Neuropeptide Y in the intermediate lobe of the frog pituitary acts as an alpha-MSH-release inhibiting factor

Sex-specific distribution of Neuropeptide Y (NPY) in the brain of the frog, Microhyla ornata

Neuropeptide Y (NPY) is involved in sex-specific behavioural processes in vertebrates. NPY integrates energy balance and reproduction in mammals. However, the relevance of NPY in reproduction of lower vertebrates is understudied. In the present study, we have investigated neuroanatomical distribution and sex-specific differences of NPY in the brain of Microhyla ornata using immunohistochemistry and quantitative real time PCR. NPY is widely distributed throughout the brain of M. ornata. We observed NPY immunoreactivity in the cells of the nucleus accumbens, striatum pars dorsalis, dorsal pallium, medial pallium, ventral pallium, bed nucleus of stria terminalis, preoptic nucleus, infundibular region, median eminence and pituitary gland of adult M. ornata. A higher number of NPY- immunoreactive cells were observed in the preoptic nucleus (p < .01), nucleus infundibularis ventralis (p < .001) and anteroventral tegmental nucleus (p < .001) of the female as compared to that of the male frog. Real-Time PCR revealed higher mRNA levels of NPY in the female as compared to male frogs in the mid-brain region that largely contains the hypothalamus. Sexual dimorphism of NPY expression in M. ornata suggests that NPY may be involved in the reproductive physiology of anurans.

Effect of neuropeptide Y on food intake in bullfrog larvae

Neuropeptide Y (NPY) is a potent orexigenic neuropeptide implicated in appetite regulation in mammals. However, except for teleost fish such as the goldfish and zebrafish, the involvement of NPY in the regulation of feeding in non-mammalian vertebrates has not been well studied. Anuran amphibian larvae feed and grow during the pre- and pro-metamorphic stages, but, thereafter they stop feeding as the metamorphic climax approaches. Therefore, orexigenic factors seem to play important roles in pre- and pro-metamorphic larvae. We investigated the role of NPY in food intake using bullfrog larvae including pre- and pro-metamorphic stages, and examined the effect of feeding status on the expression level of the NPY transcript in the hypothalamus. NPY mRNA levels in hypothalamus specimens obtained from larvae that had been fasted for 3 days were higher than those in larvae that had been fed normally. We then investigated the effect of intracerebroventricular (ICV) administration of NPY on food intake in the larvae. Cumulative food intake was significantly increased by ICV administration of NPY (5 and 10 pmol/g body weight, BW) during a 15-min observation period. The NPY-induced orexigenic action (10 pmol/g BW) was blocked by treatment with a NPY Y1 receptor antagonist, BIBP-3226 (100 pmol/g BW). These results indicate that NPY acts as an orexigenic factor in bullfrog larvae.

Analysis of the melanotrope cell neuroendocrine interface in two amphibian species, Rana ridibunda and Xenopus laevis: a celebration of 35 years of collaborative research

This review gives an overview of the functioning of the hypothalamo-hypophyseal neuroendocrine interface in the pituitary neurointermediate lobe, as it relates to melanotrope cell function in two amphibian species, Rana ridibunda and Xenopus laevis. It primarily but not exclusively concerns the work of two collaborating laboratories, the Laboratory for Molecular and Cellular Neuroendocrinology (University of Rouen, France) and the Department of Cellular Animal Physiology (Radboud University Nijmegen, The Netherlands). In the course of this review it will become apparent that Rana and Xenopus have, for the most part, developed the same or similar strategies to regulate the release of α-melanophore-stimulating hormone (α-MSH). The review concludes by highlighting the molecular and cellular mechanisms utilized by thyrotropin-releasing hormone (TRH) to activate Rana melanotrope cells and the function of autocrine brain-derived neurotrophic factor (BDNF) in the regulation of Xenopus melanotrope cell function.

