Exposure to Advertisement Calls of Reproductive Competitors Activates Vocal-Acoustic and Catecholaminergic Neurons in the Plainfin Midshipman Fish, Porichthys notatus

While the neural circuitry and physiology of the auditory system is well studied among vertebrates, far less is known about how the auditory system interacts with other neural substrates to mediate behavioral responses to social acoustic signals. One species that has been the subject of intensive neuroethological investigation with regard to the production and perception of social acoustic signals is the plainfin midshipman fish, Porichthys notatus, in part because acoustic communication is essential to their reproductive behavior. Nesting male midshipman vocally court females by producing a long duration advertisement call. Females localize males by their advertisement call, spawn and deposit all their eggs in their mate’s nest. As multiple courting males establish nests in close proximity to one another, the perception of another male’s call may modulate individual calling behavior in competition for females. We tested the hypothesis that nesting males exposed to advertisement calls of other males would show elevated neural activity in auditory and vocal-acoustic brain centers as well as differential activation of catecholaminergic neurons compared to males exposed only to ambient noise. Experimental brains were then double labeled by immunofluorescence (-ir) for tyrosine hydroxylase (TH), an enzyme necessary for catecholamine synthesis, and cFos, an immediate-early gene product used as a marker for neural activation. Males exposed to other advertisement calls showed a significantly greater percentage of TH-ir cells colocalized with cFos-ir in the noradrenergic locus coeruleus and the dopaminergic periventricular posterior tuberculum, as well as increased numbers of cFos-ir neurons in several levels of the auditory and vocal-acoustic pathway. Increased activation of catecholaminergic neurons may serve to coordinate appropriate behavioral responses to male competitors. Additionally, these results implicate a role for specific catecholaminergic neuronal groups in auditory-driven social behavior in fishes, consistent with a conserved function in social acoustic behavior across vertebrates

Catecholaminergic anatomy.

<p>Tyrosine hydroxylase (TH) immunoreactivity (ir) was used as a marker for catecholaminergic neural populations. (<b>A</b>) The bilateral noradrenergic locus coeruleus (LC). (<b>B</b>) (inset) Dorsal view of midshipman brain with relative positions of A, C, D. (<b>C</b>) Representative caudal (<b>C</b>) and rostral (<b>D</b>) sections of the dopaminergic periventricular posterior tuberculum (TPp). <b>Abbreviations:</b> Fourth ventricle (IV); Paraventricular organ (PVO); Third ventricle (III). Scale bar = 50 µm (LC) and 100 µm (TPp).</p

cFos response to social acoustic signals (advertisement calls) in hypothalamic vocal-acoustic circuitry.

<p>Representative images of cFos-ir neurons (red/pink) within the anterior tuberal nucleus (AT) (<b>A</b>,<b>B</b>) and ventral tuberal nucleus (vT) (<b>D</b>,<b>E</b>) of males who were exposed to social acoustic signals versus males exposed to ambient environmental noise. Data in <b>C</b> and <b>F</b> are represented as mean number of cFos-ir neurons per section ± SE, **<i>p</i> = 0.01. Scale bar = 100 µm. Arrows represent the dorsal (D) and lateral (L) orientation for each image.</p

Co-activation of auditory/vocal-acoustic nuclei and CA neurons.

<p>Pairwise correlations between numbers of cFos-ir neurons in auditory/vocal acoustic nuclei and percent colocalization of cFos-ir within tyrosine hydroxylase (TH-ir) neurons of locus coeruleus (LC) (<b>A–E</b>) and the periventricular posterior tuberculum (TPp) (<b>F–J</b>). Closed circles are males exposed to social signals; open circles are males exposed to ambient noise; green trend lines indicate significant correlations (<i>p</i>≤0.05).</p

Auditory and vocal-acoustic anatomy.

<p>Transverse sections with DAPI nuclear counterstain (blue) showing white borders around nuclei in which numbers of cFos-ir neurons were quantified within auditory and vocal-acoustic pathways. The caudal (<b>A</b>) and rostral (<b>B</b>) extents of the rostral intermediate descending octaval nucleus (DOri). The caudal (<b>C</b>) and rostral (<b>D</b>) extents of the periventricular nucleus centralis of the torus semicirularis (TSnc). (<b>E</b>) Compact (CPc) and diffuse (CPd) divisions of the central posterior nucleus. Ventromedial to CP is the anterior tuberal nucleus (AT) in the ventral hypothalamus. (<b>F</b>) Ventral tuberal nucleus (vT) of the anterior hypothalamus. (<b>G</b>) (inset) Dorsal view of midshipman brain with relative positions of A–F. <b>Abbreviations:</b> Cerebellum (C); Cerebral Aqueduct (CA); Horizontal commissure (HoC); Internal arcuate fiber tract (iaf); Fourth ventricle (IV); Lateral hypothalamus (LH); Midbrain (M); Magnocelluar octaval nucleus (MG); Olfactory bulb (OB); Medial nucleus preglomerulosus (PGm); Periaqueductal gray (PAG); Magnocellular preoptic nucleus (PMg); Posterior parvocellular preoptic nucleus (PPp); Paratoral tegmentum (PTT); Optic tectum (TeO); Ventral secondary octaval nucleus (SOv); Telencephalon (T); Molecular layer of the valvula (Vm). Scale Bars = 500 µm.</p

cFos response to social acoustic signals (advertisement calls) in the ascending auditory pathway.

<p>Representative images of cFos-ir neurons (red/pink) within males who were exposed to social acoustic signals (left column, A, C, E) versus males who were exposed to ambient environmental noise (right column, B, D, F). (<b>A</b>,<b>B</b>) Rostral intermediate division of the descending octaval nucleus (DOri) within the medulla. (<b>C</b>,<b>D</b>) The periventricular nucleus centralis within the midbrain torus semicircularis (TSnc). (<b>E</b>,<b>F</b>) Compact division of the central posterior nucleus (CP) in the auditory thalamus. Scale bar = 100 µm. Arrows represent the dorsal (D) and lateral (L) orientation for each image. Data in <b>G</b>–<b>I</b> are represented as mean number of cFos-ir neurons per section ± SE, *<i>p</i><0.05 **<i>p</i>≤0.01, ***<i>p</i><0.001.</p