Neurotensin-like immunoreactivity in the pituitary and hypothalamus of bony fishes

A ligand-receptor interactome atlas of the zebrafish

Studies in zebrafish can unravel the functions of cellular communication and thus identify novel bench-to-bedside drugs targeting cellular communication signaling molecules. Due to the incomplete annotation of zebrafish proteome, the knowledge of zebrafish receptors, ligands, and tools to explore their interactome is limited. To address this gap, we de novo predicted the cellular localization of zebrafish reference proteome using deep learning algorithm. We combined the predicted and existing annotations on cellular localization of zebrafish proteins and created repositories of zebrafish ligands, membrane receptome, and interactome as well as associated diseases and targeting drugs. Unlike other tools, our interactome atlas is based on both the physical interaction data of zebrafish proteome and existing human ligand-receptor pair databases. The resources are available as R and Python scripts. DanioTalk provides a novel resource for researchers interested in targeting cellular communication in zebrafish, as we demonstrate in applications studying synapse and axo-glial interactome. DanioTalk methodology can be applied to build and explore the ligand-receptor atlas of other non-mammalian model organisms.

Neurotensin-like Peptides in the CNS of Lampreys: Chromatographic Characterization and Immunohistochemical Localization with Reference to Aminergic Markers

Neurotensin (NT)-like peptides in the CNS of the lamprey Lampetra fluviatilis were studied by radioimmunoassay (C-terminal specific NT antiserum), reverse-phase HPLC and immunohistochemistry. Multiple peaks of NT-immunoreactive (-ir) material were observed upon HPLC, of which a major peak eluted in the position of bovine NT. Immunofluorescence histochemistry showed that a monoclonal antibody recognizing the N-terminal (1 - 11) fragment of NT, as well as two polyclonal NT antisera labelled a large number of cell bodies in the periventricular area of hypothalamus, including the postinfundibular commissural nucleus and the ventral and dorsal hypothalamic nuclei. Additional groups of NT-ir cells were observed in the preoptic nucleus, the postoptic commissural nucleus, the mesencephalic tegmentum (L.fluviatilis), and in the spinal cord (L.fluviatilis and Ichtyomyzon unicuspis). Dense NT-ir fibre plexuses were present in the caudal hypothalamus, corpus striatum, ventral mesencephalon, and in the dorsal horn and lateral margin of the spinal cord. At the ultrastructural level the lateral spinal margin showed NT-ir terminal structures, which in most cases were not associated with synaptic specializations, although occasional synaptic contacts with unlabelled elements were found. The relation between NT-ir and monoamine-containing cells was examined with immunofluorescence double-staining, using antisera to tyrosine hydroxylase (TH), 5-hydroxytryptamine (5-HT), and histamine respectively. In the periventricular nuclei of hypothalamus numerous TH-, 5-HT-, as well as histamine-ir cells were located in close association with NT-ir cells, but none of the aminergic markers could be detected within NT-ir neurons. The chemical properties as well as the anatomical distribution of lamprey NT-like peptides show several similarities with those present in mammals, suggesting that NT-containing neuronal systems in the CNS developed early in vertebrate phylogeny.

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.

Distribution of neurotensin-containing neurons in the central nervous system of the pigeon and the chicken

Neurotensin is widely located in neurons of the central and peripheral nervous systems among mammalian species. To obtain a comparative evaluation, we examined the distribution of neurotensin-containing cell bodies and fibers in the central nervous system of the pigeon and the chicken. The pattern of localization of neurotensin immunoreactivity was similar in the two species. Abundant accumulations of neurotensin-containing cell bodies were found in the dorsolateral corticoid area, the piriform cortex, the parahippocampal area, the medial part of the frontal neostriatum, the lateral part of the caudal neostriatum, nucleus accumbens, the bed nucleus of the stria terminalis, ventral paleostriatum, the preoptic area, the ventromedial hypothalamic nucleus, the inferior hypothalamic nucleus, the infundibular hypothalamic nucleus, and the mammillary nuclei. Extremely dense networks of neurotensin-containing fibers were found in the pallial commissure, the lateral septal nucleus, the preoptic area, the periventricular gray around the third ventricle, the dorsalis hypothalamic area, the hypothalamic nuclei, the parabrachial nucleus, the locus ceruleus, and the dorsal vagal complex. Major differences of immunoreactivity between the two species were as follows. 1) The chicken neurohypophysis contained an extremely large accumulation of immunoreactive fibers, but there were few in the median eminence. The reverse was found in the pigeon. 2) The optic tectum in the pigeon contained immunoreactive cells and fibers in layers 2 and 4, but no immunoreactivity was seen in the chicken optic tectum. 3) The cerebellar cortex in the pigeon contained a small number of immunoreactive fibers, whereas that in the chicken did not. 4) The pigeon spinal cord contained immunoreactive neurons in the subependymal layer, but the chicken spinal cord did not. Our observations suggest the presence of a very wide network of neurotensin-containing neurons in the avian brain and spinal cord, which is also the case in mammals.