Plasticity in the melanotrope neuroendocrine interface of Xenopus laevis

Melanotrope cells of the amphibian pituitary pars intermedia produce alpha-melanophore-stimulating hormone (alpha-MSH), a peptide which causes skin darkening during adaptation to a dark background. The secretory activity of the melanotrope of the South African clawed toad Xenopus laevis is regulated by multiple factors, both classical neurotransmitters and neuropeptides from the brain. This review concerns the plasticity displayed in this intermediate lobe neuroendocrine interface during physiological adaptation to the environment. The plasticity includes dramatic morphological plasticity in both pre- and post-synaptic elements of the interface. Inhibitory neurons in the suprachiasmatic nucleus, designated suprachiasmatic melanotrope-inhibiting neurons (SMINs), possess more and larger synapses on the melanotrope cells in white than in black-background adapted animals; in the latter animals the melanotropes are larger and produce more proopiomelanocortin (POMC), the precursor of alpha-MSH. On a white background, pre-synaptic SMIN plasticity is reflected by a higher expression of inhibitory neuropeptide Y (NPY) and is closely associated with postsynaptic melanotrope plasticity, namely a higher expression of the NPY Y1 receptor. Interestingly, melanotrope cells in such animals also display higher expression of the receptors for thyrotropin-releasing hormone (TRH) and urocortin 1, two neuropeptides that stimulate alpha-MSH secretion. Possibly, in white-adapted animals melanotropes are sensitized to neuropeptide stimulation so that, when the toad moves to a black background, they can immediately initiate alpha-MSH secretion to achieve rapid adaptation to the new background condition. The melanotrope cell also produces brain-derived neurotrophic factor (BDNF), which is co-sequestered with alpha-MSH in secretory granules within the cells. The neurotrophin seems to control melanotrope cell plasticity in an autocrine way and we speculate that it may also control presynaptic SMIN plasticity.

The regulation of alpha-MSH release by GABA is mediated by a chloride-dependent [Ca2+]c increase in frog melanotrope cells

In frog melanotrope cells, gamma-aminobutyric acid (GABA) induces a biphasic effect, i.e. a transient stimulation followed by a more sustained inhibition of alpha-MSH release, and both phases of the GABA effect are mediated by GABAA receptors. We have previously shown that the stimulatory phase evoked by GABAA receptor agonists can be accounted for by calcium entry. In the present study, we have investigated the involvement of the chloride flux on GABA-induced [Ca2+]c increase and alpha-MSH release. We show that GABA evokes a concentration-dependent [Ca2+]c rise through specific activation of the GABAA receptor. The GABA-induced [Ca2+]c increase results from opening of voltage-activated L- and N-type calcium channels, and sodium channels. Variations of the extracellular Cl- concentration revealed that GABA-induced [Ca2+]c rise and alpha-MSH release both depend on the Cl- flux direction and driving force. These observations suggest for the first time that GABA-gated Cl- efflux provokes an increase in [Ca2+]c increase that is responsible for hormone secretion.

Melanotrope secretory cycle is regulated by physiological inputs via the hypothalamus

Previously, it has been shown that background color conditions regulate the overall activity of the frog intermediate lobe by varying the proportions of the two subtypes of melanotropes existing in the gland, the highly active or secretory melanotropes and hormone storage melanotropes, depending on melanocyte-stimulating hormone requirements. However, the factors and mechanisms underlying these background-induced changes are still unknown. In the present study, we investigated whether hypothalamic factors known to regulate melanotrope cell function can induce changes in vitro similar to those caused by background adaptation in vivo. We found that the inhibitors apomorphine (a dopamine receptor agonist) and neuropeptide Y decreased the number of active melanotropes and increased simultaneously that of storage melanotropes. On the other hand, the stimulator TRH increased the number of active cells and concomitantly reduced that of storage cells. Inasmuch as none of these treatments modified the apoptotic and proliferation rates in melanotrope cells, it appears that these hypothalamic factors caused actual interconversions of cells from a subpopulation to its counterpart. Taken together, these findings suggest that the hypothalamus would control melanotrope activity not only through short-term regulation of hormone synthesis and release, but also through a long-term regulation of the secretory phenotype of these cells whereby the activity of the intermediate lobe would be adjusted to fulfill the hormonal requirements imposed by background conditions.

Demonstration of postsynaptic receptor plasticity in an amphibian neuroendocrine interface

Pituitary pars intermedia melanotrope cells are often used as a model to study mechanisms of neuroendocrine integration. In the amphibian Xenopus laevis, the synthesis and release of alpha-melanophore-stimulating hormone (alpha-MSH) from these cells is a dynamic process dependent upon the colour of background. In animals on a black background, there is a higher level of synthesis and secretion of alpha-MSH than in animals on a white background, and, consequently, there is skin darkening in animals on a black background. The melanotropes are innervated by hypothalamic neurones that produce neuropeptide Y (NPY), a peptide that inhibits alpha-MSH secretion via the NPY Y1 receptor. The inhibitory neurones have a higher expression of NPY in animals adapted to a white background and both the size and the number of inhibitory synapses on the melanotrope cells are enhanced. The purpose of the present study was to determine if this presynaptic plasticity displayed by the inhibitory neurones is reciprocated by postsynaptic plasticity (i.e. if there is an enhanced expression of the Y1 receptor in melanotropes of animals adapted to a white background). For this purpose quantitative real-time reverse transcriptase-polymerase chain reaction was used to determine the level of Y1 receptor mRNA in melanotropes of animals undergoing the process of background adaptation. The results showed that there is a higher Y1 receptor mRNA expression in melanotropes of white-adapted animals. We conclude that the inhibitory neuroendocrine interface in the Xenopus pars intermedia displays postsynaptic plasticity in response to changes of background colour. To our knowledge, this is the first demonstration of a physiological environmental change leading to changes in postsynaptic receptor expression in a fully identified vertebrate neuroendocrine reflex.

