464
If DA innervation has an inhibitory effect on OE fi ring, this would result in release
of cholinergic inhibition in the saccule in the summer, and again, increased sensitivity
in the reproductive season (Forlano et al. 2015a ).
Although the functional signifi cance of opposing plasticity in CA input at
primary vs. higher auditory processing centers is unclear, we propose modulatory
roles which may include optimizing signal detection in a noisy environment (see
Tomchik and Lu 2006 ) (characteristic of the summer nesting grounds), increasing
perception and salience of male vocalizations (e.g., Appeltants et al. 2002 ; Caras
2013 ; Lynch and Ball 2008 ; Maney 2013 ), and coordination of auditory responsiveness with the decision and subsequent motor response and to localize a potential
mate’s nest (Forlano et al. 2015a ).
5 Exposure to Advertisement Calls of Other Males Activates
Dopaminergic and Noradrenergic Neurons in Type I Male
Midshipman
The rocky intertidal zone where midshipman nests are found in the summer reproductive season is a dynamic soundscape at night when type I males are actively
courting female midshipman and defending their territories via advertisement and
agonistic vocalizations, respectively (McIver et al. 2014 ). Male nests are often
clumped together and vocalizations occur simultaneously (McIver et al. 2014 ;
Sisneros et al. 2009 ) and therefore the perception of another male’s mate call may
modulate calling behavior in competition for females (Petersen et al. 2013 ). Indeed,
in the closely related Gulf toadfi sh ( Opsanus ), a sound playback challenge of conspecifi c advertisement calls increases male calling rate (Remage-Healey and Bass
2005 ). In order to test the hypothesis that CA neurons are active in this naturalistic
context in midshipman in response to conspecifi c social acoustic signals, we
exposed type I male midshipman to a 30 min playback loop of fi ve other male
advertisement calls (hums) recorded in the fi eld. Males were sacrifi ced after 120 min
and brains were double-labeled for the immediate early gene (IEG) product cFos as
a marker for neural activation together with TH using fl uorescent immunohistochemistry (Petersen et al. 2013 ). This allowed us to quantify neural activation throughout
the ascending auditory pathway as well as in CA neurons in males hearing other
males vs. ambient noise conditions. Males exposed to the mate calls of other males
showed signifi cantly greater numbers of cFos-ir neurons in hindbrain (DOri), midbrain (TS), and forebrain (CP) auditory nuclei (Fig. 12 ) as well as in AT, an auditoryvocal integration site. Importantly, the percentage of TH-ir neurons in the TPp that
were double-labeled with cFos was signifi cantly greater in males exposed to hums
over ambient noise (Fig. 13a–c ). Furthermore, there was a signifi cant positive correlation between numbers of cFos-ir in both CP and AT and percent colocalization of
cFos in TH-ir TPp neurons (Fig. 14h , i) which supports functional connectivity and
projections of TPp TH-ir fi bers into these auditory nuclei (Forlano et al. 2014 ;
P.M. Forlano and J.A. Sisneros
If DA innervation has an inhibitory effect on OE fi ring, this would result in release
of cholinergic inhibition in the saccule in the summer, and again, increased sensitivity
in the reproductive season (Forlano et al. 2015a ).
Although the functional signifi cance of opposing plasticity in CA input at
primary vs. higher auditory processing centers is unclear, we propose modulatory
roles which may include optimizing signal detection in a noisy environment (see
Tomchik and Lu 2006 ) (characteristic of the summer nesting grounds), increasing
perception and salience of male vocalizations (e.g., Appeltants et al. 2002 ; Caras
2013 ; Lynch and Ball 2008 ; Maney 2013 ), and coordination of auditory responsiveness with the decision and subsequent motor response and to localize a potential
mate’s nest (Forlano et al. 2015a ).
5 Exposure to Advertisement Calls of Other Males Activates
Dopaminergic and Noradrenergic Neurons in Type I Male
Midshipman
The rocky intertidal zone where midshipman nests are found in the summer reproductive season is a dynamic soundscape at night when type I males are actively
courting female midshipman and defending their territories via advertisement and
agonistic vocalizations, respectively (McIver et al. 2014 ). Male nests are often
clumped together and vocalizations occur simultaneously (McIver et al. 2014 ;
Sisneros et al. 2009 ) and therefore the perception of another male’s mate call may
modulate calling behavior in competition for females (Petersen et al. 2013 ). Indeed,
in the closely related Gulf toadfi sh ( Opsanus ), a sound playback challenge of conspecifi c advertisement calls increases male calling rate (Remage-Healey and Bass
2005 ). In order to test the hypothesis that CA neurons are active in this naturalistic
context in midshipman in response to conspecifi c social acoustic signals, we
exposed type I male midshipman to a 30 min playback loop of fi ve other male
advertisement calls (hums) recorded in the fi eld. Males were sacrifi ced after 120 min
and brains were double-labeled for the immediate early gene (IEG) product cFos as
a marker for neural activation together with TH using fl uorescent immunohistochemistry (Petersen et al. 2013 ). This allowed us to quantify neural activation throughout
the ascending auditory pathway as well as in CA neurons in males hearing other
males vs. ambient noise conditions. Males exposed to the mate calls of other males
showed signifi cantly greater numbers of cFos-ir neurons in hindbrain (DOri), midbrain (TS), and forebrain (CP) auditory nuclei (Fig. 12 ) as well as in AT, an auditoryvocal integration site. Importantly, the percentage of TH-ir neurons in the TPp that
were double-labeled with cFos was signifi cantly greater in males exposed to hums
over ambient noise (Fig. 13a–c ). Furthermore, there was a signifi cant positive correlation between numbers of cFos-ir in both CP and AT and percent colocalization of
cFos in TH-ir TPp neurons (Fig. 14h , i) which supports functional connectivity and
projections of TPp TH-ir fi bers into these auditory nuclei (Forlano et al. 2014 ;
P.M. Forlano and J.A. Sisneros