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Cytoarchitecture of the locus coeruleus (LC). TH-ir is green, and blue is DAPI nuclear stain. A: Transverse section through the rostral LC shows small clusters of large multipolar TH-ir neurons (arrowheads) located on the dorsolateral aspect of the medial longitudinal fasciculus (MLF) whereas others are more dorsal, just lateral to the fourth ventricle (IV). Robust TH-ir fibers and terminals are found in the lateral eminentia granularis (EG) and paraventricular area. B: Parasagittal section through the LC; rostral is to the right. Note prevalence of ventral-oriented dendrites and highly intense TH-ir varicosities and terminals (arrows) on more lightly labeled LC somata and dendrites. C: Horizontal section through the LC and caudal hindbrain. The LC in this plane is seen as a rostrocaudal (r/c) bilateral column of two to three cells with lateral dendrites and projections. Some caudal LC cells are found more laterally, and a few somata of similar size and shape are located at the rostral border of the trigeminal motor nucleus (Vm) (arrowheads). A lone TH-ir cell (double arrowhead) in the hindbrain just lateral to the midline is seen at the level of the efferent bundle (EB; see Figs. 5, 11). TH-ir cells in this location are very few in number. Arrow points to bundle of TH-ir axons in EB. D: Asterisk in C denotes same location at higher magnification. For other abbreviations, see list. Scale bar in A = 500 μm in A,C; 100 μm in B,D.
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Although the neuroanatomical distribution of catecholaminergic (CA) neurons has been well documented across all vertebrate classes, few studies have examined CA connectivity to physiologically and anatomically identified neural circuitry that controls behavior. The goal of this study was to characterize CA distribution in the brain and inner ear of...
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... medial to the lateral lemniscus (ll) and dorsolateral to the medial longitudinal fasciculus (MLF) (Fig 2J,K). Rostrally, at the intersection of the caudal lateral Te and the rostral cerebellum, small clusters of TH-ir neurons are located on the dorsolateral aspect of the MLF while others are more dorsal, just lateral to the fourth ventricle (Fig. 7A). Most LC neurons have ventral and lateral oriented dendrites (Fig. 7). In the horizontal plane the LC is seen as a rostro-caudal bilateral column of 2-3 cells and more caudally cells become sparse (1-2) and are also found more laterally ( Fig. 5A; 7B-D). A few TH-ir somata of similar size and shape to other LC neurons are located ...
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... longitudinal fasciculus (MLF) (Fig 2J,K). Rostrally, at the intersection of the caudal lateral Te and the rostral cerebellum, small clusters of TH-ir neurons are located on the dorsolateral aspect of the MLF while others are more dorsal, just lateral to the fourth ventricle (Fig. 7A). Most LC neurons have ventral and lateral oriented dendrites (Fig. 7). In the horizontal plane the LC is seen as a rostro-caudal bilateral column of 2-3 cells and more caudally cells become sparse (1-2) and are also found more laterally ( Fig. 5A; 7B-D). A few TH-ir somata of similar size and shape to other LC neurons are located caudally, in line with the majority of the LC, at the rostral border of the ...
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... LC, at the rostral border of the trigeminal motor nucleus (Vm). These are likely a migrated part of the LC. Additionally, very few (1-2) large TH-ir cells, also similar in morphology to LC neurons, are found in the hindbrain just lateral to the midline at the level of the lateral efferent bundle tract of the octavolateralis efferent nucleus (EB) (Fig. 7C). Robust TH-ir fibers from LC neurons cross through the MLF and form a dense plexus along the midline at the level of the superior raphe nucleus (SR) ( Fig. 2J; 5C; Timothy and Forlano, unpublished observations). The interpeduncular nucleus (NIn) which is rostral to and contiguous with the SR is highly innervated as well ( Fig. 5C; ...
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... only small beads of neurobiotin could be seen in the TH-ir soma (not shown). Figure 17 shows a size distribution (area vs. major axis diameter) of backfilled neurons compared to measured non-backfilled TH-ir neurons in the same section. Backfilled cells tightly grouped in size with an average major axis diameter (mean ± S.E.) of 21.20 ± 0.17μm and area of 273.55 ± 7.11μm 2 . ...