Neuropeptide Y inhibits spontaneous alpha-melanocyte-stimulating hormone (alpha-MSH) release via a Y(5) receptor and suppresses thyrotropin-releasing hormone-induced alpha-MSH secretion via a Y(1) receptor in frog melanotrope cells

In amphibians, the secretion of alpha-MSH by melanotrope cells is stimulated by TRH and inhibited by NPY. We have previously shown that NPY abrogates the stimulatory effect of TRH on alpha-MSH secretion. The aim of the present study was to characterize the receptor subtypes mediating the action of NPY and to investigate the intracellular mechanisms involved in the inhibitory effect of NPY on basal and TRH-induced alpha-MSH secretion. Y(1) and Y(5) receptor mRNAs were detected by RT-PCR and visualized by in situ hybridization histochemistry in the intermediate lobe of the pituitary. Various NPY analogs inhibited in a dose-dependent manner the spontaneous secretion of alpha-MSH from perifused frog neurointermediate lobes with the following order of potency porcine peptide YY (pPYY) > frog NPY (fNPY) > porcine NPY (pNPY)-2-36) > pNPY-(13-36) > [D-Trp(32)]pNPY > [Leu(31),Pro(34)]pNPY. The stimulatory effect of TRH (10(-8)6 M) on alpha-MSH release was inhibited by fNPY, pPYY, and [Leu(31),Pro(34)]pNPY, but not by pNPY-(13-36) and [D-Trp(32)]pNPY. These data indicate that the inhibitory effect of fNPY on spontaneous alpha-MSH release is preferentially mediated through Y(5) receptors, whereas the suppression of TRH-induced alpha-MSH secretion by fNPY probably involves Y(1) receptors. Pretreatment of neurointermediate lobes with pertussis toxin (PTX; 1 microg/ml; 12 h) did not abolish the inhibitory effect of fNPY on cAMP formation and spontaneous alpha-MSH release, but restored the stimulatory effect of TRH on alpha-MSH secretion, indicating that the adenylyl cyclase pathway is not involved in the action of fNPY on TRH-evoked alpha-MSH secretion. In the majority of melanotrope cells, TRH induces a sustained and biphasic increase in cytosolic Ca(2+) concentration. Preincubation of cultured cells with fNPY (10(-7) M) or omega-conotoxin GVIA (10(-7) M) suppressed the plateau phase of the Ca(2+) response induced by TRH. However, although fNPY abrogated TRH-evoked alpha-MSH secretion, omega-conotoxin did not, showing dissociation between the cytosolic Ca(2+) concentration increase and the secretory response. Collectively, these data indicate that in frog melanotrope cells NPY inhibits spontaneous alpha-MSH release and cAMP formation through activation of a Y(5) receptor coupled to PTX- insensitive G protein, whereas NPY suppresses the stimulatory effect of TRH on alpha-MSH secretion through a Y(1) receptor coupled to a PTX-sensitive G protein-coupled receptor.

Amphibian melanotrope subpopulations respond differentially to hypothalamic secreto-inhibitors

The melanotrope population of the frog intermediate lobe consists of two subtypes of cells, referred to as high-(HD) and low-density (LD) melanotrope cells, which differ markedly in their basal morphofunctional features as well as their in vitro response to hypothalamic factors, such as the stimulator thyrotropin-releasing hormone (TRH) and the inhibitor dopamine. In this study, we have investigated whether other major hypothalamic regulators of the release of alpha-melanocyte-stimulating hormone (alpha-MSH), such as gamma-aminobutyric acid (GABA) and neuropeptide Y (NPY), also differentially regulate frog melanotrope subpopulations. Our results show that in LD cells, both factors markedly inhibited proopiomelanocortin (POMC) mRNA accumulation and alpha-MSH secretion. In contrast, the secretory and biosynthetic activity of HD cells was not modified by GABA. NPY inhibited POMC transcript accumulation and tended to reduce alpha-MSH secretion in HD cells, yet these effects were less pronounced than those evoked in LD cells. In addition, GABA and NPY inhibited the KCl-induced rise in cytosolic free calcium levels in both subpopulations. Taken together, these results further indicate that frog melanotrope subpopulations are differentially regulated by the hypothalamus and strongly suggest that the intensity of such regulation is directly related to the activity of the cell subset. Thus, the LD subpopulation represents a highly responsive cell subset which is regulated by multiple neuroendocrine factors (TRH, dopamine, GABA and NPY), whereas the hormone storage HD subpopulation shows a moderate response to single stimulatory (TRH) and inhibitory (NPY) inputs.

