Immunocytochemical demonstration of close relationships between neuropeptidergic nerve fibers and hormone-producing cell types in the adenohypophysis of the sea bass (Dicentrarchus labrax)

Galanin expression varies with parental care and social status in a wild cooperatively breeding fish

As many busy parents will attest, caring for young often comes at the expense of having time to feed and care for oneself. Galanin is a neuropeptide that regulates food intake and modulates parental care; however, the relative importance of galanin in the regulation of feeding versus caring by parents has never been evaluated before under naturalistic settings. Here, we assessed how expression of the galanin system varied in two brain regions, the hypothalamus (which regulates feeding) and the preoptic area (which modulates social behaviours including care) in a wild cichlid fish, Neolamprologus pulcher. Females with young had higher hypothalamic expression of galanin receptor 1a, and the highest expression of galanin and galanin receptor 1a was observed in females that foraged the least. However, expression of five other feeding-related neuropeptides did not change while females were caring for young suggesting that changes in the hypothalamic galanin system may not have been directly related to changes in food intake. The preoptic galanin system was unaffected by the presence of young, but preoptic galanin expression was higher in dominant females (which are aggressive, regularly reproduce and care for young) compared to subordinate females (which are submissive, rarely reproduce but often help care for young). Additionally, preoptic galanin expression was higher in fish that performed more territory defense. Overall, our results indicate that galanin has brain-region-specific roles in modulating both parental care and social status in wild animals.

Multimodal hypothalamo-hypophysial communication in the vertebrates

The vertebrate pituitary is arguably one of the most complex endocrine glands from the evolutionary, anatomical and functional perspectives. The pituitary plays a master role in endocrine physiology for the control of growth, metabolism, reproduction, water balance, and the stress response, among many other key processes. The synthesis and secretion of pituitary hormones are under the control of neurohormones produced by the hypothalamus. Under this conceptual framework, the communication between the hypophysiotropic brain and the pituitary gland is at the foundation of our understanding of endocrinology. The anatomy of the connections between the hypothalamus and the pituitary gland has been described in different vertebrate classes, revealing diverse modes of communication together with varying degrees of complexity. In this context, the evolution and variation in the neuronal, neurohemal, endocrine and paracrine modes will be reviewed in light of recent discoveries, and a re-evaluation of earlier observations. There appears to be three main hypothalamo-pituitary communication systems: 1. Diffusion, best exemplified by the agnathans; 2. Direct innervation of the adenohypophysis, which is most developed in teleost fish, and 3. The median eminence/portal blood vessel system, most conspicuously developed in tetrapods, showing also considerable variation between classes. Upon this basic classification, there exists various combinations possible, giving rise to taxon and species-specific, multimodal control over major physiological processes. Intrapituitary paracrine regulation and communication between folliculostellate cells and endocrine cells are additional processes of major importance. Thus, a more complex evolutionary picture of hypothalamo-hypophysial communication is emerging. There is currently little direct evidence to suggest which neuroendocrine genes may control the evolution of one communication system versus another. However, studies at the developmental and intergenerational timescales implicate several genes in the angiogenesis and axonal guidance pathways that may be important.

Isotocin Regulates Growth Hormone but Not Prolactin Release From the Pituitary of Ricefield Eels

The neurohypophyseal hormone oxytocin (Oxt) has been shown to stimulate prolactin (Prl) synthesis and release from the adenohypophysis in rats. However, little is known about the functional roles of Oxt-like neuropeptides in the adenohypophysis of non-mammalian vertebrates. In this study, cDNAs encoding ricefield eel oxytocin-like receptors (Oxtlr), namely isotocin (Ist) receptor 1 (Istr1) and 2 (Istr2), were isolated and specific antisera were generated, respectively. RT-PCR and Western blot analysis detected the presence of both Istr1 and Istr2 in the brain and pituitary, but differential expression in some peripheral tissues, including the liver and kidney, where only Istr1 was detected. In the pituitary, immunoreactive Istr1 and Istr2 were differentially distributed, with the former mainly in adenohypophyseal cell layers adjacent to the neurohypophysis, whereas the latter in peripheral areas of the adenohypophysis. Double immunofluorescent images showed that immunostaining of Istr1, but not Istr2 was localized to growth hormone (Gh) cells, but neither of them was expressed in Prl cells. Ist inhibited Gh release in primary pituitary cells of ricefield eels and increased Gh contents in the pituitary gland of ricefield eels at 6 h after in vivo administration. Ist inhibition of Gh release is probably mediated by cAMP, PKC/DAG, and IP3/Ca²⁺ pathways. In contrast, Ist did not affect either prl gene expression or Prl contents in primary pituitary cells. Results of this study demonstrated that Ist may not be involved in the regulation of Prl, but inhibit Gh release via Istr1 rather than Istr2 in ricefield eels, and provided evidence for the direct regulation of Gh cells by oxytocin-like neuropeptides in the pituitary of non-mammalian vertebrates.

Responsiveness of pituitary to galanin throughout the reproductive cycle of male European sea bass (Dicentrarchus labrax)

The neuropeptide galanin (Gal) is a putative factor regulating puberty onset and reproduction through its actions on the pituitary. The present study investigated the pituitary responsiveness to galanin and the patterns of galanin receptors (Galrs) expression throughout the reproductive cycle of two years old male European sea bass (Dicentrarchus labrax), an important aquaculture species. Quantitative analysis of pituitary and hypothalamus transcript expression of four galr subtypes revealed differential regulation according to the testicular developmental stage, with an overall decrease in expression from the immature stage to the mid-recrudescence stage. Incubation of pituitary cells with mammalian 1-29Gal peptide induced significant changes in cAMP concentration, with sensitivities that varied according to the testicular development stages. Furthermore 1-29Gal was able to stimulate both follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) release from pituitary cell suspensions. The magnitude of the effects and effective concentrations varied according to reproductive stage, with generalized induction of Fsh and Lh release in animals sampled in January (full spermiation). The differential expression of galrs in pituitary and hypothalamus across the reproductive season, together with the differential effects of Gal on gonadotropins release in vitro strongly suggests the involvement of the galaninergic system in the regulation the hypothalamus-pituitary-gonad axis of male sea bass. This is to our knowledge the first clear evidence for the involvement of galanin in the regulation of reproduction in non-mammalian vertebrates.

Role of Isotocin in the Regulation of the Hypophysiotropic Dopamine Neurones in the Preoptic Area of the Catfish, Clarias batrachus

Dopamine (DA) has emerged as a potent inhibitory neuromodulator of luteinsing hormone (LH) secretion and reproduction in teleosts. The DA neurones located in the anterior subdivision of nucleus preopticus periventricularis (NPPa) in the preoptic area (POA) innervate the pituitary gland and regulate LH cells. Although a reduction in the inhibitory DAergic tone is crucial for stimulatory action of gonadotrophin-releasing hormone (GnRH) on LH cells, the role of other hypothalamic factors is suggested but not fully understood. Nonapeptide, isotocin (IST) has emerged as a likely candidate that may also influence the LH cell function. IST neurones reside in the nucleus preopticus and innervate LH cells. While IST treatment dramatically elevated LH secretion, the IST levels in brain peaked during spawning. In a pilot study on the catfish, Clarias batrachus, we observed a dense network of IST-immunoreactive (IST-IR) fibres in the NPPa, the region known to harbour hypophysiotropic DA neurones. Application of the double immunofluorescence method showed a dense IST-IR fibre network around the tyrosine hydroxylase-immunoreactive (TH-IR) neurones in the NPPa region. A great majority of the TH-IR neurones in the NPPa were contacted by IST-IR fibres during the spawning phase. The NPPa therefore appears to be a site for the intense interaction of DA and IST. IST-IR fibre innervation in NPPa showed reproduction phase-dependent changes. The percent fluorescent area of IST-IR fibres showed a gradual increase from the resting through prespawning phases (resting: 7.5 ± 1.04; preparatory: 8.6 ± 0.8; prespawning: 15.5 ± 1.4), reaching a peak in the spawning phase (28 ± 2.3; P < 0.001). Compared to the spawning phase, a drastic reduction in IST-IR fibres in the NPPa was observed during the postspawning phase (8.4 ± 0.9; P < 0.001). Superfused slices of the POA of C. batrachus treated with IST peptide resulted in a significant reduction in TH immunoreactivity in the NPPa (Control: 45.3 ± 4.2; IST peptide, 5 μm: 29.4 ± 4.7; P < 0.05). We suggest that the intense interaction between IST and DA in the NPPa, most probably of an inhibitory nature, may be critical for the regulation of LH cells and reproduction in teleosts.