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... and Panula (2001) report TPp neurons send descending fibers and are reciprocally connected with LC neurons in adult zebrafish, consistent with descending targets of DA A11 neurons in mammals( Maeda et al., 1991). Thus, the intense TH-ir terminals seen on LC neurons in the present study (Fig 7) possibly originate from TPp as well, or may be local projections from LC ( Tay et al., 2011). The heavy TH-ir terminal fields in the area of the dorsal raphe area (present study; Kaslin and Panula, 2001) are also consistent with DAergic projections from A11 neurons in mammals ( Peyron et al., 1995;Smeets and Gonzalez, 2000). ...
Citations
... of teleost fish (Batrachoididae), have a limbic stream resembling that of mammals, namely direct preoptic-anterior hypothalamic input to a midbrain PAG region that projects, in turn, directly to hindbrain vocal neurons 15 . Like mammals 10 , the vocally active PAG region receives neuromodulator inputs [16][17][18][19][20][21][22] . Inactivation of this region with lidocaine or dopamine effectively silences forebrain-evoked vocal output 23,24 . ...
Vocalizations communicate information indicative of behavioural state across divergent social contexts. Yet, how brain regions actively pattern the acoustic features of context-specific vocal signals remains largely unexplored. The midbrain periaqueductal gray (PAG) is a major site for initiating vocalization among mammals, including primates. We show that PAG neurons in a highly vocal fish species (Porichthys notatus) are activated in distinct patterns during agonistic versus courtship calling by males, with few co-activated during a non-vocal behaviour, foraging. Pharmacological manipulations within vocally active PAG, but not hindbrain, sites evoke vocal network output to sonic muscles matching the temporal features of courtship and agonistic calls, showing that a balance of inhibitory and excitatory dynamics is likely necessary for patterning different call types. Collectively, these findings support the hypothesis that vocal species of fish and mammals share functionally comparable PAG nodes that in some species can influence the acoustic structure of social context-specific vocal signals.
... VMN axons exit the brain via occipital nerve roots to sound-producing vocal muscles attached to the sides of the swim bladder [25] (Fig. 1). Moreover, in a fashion comparable to songbirds [27,28], essential components of the neural circuitry underlying midshipman vocal-acoustic behavior express sex steroid receptors, receive robust catecholaminergic innervation, and overlap considerably with the SBN [2,4,23,[29][30][31][32] (Fig. 1). ...
... Two connected dots indicate reciprocal connections. Dotted green lines indicate proposed TH-ir connectivity from the locus coeruleus (LC) and vagal-associated nuclei (XL) based on recent neuroanatomical evidence [30,50]. Other abbreviations: V, area ventralis of the telencephalon; Vd, dorsal nucleus of V; Vp, postcommissural nucleus of V; Vs, supracommisural nucleus of V; Vv, ventral nucleus of V; PPa, anterior parvocellular preoptic nucleus; PPp, posterior parvocellular preoptic nucleus; AT, anterior tuberal nucleus; vT, ventral tuberal hypothalamus; VM-VL, ventromedial-ventrolateral thalamic nuclei; PAG, periaqueductal grey; IP, isthmal paraventricular nucleus; DO/SO, descending and secondary octaval nuclei; OE, octavolateralis efferent nucleus; VMN, vocal motor nucleus; VPP, vocal prepacemaker nucleus; VPN, vocal pacemaker nucleus. ...
... It was hypothesized that humming and non-humming type I males would show differences in the expression of cFos-ir within TH-ir neurons adjacent and projecting to vocal circuitry in the hindbrain and throughout the vocal-motor pathway. Quantification of cFos-ir nuclei in TH-ir neurons was carried out in the dorsal (Vd) and postcommissural (Vp) divisions of the ventral telencephalon, ventral thalamic nuclei (VM-VL), TPp, LC, and vagal-associated nuclei (XL) ( Fig. 1; Table 1; see [30]). Additionally, cFos-ir neurons were quantified exclusive of TH-ir in several SBN and vocal-acoustic nuclei, such as Vd, Vp, the ventral (Vv) and supracommisural (Vs) divisions of the ventral telencephalon, anterior (PPa) and posterior (PPp) preoptic nuclei, hypothalamic nuclei (vT and AT), and the midbrain PAG ( Fig. 1; Table 1). ...