Comparative distribution of neurotensin-like immunoreactivity in the brain of a teleost (Carassius auratus), an amphibian (Hyla meridionalis), and a reptile (Gallotia galloti)

The distribution of neurotensin (NT) was studied in the brain of three species belonging to the three major classes of cold-blooded vertebrates: teleost fishes (Carassius auratus), anuran amphibians (Hyla meridionalis), and reptiles (Gallotia galloti; Lacertidae). By using antibodies directed against synthetic bovine NT in the three species, immunoreactive cell bodies were discovered mostly in the telencephalon and diencephalon, in particular at the level of the preoptic region the mediobasal hypothalamus, and the thalamus. In the frog and the lizard, additional immunoreactive (ir) structures were observed in the optic tectum and the tegmentum of the mesencephalon. In the goldfish pituitary, an extensive innervation was consistently observed at the level of the rostral pars distalis, whereas in both frog and lizard, positive fibers were only detected in the external layer of the median eminence. In the three species there is a striking overlap between the distribution of the NT-ir cell bodies and that of the target cells for sexual steroids. The results are discussed in relation with those reported in birds and mammals, and with the possible interactions among NT, sexual steroids, and the neuroendocrine control of pituitary hormone release, in particular prolactin and gonadotrophin.

Neuropeptides in the torus semicircularis of the carp (Cyprinus carpio)

The distribution of fibers and cell bodies containing neurotensin, neurokinin A, galanin, or somatostatin-28(1-12) immunoreactivity in the torus semicircularis of the carp was studied using an indirect immunoperoxidase technique. In this mesencephalic region, a high-density of galanin-immunoreactive fibers was found, whereas neurokinin A or somatostatin-28(1-12)-immunoreactive processes were observed at a moderate density and neurotensin-immunoreactive fibers at a low density. Cell bodies containing somatostatin-28(1-12) immunoreactivity were observed in both central and lateral nuclei. The torus semicircularis was not immunoreactive for dynorphin A. The presence of these neuropeptides in the carp torus semicircularis suggests that such neuroactive substances may be involved in auditory and visual mechanisms, as well as in the control of inputs arising from the lateral line system.

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.

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.

Comparative distribution of neuropeptide-immunoreactive systems in the brain of the green molly, Poecilia latipinna