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.

Characterization and distribution of neuropeptide Y in the brain of a caecilian amphibian

Neuropeptide Y (NPY) from the brain of an amphibian from the order Gymnophiona (the caecilian, Typhlonectes natans) was characterized. We cloned a 790 base pair cDNA encoding the caecilian NPY precursor. The open reading frame consisted of 291 bases, indicating an NPY precursor of 97 amino acids. Both deduced and isolated NPY primary structures were Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu(10)-Asp-Ala-Pro-Ala-Glu-Asp-Met-Ala-Lys-Tyr(20)-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu(30)-Ile-Thr-Arg-Gln-Arg-Tyr. NH2. In caecilian brain, we observed NPY immunoreactive cells within the medial pallium, basal forebrain, preoptic area, midbrain tegmentum and trigeminal nucleus. The prevalence of preoptic and hypothalamic terminal field staining supports the hypothesis that NPY controls pituitary function in this caecilian.

Immunohistochemical distribution of neuropeptide Y-related substance in the brain and hypophysis of the arctic lamprey, Lethenteron japonica

The distribution of neuropeptide Y (NPY)-like immunoreactivity in the brain and hypophysis of the arctic lamprey, Lethenteron japonica, was studied by the use of polyclonal anti-synthetic porcine NPY antibody. Immunoreactivity was found throughout the brain, with varied densities among different areas. NPY-positive cell bodies were located in the dorsal pallium of the telencephalon; in the preoptic area, the thalamus, and the hypothalamus of the diencephalon; in the tegmentum of the mesencephalon; and in the octavolateralis nucleus, the middle reticular nucleus, and the vagal motor nucleus of the rhombencephalon. The majority of the NPY-positive cells in the thalamus and in the hypothalamus appeared as cerebrospinal fluid-contacting neurons. NPY-positive fibers were widely distributed in the brain and locally dense in the ventromedial part of the lateral pallium, in the posterior part of the interpeduncular nucleus, and in the raphe region. Conversely, they were less dense or well scattered in the olfactory bulb, the lateral pallium except for its ventromedial part, and the optic tectum. NPY-positive innervation in the neurohypophysis was evident, suggesting that involvement of NPY-related substance in the hypothalamo-hypophysial system had occurred in an early stage of vertebrate evolution.

Distribution of GAD-immunoreactive neurons in the diencephalon of the african lungfish Protopterus annectens: colocalization of GAD and NPY in the preoptic area

The distribution of GABAergic neurons was investigated in the diencephalon of the African lungfish, Protopterus annectens, by using specific antibodies directed against glutamic acid decarboxylase (GAD). A dense population of immunoreactive perikarya was observed in the periventricular preoptic nucleus, whereas the caudal hypothalamus and the dorsal thalamus contained only scattered positive cell bodies. Clusters of GAD-positive cells were found in the intermediate lobe of the pituitary. The diencephalon was richly innervated by GAD-immunoreactive fibers that were particularly abundant in the hypothalamus. In the periventricular nucleus, GAD-positive fibers exhibited a radial orientation, and a few neurons extended processes toward the third ventricle. More caudally, a dense bundle of GAD-immunoreactive fibers coursing along the ventral wall of the hypothalamus terminated into the median eminence and the neural lobe of the pituitary. Double-labeling immunocytochemistry revealed that GAD and neuropeptide tyrosine (NPY)-like immunoreactivity was colocalized in a subpopulation of perikarya in the periventricular preoptic nucleus. The proportion of neurons that coexpressed GAD and NPY was higher in the caudal region of the preoptic nucleus. The distribution of GAD-immunoreactive elements in the diencephalon and pituitary of the African lungfish indicates that GABA may act as a hypophysiotropic neurohormone in Dipnoans. The coexistence of GAD and NPY in a subset of neurons of the periventricular preoptic nucleus suggests that GABA and NPY may interact at the synaptic level.