Vocal courtship is vital to the reproductive success of many vertebrates and is therefore a highly-motivated behavioral state. Catecholamines have been shown to play an essential role in the expression and maintenance of motivated vocal behavior, such as the coordination of vocal-motor output in songbirds. However, it is not well-understood if this relationship applies to anamniote vocal species. Using the plainfin midshipman fish model, we tested whether specific catecholaminergic (i.e., dopaminergic and noradrenergic) nuclei and nodes of the social behavior network (SBN) are differentially activated in vocally courting (humming) versus non-humming males. Herein, we demonstrate that tyrosine hydroxylase immunoreactive (TH-ir) neuron number in the noradrenergic locus coeruleus (LC) and induction of cFos (an immediate early gene product and proxy for neural activation) in the preoptic area differentiated humming from non-humming males. Furthermore, we found relationships between activation of the LC and SBN nuclei with the total amount of time that males spent humming, further reinforcing a role for these specific brain regions in the production of motivated reproductive-related vocalizations. Finally, we found that patterns of functional connectivity between catecholaminergic nuclei and nodes of the SBN differed between humming and non-humming males, supporting the notion that adaptive behaviors (such as the expression of advertisement hums) emerge from the interactions between various catecholaminergic nuclei and the SBN.
... Such specializations would suggest that the fish are hearing "specialists," but in terms of signal processing such as determination of sound direction or discrimination between sounds. For example, the sea- JID: HEARES [m5G;November 25, 2021;3:14 ] sonal regulation of dopaminergic neurons in the diencephalon of midshipman and the origin of the dopaminergic efferents to the saccule are known to modulate auditory sensitivity to socially relevant acoustic signals ( Forlano et al., 2014 ;Forlano et al., 2015 ;Perelmuter et al., 2019 ). How widespread are such neurons found in other species? ...
Investigators working with fish bioacoustics used to refer to fishes that have a narrow hearing bandwidth and poor sensitivity as “hearing generalists” (or “non-specialists”), while fishes that could detect a wider hearing bandwidth and had greater sensitivity were referred to as specialists. However, as more was learned about fish hearing mechanism and capacities, these terms became hard to apply, since it was clear there were gradations in hearing capabilities. Popper and Fay, in a paper in Hearing Research in 2011, proposed that these terms be dropped because of the gradation. While this was widely accepted by investigators, it is now apparent that the lack of relatively concise terminology for fish hearing capabilities makes it hard to discuss fish hearing. Thus, in this paper we resurrect the terms specialist and non-specialist but use them with modifiers to express the specific structure of function that is considered a specialization. Moreover, this resurrection recognizes that hearing specializations in fishes may not only be related to increased bandwidth and/or sensitivity, but to other, perhaps more important, aspects of hearing such as sound source localization, discrimination between sounds, and detection of sounds in the presence of masking signals.
... Moderate label also occurred in the dorsal posterior nucleus (DPo; Figures 3f and 6a) Dense ITR staining occurred in the periventricular nucleus of the posterior tuberculum (TPp, Figures 3f,g and 6a). As with CP and AT, TPp is an integral nucleus within the central auditory network of midshipman, in this case providing dopaminergic input to CP as well as the auditory epithelium of the inner ear and the octavolateralis efferent nucleus, a rostral hindbrain nucleus that also innervates the auditory periphery (Forlano, Kim, Krzyminska, & Sisneros, 2014;Perelmuter & Forlano, 2017). Moderate receptor staining was also present in a ventral division of the habenula (Hav, Figure 6a). ...
... Expression of pS6 was also found in small ITR+ neurons surrounding the VMN that overlap the location of GABAergic neurons previously shown to densely innervate the VMN (Chagnaud et al., 2012;Forlano et al., 2014). Isotocin action here likely influences call duration given GABA's direct modulation of overall activity levels in VMN and, in turn, duration of the vocal motor volley that sets final call duration (Chagnaud et al., 2012). ...