The comparative distribution of peptidergic neural systems in the brain of the euryhaline, viviparous teleost Poecilia latipinna (green molly) was examined by immunohistochemistry. Topographically distinct, but often overlapping, systems of neurons and fibres displaying immunoreactivity (ir) related to a range of neuropeptides were found in most brain areas. Neurosecretory and hypophysiotrophic hormones were localized to specific groups of neurons mostly within the preoptic and tuberal hypothalamus, giving fibre projections to the neurohypophysis, ventral telencephalon, thalamus, and brain stem. Separate vasotocin (AVT)-ir and isotocin (IST)-ir cells were located in the nucleus preopticus (nPO), but many AVT-ir nPO neurons also displayed growth hormone-releasing factor (GRF)-like-ir, and in some animals corticotrophin-releasing factor (CRF)-like-ir. The main group of CRF-ir neurons was located in the nucleus recessus anterioris, where coexistence with galanin (GAL) was observed in some cells. Enkephalin (ENK)-like-ir was occasionally present in a few IST-ir cells of the nPO and was also found in small neurons in the posterior tuberal hypothalamus and in a cluster of large cells in the dorsal midbrain tegmentum. Thyrotrophin-releasing hormone (TRH)-ir cells were found near the rostromedial tip of the nucleus recessus lateralis. Gonadotrophin-releasing hormone (GnRH)-ir cells were present in the nucleus olfactoretinalis, ventral telencephalon, preoptic area, and dorsal midbrain tegmentum. Molluscan cardioexcitatory peptide (FMRF-amide)-ir was colocalized with GnRH-ir in the ganglion cells and central projections of the nervus terminalis. Melanin-concentrating hormone (MCH)-ir neurons were restricted to the tuberal hypothalamus, mostly within the nucleus lateralis tuberis pars lateralis, and somatostatin (SRIF)-ir neurons were numerous throughout the periventricular areas of the diencephalon. A further group of SRIF-ir neurons extending from the ventral telencephalon into the dorsal telencephalon pars centralis also contained neuropeptide Y (NPY)-, peptide YY (PYY)-, and NPY flanking peptide (PSW)-like-ir. These immunoreactivities were, however, also observed in non-SRIF-ir cells and fibres, particularly in the mesencephalon. Calcitonin gene-related peptide (CGRP)-like-ir had a characteristic distribution in cells grouped in the isthmal region and fibre tracts running forward into the hypothalamus, most strikingly into the inferior lobes. Antisera to cholecystokinin (CCK) and neurokinin A (NK) or substance P (SP) stained very extensive, separate systems throughout the brain, with cells most consistently seen in the ventral telencephalon and periventricular hypothalamus. Broadly similar, but much more restricted, distributions of cells and fibres were seen with antisera to neurotensin (NT) and vasoactive intestinal peptide (VIP).(ABSTRACT TRUNCATED AT 400 WORDS)

Thyrotropin-releasing hormone-immunoreactive system in the brain and pituitary gland of the sea bass (Dicentrarchus labrax, Teleostei)

The immunohistochemical distribution of thyrotropin-releasing hormone-like immunoreactivity (TRH-ir) in the brain and pituitary of the sea bass (Dicentrarchus labrax) was examined on cryostat sections of tissues perfuse fixed in a formaldehyde-glutaraldehyde mixture. TRH-ir fibres were found in many areas of the brain: dorsal and ventral telencephalon, preoptic and tuberal hypothalamus, thalamus, midbrain tegmentum, optic tectum, and medulla oblongata. In the hypothalamus the densest area of innervation was the nucleus anterioris tuberis and medial nucleus recessus lateralis, where small TRH-ir cell bodies were also found. In the pituitary gland, TRH-ir fibres were numerous in the posterior neurohypophysis, and these appeared to form varicosities between groups of melanocorticotropic cells of the pars intermedia. No clear relationship was seen between TRH-ir fibres and the thyrotropic cells, or any other cell type of the pars distalis. In the brain stem a notable feature was the prominent innervation of groups of motoneurons by beaded TRH-ir fibres. These observations suggest that in teleost fishes the role of TRH may be related to pars intermedia function, rather than the thyrotropin- or prolactin-releasing function established in tetrapods. In addition the tripeptide may act as a central neurotransmitter involved in sensory and autonomic motor integration.

Anatomical distribution of galanin-like immunoreactivity in the brain and pituitary of teleost fishes

Immunohistochemical study of brains of five teleost fishes (molly, sea bass, killifish, flounder, tilapia) revealed similar extensive systems of galanin immunoreactive (GAL-ir) neurons. Cell bodies were located in the anterior preoptic recess (where coexistence with corticotrophin-releasing factor-like-ir was found), posterior tuberal hypothalamus and vagal lobe of the medulla oblongata. Fibres in the fingers of neurohypophysial tissue penetrating the pituitary pars distalis suggested an anatomical relationship between GAL-ir terminals and the hormone secreting cells. Electron microscopic studies on sea bass pituitary revealed contacts of GAL-ir fibres with growth hormone cells and gonadotrophs. Thus a GAL-like peptide may be released from nerve terminals in the teleost pituitary, where it may act locally to modulate the secretion of one or more pituitary hormones.

