Anterior Tuberal Nucleus Research Articles

The Dorsal Part of the Anterior Tuberal Nucleus Responds to Auditory Stimulation in Zebrafish (Danio rerio).

The zebrafish, a widely used model in neurobiology, relies on hearing in aquatic environments. Unfortunately, its auditory pathways have mainly been studied in larvae. In this study, we examined the involvement of the anterior tuberal nucleus (AT) in auditory processing in adult zebrafish. Our tract-tracing experiments revealed that the dorsal subdivision of AT is strongly bidirectionally connected to the central nucleus of the torus semicircularis (TSc), a major auditory nucleus in fishes. Immunohistochemical visualization of the ribosomal protein S6 (pS6) phosphorylation to map neural activity in response to auditory stimulation substantiated this finding: the dorsal but not the ventral part of AT responded strongly to auditory stimulation. A similar response to auditory stimulation was present in the TSc but not in the nucleus isthmi, a visual region, which we used as a control for testing if the pS6 activation was specific to the auditory stimulation. We also measured the time course of pS6 phosphorylation, which was previously unreported in teleost fish. After auditory stimulation, we found that pS6 phosphorylation peaked between 100 and 130 min and returned to baseline levels after 190 min. This information will be valuable for the design of future pS6 experiments. Our results suggest an anatomical and functional subdivision of AT, where only the dorsal part connects to the auditory network and processes auditory information.

Androgen receptor deficiency is associated with reduced aromatase expression in the ventromedial hypothalamus of male cichlids.

Social behaviors are regulated by sex steroid hormones, such as androgens and estrogens. However, the specific molecular and neural processes modulated by steroid hormones to generate social behaviors remain to be elucidated. We investigated whether some actions of androgen signaling in the control of social behavior may occur through the regulation of estradiol synthesis in the highly social cichlid fish, Astatotilapia burtoni. Specifically, we examined the expression of cyp19a1, a brain-specific aromatase, in the brains of male A. burtoni lacking a functional ARα gene (ar1), which was recently found to be necessary for aggression in this species. We found that cyp19a1 expression is higher in wild-type males compared to ar1 mutant males in the anterior tuberal nucleus (ATn), the putative fish homolog of the mammalian ventromedial hypothalamus, a brain region that is critical for aggression across taxa. Using insitu hybridization chain reaction, we determined that cyp19a1+ cells coexpress ar1 throughout the brain, including in the ATn. We speculate that ARα may modulate cyp19a1 expression in the ATn to govern aggression in A. burtoni. These studies provide novel insights into the hormonal mechanisms of social behavior in teleosts and lay a foundation for future functional studies.

Neural connections of the torus semicircularis in the adult Zebrafish.

The torus semicircularis (TS) of teleosts is a key midbrain center of the lateral line and acoustic sensory systems. To characterize the TS in adult zebrafish, we studied their connections using the carbocyanine tracers applied to the TS and to other related nuclei and tracts. Two main TS nuclei, central and ventrolateral, were differentiable by their afferent connections. From central TS, (TSc) numerous toropetal cells were labeled bilaterally in several primary octaval nuclei (anterior, magnocellular, descending, and posterior octaval nuclei), in the secondary octaval nucleus, in the caudal octavolateralis nucleus, and in the perilemniscular region. In the midbrain, numerous toropetal cells were labeled in the contralateral TSc. In the diencephalon, toropetal cells labeled from the TSc were observed ipsilaterally in the medial prethalamic nucleus and the periventricular posterior tubercle nucleus. TSc toropetal neurons were also labeled bilaterally in the hypothalamic anterior tuberal nucleus (ATN) and ipsilaterally in the parvicellular preoptic nucleus but not in the telencephalon. Tracer application to the medial octavolateralis nucleus revealed contralateral projections to the ventrolateral TS (TSvl), whereas tracer application to the secondary octaval nucleus labeled fibers bilaterally in TSc and neurons in rostral TSc. The TSc sends ascending fibers to the ipsilateral lateral preglomerular region that, in turn, projects to the pallium. Application of DiI to the optic tectum labeled cells and fibers in the TSvl, whereas application of DiI to the ATN labeled cells and fibers in the TSc. These results reveal that the TSvl and TSc are mainly related with the mechanosensory lateral line and acoustic centers, respectively, and that they show different higher order connections.