... Isotocin action here likely influences call duration given GABA's direct modulation of overall activity levels in VMN and, in turn, duration of the vocal motor volley that sets final call duration (Chagnaud et al., 2012). The VMN also receives catecholaminergic and serotonergic inputs (Forlano et al., 2014;Timothy & Forlano, 2020); their influence on VMN physiology remains to be investigated. ...
Neuropeptides, including oxytocin-like peptides, are a conserved group of hormones that regulate a wide range of social behaviors, including vocal communication. In the current study, we evaluate whether putative brain sites for the actions of isotocin (IT), the oxytocin (OT) homolog of teleost fishes, are associated with vocal courtship and circuitry in the plainfin midshipman fish (Porichthys notatus). During the breeding season, nesting males produce advertisement calls known as ‘hums’ to acoustically court females at night and attract them to nests. We first identify IT receptor (ITR) mRNA in evolutionarily conserved regions of the forebrain preoptic area (POA), anterior hypothalamus (AH), and midbrain periaqueductal gray (PAG), and in two topographically separate populations within the hindbrain vocal pattern generator– duration-coding vocal prepacemaker (VPP) and amplitude-coding vocal motor (VMN) nuclei that also innervate vocal muscles. We also verify that ITR expression overlaps known distribution sites of OT-like immunoreactive fibers. Next, using phosphorylated ribosomal subunit 6 (pS6) as a marker for activated neurons, we demonstrate that ITR-containing neurons in the anterior parvocellular POA, AH, PAG, VPP, and VMN are activated in humming males. Posterior parvocellular and magno/gigantocellular divisions of the POA remain constitutively active in non-humming males that are also in a reproductive state. Together with prior studies of midshipman fish and other vertebrates, our findings suggest that IT-signaling influences male courtship behavior, in part, by acting on brain regions that broadly influence behavioral state (POA) as well as the initiation (POA, PAG) and temporal structure (VPP, VMN) of advertisement hums.
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... Several studies describe a variety of inputs to the vocal (Forlano et al., 2014;Rosner et al., 2018;Timothy and Forlano, 2020) and electromotor (Borde et al., 2020) pattern generating circuits in the hindbrain (Figures 1C,D). One interesting aspect of a recent study investigating the neurophysiological correlates of such inputs is the identification of gap junction coupled, glycinergic neurons within the vocal circuit . ...
The communication behaviors of vocal fish and electric fish are among the vertebrate social behaviors best understood at the level of neural circuits. Both forms of signaling rely on midbrain inputs to hindbrain pattern generators that activate peripheral effectors (sonic muscles and electrocytes) to produce pulsatile signals that are modulated by frequency/repetition rate, amplitude and call duration. To generate signals that vary by sex, male phenotype, and social context, these circuits are responsive to a wide range of hormones and neuromodulators acting on different timescales at multiple loci. Bass and Zakon (2005) reviewed the behavioral neuroendocrinology of these two teleost groups, comparing how the regulation of their communication systems have both converged and diverged during their parallel evolution. Here, we revisit this comparison and review the complementary developments over the past 16 years. We (a) summarize recent work that expands our knowledge of the neural circuits underlying these two communication systems, (b) review parallel studies on the action of neuromodulators (e.g., serotonin, AVT, melatonin), brain steroidogenesis (via aromatase), and social stimuli on the output of these circuits, (c) highlight recent transcriptomic studies that illustrate how contemporary molecular methods have elucidated the genetic regulation of social behavior in these fish, and (d) describe recent studies of mochokid catfish, which use both vocal and electric communication, and that use both vocal and electric communication and consider how these two systems are spliced together in the same species. Finally, we offer avenues for future research to further probe how similarities and differences between these two communication systems emerge over ontogeny and evolution.
... In the summer, projections are decreased from the dopaminergic periventricular posterior tuberculum (TPp) in the forebrain to the saccule, the main end organ of hearing in midshipman. In contrast, TPp projections to the octavolateralis efferent nucleus (OE), the source of cholinergic efferent projections to the inner ear, are increased in the summer ( Fig. 1; Forlano et al. 2014;Forlano et al. 2015a;Perelmuter and Forlano 2017). Catecholaminergic innervation also differs seasonally within auditory divisions of the hindbrain and thalamic forebrain ( Fig. 1; Forlano et al. 2015a). ...