Sexual dimorphism in the hypophysiotropic tyrosine hydroxylase-positive neurons in the preoptic area of the teleost, Clarias batrachus

BACKGROUND

Dopamine (DA) neurons in the anteroventral periventricular nucleus (AVPV) in the preoptic area (POA) of mammals express estrogen receptors, regulate luteinizing hormone (LH) secretion, and show distinct sexual dimorphism. In teleosts, hypophysiotropic DA neurons of the nucleus preopticus periventricularis (NPP), located in the anteroventral POA, express estrogen receptors, innervate LH cells, and emerged as a neuroanatomical substrate for inhibiting LH cells. Interestingly, the NPP and AVPV seem to share several similarities. Whether DAergic neurons in the NPP show sexual dimorphism is, however, not known. Based on the proposed homology to AVPV and previous studies showing greater tyrosine hydroxylase (TH) mRNA and enzyme activity levels in the brain of female catfish, we hypothesize that females have greater number of DAergic neurons in the NPP and correspondingly more TH-immunoreactive fiber innervation of the pituitary.

METHODS

Adult, male and female Clarias batrachus collected during the prespawning phase of their reproductive cycle were used. Fish were anesthetized and perfused transcardially with phosphate-buffered saline (pH 7.4) and 4 % paraformaldehyde in phosphate buffer. Sections through the rostro-caudal extent of the POA and pituitary were processed for TH immunofluorescence. Using double immunofluorescence, the association between TH-immunoreactive fibers and LH cells in the pituitary was explored. Sections were analyzed using semiquantitative analysis.

RESULTS

NPP in POA of C. batrachus has two distinct subdivisions, viz, anterior (NPPa) and posterior (NPPp), and TH neurons were observed in both the subdivisions. Compared to that in the males, a significantly higher (P < 0.05) number of TH neurons was consistently observed in the NPPa of females. TH neurons in NPPp, however, showed no difference in the number or immunoreactivity. Since DA neurons in NPPa are hypophysiotropic, we compared TH-fiber innervation of the pituitary in both sexes. Compared to males, proximal pars distalis and LH cells in this region of the pituitary in females were densely innervated by TH fibers.

CONCLUSIONS

Neurons of NPPa and their innervation to the pituitary seem to be a distinct sexually dimorphic DAergic system in C. batrachus. The DAergic system may serve as a component of the neural mechanisms controlling the sexually dimorphic LH surge in teleosts. Given the similarities shared by NPPa and AVPV, homology between these two nuclei is suggested.

Naltrexone attenuates stress-induced suppression of LH secretion in the pituitary gland in the Cichlid fish Oreochromis mossambicus: evidence for the opioidergic mediation of reproductive stress response

Opioid peptide β-endorphin (β-EP) plays a modulatory role in vertebrate reproduction. However, the role of opioid peptides in reproductive stress response is least understood in fishes. The aim of the present study was to determine the effect of different doses of β-EP on luteinizing hormone (LH) secretion in normal and the opioid receptor antagonist naltrexone (NALT) in stressed female tilapia Oreochromis mossambicus. Administration of 4 μg β-EP, but not 0.5 or 1.5 μg β-EP, daily for 22 days caused suppression of LH-secreting cells at the proximal pars distalis of the pituitary gland, concomitant with a significant reduction in the mean GSI and HSI in 4 μg β-EP-treated fish compared to controls. On the other hand, exposure of the fish to mild acute stressors for 22 days caused changes in the LH-secreting cells similar to that of high dose of β-EP, whereas administration of NALT attenuated these effects. Taken together, the results indicate that increased concentration of β-EP as may occur during stressful conditions can cause suppression of LH secretion, leading to the inhibition of spawning, and that treatment of NALT attenuates the stress-induced inhibition of LH secretion in fish.

Orexin-B-like immunoreactivity localizes in both luteinizing-hormone-containing cells and melanin-concentrating hormone-containing fibers in the red-bellied piranha (Pygocentrus nattereri) pituitary

We examined orexin-like immunoreactivity in the pituitary of the red-bellied piranha (Pygocentrus nattereri). Orexin-B-immunoreactive (IR) cells corresponded to luteinizing hormone (LH)-containing cells in the pars distalis, and orexin-B-IR fibers corresponded to melanin-concentrating hormone (MCH)-containing fibers in the pars nervosa. In the pars distalis, orexin-B-IR puncta that were also immunoreactive for MCH were observed around the orexin-B-IR cells. In the ventral hypothalamus, orexin-B-IR and MCH-IR neurons were found in the nucleus lateralis tuberis. Immunoelectron-microscopic analysis revealed that the orexin-B-like substance co-localized with LH in secretory granules and with MCH in MCH-containing neurons. Some of the MCH secreted in the pituitary might participate in the modulation of LH secretion from the gonadotrophs, together with orexin-B, leading to food intake by the stimulation of growth hormone secretion from the somatotrophs.

Interaction between dopamine- and isotocin-containing neurones in the preoptic area of the catfish, Clarias batrachus: role in the regulation of luteinising hormone cells

Apart from gonadotrophin-releasing hormone (GnRH) and dopamine (DA), oxytocin has emerged as an important endogenous agent that regulates reproduction. Although the interaction between these factors has been extensively studied in mammals, parallel information in teleosts is much limited. We studied the organisation of tyrosine hydroxylase (TH; a marker for dopamine) and isotocin neurones in the preoptic area (POA) and hypothalamus of the catfish, Clarias batrachus and its implication in the regulation of luteinising hormone (LH) cells in the pituitary. Nucleus preopticus periventricularis (NPP), a major dopaminergic centre in the brain, consists of anterior (NPPa) and posterior (NPPp) subdivisions. Using retrograde neuronal tracing, we found that majority of the DA neurones in NPPa, but none from NPPp, project to the pituitary. The nucleus preopticus (NPO) of C. batrachus contains a conspicuous assemblage of large isotocin-positive neurones. It consists of a paraventricular subdivision (NPOpv) located on either side of the third ventricle and lies roughly sandwiched between the dopaminergic neurones of NPPa and NPPp. An additional subset of isotocin neurones was located above the optic chiasm in the supraoptic subdivision of the NPO (NPOso). Isotocin-containing neurones in both the subdivisions of NPO were densely innervated by DA fibres. Superfusion of the POA-containing brain slices with DA D(1) -like receptor agonist (SKF-38393) resulted in significant increase in isotocin immunoreactivity in the NPOpv neurones; NPOso neurones did not respond. However, treatment with DA D(2) -like receptor agonist (quinpirole) reduced isotocin immunoreactivity in the NPOso, but not in the NPOpv. Thus, DA appears to differentially regulate the components of isotocinergic system. Isotocin fibres extend to the pituitary and terminate on LH cells and the superfused pituitary slices treated with isotocin caused significant reduction in LHβ-immunoreactivity. An elaborate interplay between the DA and isotocin systems appears to be an important component of the LH regulatory system.

Galanin systems in non-mammalian vertebrates with special focus on fishes

Galanin is a well characterized multifunctional neuropeptide in mammals. Galanin has been identified from several fishes, amphibians, reptiles and birds. A large set of data is available on galanin-like protein distribution and peptide and/or mRNA sequences in non-mammalian vertebrates. Galanin receptor sequences from fishes and birds are known, but its distribution and mechanisms of actions are poorly understood. While some biological actions of galanin are known in non-mammals, the functional role of galanin in lower vertebrates is limited. For example, galanin has been shown to regulate feeding, pituitary hormone secretion and gut motility in fishes. Several aspects of galanin biology remain unknown, yet, there is enough evidence to implicate galanin as an important physiological modulator in lower vertebrates. Majority of the research articles on galanin in non-mammals arise from studies that used fishes. The objective of this chapter is to provide a summarized discussion of current knowledge on galanin peptide and gene sequences and organization, distribution of galanin gene and protein, and physiological functions of galanin in non-mammalian vertebrates with a special focus on fishes.