The pituitary-skin connection in amphibians. Reciprocal regulation of melanotrope cells and dermal melanocytes

In amphibians, alpha-MSH secreted by the pars intermedia of the pituitary plays a pivotal role in the process of skin color adaptation. Reciprocally, the skin of amphibians contains a number of regulatory peptides, some of which have been found to regulate the activity of pituitary melanotrope cells. In particular, the skin of certain species of amphibians harbours considerable amounts of thyrotropin-releasing hormone, a highly potent stimulator of alpha-MSH release. Recently, we have isolated and sequenced from the skin of the frog Phyllomedusa bicolor--a novel peptide named skin peptide tyrosine tyrosine (SPYY), which exhibits 94% similarity with PYY from the frog Rana ridibunda. For concentrations ranging from 5 x 10(-10) to 10(-7) M, SPYY induces a dose-related inhibition of alpha-MSH secretion. At a dose of 10(-7) M, SPYY totally abolished alpha-MSH release. These data strongly suggest the existence of a regulatory loop between the pars intermedia of the pituitary and the skin in amphibians.

Autoradiographic distribution of neuropeptide tyrosine binding sites in the brain of the African lungfish, Protopterus annectens

The distribution of neuropeptide tyrosine (NPY) binding sites in the brain of the African lungfish, Protopterus annectens, was studied by autoradiography using radioiodinated NPY as a tracer. The highest concentrations of binding sites were found in the dorsal and intermediate parts of the medial pallium, the dorsal pallium, and in the medial and lateral subpallium. These observations, together with the finding of a moderate density of binding sites in the olfactory bulbs, suggest that NPY may be involved in the processing of olfactory information and/or neuromodulation of limbic activities. High densities of binding sites were also found in several rhombencephalic nuclei, including the nucleus fascicoli solitarii, the nucleus motorius nervi vagi, the spinal motor column and all components of the reticular formation, indicating that NPY may play a role in the regulation of neurovegetative functions. Concurrently, the presence of high concentrations of binding sites in the hypophysis suggests that, in the lungfish, NPY may exert a direct control of pituitary hormone secretion.

Effect of centrally administered neuropeptide Y on hypothalamic and hypophyseal proopiomelanocortin-derived peptides in the rat

In a previous study, we have shown that neuropeptide Y inhibits the release of alpha-melanocyte-stimulating hormone from the rat hypothalamus in vitro. The aim of the present study was to investigate the possible effect of neuropeptide Y on the regulation of proopiomelanocortin-derived peptides in vivo. Rats received acute or chronic administration of neuropeptide Y in the lateral ventricle and the amount of alpha-melanocyte-stimulating hormone was measured in the hypothalamus and in the neurointermediate lobe of the pituitary. In the same experiments, the amounts of corticotropin-releasing factor and corticotropin were quantified in the hypothalamus and anterior pituitary, respectively. Acute treatment with synthetic neuropeptide Y (0.1 to 10 micrograms/rat) did not modify the amount of alpha-melanocyte-stimulating hormone in the hypothalamus. In contrast, chronic infusion of neuropeptide Y (1.25 micrograms/h) over a seven day period significantly decreased the hypothalamic content of alpha-melanocyte-stimulating hormone, suggesting that neuropeptide Y regulates the synthesis and/or the processing of proopiomelanocortin. Concurrently, we found that both acute and chronic infusion of neuropeptide Y induced a significant reduction in corticotropin-releasing factor in the hypothalamus as well as a significant decrease in alpha-melanocyte-stimulating hormone and corticotropin in the neurointermediate and anterior lobes, respectively. Quantitative in situ hybridization histochemistry showed that chronic administration of neuropeptide Y also caused a reduction of proopiomelanocortin messenger RNA levels both in the intermediate and anterior lobes of the pituitary. Administration of neuropeptide Y (10(-6) M) on perifused rat hypothalamic slices caused a significant increase in corticotropin-releasing factor release.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide tyrosine in the brain of the African lungfish, Protopterus annectens: immunohistochemical localization and biochemical characterization

Lungfishes, which share similarities with both fishes and amphibians, represent an interesting group in which to investigate the evolutionary transition from fishes to tetrapods. In the present study, we have investigated the localization and biochemical characteristics of neuropeptide Y (NPY)-immunoreactive material in the central nervous system of the African lungfish, Protopterus annectens. NPY-immunoreactive cell bodies were found in various regions of the brain, most notably in the telencephalon (septal area, ventral striatum, and nucleus accumbens), in the diencephalon (preoptic nucleus, periventricular region of the hypothalamus, and ventral thalamus), and in the tegmentum of the mesencephalon. A strong immunoreaction was also detected in cell bodies of the nervus terminalis. Immunoreactive nerve fibers were particularly abundant in the ventral striatum, the nucleus accumbens, the diagonal band of Broca, the hypothalamus, and the mesencephalic tegmentum. Positive fibers were also seen in the median eminence and in the neural lobe of the pituitary. The NPY-immunoreactive material localized in the brain and pituitary was characterized by combining high-performance liquid chromatography (HPLC) analysis and radioimmunological quantitation. The displacement curves obtained with synthetic porcine and frog NPY and serial dilutions of brain and pituitary extracts were parallel. Reversed-phase HPLC analysis of telencephalon, diencephalon, and pituitary extracts resolved a major NPY-immunoreactive peak that coeluted with frog NPY. The similarity between the distribution of NPY-containing neurons and the biochemical characteristics of the immunoreactive peptide in the brain of lungfish and frog strongly favors a close phylogenetic relationship between dipnoans and amphibians.