... TH-ir fiber area did not differ in CP, OE, or PGl (Table 2A). Although TPp is known to be dopaminergic and presumed to project to DOdm/dl (Forlano et al. 2014), we looked for the colocalization of DBH and TH to exclude the possibility that DOdm/dl also receives noradrenergic input. Locus coeruleus (LC) neurons were TH-ir and DBH-ir positive, TPp neurons were only TH-ir positive and DOdm/dl was devoid of DBH-ir ( Fig. 4D-F). ...
... We also did not observe any of the summer increases to TH-ir innervation within other auditory nuclei: CP, PGl, and OE (Table 2A). Tract tracing experiments have confirmed that the dopaminergic TPp is the sole source of catecholaminergic input to both the saccule and OE, a cholinergic hindbrain nucleus with efferent projections to the saccule (Forlano et al. 2014;Perelmuter and Forlano 2017). Ascending and local TPp projections within the diencephalon innervate CP and PGl while a robust TH-ir fiber track descends into the hindbrain and appears to innervate DOdm/dl (Forlano et al. 2014). ...
In seasonally breeding vertebrates, hormones coordinate changes in nervous system structure and function to facilitate reproductive readiness and success. Steroid hormones often exert their effects indirectly via regulation of neuromodulators, which in turn can coordinate the modulation of sensory input with appropriate motor output. Female plainfin midshipman fish (Porichthys notatus) undergo increased peripheral auditory sensitivity in time for the summer breeding season, improving their ability to detect mates, which is regulated by steroid hormones. Reproductive females also show differences in catecholaminergic innervation of auditory circuitry compared to winter, non-reproductive females as measured by tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholaminergic synthesis. Importantly, catecholaminergic input to the inner ear from a dopaminergic-specific forebrain nucleus is decreased in the summer and dopamine inhibits the sensitivity of the inner ear, suggesting that gonadal steroids may alter auditory sensitivity by regulating dopamine innervation. In this study, we gonadectomized non-reproductive females, implanted them with estradiol (E2) or testosterone (T), and measured TH immunoreactive (-ir) fibers in auditory nuclei where catecholaminergic innervation was previously shown to be seasonally plastic. We found that treatment with T, but not E2, reduced TH-ir innervation in the auditory hindbrain. T-treatment also reduced TH-ir fiber density in the forebrain dopaminergic cell group that projects to the inner ear, and likely to the auditory hindbrain. Higher T plasma in the treatment group was correlated with reduced-ir TH terminals in the inner ear. These T-treatment induced changes in TH-ir fibers mimic the seasonal downregulation of dopamine in the midshipman inner ear and provide evidence that steroid hormone regulation of peripheral auditory sensitivity is mediated by dopamine.
... Magnocellular THir somata also lay adjacent to PVO and ventral caudal to the magnocellular THir somata of TPp (Fig 3a, b). These THir type 2 cells were significantly smaller (t-test; p-value < 0.001) than those of TPp in both Astyanax forms, which led us to represent them separately than the TPp type 2 population, although they may be one contiguous population (Forlano et al., 2014). PVO adjacent THir somata lay both lateral and ventral to the borders of PVO (Fig 10g, h) and were significantly larger (t-test; p-value < 0.001) in cave Astyanax (mean diameter of 22.8 ± 8.5 μm; N = 67) than in surface Astyanax (mean diameter of 15.4 ± 5.5 μm; N = 48; Fig 10i). ...
... The pattern of THir neuron staining in the Astyanax brain is consistent with reports in other teleost fishes. Conserved regions of THir include the olfactory bulb, basal telencephalon, preoptic, pretectal, tuberal, and rhombenclephalic areas Hornby & Piekut, 1990;Sas et al., 1990;Manso et al., 1993;Ma 1994aMa , 1994bMa , 1997Ma , 2003Meek & Joosten, 1993;Brinon et al., 1998;Rodnguez-Gomez et al., 2000;Rink & Wullimann, 2001;Filippi et al., 2009;Forlano et al., 2014;Goebrecht et al., 2014). For a review of THir reactivity in bony fishes see Meek (1994). ...