Sex and temporal variations of the vasotocin neuronal system in the damselfish brain

The neuropeptide vasotocin (VT) is an important regulator of reproduction and social behaviors, and hypothesized to function as a neuromodulator of sensory and motor processing. In adult fishes, VT is primarily produced in three different cell groups (parvocellular, magnocellular, and gigantocellular) within preoptic nuclei, but little is known about sex and seasonal variations of these somata and their relationship to sensory and motor processing. I used immunocytochemistry to (1) test for sex and seasonal variations in VT-immunoreactive (-ir) somata number, size, and fiber densities in the brain of a soniferous damselfish, and (2) test the hypothesis that VT-ir axons project to and vary seasonally in sensory and motor regions of the brain. Sex differences in somata number and size were restricted to parvocellular neurons, while seasonal variations were found within parvocellular and gigantocellular, but not magnocellular neurons. Both males and females had more gigantocellular neurons during peak spawning compared to other times. VT-ir fibers were most abundant in sensory and motor processing regions of the auditory-mechanosensory torus semicircularis (TS), facial lobe, and vagal motor nucleus (VMN), while sparse innervation was found to the tectum and hindbrain auditory and mechanosensory nuclei. VT-ir fiber densities in the TS and VMN were higher during peak spawning, and correlated with gigantocellular (TS, VMN) and parvocellular (TS) somata number. These results provide neuroanatomical support for a relationship between temporal changes in specific VT somata and projections to some sensory and motor processing regions in the damselfish brain that may influence complex communicative and social behaviors.

Endocrine effects of growth hormone overexpression in transgenic coho salmon

Non-transgenic (wild-type) coho salmon (Oncorhynchus kisutch), growth hormone (GH) transgenic salmon (with highly elevated growth rates), and GH transgenic salmon pair fed a non-transgenic ration level (and thus growing at the non-transgenic rate) were examined for plasma hormone concentrations, and liver, muscle, hypothalamus, telencephalon, and pituitary mRNA levels. GH transgenic salmon exhibited increased plasma GH levels, and enhanced liver, muscle and hypothalamic GH mRNA levels. Insulin-like growth factor-I (IGF-I) in plasma, and growth hormone receptor (GHR) and IGF-I mRNA levels in liver and muscle, were higher in fully fed transgenic than non-transgenic fish. GHR mRNA levels in transgenic fish were unaffected by ration-restriction, whereas plasma GH was increased and plasma IGF-I and liver IGF-I mRNA were decreased to wild-type levels. These data reveal that strong nutritional modulation of IGF-I production remains even in the presence of constitutive ectopic GH expression in these transgenic fish. Liver GHR membrane protein levels were not different from controls, whereas, in muscle, GHR levels were elevated approximately 5-fold in transgenic fish. Paracrine stimulation of IGF-I by ectopic GH production in non-pituitary tissues is suggested by increased basal cartilage sulphation observed in the transgenic salmon. Levels of mRNA for growth hormone-releasing hormone (GHRH) and cholecystokinin (CCK) did not differ between groups. Despite its role in appetite stimulation, neuropeptide Y (NPY) mRNA was not found to be elevated in transgenic groups.

Distribution of somatostatin-like immunoreactivity in the brain of the caecilian Dermophis mexicanus (Amphibia: Gymnophiona): comparative aspects in amphibians

The organization of the somatostatin-like-immunoreactive (SOM-ir) structures in the brain of anuran and urodele amphibians has been well documented, and significant differences were noted between the two amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study, we analyzed the anatomical distribution of SOM-ir cells and fibers in the brain of the gymnophionan Dermophis mexicanus. In addition, because of its known relationship with catecholamines in other vertebrates, double immunostaining for SOM and tyrosine hydroxylase was used to investigate this situation in the gymnophionan. Abundant SOM-ir cell bodies and fibers were widely distributed throughout the brain. In the telencephalon, pallial and subpallial cells were labeled, being most numerous in the medial pallium and amygdaloid region. Most of the SOM-ir neurons were found in the preoptic area and hypothalamus and showed a clear projection to the median eminence. Less conspicuously, SOM-ir structures were found in the thalamus, tectum, tegmentum, and reticular formation. Both SOM-ir cells and fibers were demonstrated in the spinal cord. The double-immunohistofluorescence technique revealed that catecholaminergic neurons and SOM-ir cells are largely intermingled in many brain regions but form totally separated populations. Many differences were found between the distribution of SOM-ir structures in Dermophis and that in anurans or urodeles. Some features were shared only with anurans, such as the abundant pallial SOM-ir cells, whereas others were common only to urodeles, such as the organization of the hypothalamohypophysial SOM-ir system. In addition, some characteristics were found only in Dermophis, such as the localization of the SOM-ir spinal cells and the lack of colocalization of catecholamines and SOM throughout the brain. Therefore, any conclusions concerning the SOM system in amphibians are incomplete without considering evidence for gymnophionans.

Reproduction phase-related variations in neuropeptide Y immunoreactivity in the olfactory system, forebrain, and pituitary of the female catfish,Clarias batrachus (Linn.)

The aim of this study was to determine whether neuropeptide Y (NPY) immunoreactivity in the cells and fibers in the forebrain and pituitary of Clarias batrachus is linked to the annual reproductive cycle. A steady rise in luteinizing hormone (LH) immunoreactivity was seen in the pituitary through preparatory (February-April) and prespawning (May-June) phases; it was greatly reduced during spawning (July-August; P < 0.001) and partially replenished during postspawning (September-November; P < 0.01) through resting (December-January) phases. Although NPY immunoreactivity in olfactory receptor neurons and olfactory nerve layer in olfactory bulb was gradually augmented during resting through prespawning phases (P < 0.001), attaining a peak in spawning phase (P < 0.001), a dramatic decline was encountered during postspawning phase (P < 0.001). A similar pattern was also observed in NPY-containing fibers of the medial olfactory tract (MOT) and pituitary. However, a different pattern of NPY immunoreactivity was observed in the neurons of nucleus entopeduncularis (NE) and nucleus preopticus periventricularis (NPP). Whereas these neurons and fibers in the forebrain showed significant augmentation during the resting through prespawning phases (P < 0.001), the immunoreactivity dramatically declined during spawning (P < 0.001) and was partially replenished in the postspawning phase. Testosterone injection of juveniles significantly augmented (P < 0.001) NPY immunoreactivity in NE neurons. We suggest that NPY cells of NE and NPP, and related fiber systems, might be involved in processing of sex steroid-borne information and regulation of the gonadotropin-releasing hormone-LH axis.

Galanin and its binding sites in the brain of eels subjected to different osmolar conditions

A galanin (GAL)-like peptidergic system was investigated in the brain of Anguilla anguilla subjected to hyperosmolar and hypoosmolar conditions, by using antisera raised against porcine 1-29 GAL. A group of immunoreactive perikaria was identified in the periventricular hypothalamus, in the ventral thalamus, in the pretectal areas and in the optic tectum. Immunoreactive perikaria were present in the nucleus lateralis of the torus semicircularis in seawater (SW) adapted eels, and were absent in the freshwater (FW) adapted eels. Galaninergic fibres were observed in many areas of the brain. The immunoreactive perikaria and fibres, when localised in the same areas, were more strongly labelled and numerous in the SW adapted eels in comparison to the FW adapted animals. GAL-specific binding sites, investigated by autoradiography using iodinated porcine GAL, occurred in several regions of the brain, in particular in the dorsal telencephalon, in the dorsal thalamus and in the torus semicircularis, where a high density of binding sites was observed in the SW adapted eels. Conversely, a higher density of binding sites was observed in the caudal substantia reticularis and in the corpus cerebelli in the FW adapted eels. We conclude that different distributions and intensity in immunoreactive elements occur in response to the two environmental conditions.

Development of galanin-like immunoreactivity in the brain of the brown trout (Salmo trutta fario), with some observations on sexual dimorphism

The development of galanin-like immunoreactive (GAL-ir) cells and fibers was investigated in the brain of brown trout embryos, alevins, juveniles, and adults (some spontaneously releasing their gametes). The earliest GAL-ir neurons appeared in the preoptic region and the primordial hypothalamic lobe of 12-mm embryos. After hatching, new GAL-ir neurons appeared in the lateral, anterior, and posterior tuberal nuclei, and in late alevins, GAL-ir neurons appeared in the area postrema. In juveniles, further GAL-ir populations appeared in the nucleus subglomerulosus and magnocellular preoptic nucleus. The GAL-ir neuronal groups present in juveniles were also observed in sexually mature adults, although the area postrema of males lacked immunoreactive neurons. Moreover, spawning males exhibited GAL-ir somata in the olfactory bulb and habenula, which were never observed in adult females or in developing stages. In adults, numerous GAL-ir fibers were observed in the ventral telencephalon, preoptic area, hypothalamus, neurohypophysis, mesencephalic tegmentum, ventral rhombencephalon, and area postrema. Moderate to low GAL-ir innervation was seen in the olfactory bulbs, dorsomedial telencephalon, epithalamus, medial thalamus, optic tectum, cerebellum, and rhombencephalic alar plate. There were large differences among regions in the GAL-ir innervation establishment time. In embryos, GAL-ir fibers appeared in the preoptic area and hypothalamus, indicating early expression of galanin in hypophysiotrophic centers. The presence of galanin immunoreactivity in the olfactory, reproductive, visual, and sensory-motor centers of the brain suggest that galanin is involved in many other brain functions. Furthermore, the distribution of GAL-ir elements observed throughout trout development indicates that galaninergic system maturation continues until sexual maturity.

