459
report D 1A and D 2 in TS, CP, and AT of the cichlid A. burtoni . In European eel, D 1B
and D 2A/B mRNA expression is localized in TS and D 1A2 and D 2A/B mRNA in MG
(Kapsimali et al. 2000 ; Pasqualini et al. 2009 ). Ampatzis and Dermon ( 2010 )
showed β 2 adrenergic receptor (AR) in CP, TS, PGl, MG and medial octaval nucleus
(MON) in adult zebrafi sh which largely overlaps the distribution of α 2A AR-ir in the
same areas (Ampatzis et al. 2008 ). The red porgy ( Pagrus ) shows similar distributions of ARs in forebrain and midbrain, but hindbrain nuclei are not reported
(Zikopoulos and Dermon 2005 ).
4 Catecholaminergic Innervation of the Auditory System
Varies with Reproductive State in Female Midshipman
As summarized in Sect. 2.2 , midshipman exhibit a dramatic seasonal change in
frequency encoding and sensitivity at the level of the saccule that is mediated by a
change in circulating steroid hormones (Sisneros 2009b ). While an increase in number of hair cells and expression of BK channels are mechanisms which contribute to
physiological changes to better encode the male advertisement call (Coffi n et al.
2012 ; Rohmann et al. 2013 ), neurotransmitters such as dopamine may directly modulate peripheral and central auditory sensitivity (e.g., Gittelman et al. 2013 ; Ruel
et al. 2001 ) as well as coordinate the behavioral response to acoustic social signals
(Forlano et al. 2015b ). Therefore, after we established that both the central and
peripheral auditory system in midshipman are major targets of CA innervation, we
next tested the hypothesis that CA innervation of the auditory system is seasonally
plastic and dependent on reproductive state in females.
Gravid females were collected by hand from nests of type I males in the intertidal
zone at low tide in June during the reproductive season or in deep offshore waters
by otter trawl in December during the non-reproductive season when ovaries are
regressed (Sisneros et al. 2004b ). We then utilized quantitative fl uorescent immunohistochemistry to measure TH-ir fi ber density in six auditory nuclei that span the
forebrain, midbrain, and hindbrain (Fig. 1 ). By double-labeling with a choline acetyltransferase (ChAT) antibody, we were able to quantify both TH-ir and ChAT-ir
putative terminals on the sensory epithelium of the saccule of the inner ear. Using
this method we could also analyze TH-ir innervation of somata and dendrites of the
cholinergic OE (Forlano et al. 2015a ). Summer females showed greater TH-ir fi ber
density in higher auditory processing areas such as CP and PGl (Fig. 8 ), while no
seasonal differences were found in AT, TS or in SOv in the hindbrain. In contrast,
winter females had greater TH-ir fi ber density within the primary auditory hindbrain, specifi cally in a region spanning laterally within and between the dorsolateral
division of descending octaval nucleus (DOdl) and the medial octavolateralis
nucleus (MED) (Fig. 9 ). While DOdl receives direct input from the saccule, it is
interconnected with MED, a lateral line recipient nucleus (Bass et al. 2000 ; Weeg
and Bass 2000 ), and lateral line afferents are able to encode frequencies that overlap
with the hum (Weeg and Bass 2002 ). Similar to CP and PGl, summer females
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…
report D 1A and D 2 in TS, CP, and AT of the cichlid A. burtoni . In European eel, D 1B
and D 2A/B mRNA expression is localized in TS and D 1A2 and D 2A/B mRNA in MG
(Kapsimali et al. 2000 ; Pasqualini et al. 2009 ). Ampatzis and Dermon ( 2010 )
showed β 2 adrenergic receptor (AR) in CP, TS, PGl, MG and medial octaval nucleus
(MON) in adult zebrafi sh which largely overlaps the distribution of α 2A AR-ir in the
same areas (Ampatzis et al. 2008 ). The red porgy ( Pagrus ) shows similar distributions of ARs in forebrain and midbrain, but hindbrain nuclei are not reported
(Zikopoulos and Dermon 2005 ).
4 Catecholaminergic Innervation of the Auditory System
Varies with Reproductive State in Female Midshipman
As summarized in Sect. 2.2 , midshipman exhibit a dramatic seasonal change in
frequency encoding and sensitivity at the level of the saccule that is mediated by a
change in circulating steroid hormones (Sisneros 2009b ). While an increase in number of hair cells and expression of BK channels are mechanisms which contribute to
physiological changes to better encode the male advertisement call (Coffi n et al.
2012 ; Rohmann et al. 2013 ), neurotransmitters such as dopamine may directly modulate peripheral and central auditory sensitivity (e.g., Gittelman et al. 2013 ; Ruel
et al. 2001 ) as well as coordinate the behavioral response to acoustic social signals
(Forlano et al. 2015b ). Therefore, after we established that both the central and
peripheral auditory system in midshipman are major targets of CA innervation, we
next tested the hypothesis that CA innervation of the auditory system is seasonally
plastic and dependent on reproductive state in females.
Gravid females were collected by hand from nests of type I males in the intertidal
zone at low tide in June during the reproductive season or in deep offshore waters
by otter trawl in December during the non-reproductive season when ovaries are
regressed (Sisneros et al. 2004b ). We then utilized quantitative fl uorescent immunohistochemistry to measure TH-ir fi ber density in six auditory nuclei that span the
forebrain, midbrain, and hindbrain (Fig. 1 ). By double-labeling with a choline acetyltransferase (ChAT) antibody, we were able to quantify both TH-ir and ChAT-ir
putative terminals on the sensory epithelium of the saccule of the inner ear. Using
this method we could also analyze TH-ir innervation of somata and dendrites of the
cholinergic OE (Forlano et al. 2015a ). Summer females showed greater TH-ir fi ber
density in higher auditory processing areas such as CP and PGl (Fig. 8 ), while no
seasonal differences were found in AT, TS or in SOv in the hindbrain. In contrast,
winter females had greater TH-ir fi ber density within the primary auditory hindbrain, specifi cally in a region spanning laterally within and between the dorsolateral
division of descending octaval nucleus (DOdl) and the medial octavolateralis
nucleus (MED) (Fig. 9 ). While DOdl receives direct input from the saccule, it is
interconnected with MED, a lateral line recipient nucleus (Bass et al. 2000 ; Weeg
and Bass 2000 ), and lateral line afferents are able to encode frequencies that overlap
with the hum (Weeg and Bass 2002 ). Similar to CP and PGl, summer females
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…