Astyanax mexicanus is a teleost fish that is in the process of allopatric speciation. Ancestral Astyanax are found in surface rivers and derived blind forms are found in cave systems. Adaptation to life in nutrient poor caves without predation includes the evolution of enhanced food seeking behaviors and loss of defensive responses. These behavioral adaptations may be mediated by changes in catecholaminergic control systems in the brain. We examined the distribution of tyrosine hydroxylase, a conserved precursor for the synthesis of the catecholamines dopamine and noradrenaline, in the brains of surface and cave Astyanax using immunohistochemistry. We found differences in tyrosine hydroxylase staining in regions that are associated with non‐visual sensory perception, motor control, endocrine release, and attention. These differences included significant increases in the diameters of tyrosine hydroxylase immunoreactive soma in cave Astyanax in the olfactory bulb, basal telencephalon, preoptic nuclei, ventral thalamus, posterior tuberculum, and locus coeruleus. These increases in modulation by dopamine and noradrenaline likely indicate changes in behavioral control that underlie adaptations to the cave environment.
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... Magnocellular THir somata also lay adjacent to PVO and ventral caudal to the magnocellular THir somata of TPp (Fig 3a, b). These THir type 2 cells were significantly smaller (t-test; p-value < 0.001) than those of TPp in both Astyanax forms, which led us to represent them separately than the TPp type 2 population, although they may be one contiguous population (Forlano et al., 2014). PVO adjacent THir somata lay both lateral and ventral to the borders of PVO (Fig 10g, h) and were significantly larger (t-test; p-value < 0.001) in cave Astyanax (mean diameter of 22.8 ± 8.5 μm; N = 67) than in surface Astyanax (mean diameter of 15.4 ± 5.5 μm; N = 48; Fig 10i). ...
... The pattern of THir neuron staining in the Astyanax brain is consistent with reports in other teleost fishes. Conserved regions of THir include the olfactory bulb, basal telencephalon, preoptic, pretectal, tuberal, and rhombenclephalic areas Hornby & Piekut, 1990;Sas et al., 1990;Manso et al., 1993;Ma 1994aMa , 1994bMa , 1997Ma , 2003Meek & Joosten, 1993;Brinon et al., 1998;Rodnguez-Gomez et al., 2000;Rink & Wullimann, 2001;Filippi et al., 2009;Forlano et al., 2014;Goebrecht et al., 2014). For a review of THir reactivity in bony fishes see Meek (1994). ...
Astyanax mexicanus is a teleost fish that is in the process of allopatric speciation. Ancestral Astyanax are found in surface rivers and derived blind forms are found in cave systems. Adaptation to life in nutrient poor caves without predation includes the evolution of enhanced food seeking behaviors and loss of defensive responses. These behavioral adaptations may be mediated by changes in catecholaminergic control systems in the brain. We examined the distribution of tyrosine hydroxylase, a conserved precursor for the synthesis of the catecholamines dopamine and noradrenaline, in the brains of surface and cave Astyanax using immunohistochemistry. We found differences in tyrosine hydroxylase staining in regions that are associated with nonvisual sensory perception, motor control, endocrine release, and attention. These differences included significant increases in the diameters of tyrosine hydroxylase immunoreactive soma in cave Astyanax in the olfactory bulb, basal telencephalon, preoptic nuclei, ventral thalamus, posterior tuberculum, and locus coeruleus. These increases in modulation by dopamine and noradrenaline likely indicate changes in behavioral control that underlie adaptations to the cave environment.
... In the telencephalon, moderate to dense fibers were present in the supracommisural nucleus of the ventral telencephalon that has reciprocal connections with the central posterior nucleus, the auditory-recipient region in the dorsal thalamus (Goodson & Bass, 2002). In the diencephalon, both the central posterior nucleus and the periventricular nucleus of the posterior tuberculum that innervates both the hair cell epithelium of the auditory saccule and the hindbrain octaval efferent nucleus that innervates the saccule (Forlano, Kim, Krzyminska, & Sisneros, 2014;Perelmuter & Forlano, 2017), contain ...