Differential expression and cellular localization of somatolactin-1 and -2 during early development in the gilthead sea bream

The patterns of expression of the somatolactin 1 and 2 (SL1 and SL2) transcripts were studied during the early development of the gilthead sea bream (Sparus aurata). Gene expression of SL1 and SL2 were detected in embryos and in larvae, although both transcripts presented different levels of expression. The SL1 transcripts in contrast to the SL2 transcripts presented high expression levels in embryos and younger larvae. Moreover, the SL2 transcripts were slightly present or absence in embryonic stage and the newly hatched larvae, respectively. The differences in the expression levels of SL1 and SL2 in embryos and larvae may be due to the fact that two distinct genes express both isoforms of the protein. Thus, both SLs may play different physiological roles throughout development. Moreover, the hybridization signals for SL1- and SL2-mRNAs were detected in 4-day-old larvae. Both in larvae and adults the somatolactotroph cells co-expressed both transcripts of SL and were located bordering the neurohypophysis in the pars intermedia.

Somatostatin-like immunoreactivity in the brain of the urodele amphibian Pleurodeles waltl. Colocalization with catecholamines and nitric oxide

The neuronal structures with somatostatin-like immunoreactivity have been studied in the brain of the urodele amphibian Pleurodeles waltl. Intense immunoreactivity was observed in neurons and fibers distributed throughout the brain. Within the telencephalon, the subpallial regions were densely labeled containing both cells and fibers, primarily in the striatum and amygdala. The majority of the somatostatin immunoreactive neurons were located in the preoptic area and hypothalamus, although less numerous cells were also found in the thalamus. A conspicuous innervation of the median eminence was revealed, which arises from the hypothalamic cell populations. In the brainstem, intense fiber labeling was present in the tectum and tegmentum, whereas cell bodies were located only in the tegmentum of the mesencephalon and in the interpeduncular, raphe and reticular nuclei of the rhombencephalon. Longitudinal fiber tracts throughout the brainstem were observed and they continued into the spinal cord in the laterodorsal funiculus. The localization of somatostatin in catecholaminergic and nitrergic neurons was studied by double labeling techniques with antisera against tyrosine hydroxylase and nitric oxide synthase. Catecholamines and somatostatin only colocalized in a cell population in the ventral preoptic area. In turn, the striatum and amygdala contained neurons with somatostatin and nitric oxide synthase. Our results demonstrated that the somatostatin neuronal system in the brain of Pleurodeles waltl is consistent with that observed in anuran amphibians and shares many characteristics with those of amniotes. Colocalization of somatostatin with catecholamines and nitric oxide is very restricted in the urodele brain, but in places that can be easily compared to those reported for mammals, suggesting that interactions between these neurotransmitter systems are a primitive feature shared by tetrapod vertebrates.

The hypothalamo-hypophyseal system of the white seabream Diplodus sargus: immunocytochemical identification of arginine-vasotocin, isotocin, melanin-concentrating hormone and corticotropin-releasing factor

The distribution of the neurosecretory hormones vasotocin, isotocin and melanin-concentrating hormone and the hypophysiotropic hormone corticotropin-releasing factor was studied in the hypothalamo-hypophyseal system of the white seabream (Diplodus sargus) using immunocytochemical techniques. Magnocellular and parvocellular perikarya immunoreactive for arginine-vasotocin and isotocin were present in the nucleus preopticus. Perikarya immunoreactive for arginine-vasotocin extended more caudally with respect to isotocin-immunoreactive perikarya. Parvocellular perikarya were located at rostroventral levels and magnocellular perikarya in the dorsocaudal portion of the nucleus. Arginine-vasotocin and isotocin did not coexist in the same neuron. Fibres immunoreactive for arginine-vasotocin and isotocin innervated all areas of neurohypophysis and terminate close to corticotropic and melanotropic cells. Perikarya immunoreactive for melanin-concentrating hormone and corticotropin-releasing factor were observed in the nucleus lateralis tuberis, with a few neurons in the nucleus periventricularis posterior. In addition, melanin-concentrating hormone immunoreactive perikarya were detected in the nucleus recessus lateralis. The preoptic nucleus did not show immunoreactivity for these antisera. Fibres showing melanin-concentrating hormone and corticotropin-releasing factor immunoreactivity ended close to the melanotropic and somatolactotrophic cells of the pars intermedia, and close to the corticotrophic cells of the rostral pars distalis.

Distribution of neuropeptide Y-like immunoreactivity in the brain of the Senegalese sole (Solea senegalensis)

We present the results of an immunohistochemical study aimed at localizing the neuropeptide Y (NPY) in the brain of the Senegalese sole, Solea senegalensis, using an antiserum raised against porcine NPY and the streptavidin-biotin-peroxidase method. In this species, we have identified immunoreactive cells in the ventral and dorsal telencephalon, caudal preoptic area, ventrocaudal hypothalamus, optic tectum, torus longitudinalis, synencephalon and isthmic region. NPY-immunoreactive fibers were profusely distributed throughout the brain, also reaching the adenohypophysis. The extensive distribution of NPY suggests an important role for this neuropeptide in a variety of physiological processes, including the neuroendocrine control of adenohypophyseal functions. Our results are compared with those obtained in other teleosts and discussed in relation to putative functions of NPY in the control of metabolism and reproduction in the Senegalese sole.

Peptide YY (PYY) and fish pancreatic peptide Y (PY) expression in the brain of the sea bass (Dicentrarchus labrax) as revealed by in situ hybridization

Tetrapod vertebrates express three neuropeptide Y (NPY)-related peptides: NPY, peptide YY (PYY), and pancreatic polypeptide (PP). Both NPY and PYY mRNA have been localized in the brain of tetrapods whereas PP expression is restricted to the pancreas. Some teleost fish commonly produce NPY and PYY but pancreatic peptide Y (PY) instead of PP. Both NPY and PYY mRNAs are widely distributed in the brain of non-tetrapod species, but no information about PY central expression is available. In the present study, molecular riboprobes were used to study PYY and PY mRNA central distribution in the sea bass (Dicentrarchus labrax). PYY and PY gene expression was predominantly detected within the sea bass forebrain. Telencephalic PYY gene expression was restricted to the ventral part of the ventral telencephalon, and no PY expression was detected in the cerebral hemispheres. Both PYY and PY mRNAs were found within the preoptic area and lateral hypothalamus. Distinct PY or PYY mRNA cell groups were localized in the pretectal area and synencephalon or posterior tubercle, respectively. Caudally, PY gene expression was found in the medial reticular formation, whereas PYY transcripts were localized within the vagal lobe. The results demonstrate that vertebrate brain expresses three NPY-related genes and further support the hypothesis that PP and PY arose by independent gene duplications from PYY. The receptor system of the NPY family as well as gene expression within the main hypophysiotropic and feeding behavior areas suggest an involvement of both peptides in the control of food intake and pituitary secretion.

Characterization of neuropeptide Y expression in the brain of a perciform fish, the sea bass (Dicentrarchus labrax)

The distribution of neuropeptide Y (NPY) gene expression was mapped in the brain of the sea bass (Dicentrarchus labrax) by in situ hybridization with 35S-UTP labeled cRNA probes. Gene expression was mainly detected within the forebrain, although NPY mRNA transcripts were also localized in the tectum and tegmentum mesencephali and posterior brain. New NPY-expressing nuclei were found in the dorsal and ventral telencephalon, preoptic area, tuberal hypothalamus, synencephalon, tegmentum mesencephali and posterior brain. The profuse NPY gene expression within the main neuroendocrine areas of the teleost fish further supports a physiological role in the control of the pituitary secretion. In addition, NPY gene was expressed within the primary visual, olfactory and gustatory circuits of teleost which, subsequently, project to hypothalamic feeding center in teleost fish. Our results extend the NPY-expressing areas known in teleost species.