Chronological appearance of the different hypophysial hormones in the pituitary of sea bass larvae (Dicentrarchus labrax) during their early development: an immunocytochemical demonstration

Antisera raised against chum salmon prolactin (PRL), rainbow trout growth hormone (GH), mammalian adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), and luteinizing hormone (LH) were used to study the chronological appearance of immunoreactivity for PRL, GH, ACTH, TSH, LH, and melanocyte-stimulating hormone (MSH) in the pituitary of sea bass larvae (Dicentrarchus labrax) during the first 26 days after hatching. The anti-ACTH gives positive immunostaining in the ACTH cells as well as in the MSH cells; however, the two cell types can easily be distinguished by their different localization in the pituitary: ACTH in the rostral pars distalis, MSH in the pars intermedia. The first day after hatching cells immunoreactive for TSH, GH and ACTH could already be noticed, ACTH reacted strong in the pars intermedia but very weak in the rostral pars distalis. Cells immunopositive for PRL became visible between Days 9 and 15. With anti-LH, no positive reaction could be obtained during the first 26 days after hatching.

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

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.

Peptidergic innervation of the adrenocorticotropic hormone (ACTH)- and growth hormone (GH)-producing cells in the pars distalis of the sea bass (Dicentrarchus labrax)

Due to its unique organization, the teleost pituitary is an ideal model in which to investigate the relationship of the nervous system with the pituitary endocrine cells. A light microscope immunocytochemical study of the sea bass pituitary revealed six different neuropeptides in nerve fibers which projected into the pituitary neurohypophysis and bordered the adenohypophysial cells. Double staining showed separate nerve fibers immunoreactive for corticotropin-releasing factor (CRF), vasotocin (VT), somatostatin (SRIF), growth hormone-releasing factor (GRF), and neurotensin (NT) in the vicinity of the adrenocorticotropic hormone-releasing cells (ACTH-cells) in the rostral pars distalis (PD). In the proximal PD cholecystokinin (CCK)-, SRIF-, GRF-, and VT-immunoreactive fibers penetrated between the growth hormone-releasing cells (GH-cells). These results suggest a possible role for CCK, GRF, SRIF, and VT in the modulation of GH-cell activity, while the synthesis and/or secretion of the ACTH-cells might be affected by the release of VT, CRF, SRIF, GRF, and NT.

Visualisation of CGRP and ChAT-like immunoreactivity in identified trigeminal neurones by combined peroxidase and alkaline phosphatase enzymatic reactions

We report here a method that allows simultaneous visualisation of two antigens within single neurones. In essence this involves the combined use of horseradish peroxidase and alkaline phosphatase reactions to visualise two markers. Using this method we show that ChAT-and CGRP-like immunoreactivity can be co-localised within single neurones of the V to VII motor nuclei. In the case of the V motor nucleus, we show that each marker can be localised in motoneurones labelled with horseradish peroxidase.

Melanin-concentrating hormone (MCH) immunoreactive hypophysial neurosecretory system in the teleost Poecilia latipinna: light and electron microscopic study

Neurons containing immunoreactivity for melanin-concentrating hormone (MCH) were located in the brain of the teleost Poecilia latipinna by light microscopic (peroxidase antiperoxidase) and electron microscopic (immunogold) methods. Neuronal cell bodies were found in the tuberal hypothalamus, mostly within the nucleus lateralis tuberis, pars lateralis, containing MCH-immunoreactive granules up to 150 nm in diameter. From here bundles of immunoreactive fibers could be traced through the preoptic area as far forward as the olfactory bulb, and through the posterior hypothalamus up into the pretectal thalamus and midbrain. The main projection was, however, to the neurohypophysis, where MCH fibers were observed to form contacts with pituicytes, basement membranes around blood vessels, and the endocrine cells of the pars intermedia. Occasionally MCH-immunoreactive terminals were also seen near the corticotrophs of the rostral pars distalis. These results support the hypothesis that MCH may act as a systemic hormone, a central neurotransmitter, and a modulator of pituitary function.