Neuronal responses of melanin-concentrating hormone and corticotropin-releasing hormone to background color in the self-fertilizing fish, Kryptolebias marmoratus.

We examined neuronal responses of hypothalamic melanin-concentrating hormone (MCH) and corticotropin-releasing hormone (CRH) to background color in the self-fertilizing fish, Kryptolebias marmoratus. Fish were individually reared in lidless white or black cylindrical plastic containers for 15days. The number of MCH-immunoreactive (ir) cell bodies in the nucleus lateralis tuberis (NLT) of the hypothalamus was significantly greater in the white-acclimated fish, while no significant differences were observed in the nucleus anterior tuberis (NAT) of the hypothalamus. Significant differences were not seen in the number of CRH-ir cell bodies in the NLT between the groups. The body of the white- and black-acclimated fish appeared lighter and darker, respectively, compared with the baseline color. In the black-acclimated fish, feeding activity was significantly greater with a tendency toward higher specific growth rate compared with the observations in white-acclimated fish. No significant inter-group cortisol level differences were observed. These results indicate that background color affects MCH neuronal activity in the NLT as well as body color adaptation but does not affect CRH neuronal activity in K. marmoratus.

Behavioral and neurochemical profile of MK-801 adult zebrafish model: Forebrain β2-adrenoceptors contribute to social withdrawal and anxiety-like behavior

Deficits in social communication and interaction are core clinical symptoms characterizing multiple neuropsychiatric conditions, including autism spectrum disorder (ASD) and schizophrenia. Interestingly, elevated anxiety levels are a common comorbid psychopathology characterizing individuals with aberrant social behavior. Despite recent progress, the underlying neurobiological mechanisms that link anxiety with social withdrawal remain poorly understood. The present study developed a zebrafish pharmacological model displaying social withdrawal behavior, following a 3-h exposure to 4 μΜ (+)-MK-801, a non–competitive N-methyl-d-aspartate (NMDA) receptor antagonist, for 7 days. Interestingly, MK-801-treated zebrafish displayed elevated anxiety levels along with higher frequency of stereotypical behaviors, rendering this zebrafish model appropriate to unravel a possible link of catecholaminergic and ASD–like phenotypes. MK-801-treated zebrafish showed increased telencephalic protein expression of metabotropic glutamate 5 receptor (mGluR5), dopamine transporter (DAT) and β2–adrenergic receptors (β2-ARs), supporting the presence of excitation/inhibition imbalance along with altered dopaminergic and noradrenergic activity. Interestingly, β2-ARs expression, was differentially regulated across the Social Decision-Making (SDM) network nodes, exhibiting increased levels in ventral telencephalic area (Vv), a key-area integrating reward and social circuits but decreased expression in dorso-medial telencephalic area (Dm) and anterior tuberal nucleus (ATN). Moreover, the co-localization of β2-ARs with elements of GABAergic and glutamatergic systems, as well as with GAP-43, a protein indicating increased brain plasticity potential, support the key-role of β2-ARs in the MK-801 zebrafish social dysfunctions. Our results highlight the importance of the catecholaminergic neurotransmission in the manifestation of ASD–like behavior, representing a site of potential interventions for amelioration of ASD-like symptoms.

Alpha-melanocyte stimulating hormone immunoreactivity in the brain of the cichlid fish Oreochromis mossambicus