Vasotocin innervation and modulation of vocal-acoustic circuitry in the teleost Porichthys notatus

Arginine vasotocin (AVT) and its mammalian homologue arginine vasopressin (AVP) modulate reproduction-related and other social behaviors in a broad range of vertebrate species. These functions of AVT/AVP may be in part achieved through the modulation of sensorimotor integration, although experimental evidence supporting this hypothesis remains limited. In the present experiments, we demonstrate (1) AVT innervation of candidate vocal-acoustic brain regions, and (2) AVT modulation of vocal-motor physiology in the plainfin midshipman fish (Porichthys notatus), which uses vocalizations in both mate attraction and agonistic contexts. AVT distribution was compared with known vocally active brain regions and to central auditory and vocal pathways. AVT-immunoreactive fibers and putative terminals descend almost exclusively from the preoptic area and are found in two primary candidate sites for vocal-acoustic integration - the anterior tuberal hypothalamus and paralemniscal midbrain tegmentum. AVT immunoreactivity is also located in several other vocally active regions, including the ventral tuberal nucleus, periaqueductal gray, and paraventricular regions of the isthmus and rostral hindbrain. The parvocellular preoptic area itself is also vocally active, although thresholds are substantially higher than for other regions. The functional significance of AVT input to vocal-acoustic regions was demonstrated in the paralemniscal midbrain where local delivery of AVT modulated electrically evoked, rhythmic vocal-motor output, which precisely mimicked natural vocalizations. AVT produced dose-dependent inhibitions of parameters associated with call initiation (burst latency and number of vocal-motor bursts elicited) but not of vocal-motor patterning (fundamental frequency and burst duration). Together, these findings provide support for the proposal that AVT modulates sensorimotor processes underlying social/acoustic communication.

cNeuropeptide Y family of peptides: Structure, anatomical expression, function, and molecular evolution

Evolutionary relationships between neuroendocrine peptides are often difficult to resolve across divergent phyla due to independent duplication events in different lineages. Thanks to peptide purification and molecular cloning in many different species, the situation is beginning to clear for the neuropeptide Y (NPY) family, which also includes peptide YY (PYY), the tetrapod pancreatic polypeptide (PP) and the fish pancreatic peptide Y (PY). It has long been assumed that the first duplication to occur in vertebrate evolution generated NPY and PYY, as both of these are found in all gnathostomes as well as lamprey. Evidence from other gene families show that this duplication was probably a chromosome duplication event. The origin of a second PYY peptide found in lamprey remains to be explained. Our recent cloning of NPY, PYY and PY in the sea bass proves that fish PY is a separate gene product. We favour the hypothesis that PY is a duplicate of the PYY gene and that it may have occurred late in fish evolution, as PY has so far only been found in acanthomorph fishes. Thus, this duplication seems to be independent of the one that generate PP from PYY in tetrapods, although both tetrapod PP and fish PY are expressed in the pancreas. Studies in the sea bass and other fish show that PY, in contrast to PP, is expressed in the nervous system. We review the literature on the distribution and functional aspects of the various NPY-family peptides in vertebrates.

Key words: neuropeptide Y, pancreatic polypeptide, fish pancreatic peptide, gene duplication.

Localization of galanin-like immunoreactive structures in the brain of the Senegalese sole, Solea senegalensis

The distribution of galanin-like immunoreactive structures was studied in the brain of the Senegalese sole, Solea senegalensis, using immunohistochemical methods. Periventricular immunoreactive cell bodies were observed in the rostral pole of the preoptic recess, within the pars parvocellularis of the nucleus preopticus parvocellularis. Another galanin-immunoreactive cell population was observed more caudal in the ventromedial hypothalamus, along the medial evaginations of the lateral recess. These cells appear within the cytoarchitectonic limits of the nucleus recessus lateralis pars ventralis. We found an extensive presence of galanin-immunoreactive fibres throughout the entire brain, although the most massive network of fibres was observed in the caudal olfactory bulbs, ventral telencephalon, preoptic area and around diencephalic ventricular recesses. Also, the hypophysis, ventricular mesencephalic area, median reticular formation and viscerosensory rhombencephalon displayed important plexuses of galanin-immunoreactive axons. The widespread distribution of these immunoreactive structures in the brain and pituitary of the Senegalese sole suggests an important role for galanin in neuroendocrine regulation of brain and adenohypophyseal functions.

Colocalization of GnRH binding sites with gonadotropin-, somatotropin-, somatolactin-, and prolactin-expressing pituitary cells of the pejerrey, Odontesthes bonariensis, in vitro

Previous studies in the pejerrey, Odontesthes bonariensis, have demonstrated that fibers with immunoreactivity to gonadotropin-releasing hormone (ir-GnRH) reach all areas of the pituitary gland, the rostral pars distalis (RPD), the proximal pars distalis (PPD), and the pars intemedia (PI). A close association was shown between ir-GnRH fibers and gonadotropin (GtH)-, growth hormone (GH)-, somatolactin (SL)-, and prolactin (PRL)-expressing cells. The presence of only one GnRH variant, suspected to be a novel form, has been shown in pituitary extracts of this fish. In addition, GnRH may stimulate GtHs, GH, SL, and PRL levels in different fish species. The objective of the present study was to seek GnRH receptors and therefore colocalization with GtHs, GH, SL, and PRL cells in O. bonariensis using a pituitary primary cell culture system. GnRH binding sites were revealed by autoradiography of an iodinated superactive GnRH agonist ([(125)I]GnRH-A) and pituitary cells were identified by immunocytochemistry using piscine antisera. Following autoradiography, silver grains representing specific [(125)I]GnRH-A binding were associated with anti GtH, GH, SL, and PRL positive cells. These results demonstrate the presence of GnRH binding sites on these cells. It is suggested that GnRH may play a wide role in the neuroendocrine control of different pituitary hormones in addition to the GtHs.

Evidence that corticotropin-releasing hormone acts as a growth hormone-releasing factor in a primitive teleost, the European eel (Anguilla anguilla)

The inhibitory control of growth hormone (GH) release by somatostatin (SRIH) has been conserved throughout vertebrate evolution. In contrast, the neuropeptides involved in the stimulatory control of GH vary according to species and/or physiological situations. We investigated the direct pituitary regulation of GH release in a primitive teleost, the European eel (Anguilla anguilla L.) at the juvenile stage. Short-term serum-free primary cultures of dispersed pituitary cells were used, and GH release was measured by an homologous radioimmunoassay. Whereas growth hormone-releasing hormone (GHRH), gonadotropin-releasing hormone (GnRH), thyrotropin-releasing hormone (TRH), neuropeptide Y (NPY) and cholecystokinin (CCK) failed to induce any change in GH release, corticotropin-releasing hormone (CRH) dose-dependently stimulated GH release with a significant effect at 1 nM and a maximal effect (> or =400% of controls at 24 h) at 100 nM. In agreement with our previous studies, PACAP also stimulated GH release but its maximal effect was lower than that of CRH. Proopiomelanocortin (POMC)-peptides, corticotropin (ACTH), melanotropin (alpha-MSH), beta-endorphin) had no effect on GH release, at any dose tested (0.1-1000 nM), indicating that the stimulatory effect of CRH on GH release by somatotrophs was not mediated by CRH-induced release of POMC-peptides from corticotrophs and melanotrophs. The CRH antagonist, alpha-helical CRH(9-41), significantly inhibited the stimulatory effect of CRH on GH release, suggesting the implication of specific CRH receptors related to mammalian ones. The stimulatory effect of CRH on GH release was reduced after 24 h of incubation, indicating a desensitization. In contrast, no desensitization to the inhibitory effect of SRIH was observed. SRIH inhibited CRH action in a dose-dependent manner. The effect of SRIH was overriding, 1 nM SRIH being able to abolish the effect of 1000 nM CRH. In conclusion, in the eel, CRH stimulates GH release directly at the pituitary cell level. GH and cortisol secretions could interact in controlling several physiological functions such as metabolism and ion exchange. This study suggests that CRH may have played an important early role in vertebrates co-ordinating the activation of various endocrine axes involved in metamorphosis, osmoregulation, stress and fasting. The stimulatory role of CRH on GH release may have been partially conserved during evolution, as it is found in some human physio-pathological situations such as stress, fasting and depression.