Central nervous system pharmacology of neuropeptide Y

Neuropeptide Y (NPY) is a 36-amino acid peptide belonging to the pancreatic polypeptide family that has marked and diverse biological activity across species. NPY originally was isolated from mammalian brain tissue somewhat more than 10 years ago and, since that time, has been the subject of numerous scientific publications. NPY and its proposed three receptors (Y1, Y2 and Y3) are relatively abundant in and uniquely distributed throughout the brain and spinal cord. This review will highlight the results from a number of research-oriented studies that have examined how NPY is involved in CNS function and behavior, and how these studies may relate to the possible development of medicines, either NPY-like agonists or antagonists, directed towards the treatment of disorders such as anxiety, pain, hypertension, schizophrenia, memory dysfunction, abnormal eating behavior and depression.

Neuropeptide Y inhibits Ca2+ oscillations, cyclic AMP, and secretion in melanotrope cells of Xenopus laevis via a Y1 receptor

The melanotrope cells in the pituitary gland of Xenopus laevis are innervated by neurons containing neuropeptide Y (NPY). In the present study, the mechanism of action of NPY on the melanotropes has been investigated. NPY inhibited in vitro secretion from melanotropes in intact neurointermediate lobes as well as from isolated, single melanotropes. Inhibition of secretion from neurointermediate lobes was mimicked by the NPY analogues PYY and [Leu31,Pro34]NPY, whereas NPY(13-36) was inactive. Secretion from isolated melanotropes was inhibited by [Leu31,Pro34]NPY and NPY(13-36), but NPY(13-36) was 10-fold less potent than [Leu31,Pro34]NPY. Studies on isolated cells revealed that NPY and its analogues inhibited the occurrence of intracellular Ca2+ oscillations with the same potency as they inhibited secretion from isolated cells. In addition to inhibiting basal secretion and spontaneous Ca2+ oscillations, NPY inhibited the basal production of cyclic AMP. On the basis of these results it is proposed that NPY inhibits secretion from Xenopus melanotropes by inhibiting cyclic AMP-dependent spontaneous Ca2+ oscillations through a Y1-like receptor.

Inhibitory effect of adenosine on electrical activity of frog melanotrophs mediated through A1 purinergic receptors

1. The effects of adenosine were studied in cultured frog melanotrophs by the patch-clamp technique. 2. In cell-attached experiments, most cells responded to adenosine (50 microM) by a reversible inhibition of action current discharges without any apparent desensitization. 3. In whole-cell experiments, adenosine provoked a hyperpolarization accompanied by a depression of spontaneous action potentials and a decrease in membrane resistance. When adenosine was repeatedly applied, tachyphylaxis was observed. Addition of GTP (100 microM) in the intracellular solution augmented the percentage of cells hyperpolarized by adenosine, and the duration and amplitude of the hyperpolarization, and prevented the tachyphylaxis. 4. Pretreatment with pertussis toxin (1 microgram ml-1) blocked adenosine-induced inhibition. 5. In cells dialysed with the non-hydrolysable GTP analogue GTP gamma S (100 microM), adenosine caused a sustained, strong hyperpolarization and an irreversible inhibition of spikes. 6. The effect of adenosine was mimicked by the A1 receptor agonist R-PIA (R-N6-phenylisopropyl-adenosine; 50 microM) and blocked by the A1 receptor antagonist CPDPX (8-cyclopentyl-1,3-dipropylxanthine, 50 microM). The A2 receptor antagonist CGS15943 (9-chloro-2-(2-furanyl)-5,6-dihydro-1,2,4-triazolo[1,5-c] quinazoline-5-imine; 50 microM) did not affect the adenosine-induced response. 7. The results suggest that, in frog melanotrophs, adenosine exerts a direct hyperpolarizing effect accompanied by blockage of spontaneous action potentials. The effect of adenosine is mediated through A1 receptors coupled to a Gi/o protein.