This study reports the distribution of a pro-opiomelanocortin-derived neuropeptide α–MSH in the brain of the cichlid fish Oreochromis mossambicus. α–MSH-ir fibres were found in the granule cell layer of the olfactory bulb, the medial olfactory tract, the pallium and the subpallium, whereas in the preoptic area of the telencephalon, few large α–MSH-ir perikarya along with extensively labeled fibres were observed close to the ventricular border. Dense network of α–MSH-ir fibres were seen in the hypothalamic areas such as the nucleus preopticus pars magnocellularis, the nucleus preopticus pars parvocellularis, the suprachiasmatic nucleus, the nucleus anterior tuberis, the paraventricular organ, the subdivisions of the nucleus recessus lateralis and the nucleus recessus posterioris. In the nucleus lateralis pars medialis, some α–MSH-ir perikarya and fibres were found along the ventricular margin. In the diencephalon, numerous α–MSH-ir fibres were detected in the nucleus posterior tuberis, the nucleus of the fasciculus longitudinalis medialis and the nucleus preglomerulosus medialis, whereas in the mesencephalon, α–MSH-ir fibres were located in the optic tectum, the torus semicircularis and the tegmentum. In the rhombencephalon, α–MSH-ir fibres were confined to the medial octavolateralis nucleus and the descending octaval nucleus. In the pituitary gland, densely packed α–MSH-ir cells were observed in the pars intermedia region. The widespread distribution of α–MSH-immunoreactivity throughout the brain and the pituitary gland suggests a role for α–MSH peptide in regulation of several neuroendocrine and sensorimotor functions as well as darkening of pigmentation in the tilapia.

Brain Activation Patterns in Response to Conspecific and Heterospecific Social Acoustic Signals in Female Plainfin Midshipman Fish, Porichthys notatus

While the peripheral auditory system of fish has been well studied, less is known about how the fish’s brain and central auditory system process complex social acoustic signals. The plainfin midshipman fish, Porichthys notatus, has become a good species for investigating the neural basis of acoustic communication because the production and reception of acoustic signals is paramount for this species’ reproductive success. Nesting males produce long-duration advertisement calls that females detect and localize among the noise in the intertidal zone to successfully find mates and spawn. How female midshipman are able to discriminate male advertisement calls from environmental noise and other acoustic stimuli is unknown. Using the immediate early gene product cFos as a marker for neural activity, we quantified neural activation of the ascending auditory pathway in female midshipman exposed to conspecific advertisement calls, heterospecific white seabass calls, or ambient environment noise. We hypothesized that auditory hindbrain nuclei would be activated by general acoustic stimuli (ambient noise and other biotic acoustic stimuli) whereas auditory neurons in the midbrain and forebrain would be selectively activated by conspecific advertisement calls. We show that neural activation in two regions of the auditory hindbrain, i.e., the rostral intermediate division of the descending octaval nucleus and the ventral division of the secondary octaval nucleus, did not differ via cFos immunoreactive (cFos-ir) activity when exposed to different acoustic stimuli. In contrast, female midshipman exposed to conspecific advertisement calls showed greater cFos-ir in the nucleus centralis of the midbrain torus semicircularis compared to fish exposed only to ambient noise. No difference in cFos-ir was observed in the torus semicircularis of animals exposed to conspecific versus heterospecific calls. However, cFos-ir was greater in two forebrain structures that receive auditory input, i.e., the central posterior nucleus of the thalamus and the anterior tuberal hypothalamus, when exposed to conspecific calls versus either ambient noise or heterospecific calls. Our results suggest that higher-order neurons in the female midshipman midbrain torus semicircularis, thalamic central posterior nucleus, and hypothalamic anterior tuberal nucleus may be necessary for the discrimination of complex social acoustic signals. Furthermore, neurons in the central posterior and anterior tuberal nuclei are differentially activated by exposure to conspecific versus other acoustic stimuli.

Changes in behavior and brain immediate early gene expression in male threespined sticklebacks as they become fathers

Motherhood is a period of intense behavioral and brain activity. However, we know less about the neural and molecular mechanisms associated with the demands of fatherhood. Here, we report the results of two experiments designed to track changes in behavior and brain activation associated with fatherhood in male threespined stickleback fish (Gasterosteus aculeatus), a species in which fathers are the sole providers of parental care. In experiment 1, we tested whether males' behavioral reactions to different social stimuli depends on parental status, i.e. whether they were providing parental care. Parental males visited their nest more in response to social stimuli compared to nonparental males. Rates of courtship behavior were high in non-parental males but low in parental males. In experiment 2, we used a quantitative in situ hybridization method to compare the expression of an immediate early gene (Egr-1) across the breeding cycle – from establishing a territory to caring for offspring. Egr-1 expression peaked when the activities associated with fatherhood were greatest (when they were providing care to fry), and then returned to baseline levels once offspring were independent. The medial dorsal telencephalon (basolateral amygdala), lateral part of dorsal telencephalon (hippocampus) and anterior tuberal nucleus (ventral medial hypothalamus) exhibited high levels of Egr-1 expression during the breeding cycle. These results help to define the neural circuitry associated with fatherhood in fishes, and are consistent with the hypothesis that fatherhood – like motherhood – is a period of intense behavioral and neural activity.

