it has been
proposed from multiple studies in songbirds that seasonal changes in steroid hormones may regulate brain catecholamines, which in turn increase incentive salience
of conspecifi c vocalizations (Caras 2013 ; Maney 2013 ; Maney and Pinaud 2011 ).
In particular, the ascending DA system, largely studied in the context of rewardseeking behavior, is thought to interact with the highly conserved vertebrate social
behavior network (SBN), a group of interconnected nuclei within the basal forebrain and midbrain of all vertebrate taxa, to reinforce and mediate appropriate
behavioral responses to social acoustic signals (Goodson 2005 ; Goodson and
Kabelik 2009 ; Goodson and Kingsbury 2013 ; O’Connell and Hofmann 2011 ).
Furthermore, several studies spanning diverse vertebrate taxa have identifi ed auditory nuclei in the central nervous system (CNS) as clear targets of catecholaminergic (CA) projections from both DA and NA cell populations (e.g., Appeltants et al.
2001 ; Endepols et al. 2000 ; Forlano et al. 2014 ; Klepper and Herbert 1991 ; Mello
et al. 1998 ) and neurophysiological preparations have demonstrated catecholamines as potent modulators of auditory response properties in both the central
(Edeline et al. 2011 ; Gittelman et al. 2013 ; Kossl and Vater 1989 ; Schall et al.
1999 ) and peripheral auditory system (Garrett et al. 2011 ; Maison et al. 2012 ; Niu
and Canlon 2006 ; Ruel et al. 2001 ; Ruel et al. 2007 ), although the latter has only
been investigated in rodents.
Studies which have investigated mechanisms of action of dopamine signaling
on the inner ear have suggested a role for dopamine in protection from acoustic
trauma damage, as dopamine appears to suppress the excitotoxic effects of acoustic overstimulation (Lendvai et al. 2011 ). One might argue that while informative,
these studies (and conclusions) are unsatisfying for those researchers interested in
the neural adaptations of natural behavior, as vertebrate auditory efferent systems
did not evolve in the presence of equivalent noise levels in those studies (see Kirk
and Smith 2003 ; Koppl 2011 ; Smith and Keil 2015 for similar discussion on mammalian cholinergic efferent system). Thus, to date, the natural biological function
of dopamine in the inner ear and its role in normal auditory processing and behavior remains unknown. Surprisingly, the functional signifi cance of the auditory
efferent system as a whole remains unclear (Koppl 2011 ). Here, we will discuss the
advantages and appropriateness of the midshipman model as an unparalleled
opportunity to gain insight on the structure and function of catecholamines in auditory processing and behavior.
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…
1.1 Catecholamines as Good Candidates for Modulation
of Audition and Auditory-Driven Behaviors
Catecholamines are well documented as regulators of motivation, attention,
arousal, and reward as well as modulators of motor and sensory systems across
vertebrates (Berridge 2008 ; Berridge and Waterhouse 2003 ; Hurley et al. 2004 ;
Joshua et al. 2009 ; Kelly and Goodson 2015 ; Riters 2012 ). Importantly, it has been
proposed from multiple studies in songbirds that seasonal changes in steroid hormones may regulate brain catecholamines, which in turn increase incentive salience
of conspecifi c vocalizations (Caras 2013 ; Maney 2013 ; Maney and Pinaud 2011 ).
In particular, the ascending DA system, largely studied in the context of rewardseeking behavior, is thought to interact with the highly conserved vertebrate social
behavior network (SBN), a group of interconnected nuclei within the basal forebrain and midbrain of all vertebrate taxa, to reinforce and mediate appropriate
behavioral responses to social acoustic signals (Goodson 2005 ; Goodson and
Kabelik 2009 ; Goodson and Kingsbury 2013 ; O’Connell and Hofmann 2011 ).
Furthermore, several studies spanning diverse vertebrate taxa have identifi ed auditory nuclei in the central nervous system (CNS) as clear targets of catecholaminergic (CA) projections from both DA and NA cell populations (e.g., Appeltants et al.
2001 ; Endepols et al. 2000 ; Forlano et al. 2014 ; Klepper and Herbert 1991 ; Mello
et al. 1998 ) and neurophysiological preparations have demonstrated catecholamines as potent modulators of auditory response properties in both the central
(Edeline et al. 2011 ; Gittelman et al. 2013 ; Kossl and Vater 1989 ; Schall et al.
1999 ) and peripheral auditory system (Garrett et al. 2011 ; Maison et al. 2012 ; Niu
and Canlon 2006 ; Ruel et al. 2001 ; Ruel et al. 2007 ), although the latter has only
been investigated in rodents.
Studies which have investigated mechanisms of action of dopamine signaling
on the inner ear have suggested a role for dopamine in protection from acoustic
trauma damage, as dopamine appears to suppress the excitotoxic effects of acoustic overstimulation (Lendvai et al. 2011 ). One might argue that while informative,
these studies (and conclusions) are unsatisfying for those researchers interested in
the neural adaptations of natural behavior, as vertebrate auditory efferent systems
did not evolve in the presence of equivalent noise levels in those studies (see Kirk
and Smith 2003 ; Koppl 2011 ; Smith and Keil 2015 for similar discussion on mammalian cholinergic efferent system). Thus, to date, the natural biological function
of dopamine in the inner ear and its role in normal auditory processing and behavior remains unknown. Surprisingly, the functional signifi cance of the auditory
efferent system as a whole remains unclear (Koppl 2011 ). Here, we will discuss the
advantages and appropriateness of the midshipman model as an unparalleled
opportunity to gain insight on the structure and function of catecholamines in auditory processing and behavior.
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…