448
both the ventral divisions [supracommissural (Vs), ventral (Vv) and postcommissural (Vp)] and dorsomedial telencephalon (Bass et al. 2000 ; Bass et al. 1994 ;
Goodson and Bass 2002 ).
3.2 Catecholaminergic Connectivity to Auditory Circuitry
We mapped the distribution of tyrosine hydroxylase (TH; the rate limiting enzyme
in catecholamine synthesis) immunoreactive (-ir) fi bers and terminals throughout
the midshipman brain with focus on nuclei within the central auditory system
(Fig. 1 ). In addition, we utilized bulk neurobiotin labeling of the saccule combined
with immunohistochemistry to show TH-ir innervation on and around neurons
directly connected within nuclei of the ascending auditory system as delineated by
this technique (Figs. 2 , 3 , and 4 ) (Forlano et al. 2014 ).
3.2.1 Higher Auditory Nuclei
With the exception of the dorsal medial telencephalon (Dm; Goodson and Bass 2002 ),
all higher order auditory nuclei contain robust CA innervation (Fig. 1 ) (Forlano et al.
2014 ). The major recipient of ascending projections from hindbrain auditory nuclei is
the nucleus centralis (NC) division of the midbrain TS (Bass et al. 2000 ; Bass et al.
2005 ; McCormick 1999 ). Interestingly, NC is more robustly innervated with TH-ir
fi bers and terminals compared to lateral and deeper cell layers that process lateral line
stimuli (Figs. 1e-g and 2a , b; Bass et al. 2000 ; Weeg and Bass 2000 ). Major efferent
targets of NC include AT, CP, and PGl, which are all heavily innervated by TH-ir
fi bers and terminals (Fig. 2c–f ). After saccular backfi ll experiments, neurobiotinlabeled cells with putative TH-ir contacts are occasionally found in both AT and CP
(Fig. 2d (inset), f ; Forlano et al. 2014 ). Neurobiotin-labeled cells and terminals also
intermixed with abundant TH-ir varicosities were consistently found in the eminentia
granularis, which contains input from the vocal hindbrain (Bass et al. 1994 ) (Fig. 2g ).
In addition, neurobiotin-fi lled cells were consistently found as far rostral as the posterior parvocellular preoptic nucleus (PPp), whose dendritic fi eld is densely innervated
by TH-ir varicose fi bers. Although PPp and AT contain their own small population of
TH-ir somata, backfi lled cells in these areas were never found to be TH-ir (Forlano
et al. 2014 ). Parvocellular preoptic nuclei (PPa/p), AT as well as Vs and Vp all have
reciprocal connections with CP (Goodson and Bass 2002 ). Vs and Vp also contain
their own local population of TH-ir (DA) neurons (Fig. 1 ).
3.2.2 Auditory Hindbrain
Saccular backfi lls produced neurobiotin-labeled cells in hindbrain auditory nuclei
including the dorsomedial (dm) and rostrointermediate (ri) divisions of the descending octaval nucleus (DO), ventral secondary octaval nucleus (SOv), ventral
P.M. Forlano and J.A. Sisneros
both the ventral divisions [supracommissural (Vs), ventral (Vv) and postcommissural (Vp)] and dorsomedial telencephalon (Bass et al. 2000 ; Bass et al. 1994 ;
Goodson and Bass 2002 ).
3.2 Catecholaminergic Connectivity to Auditory Circuitry
We mapped the distribution of tyrosine hydroxylase (TH; the rate limiting enzyme
in catecholamine synthesis) immunoreactive (-ir) fi bers and terminals throughout
the midshipman brain with focus on nuclei within the central auditory system
(Fig. 1 ). In addition, we utilized bulk neurobiotin labeling of the saccule combined
with immunohistochemistry to show TH-ir innervation on and around neurons
directly connected within nuclei of the ascending auditory system as delineated by
this technique (Figs. 2 , 3 , and 4 ) (Forlano et al. 2014 ).
3.2.1 Higher Auditory Nuclei
With the exception of the dorsal medial telencephalon (Dm; Goodson and Bass 2002 ),
all higher order auditory nuclei contain robust CA innervation (Fig. 1 ) (Forlano et al.
2014 ). The major recipient of ascending projections from hindbrain auditory nuclei is
the nucleus centralis (NC) division of the midbrain TS (Bass et al. 2000 ; Bass et al.
2005 ; McCormick 1999 ). Interestingly, NC is more robustly innervated with TH-ir
fi bers and terminals compared to lateral and deeper cell layers that process lateral line
stimuli (Figs. 1e-g and 2a , b; Bass et al. 2000 ; Weeg and Bass 2000 ). Major efferent
targets of NC include AT, CP, and PGl, which are all heavily innervated by TH-ir
fi bers and terminals (Fig. 2c–f ). After saccular backfi ll experiments, neurobiotinlabeled cells with putative TH-ir contacts are occasionally found in both AT and CP
(Fig. 2d (inset), f ; Forlano et al. 2014 ). Neurobiotin-labeled cells and terminals also
intermixed with abundant TH-ir varicosities were consistently found in the eminentia
granularis, which contains input from the vocal hindbrain (Bass et al. 1994 ) (Fig. 2g ).
In addition, neurobiotin-fi lled cells were consistently found as far rostral as the posterior parvocellular preoptic nucleus (PPp), whose dendritic fi eld is densely innervated
by TH-ir varicose fi bers. Although PPp and AT contain their own small population of
TH-ir somata, backfi lled cells in these areas were never found to be TH-ir (Forlano
et al. 2014 ). Parvocellular preoptic nuclei (PPa/p), AT as well as Vs and Vp all have
reciprocal connections with CP (Goodson and Bass 2002 ). Vs and Vp also contain
their own local population of TH-ir (DA) neurons (Fig. 1 ).
3.2.2 Auditory Hindbrain
Saccular backfi lls produced neurobiotin-labeled cells in hindbrain auditory nuclei
including the dorsomedial (dm) and rostrointermediate (ri) divisions of the descending octaval nucleus (DO), ventral secondary octaval nucleus (SOv), ventral
P.M. Forlano and J.A. Sisneros