Arginine Vasotocin Preprohormone Is Expressed in Surprising Regions of the Teleost Forebrain.

Nonapeptides play a fundamental role in the regulation of social behavior, among numerous other functions. In particular, arginine vasopressin and its non-mammalian homolog, arginine vasotocin (AVT), have been implicated in regulating affiliative, reproductive, and aggressive behavior in many vertebrate species. Where these nonapeptides are synthesized in the brain has been studied extensively in most vertebrate lineages. While several hypothalamic and forebrain populations of vasopressinergic neurons have been described in amniotes, the consensus suggests that the expression of AVT in the brain of teleost fish is limited to the hypothalamus, specifically the preoptic area (POA) and the anterior tuberal nucleus (putative homolog of the mammalian ventromedial hypothalamus). However, as most studies in teleosts have focused on the POA, there may be an ascertainment bias. Here, we revisit the distribution of AVT preprohormone mRNA across the dorsal and ventral telencephalon of a highly social African cichlid fish. We first use in situ hybridization to map the distribution of AVT preprohormone mRNA across the telencephalon. We then use quantitative real-time polymerase chain reaction to assay AVT expression in the dorsomedial telencephalon, the putative homolog of the mammalian basolateral amygdala. We find evidence for AVT preprohormone mRNA in regions previously not associated with the expression of this nonapeptide, including the putative homologs of the mammalian extended amygdala, hippocampus, striatum, and septum. In addition, AVT preprohormone mRNA expression within the basolateral amygdala homolog differs across social contexts, suggesting a possible role in behavioral regulation. We conclude that the surprising presence of AVT preprohormone mRNA within dorsal and medial telencephalic regions warrants a closer examination of possible AVT synthesis locations in teleost fish, and that these may be more similar to what is observed in mammals and birds.

GABAergic Neurons and Their Modulatory Effects on GnRH3 in Zebrafish.

γ-Aminobutyric acid (GABA) is a major amino acid neurotransmitter in the vertebrate brain. To provide detailed information on the distribution of the GABA in zebrafish (Danio rerio), neurons were labeled with mCherry driven by the glutamic acid decarboxylase 67 (gad67) promoter. In the transgenic line Tg(gad67:mCherry), mCherry-positive gad67 cell bodies were predominantly localized to the olfactory bulb, pallial zones, subpallium zones, parvocellular preoptic nucleus, periventricular gray zone of optic tectum, torus semicircularis, posterior tuberculum, medial longitudinal fascicle, caudal zone of periventricular hypothalamus, and oculomotor nucleus. mCherry-positive fibers were widely distributed in the olfactory bulbs, subpallium, thalamus, ventral hypothalamic zone, tectum opticum, mesencephalon, and rhombencephalon. mCherry-positive neurons were also observed in the retina and the spinal cord. The anatomical relationships between GABAergic and gonadotrophin-releasing hormone 3 (GnRH3) neurons were investigated by crossing Tg(gad67:mCherry) fish with the previously established Tg(gnrh3:EGFP) transgenic line. GnRH3 cell bodies and fibers were contacted by GABAergic fibers directly in the ventral telencephalon and anterior tuberal nucleus. A subpopulation of GnRH3 neurons in the ventral telencephalic area was also labeled with mCherry, so some GnRH3 neurons are also GABAergic. GABAB receptor agonist (baclofen) and antagonist (CGP55845) treatments indicated that GABAB receptor signaling inhibited gnrh3 expression in larval fish but was stimulatory in adult fish. The expression of pituitary lhβ and fshβ was stimulated by intraperitoneal injection of baclofen in adult fish. We conclude that GABA via GABAB receptors regulates GnRH3 neurons in a developmentally dependent manner in zebrafish.

Acute anorexigenic action of leptin in rainbow trout is mediated by the hypothalamic Pi3k pathway.