Immunohistochemical localization of corticotropin-releasing factor in the brain and corticotropin-releasing factor and thyrotropin-stimulating hormone in the pituitary of chinook salmon (Oncorhynchus tshawytscha)

This report describes the distribution of corticotropin-releasing factor (CRF)-like immunoreactivity in the brain and the contiguous localization of CRF- and thyrotropin-stimulating hormone (TSH)-like immunoreactivity in the pituitary of hatchery-reared, juvenile chinook salmon (Oncorhynchus tshawytscha). Results show that CRF-immunoreactive cell bodies exist in the parvocellular and magnocellular nuclei of the preoptic area and in a ventral hypothalamic region corresponding to the nucleus lateralis tuberis. CRF-immunoreactive fibers are observed along the rostral edge of the hypothalamus, in the pituitary stalk, and in the pituitary gland. Within the pituitary, CRF-immunoreactive fibers, with terminal-like boutons, were distinguishable in the neurohypophysis, pars distalis (PD), and pars intermedia (PI). In the PD, the CRF-immunoreactive fibers terminate in regions that contain TSH-positive pituitary cells. From this study, we conclude that CRF-immunoreactive fibers travel through, and terminate in, the neurohypophysis. CRF-immunoreactive fibers were also observed to terminate within the basement membrane and within the PD and PI of the adenohypophysis. Furthermore, the contiguous localization of CRF-immunoreactive fibers and TSH-immunoreactive pituitary cells suggests that CRF may mediate release of TSH.

Immunocytochemical study on the localization and distribution of the somatolactin cells in the pituitary gland and the brain of Oreochromis niloticus (Teleostei, cichlidae)

Using specific antibody for chum salmon somatolactin (SL), immunocytochemical studies were employed to determine the distribution of this hormone in the pituitary gland and the brain of Orechromis niloticus. The results indicated that the SL-immunoreactive (ir) cells are found in the pars intermedia (PI) of the pituitary gland. The SL-ir cells showed strong and specific immunoreactivity to anti-chum salmon SL. Moreover, SL-ir cells were found to be widely distributed in most brain regions. Most of the SL-ir cell bodies were scattered along a nearly continuous line extending posteriorly from the olfactory bulb to the medulla oblongata through the nucleus preopticus periventricularis, habenula, and midbrain tegmentum and ventral to the nucleus lateralis tuberis pars posterior through the nucleus preopticus basalis lateralis and organum vasculosum luminae terminalis. Also SL-ir cells were observed in the cerebellum. The synthetic and secretory activity of the SL-ir cells, in the pituitary and the brain, showed an increase during sexual maturation and spawning. The highly organized SL-containing system and the gradual stimulation of SL synthesis and release during sexual maturation and spawning of O. nilotcus suggest that SL may be involved in the control of some steps of reproductive processes.

Innervation and control of the adenohypophysis by hypothalamic peptidergic neurons in teleost fishes: EM immunohistochemical evidence

Previous light microscopic studies have revealed neuropeptide-immunoreactive neurosecretory fibers in the teleostean neurohypophysis, and ultrastructural work has reported direct innervation of endocrine cells by the terminals of fibers penetrating the adenohypophysis. This paper reviews our recent data from ultrastructural, immunohistochemical, receptor localization, and superfusion studies, which suggest a role for neuropeptides in the control of teleost pituitary secretion. We have used a combination of pre- and post-embedding electron microscopic immunolabeling methods to determine which neuropeptides are present in fibers innervating the pituitaries of three species: Poecilia latipinna, Dicentrarchus labrax, and Clarias gariepinus. Numerous axon profiles with immunoreactivity for the neurosecretory peptides vasotocin and isotocin formed large Herring bodies and terminal-like boutons in contact with corticotropic, growth hormone, thyrotropic, and pars intermedia cells. Numerous melanin-concentrating hormone-immunoreactive fibers and scarcer neurotensin and corticotropin-releasing factor-immunoreactive fibers showed similar distributions, terminating close to pars intermedia and corticotropic cells. Somatostatin, cholecystokinin, galanin, substance P, neuropeptide Y, growth hormone-releasing factor, thyrotropin-releasing hormone, and gonadotropin-releasing hormone-immunoreactivities were found in small calibre fibers penetrating among growth hormone, thyrotropic, and gonadotropic cells. These morphological findings have been supplemented by autoradiographic studies, which showed the distribution of binding sites for vasotocin, isotocin, galanin, and neuropeptide Y ligands over specific groups of pituitary cells, and superfusion studies that showed growth hormone release was stimulated by growth hormone-releasing factor and thyrotropin-releasing hormone, but inhibited by somatostatin. The implications of these results for neuropeptidergic control of teleostean pituitary secretions are discussed.

The localization of somatostatin receptor 1 (sst1) immunoreactivity in the rat brain using an N-terminal specific antibody

The biological actions of somatostatin are mediated via a family of G protein-coupled receptors named sst1 to sst5. We used an affinity-purified polyclonal antibody AS-65, directed against a specific N-terminal peptide sequence of sst1 to determine the immunohistochemical distribution of N-terminal sst1 immunoreactivity in the rat brain. The specificity of the antibody was shown by western blotting experiments using an N-terminal sst1 fusion protein. Enzymatic deglycosylation experiments were combined with blotting experiments on a sst1-transfected cell line and rat brain membrane proteins and with immunocytochemistry on an sst1-transfected cell line. These studies showed that the antibody detected the deglycosylated sst1 receptor protein. Immunohistochemical staining showed that sst1 immunoreactivity (presumably the deglycosylated receptor) recognised by this N-terminal antiserum was widely distributed throughout the brain with cells and processes labelled in the cerebral cortex, regions of the limbic system (including the hippocampal formation and some basal ganglia nuclei), the epithalamus, the thalamus, different subthalamic structures (subthalamic nucleus, zona incerta), the colliculi, the hypothalamus, the reticular formation, the cerebellum and regions of the trigeminal nerve complex. The distribution of immunoreactivity was in good general agreement with that predicted from the localization of sst1 messenger RNA and radioligand binding studies. This study on the immunohistochemical distribution of the sst1 receptor in the brain will provide a better understanding of the central actions of somatostatin at its receptor types.

Molecular cloning and expression of cDNA encoding brain preprocholecystokinin in goldfish

A cholecystokinin (CCK) precursor cDNA of 782 bp was identified from goldfish brain. The open reading frame (369 bp) encodes the 123 amino acid precursor which contains mono- and di-basic amino acid endoproteolytic cleavage, C-terminal alpha-amidation and tyrosyl sulfation sites. Expression studies revealed the presence of preproCCK mRNA in the gastrointestinal tract, pituitary and a wide range of brain areas from the olfactory bulbs to the posterior brain region. We have also confirmed the presence of CCK mRNA in the posterior ventrolateral hypothalamus by in situ hybridization, supporting a role of CCK in feeding behavior and regulation of pituitary hormone secretion.

Sexual dimorphism of galanin-like immunoreactivity in the brain and pituitary of goldfish, Carassius auratus

A sexually dimorphic distribution of galanin (GAL)-like immunoreactive (ir) neurons and fibers was found in the brain and pituitary of goldfish. The rostralmost GAL-ir perikarya were found in the area ventralis telencephali pars supracommissuralis dorsal to the anterior commissure. In the diencephalon, there was several GAL-ir perikarya in the nucleus preopticus periventricularis (NPP). Males had many GAL-ir perikarya in the nucleus preopticus pars parvocellularis (NPOpp) and isolated GAL-ir perikarya in the NPO pars magnocellularis, and lateral to the NPO; in females GAL-ir perikarya were not found in these sites. A large GAL-ir neuronal aggregation was observed in the nucleus lateralis tuberis pars posterioris (NLTp). Several ir perikarya were present in the nucleus posterioris tuberis; however, unlike in other regions the males revealed fewer neurons than females. Besides the established innervation of the pituitary gland by the NPP, NPO and NLT, the present study revealed GAL-ir perikarya of these nuclei apparently also innervating the telencephalon, thalamus, optic tectum, tegmentum and even some areas of the rhombencephalon. Isolated perikarya were found in the nucleus posterioris periventricularis, the dorsal vicinities of the nucleus recessus lateralis (NRL), nucleus recessus posterioris, and nucleus saccus vasculosus, and in the medulla oblongata ventral to the vagal lobes. In the pituitary gland, GAL-ir fibers ramify and terminate among the pars distalis cells. A small percentage of growth hormone-secreting cells colocalize GAL. In males, most GAL-ir cells of the proximal pars distalis (PPD) showed granular ir product in the entire cell, and some had one or two large granules; in females the ir PPD cells showed clusters of a few fine ir granules of uniform size in each. Sexual dimorphism was also found in the olfactory bulb, telencephalon, infundibulum, mesencephalic tegmentum, optic tectum and medulla oblongata, the males having a more extensive GAL-ir fiber system than the females. Galanin may play a role in both hypophysiotropic and motor functions.

