455
and innervate dorsal DO areas such as dm (Figs. 3a–c and 5b ; Forlano et al. 2014 ).
In addition, at the level of the TPp in the diencephalon, fi bers can clearly be seen
originating in TPp and projecting dorsally into CP (Fig. 1D, E ) as well as PAG,
which has reciprocal connections with TPp and receives auditory information
through the TS in the midbrain (Fig. 6a ) (Forlano et al. 2014 ; Kittelberger and Bass
2013 ). Thus, the PAG is likely the conduit through which DA neurons in TPp receive
auditory input (see below). In the diencephalon, aside from CP, PGl is also heavily
innervated by TH-ir terminals (Fig. 2c ). These fi bers may originate from lateral
projections of TPp or from more rostral ventral medial and ventrolateral thalamic
TH-ir groups (VM/VL; Fig. 1C ) (Forlano et al. 2014 ). Since TPp projections are
also known to ascend to the ventral forebrain (Rink and Wullimann 2001 ; Tay et al.
2011 ), DA neurons from this area may also innervate various preoptic nuclei as well
as the subdivisions of areas ventralis connected to the auditory thalamus (above),
also these areas as well as AT likely receive input from local DA populations. The
TS likely receives mixed CA input composed of both DA and NA fi bers, as the locus
coeruleus is known to project to TS (Ma 1994 ), and studies in other teleosts have
reported dopamine beta hydroxylase (rate limiting enzyme in NA synthesis) as well
as DA-ir in addition to TH-ir in this area (see below; Forlano et al. 2014 ).
3.4 Comparisons to Other Fishes
Outside of studies in mammals (mainly rodents), CA innervation of the peripheral
auditory system has only been described in midshipman fi sh to date but we predict
it is a conserved trait across vertebrates. Curiously, the robust TH-ir innervation
Fig. 5 (continued) and passes ventral to the locus coeruleus (LC) further into the hindbrain.
Prominent terminations are seen within the rostral (r) and caudal (c) dendritic fi eld (d) of the
octavolateralis efferent nucleus (OE). ( b ) Composite parasagittal section lateral to a showing
descending TH-ir fi ber tracts which innervate ventral secondary octaval (SOv) and the dorsal medial
descending octaval nuclei (DOdm). Arrows in a and b indicate cross-sections through TH-ir axons
within the efferent bundle (EB). ( c ) Composite horizontal section showing TH-ir tracts from the
caudal diencephalon to the level of the OE in the hindbrain. Asterisks ( * ) indicate cross-sections
through thick dorsal TH-ir projections from the TPp on either side of the third ventricle (III). The
medial longitudinal catecholaminergic tract (mlct) is evident in this plane of section where a large
subset of fi bers turn sharply medial into the rostral and caudal OEd. TH-ir fi bers also heavily innervate nucleus interpeduncularis (NIn) and superior raphe (SR). ( d ) Horizontal section dorsal to c
showing robust TH-ir innervation of the medially located somata of the OE. Arrow indicates bundle
of TH-ir axons within the lateral portion of the EB that will eventually merge with cranial nerve
VIII. ( e ) A bundle of several robust TH-ir axons appear to branch off the mlct and continue laterally
as seen in d ( horizontal plane ). ( f ) A more dorsal horizontal section to e shows TH-ir axons (of the
same caliber as in e ) converge medially within the descending EB tract. The EB serves as the conduit for the OE efferent fi bers to reach VIII. Compare with transverse sections through the medulla
in Figs. 3 and 4 . Scale bar = 250 μm in a–d , 50 μm in e and f . From Forlano et al. ( 2014 )
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…
and innervate dorsal DO areas such as dm (Figs. 3a–c and 5b ; Forlano et al. 2014 ).
In addition, at the level of the TPp in the diencephalon, fi bers can clearly be seen
originating in TPp and projecting dorsally into CP (Fig. 1D, E ) as well as PAG,
which has reciprocal connections with TPp and receives auditory information
through the TS in the midbrain (Fig. 6a ) (Forlano et al. 2014 ; Kittelberger and Bass
2013 ). Thus, the PAG is likely the conduit through which DA neurons in TPp receive
auditory input (see below). In the diencephalon, aside from CP, PGl is also heavily
innervated by TH-ir terminals (Fig. 2c ). These fi bers may originate from lateral
projections of TPp or from more rostral ventral medial and ventrolateral thalamic
TH-ir groups (VM/VL; Fig. 1C ) (Forlano et al. 2014 ). Since TPp projections are
also known to ascend to the ventral forebrain (Rink and Wullimann 2001 ; Tay et al.
2011 ), DA neurons from this area may also innervate various preoptic nuclei as well
as the subdivisions of areas ventralis connected to the auditory thalamus (above),
also these areas as well as AT likely receive input from local DA populations. The
TS likely receives mixed CA input composed of both DA and NA fi bers, as the locus
coeruleus is known to project to TS (Ma 1994 ), and studies in other teleosts have
reported dopamine beta hydroxylase (rate limiting enzyme in NA synthesis) as well
as DA-ir in addition to TH-ir in this area (see below; Forlano et al. 2014 ).
3.4 Comparisons to Other Fishes
Outside of studies in mammals (mainly rodents), CA innervation of the peripheral
auditory system has only been described in midshipman fi sh to date but we predict
it is a conserved trait across vertebrates. Curiously, the robust TH-ir innervation
Fig. 5 (continued) and passes ventral to the locus coeruleus (LC) further into the hindbrain.
Prominent terminations are seen within the rostral (r) and caudal (c) dendritic fi eld (d) of the
octavolateralis efferent nucleus (OE). ( b ) Composite parasagittal section lateral to a showing
descending TH-ir fi ber tracts which innervate ventral secondary octaval (SOv) and the dorsal medial
descending octaval nuclei (DOdm). Arrows in a and b indicate cross-sections through TH-ir axons
within the efferent bundle (EB). ( c ) Composite horizontal section showing TH-ir tracts from the
caudal diencephalon to the level of the OE in the hindbrain. Asterisks ( * ) indicate cross-sections
through thick dorsal TH-ir projections from the TPp on either side of the third ventricle (III). The
medial longitudinal catecholaminergic tract (mlct) is evident in this plane of section where a large
subset of fi bers turn sharply medial into the rostral and caudal OEd. TH-ir fi bers also heavily innervate nucleus interpeduncularis (NIn) and superior raphe (SR). ( d ) Horizontal section dorsal to c
showing robust TH-ir innervation of the medially located somata of the OE. Arrow indicates bundle
of TH-ir axons within the lateral portion of the EB that will eventually merge with cranial nerve
VIII. ( e ) A bundle of several robust TH-ir axons appear to branch off the mlct and continue laterally
as seen in d ( horizontal plane ). ( f ) A more dorsal horizontal section to e shows TH-ir axons (of the
same caliber as in e ) converge medially within the descending EB tract. The EB serves as the conduit for the OE efferent fi bers to reach VIII. Compare with transverse sections through the medulla
in Figs. 3 and 4 . Scale bar = 250 μm in a–d , 50 μm in e and f . From Forlano et al. ( 2014 )
Neuroanatomical Evidence for Catecholamines as Modulators of Audition…