Leptin (Lep) is an anorexigenic hormone and regulates appetite-related neuropeptides in mammals. A number of neuropeptides have also been linked to appetite regulation in teleost fish, but Lep signaling activation and effects on appetite-regulating neurons are poorly elucidated in early vertebrates. This study uses cellular, tissue and organismal approaches to elucidate the acute, central Lep action in rainbow trout. The results demonstrate that Lep activates phosphorylation of protein kinase B (Akt) and signal transducer and activator of transcription 3 in rainbow trout hypothalamus-derived cells, and that the phosphatidylinositol-3-kinase (Pi3k) inhibitor LY294002 can suppress the Lep-induced Akt phosphorylation. Intracerebroventricular (ICV) Lep administration strongly suppresses food intake at the doses of 0.05 and 0.5 µg Lep fish(-1) At low dose, Lep stimulates hypothalamic transcription of anorexigenic cocaine- and amphetamine-regulated transcript (Cart) and orexigenic neuropeptide Y. At high dose, Lep stimulates hypothalamic transcription of anorexigenic proopiomelanocortin (Pomc) A1, A2, and B, while coinjection with LY294002 reverses this upregulation. The data suggest that the anorexigenic action of Lep in rainbow trout is mediated through stimulation of the anorexigenic neuropeptides Pomc and Cart. Furthermore, ICV Lep treatment increases phosphor-Akt-immunoreactive cells in the nucleus lateralis tuberis, periventricular zone along infundibulum, and lateral recess surrounded by nucleus anterior tuberis, while LY294002 inhibits this effect. Lep receptor-immunoreactive cells are also predominant in these regions. These results demonstrate that Lep activates the Pi3k-Akt pathway in the lateral tuberal hypothalamus of rainbow trout for acute appetite regulation, indicating the conservation of anorexigenic Lep action in the mediobasal hypothalamus.

Blockade of arginine vasotocin signaling reduces aggressive behavior and c-Fos expression in the preoptic area and periventricular nucleus of the posterior tuberculum in male Amphiprion ocellaris

Many marine fishes change sex in response to social cues when the dominance hierarchy is perturbed. Arginine-vasotocin (AVT) and the mammalian homolog arginine vasopressin are neuropeptides involved in social and reproductive behaviors across vertebrate taxa. The goal of this study was to determine whether AVT signaling influences aggression and expression of c-Fos, a marker of neuroplasticity, in key brain regions of the social decision circuit in Amphiprion ocellaris clownfish, a species where behavioral dominance precedes gonadal sex change from male to female. In experiment 1, juvenile clownfish (average mass 2.5g) were paired together in a tank (a total of 24 pairs), matched approximately for size with one fish randomly receiving either an intraperitoneal injection of the arginine vasopressin V1a receptor antagonist (Manning compound) or saline vehicle, and evaluated for aggressive and submissive behaviors over a 10-min period. The second experiment was a repeat of the first using five pairs of mature, reproductive males, except the animals interacted for 90-min immediately followed by euthanasia for immunohistochemical detection of c-Fos protein. Numbers of c-Fos-positive cells were quantified in the preoptic area of the hypothalamus (POA), the anterior tuberal nucleus (aTn), and periventricular nucleus of the posterior tuberculum (TPp). Manning compound significantly reduced aggression and the probability of winning the contest relative to saline (vehicle) controls. In experiment 2, saline-treated fish displayed approximately twice as many c-Fos-positive cells in the POA and 25% more in the TPp than the Manning-treated fish, no differences were observed in the aTn. Taken together, results suggest AVT signaling is necessary for aggressive behavior and expression of neuroplasticity in the POA and TPp that likely contributes to behavioral dominance and hence, sex change in A. ocellaris.