Skin peptide tyrosine-tyrosine, a member of the pancreatic polypeptide family: isolation, structure, synthesis, and endocrine activity

Pancreatic polypeptide, peptide tyrosine-tyrosine (PYY), and neuropeptide tyrosine (NPY), three members of a family of structurally related peptides, are mainly expressed in the endocrine pancreas, in endocrine cells of the gut, and in the brain, respectively. In the present study, we have isolated a peptide of the pancreatic polypeptide family from the skin of the South American arboreal frog Phyllomedusa bicolor. The primary structure of the peptide was established as Tyr-Pro-Pro-Lys-Pro-Glu-Ser-Pro-Gly-Glu10-Asp-Ala-Ser-Pro-Glu-Glu- Met-Asn- Lys-Tyr20-Leu-Thr-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu30-Val-Thr- Arg-Gln-Arg-Tyr-NH2 . This unusual peptide, named skin peptide tyrosine-tyrosine (SPYY), exhibits 94% similarity with PYY from the frog Rana ridibunda. A synthetic replicate of SPYY inhibits melanotropin release from perifused frog neurointermediate lobes in very much the same way as NPY. These results demonstrate the occurrence of a PYY-like peptide in frog skin. Our data also suggest the existence of a pituitary-skin regulatory loop in amphibians.

Multiple sources of the pituitary pars intermedia innervation in amphibians: a DiI retrograde tract-tracing study

Afferent projections to the pituitary pars intermedia were studied using the DiI tract-tracing technique in two amphibian species, the urodelan Triturus carnifex, and the anuran Rana esculenta. After DiI crystal application into the pituitary intermediate lobe, in both species cells were retrogradely labeled in the preoptic nucleus, in the supra- and retro-chiasmatic hypothalamus and in the brainstem (especially in the area indicated as locus coeruleus). The findings are discussed in relation to data on the neurochemical nature of the innervation of the pars intermedia in amphibians.

Melanostatin (NPY) inhibited electrical activity in frog melanotrophs through modulation of K+, Na+ and Ca2+ currents

1. Melanostatin, a thirty-six amino acid peptide recently isolated from the frog brain due to its ability to inhibit alpha-melanocyte-stimulating hormone (alpha-MSH) release, is the amphibian counterpart of mammalian neuropeptide Y (NPY). The effect of synthetic melanostatin on the bioelectrical activity of cultured frog melanotrophs was studied in 124 cells by using the whole-cell patch-clamp technique. 2. In current-clamp experiments, melanostatin (1 microM) provoked a reversible hyperpolarization and a suppression of spontaneous action potentials. In some cells the hyperpolarizing response was absent, but an arrest of spike firing still occurred. 3. Melanostatin-induced hyperpolarization was associated with a decrease in membrane resistance. In voltage-clamp experiments, melanostatin induced an outward current at a constant command potential. This hyperpolarizing outward current appeared to be carried by potassium ions. 4. Cell dialysis with the non-hydrolysable GTP analogue guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S) sustained the outward current produced by melanostatin. Dopamine (1 microM), which generates a similar hyperpolarizing outward current in frog melanotrophs, was not capable of increasing the current provoked by melanostatin and sustained by GTP gamma S. 5. Melanostatin also modulated voltage-operated currents. The amplitude of voltage-activated potassium current was increased by 30%. 6. Melanostatin reduced the fast sodium current. This inhibitory effect was rather persistent compared to the other modulated currents. 7. Melanostatin markedly scaled down high voltage-activated N- and L-like calcium currents. The activation kinetics of these two calcium currents were not altered by the peptide. 8. Pretreatment of melanotrophs with pertussis toxin (1 microgram ml-1) blocked melanostatin-induced inhibition of N- and L-like calcium currents. 9. It is concluded that the NPY-related peptide melanostatin generates a very complex pattern of electrical responses in frog melanotrophs, including hyperpolarization and modulation of voltage-activated currents underlying action potentials. G proteins appear to mediate at least part of these effects.