Galanin is a peptide that regulates pituitary hormone release, feeding, and reproductive and parental care behaviors. In teleost fish, increased galanin expression is associated with territorial, reproductively active males. Prior transcriptome studies of the plainfin midshipman (Porichthys notatus), a highly vocal teleost fish with two male morphs that follow alternative reproductive tactics, show that galanin is upregulated in the preoptic area-anterior hypothalamus (POA-AH) of nest-holding, courting type I males during spawning compared to cuckolding type II males. Here, we investigate possible differences in galanin immunoreactivity in the brain of both male morphs and females with a focus on vocal-acoustic and neuroendocrine networks. We find that females differ dramatically from both male morphs in the number of galanin-expressing somata and in the distribution of fibers, especially in brainstem vocal-acoustic nuclei and other sensory integration sites that also differ, though less extensively, between the male morphs. Double labelling shows that primarily separate populations of POA-AH neurons express galanin and the nonapeptides arginine-vasotocin or isotocin, homologues of mammalian arginine vasopressin and oxytocin that are broadly implicated in neural mechanisms of vertebrate social behavior including morph-specific actions on vocal neurophysiology in midshipman. Finally, we report a small population of POA-AH neurons that co-express galanin and the neurotransmitter GABA. Together, the results indicate that galanin neurons in midshipman fish likely modulate brain activity at a broad scale, including targeted effects on vocal motor, sensory and neuroendocrine systems; are unique from nonapeptide-expressing populations; and play a role in male-specific behaviors. This article is protected by copyright. All rights reserved.
... In addition, the TP of actinopterygians also houses a remarkable TH-ir (dopaminergic) cell population that, at less in part, is considered equivalent to the ventral tegmental area/substantia nigra complex of amniotes by its ascending projections to the subpallium (Forlano, Kim, Krzyminska, & Sisneros, 2014;Karoubi, Segev, & Wullimann, 2016;López et al., 2016;López, Lozano, Morales, & González, 2017;Rink & Wullimann, 2001;Ryczko et al., 2016;Tay, Ronneberger, Ryu, Nitschke, & Driever, 2011;Yamamoto & Vernier, 2011). Of note, a comparable connectivity from TP/mesencephalic tegmentum to basal ganglia has been corroborated in amphibians (Marín, Smeets, & González, 1998a, 1998b. ...
The Australian lungfish Neoceratodus forsteri is the only extant species of the order Ceratodontiformes, which retained most of the primitive features of ancient lobe finned‐fishes. Lungfishes are the closest living relatives of land vertebrates and their study is important for deducing the neural traits that were conserved, modified, or lost with the transition from fishes to land vertebrates. We have investigated the nitrergic system with neural nitric oxide synthase (NOS) immunohistochemistry and NADPH‐diaphorase (NADPH‐d) histochemistry, which yielded almost identical results except for the primary olfactory projections and the terminal and preoptic nerve fibers labeled only for NADPH‐d. Combined immunohistochemistry was used for simultaneous detection of NOS with catecholaminergic, cholinergic and serotonergic structures, aiming to establish accurately the localization of the nitrergic elements and to assess possible interactions between these neurotransmitter systems. The results demonstrated abundant nitrergic cells in the basal ganglia, amygdaloid complex, preoptic area, basal hypothalamus, mesencephalic tectum and tegmentum, laterodorsal tegmental nucleus, reticular formation, spinal cord, and retina. In addition, low numbers of nitrergic cells were observed in the olfactory bulb, all pallial divisions, lateral septum, suprachiasmatic nucleus, prethalamic and thalamic areas, posterior tubercle, pretectum, torus semicircularis, cerebellar nucleus, interpeduncular nucleus, the medial octavolateral nucleus, nucleus of the solitary tract, and the dorsal column nucleus. Colocalization of NOS and tyrosine hydroxylase was observed in numerous cells of the ventral tegmental area/substantia nigra complex. Comparison with other vertebrates, using a neuromeric analysis, reveals that the nitrergic system of Neoceratodus shares many neuroanatomical features with tetrapods and particularly with amphibians.
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