Nesfatin-1 Regulates the Hypothalamo-Pituitary-Ovarian Axis of Fish1

Nesfatin-1 is an anorexigen in goldfish. In the present study, we provide novel data indicating the presence and regulatory effects of nesfatin-1 on the hypothalamo-pituitary-ovarian (HPO) axis of goldfish. Nucleobindin-2 (NUCB2)/nesfatin-1-like immunoreactive (ir) cells are present in the hypothalamus and in the pituitary, suggesting a hypophysiotropic role for nesfatin-1. NUCB2/nesfatin-1-like ir cells colocalize gonadotropin-releasing hormone (GnRH) in the nucleus lateralis tuberis posterioris and the nucleus anterior tuberis of the goldfish hypothalamus. The presence of nesfatin-1 with GnRH in these two nuclei implicated in pituitary hormone release suggests a role for nesfatin-1 on gonadotropin secretion. A single i.p. injection of synthetic goldfish nesfatin-1 (50 ng/g body wt) resulted in an acute decrease (∼75%) in the expression of hypothalamic chicken GnRH-II and salmon GnRH mRNAs at 15 min postinjection in goldfish. Meanwhile, pituitary luteinizing hormone (LH) beta and follicle-stimulating hormone beta mRNAs were also inhibited (∼80%), but only at 60 min postinjection. Nesfatin-1 administration also resulted in a significant reduction (∼60%) in serum LH levels at 60 min postadministration. Nesfatin-1-like immunoreactivity was also found in the follicle cells, but not the oocytes, in zebrafish and goldfish ovaries. Incubation of zebrafish follicles with nesfatin-1 resulted in a significant reduction in basal germinal vesicle breakdown (∼50%) during the oocyte maturation. In addition, nesfatin-1 also attenuated the stimulatory effects of maturation-inducing hormone on germinal vesicle breakdown. Together, the current results indicate that nesfatin-1 is a metabolic hormone with an inhibitory tone on fish reproduction. Nesfatin-1 appears to elicit this suppressive effect through actions on all three tissues in the fish HPO axis.

Organization of the gymnotiform fish pallium in relation to learning and memory: II. Extrinsic connections

This study describes the extrinsic connections of the dorsal telencephalon (pallium) of gymnotiform fish. We show that the afferents to the dorsolateral and dorsomedial pallial subdivisions of gymnotiform fish arise from the preglomerular complex. The preglomerular complex receives input from four clearly distinct regions: (1) descending input from the pallium itself (dorsomedial and dorsocentral subdivisions and nucleus taenia); (2) other diencephalic nuclei (centroposterior, glomerular, and anterior tuberal nuclei and nucleus of the posterior tuberculum); (3) mesencephalic sensory structures (optic tectum, dorsal and ventral torus semicircularis); and (4) basal forebrain, preoptic area, and hypothalamic nuclei. Previous studies have implicated the majority of the diencephalic and mesencephalic nuclei in electrosensory, visual, and acousticolateral functions. Here we discuss the implications of preglomerular/pallial electrosensory-associated afferents with respect to a major functional dichotomy of the electric sense. The results allow us to hypothesize that a functional distinction between electrocommunication vs. electrolocation is maintained within the input and output pathways of the gymnotiform pallium. Electrocommunication information is conveyed to the pallium through complex indirect pathways that originate in the nucleus electrosensorius, whereas electrolocation processing follows a conservative pathway inherent to all vertebrates, through the optic tectum. We hypothesize that cells responsive to communication signals do not converge onto the same targets in the preglomerular complex as cells responsive to moving objects. We also hypothesize that efferents from the dorsocentral (DC) telencephalon project to the dorsal torus semicircularis to regulate processing of electrocommunication signals, whereas DC efferents to the tectum modulate sensory control of movement.

Glomerular nucleus of the weakly electric fish, Gymnotus sp.: Cytoarchitecture, histochemistry, and fiber connections—Insights from neuroanatomy to evolution and behavior