Embryonic development of gonadotropin-releasing hormone neurons in the sockeye salmon

Immunocytochemistry and in situ hybridization were used to test the hypothesis that gonadotropin-releasing hormone (GnRH) neurons are formed in the olfactory placode during embryonic development in a salmonid, Oncorhynchus nerka. The development of GnRH neurons and the pituitary cell types was examined from 19 through 910 days after fertilization. Immunoreactive GnRH was first detected at 19 days in the cells of the olfactory placode. GnRH immunoreactivity was not detected in any other structure of the central nervous system at this age. By day 24, GnRH-immunoreactive neurons were seen in the apical, intermediate, and basal layers of the olfactory placode. From days 30 through 51, GnRH neurons were seen emerging from the epithelium, along the olfactory nerve, and at the rostral olfactory bulb. By day 41, GnRH immunoreactivity was lost in the nasal epithelium. In the 72-day-old fish, most of the GnRH neuronal population was found in ganglia of the nervus terminalis, at the cribriform bone (gCB), and at the rostral olfactory bulb (gROB). On day 293, a decrease in GnRH-immunoreactive neurons in the gCB and gROB was concomitant with an initial appearance of GnRH-immunoreactive neurons and fibers along the caudoventral olfactory bulb. By day 462, the distribution of GnRH neurons and fibers was almost similar to adults. In maturing adults (910 days), GnRH-immunoreactive neurons were rarely seen in the nasal regions, but were primarily found in the basal forebrain. GnRH fibers were widespread in the brain, proximal para distalis, and in the pars intermedia of the pituitary. Our study supports the notion that neurons expressing salmon-GnRH mRNA and peptide originate in the medial olfactory placode and migrate into the basal forebrain during development. The midbrain neurons did not express salmon-GnRH mRNA or peptide in the larval and juvenile fish.

Gonadotropin releasing hormone (GnRH) neurons project to growth hormone and somatolactin cells in the steelhead trout

Analysis of gene expression using gonadotropin-releasing hormone (GnRH) antisense oligonucleotide confirmed by immunocytochemical localization the occurrence of GnRH neurons along the nervus terminalis in the steelhead trout (Oncorhynchus mykiss). Double-label immunocytochemistry revealed the distribution of mammalian (m), salmon (s) and chicken II (cII)-type GnRHs and various pituitary hormones. Both sGnRH and mGnRH appeared to be colocalized in the same cells of the nervus terminalis. Chicken GnRH II-immunoreactivity was found only in fibers and terminals. In the younger fish [73 and 186 days after fertilization (DAF)] GnRH neurons were seen rostral to the olfactory bulb. A novel GnRH ganglion, along the nervus terminalis, was found at the cribiform bone (gCB). A few non-immunoreactive rounded cells were seen among the GnRH neurons. A second smaller ganglion was seen at the most rostrally located part of the ventromedial olfactory bulb (gROB). In the older fish (850 DAF) GnRH neurons were also observed in the basal forebrain. A small group of neurons (2-3 cells), at the caudoventromedial border of the olfactory bulb, formed the ganglion terminale. Occasionally isolated GnRH-immunoreactive cells were seen at the base of the olfactory epithelium, along the ventromedial margins of the olfactory nerve. GnRH-immunoreactive and GnRH mRNA expressing neurons were absent from midbrain regions at the ages observed. GnRH-immunoreactive fibers were present only in older fish. The pattern of distribution of fibers that were immunoreactive to all three forms of GnRH was identical. Fibers were seen along the medial side of the olfactory nerve, throughout the brain and in the pituitary, associated with growth hormone and somatolactin cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunolocalization of catecholamine enzymes, serotonin, dopamine and L-dopa in the brain of Dicentrarchus labrax (Teleostei)

Antisera to serotonin (5-HT), dopamine, and L-dopa, and to the catecholamine synthesizing enzymes, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyl transferase (PNMT), were used to localize monoamine containing neurones in the brain of Dicentrarchus labrax (sea bass). In the brain stem, 5-HT-immunoreactive (ir) neurones were recognized in the ventrolateral medulla, vagal motor area, medullary, and mesencephalic raphe nuclei and in the dorsolateral isthmal tegmentum. In the hypothalamus, liquor-contacting 5-HT neurones were seen in various regions of the paraventricular organ. Virtually all regions of the brain contained a dense innervation by 5-HT fibres and terminals. DBH-ir neurones were restricted to three brain stem areas: the locus coeruleus, the area postrema, and the reticular formation of the lower medulla. Neurones in these three groups also displayed TH-ir, and in the latter area, PNMT-ir in addition. In the locus coeruleus and area postrema, TH-ir neurones outnumbered DBH-ir neurones, an observation substantiated by the presence of dopamine-ir neurones. In the forebrain, dopamine- and TH-ir neurones were found in the olfactory bulb, ventral/central telencephalon, periventricular preoptic, and suprachiasmatic areas, dorsolateral and ventromedial thalamus, and posterior tuberal nucleus. In the paraventricular organ, the distribution and morphology of dopamine-ir neurones was similar to that observed with anti-5-HT, but the vast majority of cells were not TH-ir, suggesting accumulation of dopamine by uptake from the ventricle, rather than by synthesis. L-dopa-ir neurones were found only in the central telencephalon, preoptic recess, and dorsolateral thalamus. Fibres and terminals immunoreactive for dopamine, TH, and DBH showed a broadly similar distribution. The results are discussed in relation to the monoaminergic systems previously reported in other teleostean species and the mammalian brain.

Galanin receptors in the brain of a teleost: autoradiographic distribution of binding sites in the Atlantic salmon

The distribution of galanin (GAL) binding sites in the brain of the Atlantic salmon (Salmo salar) was investigated by means of radioligand binding in conjunction with autoradiography by using high-performance liquid chromatography (HPLC) characterized radio-iodinated porcine galanin ([125I]GAL). On slide-mounted sections of frozen salmon brain homogenate, [125I]GAL (4 nM) bound rapidly and reversibly to a single population of sites with a Kd of 1.0 +/- 0.08 nM (n = 3) and Bmax of 2.38 +/- 0.19 fmol/mg wet tissue. Specific [125I]GAL binding was found in cellular regions, in fiber tracts, and in neuropil areas throughout the brain, except for in the olfactory bulb, pineal organ, and cerebellum. Autoradiographic microdensitometric measurements revealed high total [125I]GAL binding in the ventral hypothalamus (inferior lobes; around 7-12 fmol/mg tissue), the dorsal spinal cord (between 6 and 12 fmol/mg tissue), sublayers of the optic tectum (around 8 fmol/mg), torus semicircularis (around 7 fmol/mg), and glomerular complex (around 6 fmol/mg). Intermediate densities of [125I]GAL binding (3-5 fmol/mg tissue) were found in the pituitary, telencephalon, dorsolateral thalamic nucleus, and raphe nuclei and in association with the forebrain bundles. Except for in the optic tectum, there is a good concordance of [125I]GAL binding sites and GAL-immunoreactive fiber projections in most brain areas of the salmon. The wide distribution of GAL binding sites provides further evidence that a GAL-like substance might be involved in a diversity of brain functions of teleosts. The topographic distribution of target sites in the hypothalamo-hypophyseal axis indicates that GAL-like substances may have both direct and indirect effect on pituitary functions while in extrahypothalamic areas, functional implications by GAL may include involvement in somatosensory, central gustatory, olfactory, and visual functions. This study provides evidence for the presence of a specific GAL receptor in the brain of the Atlantic salmon. Together the distribution of GAL binding and GAL-like molecules provide a covering delineation of the GAL neuronal system in the brain of the Atlantic salmon. Comparisons with mammals suggest that the GAL receptor molecule has been well preserved during evolution and that GAL-like substances may be present, and even possess similar functional properties, throughout the vertebrate phylogeny.