The present study provides a detailed description of morphological and hodological aspects of the glomerular nucleus in the weakly electric fish Gymnotus sp., and explores the evolutionary and functional implications flowing from this analysis. The glomerular nucleus of Gymnotus shows numerous morphological similarities with the glomerular nucleus of percomorph fish, although cytoarchitectonically simpler. In addition, congruence of the histochemical acetylcholinesterase (AChE) distribution with cytoarchitectonic data suggests that the glomerular nucleus, together with the ventromedial cell group of the medial subdivision of the preglomerular complex (PGm-vmc) rostrally, and the subglomerular nucleus (as identified by Maler et al. [1991] J Chem Neuroanat 4:1–38) caudally, may form a distinct longitudinally organized glomerular complex. Our results show that an important source of sensory afferents to the glomerular nucleus originates in the pretectal and electrosensorius nuclei. The glomerular nucleus in turn projects to the hypothalamus (inferior lobe and anterior hypothalamus), to the anterior tuberal nucleus, and to the medial region of the preglomerular nucleus (PGm). These data suggest that visual and electrosensory information reach the glomerular nucleus and are relayed to the hypothalamus and, via PGm, to the pallium. Such connections are similar to those of the glomerular nucleus in percomorphs and the posterior pretectal nucleus in osteoglossomorph, esocids, and salmonids, where they comprise one component of a visual processing pathway. In Gymnotiform fish, however, the pretectal region that projects to the glomerular nucleus is dominated by electrosensory input (visual input is minor), which is consistent with the dominant role of electroreception in these fish.

Distribution of androgen receptor mRNA expression in vocal, auditory, and neuroendocrine circuits in a teleost fish

Across all major vertebrate groups, androgen receptors (ARs) have been identified in neural circuits that shape reproductive-related behaviors, including vocalization. The vocal control network of teleost fishes presents an archetypal example of how a vertebrate nervous system produces social, context-dependent sounds. We cloned a partial cDNA of AR that was used to generate specific probes to localize AR expression throughout the central nervous system of the vocal plainfin midshipman fish (Porichthys notatus). In the forebrain, AR mRNA is abundant in proposed homologs of the mammalian striatum and amygdala, and in anterior and posterior parvocellular and magnocellular nuclei of the preoptic area, nucleus preglomerulosus, and posterior, ventral and anterior tuberal nuclei of the hypothalamus. Many of these nuclei are part of the known vocal and auditory circuitry in midshipman. The midbrain periaqueductal gray, an essential link between forebrain and hindbrain vocal circuitry, and the lateral line recipient nucleus medialis in the rostral hindbrain also express abundant AR mRNA. In the caudal hindbrain-spinal vocal circuit, high AR mRNA is found in the vocal prepacemaker nucleus and along the dorsal periphery of the vocal motor nucleus congruent with the known pattern of expression of aromatase-containing glial cells. Additionally, abundant AR mRNA expression is shown for the first time in the inner ear of a vertebrate. The distribution of AR mRNA strongly supports the role of androgens as modulators of behaviorally defined vocal, auditory, and neuroendocrine circuits in teleost fish and vertebrates in general.

Immunohistochemical localization of glucokinase in rainbow trout brain

In mammals, glucosensing neurons reside in brain areas known to play a critical regulatory role in energy homeostasis and neuroendocrine function. In fish, although no glucosensing neurons have been characterized to date, glucokinase (GCK; the main glucosensing marker in mammals) activity and expression were found in hypothalamus and hindbrain of rainbow trout where they related to food intake regulation and glucose homeostasis. However, there are no available studies in literature regarding GCK distribution in brain areas as well as the cell types expressing that protein. In the present study we hypothesize that, as occurs in mammals, GCK would be localized where glucosensing areas have been described. In this sense, we have found GCK immunoreactivity in several areas of trout hypothalamus, of which some of them are related to glucose metabolism, energy homeostasis and food intake, including the lateral hypothalamus, anterior tuberal nucleus, posterior tuberal nucleus and lateral tuberal nucleus. On the other hand, GCK immunoreactivity was also observed in other areas where the glucosensor system is probably functional, such as the preoptic area and the oculomotor nucleus. Therefore, in this study using immunoreactive techniques, we have demonstrated in those specific areas of the rainbow trout brain previously described as glucosensor the presence of GCK in different cell types.

Visual, lateral line, and auditory ascending pathways to the dorsal telencephalic area through the rostrolateral region of the lateral preglomerular nucleus in cyprinids

Fiber connections of the rostrolateral region of the lateral preglomerular nucleus (PGlr) were studied by tract-tracing methods in carp and goldfish. The PGlr receives fibers from the optic tectum, ventrolateral nucleus of semicircular torus, ventromedial thalamic nucleus, medial pretoral nucleus, anterior tuberal nucleus, subglomerular nucleus, and (unexpectedly) also from the retina. Dendritic morphology of tecto-preglomerular neurons suggests that they receive retinal inputs. The PGlr can be further subdivided into dorsal (PGlr-d) and ventral (PGlr-v) zones, both of which are composed of somata and neuropil layers. Retinal and tectal fibers terminate mostly in the neuropil layer of the PGlr-d with the retinal terminals concentrated medially and tectal terminals laterally. Lateral line toral fibers terminate mainly in a lateral portion and ventromedial thalamic fibers in a medial portion of the somata layer of the PGlr-d. Auditory fibers from the medial pretoral nucleus and anterior tuberal nucleus terminate in the PGlr-v. The central nucleus of the semicircular torus also projects sparse fibers to the PGlr-v. The PGlr projects to the lateral, central, and medial parts of the dorsal telencephalic area, and the latter telencephalic part sends descending fibers to the PGlr. Differential distribution patterns of PGlr-d and PGlr-v fibers are noted within the dorsal telencephalic parts, suggesting that different sensory modalities may be represented in distinct regions at least to a certain degree.

Fiber connections of the anterior preglomerular nucleus in cyprinids with notes on telencephalic connections of the preglomerular complex

Fiber connections of the anterior preglomerular nucleus (PGa) were studied in carp and goldfish by tracer injection experiments to the nucleus and telencephalon. The PGa received fibers from the central nucleus of semicircular torus, perilemniscular nucleus, anterior tuberal nucleus, and medial pretoral nucleus, all of which are presumed auditory structures. The PGa projected to the dorsal (dDm) and ventral (vDm) regions of medial part of dorsal telencephalic area. The caudomedial region of lateral preglomerular nucleus (PGl) and medial zone of medial preglomerular nucleus (PGm), which also receive auditory toral fibers, projected to the same telencephalic regions as did PGa. These preglomerular structures and the PGa also received in common descending fibers from a rostromedial portion of dDm. The PGa also received fibers from the parvocellular and magnocellular preoptic nuclei, and suprachiasmatic nucleus and projected to the anterior tuberal nucleus and medial inferior lobe, suggesting neurohormonal and circadian control on the PGa and auditory influences on hypothalamic functions. Of other diencephalic nuclei that receive auditory toral fibers, only small numbers of neurons were labeled in the central posterior thalamic nucleus and anterior tuberal nucleus even after large injections to the dorsal telencephalic area. Thus, the PGa and closely related preglomerular regions, not the dorsal thalamus, appear to constitute the major auditory relay station to the dorsal telencephalic area. The rostrolateral region of PGl, rostral and lateral zones of PGm, commissural preglomerular nucleus, and preglomerular tertiary gustatory nucleus, which do not receive auditory toral fibers, also projected to the dorsal telencephalic area.

Fiber connections of the central nucleus of semicircular torus in cyprinids

Fiber connections of the presumed auditory portion of the semicircular torus or the central nucleus (TSc) as well as other central and peripheral auditory structures were studied by tract-tracing methods in carp and goldfish. Major ascending projections to the TSc originated from the descending octaval nucleus (DO) and medullary secondary octaval population (SO). Toropetal neurons of the DO were within the saccular terminal zone. A small number of toropetal DO neurons might receive inputs from other inner ear and lateral line endorgans as well. Fibers from the DO terminated in a deep zone of the TSc, while those from the SO in both deep and superficial zones. Afferents to the TSc also arose from the rhombencephalic reticular formation, anterior octaval nucleus, isthmic reticular nucleus, perilemniscular nucleus, medial pretoral nucleus, anterior tuberal nucleus, and central posterior thalamic nucleus. The TSc projected ascending fibers to the medial pretoral nucleus, anterior tuberal nucleus, central posterior thalamic nucleus, and the preglomerular complex (anterior preglomerular nucleus, the caudomedial region of lateral preglomerular nucleus, and a medial zone of medial preglomerular nucleus). These parts of preglomerular complex appear structurally continuous sharing common hodological and cytoarchitectonic features, and thus might be regarded as a single neuronal population. Abundant descending pathways were also noted in the present study. Of particular note is the medial pretoral nucleus, which received fibers from diencephalic auditory nuclei. The nucleus gave rise to indirect descending pathways to a medial zone of the cerebellar crest where dendrites of crest cells in the SO ramify.