Distribution of somatostatin-immunoreactivity in the brain of the larval lamprey (Petromyzon marinus)

The detailed distribution of somatostatinergic neurons and fibre tracts in the brain of larval lamprey was studied in serially sectioned material using immunocytochemical techniques. Neurons were found to be arranged in four nuclei: a hypothalamic nucleus consisting of both small cerebrospinal fluid-contacting neurons and larger non-contacting neurons, a thalamomesencephalic nucleus and two isthmotrigeminal reticular nuclei. The hypothalamic nucleus is the first to differentiate. Analysis of young larvae showed that somatostatin-immunoreactivity first appeared in hypothalamic cells (12 mm larvae), while it appeared later in the other nuclei. The different somatostatin-immunoreactive fibre tracts innervate different regions of the brain. In addition, somatostatin-immunoreactive fibres originating from hypothalamic neurons were found in the anterior neurohypophysis, which suggests the presence of a hypothalamohypophysial somatostatinergic system in lampreys.

FMRFamide-like immunoreactivity in the brain and pituitary of the goldfish, Carassius auratus

The distribution of FMRFamide-like immunoreactivity was determined in the brain and the pituitary of the goldfish, Carassius auratus. Immunoreactive perikarya were observed in the olfactory nerve, nucleus entopeduncularis, nucleus anterioris periventricularis, nucleus posterioris periventricularis, lateral part of the nucleus lateralis tuberis pars posterioris, midbrain tegmentum, and medulla oblongata. Immunoreactive fibers were widely distributed in the brain, in particular in the ventral telencephalon and the hypothalamus. A few immunoreactive nerve fibers were observed in the pituitary. The findings are discussed in relation to male sexual behavior and the involvement of FMRFamide-like peptide in pituitary functions in the goldfish.

Comparative distribution of substance P (SP) and cholecystokinin (CCK) binding sites and immunoreactivity in the brain of the sea bass (Dicentrarchus labrax)

Specific binding sites for cholecystokinin (CCK) and substance P (SP) were detected in the brain of a marine teleost fish, the sea bass, after in vitro incubation of tissue sections with the tritiated peptides and light microscopic autoradiography. Specific binding sites for [3H]-CCK were detected in the dorsal and ventral telencephalon, in the preoptic, tuberal and posterior hypothalamus, in the optic tectum, in the valvulla cerebelli, in the vagal lobe and further in a dorsal location in the medulla oblongata. Areas rich in [3H]-SP binding were located in the ventral telencephalon, in the entire hypothalamic and thalamic region, in the midbrain tegmentum, in the optic tectum, in the valvulla cerebelli and in the medulla oblongata. The distribution of these binding sites seemed to match fairly well with the location of the corresponding immunoreactive elements, although some minor mismatches could be observed. These autoradiographic findings provide the first anatomical evidence for the presence of CCK-like and SP-like binding sites in the brain of a teleost fish.

Immunocytochemical localization of a galanin-like peptidergic system in the brain and pituitary of some teleost fish

Immunostaining of brain and pituitary sections of teleost fishes (eels, salmonidae, cyprinidae, gourami, sculpin, mullet) with anti porcine galanin (GAL) revealed the presence of immunoreactive (ir) perikarya and a rich network of fibers. Ir-perikarya were located rostrodorsally to the recessus preopticus, and in the posterior tuberal hypothalamus. Ir-fibers were abundant in basal telencephalon and around diencephalic ventricular recesses but never contacted their lumen. Furthermore, they were observed in basal hypothalamus, brainstem and ventral medulla. Ir-fibers passed along corticotropic (ACTH), gonadotropic cells and somatotropes (GH cells) in eel and trout pars distalis, but rarely ended in caudal neurohypophysis. In goldfish pituitary ir-fibers occurred in neural digitations and among different cell types which however did not contain a GAL-like peptide. The relation GAL fibers/GH cells appeared more evident in species with a high growth rate. The other species showed a similar distribution of brain GAL. In eels and trout, ir-perikarya were not observed in areas containing somatostatin, GH- and ACTH-releasing factor, and ACTH-like perikarya, suggesting that GAL did not coexist with these peptides. The widespread distribution of a GAL-like peptide in teleost brain suggests that it could play a role of neurotransmitter and/or neuromodulator and regulate the secretion of adenohypophysial hormone(s).

Immunoaffinity purification and partial characterization of sea bass (Dicentrarchus labrax) growth hormone

Growth hormone (GH) was isolated from sea bass (Dicentrarchus labrax) pituitary extract by a simple one-step procedure involving immunoaffinity chromatography. A monoclonal antibody raised against chicken GH and found to immunostain very specifically the GH cells in the pituitary of the sea bass was coupled to CNBr-activated Sepharose 4B. Sea bass pituitary extracts were run on the affinity column, and the eluted material was analyzed on reversed-phase HPLC and found to consist of one single peak. The yield of purified hormone was 2.4 mg/g pituitary. Two monomeric forms (MW = 20,000 and 22,000 Da) of sea bass GH were identified by gel electrophoresis. Gel electrofocusing revealed apparent isoelectric points of 6.15, 6.50, and 6.95. Amino acid composition is consistent with other vertebrate GHs. The immunological relatedness was tested by immunoblotting using antisera raised against GH of different species. Polyclonal antisera raised against the isolated hormone exhibited a specific labeling of the GH cells in sea bass pituitary sections as well as of the immunoblotted purified GH.

Galanin-like immunoreactivity in the brain of teleosts: distribution and relation to substance P, vasotocin, and isotocin in the Atlantic salmon (Salmo salar)

The presence of galanin-like substances and their relation to substance P-, vasotocin-, and isotocin-immunoreactive neurons and fibers in the brain of teleosts was investigated with immunohistochemical methods. Two specific antisera against synthetic porcine galanin (GAL) revealed cell bodies and fibers in the brain of four different teleost species (Salmo salar, Carassius carassius, Gasterosteus aculeatus, and Anguilla anguilla). In all four species the main location of galanin immunoreactivity was in the hypothalamo-pituitary region. A detailed study of the distribution of galanin immunoreactivity in S. salar showed that galanin immunoreactive (GALir) perikarya were present in the nucleus preopticus periventricularis, an area that may be compared to the supraoptic nucleus in mammals, and in the nucleus lateralis tuberis, a nucleus involved in pituitary control in fishes that may be compared with the arcuate nucleus in mammals. GALir perikarya were found also in the nucleus recessus lateralis and in the nucleus recessus posterior. Numerous GALir fibers were present in the telencephalon and diencephalon, whereas only small numbers of fibers were found in the brainstem. In contrast to the situation in mammals, no GALir perikarya were observed in the brainstem areas corresponding to the noradrenergic locus coeruleus and serotonergic raphe nuclei in S. salar. We did not find any coexistence of GALir substances with arginine vasotocin or isotocin in neurosecretory neurons, as has been shown for galanin with the mammalian counterparts vasopressin and oxytocin. Also, the galanin-like substance(s) and their structurally closest related peptide family, the tachykinins, belong to separate neuronal systems in teleosts. The presence of GALir neurons in brain areas known to be involved in pituitary control, and a massive GALir innervation of the pituitary, strongly indicate a role for galanin-like substances in pituitary control also in teleosts. Furthermore, the presence of extrahypothalamic GALir fibers suggests involvement of galanin-like substances in other brain functions in teleosts. In conclusion, there are general similarities between teleosts and mammals concerning the distribution of galanin-like substances. However, there seem to be substantial differences in their distribution relative to functionally related peptides within the hypothalamo-pituitary system. Whereas galanin appears to be colocalized and released together with vasopressin and oxytocin in mammals, in teleosts the homologous substances are contained within different sets of neurons that innervate the same target, the pituitary.

Autoradiographic distribution of galanin binding sites in the brain and pituitary of the sea bass (Dicentrarchus labrax)

Specific binding sites for galanin (GAL) were detected in brain and pituitary of a marine teleost fish, the sea bass, after in vitro incubation of tissue sections with [125I]GAL and light microscopic autoradiography. Binding conditions were optimized and as a result the binding was saturable and specific. In the brain, [125I]GAL binding was found to occur in all parts of the dorsal and ventral telencephalon, in the anterior, tuberal and posterior hypothalamus, in the thalamus and in the tectum opticum, in the inferior lobe and in the ventral medulla oblongata. In the pituitary dense [125I]GAL binding was confined to the area occupied by the prolactin cells in the rostral part of the adenohypophysis. These findings provide the first anatomical evidence for the presence of GAL specific binding sites in the teleost brain and pituitary.