Adenosine inhibits alpha-melanocyte-stimulating hormone release from frog pituitary melanotrophs. Evidence for the involvement of a(1) adenosine receptors negatively coupled to adenylate cyclase

Adenosine is recognized as an important modulator of cell activity. In particular, adenosine regulates the secretion of adrenocorticotropin from anterior pituitary cells. However, the possible role of adenosine on the pars intermedia has never been investigated. In the present study, we have examined the effect of adenosine on α-melanotropin (α-MSH) secretion from the intermediate lobe of the pituitary of the frog (Rana ridibunda), using the perifusion technique. When whole neurointermediate lobes were exposed to graded doses of adenosine (10(-9) to 10(-4) M), a dose-dependent inhibition of a-MSH release was observed. Repeated pulses of adenosine (5 ± 10(-5) M) induced a reproducible inhibition of α-MSH secretion without any desensitization phenomenon. The effect of adenosine was mimicked by the non-selective agonist 5'-N-ethylcarboxamide-adenosine and the highly specific adenosine A, receptor agonist N(6) -[R-phenylisopropyl]-adenosine (R-PIA). In contrast the selective adenosine A(2) receptor agonist, CGS 21680, induced a slight stimulation of α-MSH release. Adenosine-induced inhibition of α-MSH secretion was blocked by the non-selective adenosine antagonist, 8-(p-sulfophenyl)-theophyline. Adenosine and R-PIA also inhibited α-MSH secretion from acutely dispersed pars intermedia cells. Adenosine did not block thyrotropin-releasing hormone-induced α-MSH release from perifused neurointermediate lobes. In contrast, adenosine inhibited both acetylcholine-evoked and muscarine-evoked α-MSH secretion. Finally, R-PIA induced a significant inhibition of basal and forskolin-stimulated cyclic AMP levels in whole neurointermediate lobes. The present results demonstrate that adenosine exerts a direct inhibitory effect on α-MSH release from melanotrope cells through activation of the A(1) receptor subtype, negatively coupled to adenylate cyclase. These data suggest that adenosine may play a physiological role in the regulation of hormone release from the intermediate lobe of the pituitary.

Neuropeptide Y inhibits alpha-MSH release from rat hypothalamic slices through a pertussis toxin-sensitive G protein

The arcuate nucleus of the hypothalamus contains various types of peptidergic neurons. In particular, two distinct populations of neurosecretory neurons containing neuropeptide Y (NPY)- and alpha-melanocyte-stimulating hormone (alpha-MSH)-like immunoreactivity have been identified in the arcuate nucleus. Double-labeling immunocytochemical data have recently shown that NPY-containing fibers make synaptic contacts with proopiomelanocortin (POMC) immunoreactive neurons. We have thus investigated the possible effect of NPY on the release of alpha-MSH from rat hypothalamic slices in vitro, using the perifusion technique. NPY significantly inhibited KCl-stimulated alpha-MSH release in a dose-dependent manner. The inhibitory effect of NPY was mimicked by the Y2 agonist, NPY-(13-36), while the Y1 agonist, [Leu31,Pro34]NPY, was devoid of effect. Pretreatment of hypothalamic slices with pertussis toxin (PTX) blocked the inhibitory effect of NPY, suggesting that the action of NPY on POMC neurons is mediated through a PTX-sensitive G protein. These results support the notion that NPY may play a physiological role in the regulation of alpha-MSH release from hypothalamic neurons.

Structural requirements for the effects of neuropeptide Y on the hypothalamic-pituitary-adrenal axis in the dog

Neuropeptide Y (NPY), administered into the third cerebral ventricle of the dog stimulates plasma ACTH and cortisol secretion. To further investigate the structure-activity relationships of this action, we examined the effect of COOH-terminal fragment, NPY 19-36 and its analogues, NPY-(1-36)-OH (deamidated NPY) and avian pancreatic polypeptide (APP) on ACTH-cortisol secretion following intracerebroventricular (i.c.v.) injection in the dog. NPY (1.19 nmol) evoked a significant increase in the secretion of both plasma ACTH and cortisol. However, NPY 19-36 and NPY-(1-36)-OH each failed to increase plasma ACTH and cortisol secretion at doses of 1.19-11.9 nmol injected i.c.v. APP was less active than NPY. These data demonstrate that the entire NPY molecule is required for the full expression of the stimulatory effect of NPY on the secretion of ACTH and cortisol.

Lack of effect of TRH on alpha-MSH release from the neurointermediate lobe of the lizard Lacerta vivipara

Thyrotropin-releasing hormone (TRH) is a potent stimulator of melanotropin (alpha-MSH) release from pituitary melanotrophs in pig, frog, and fish. Concurrently, it has recently been shown that injection of TRH induces skin darkening in the lizard Anolis carolinensis (Licht and Denver, 1988). In the present study, we have thus investigated in vitro the possible effect of TRH on alpha-MSH release from the lizard (Lacerta vivipara) neurointermediate lobe, by means of the perifusion technique. Using our radioimmunoassay procedure, we found that serial dilutions of L. vivipara NIL extracts and synthetic alpha-MSH gave parallel binding curves. Administration of graded doses of TRH (10(-8)-10(-6) M) did not cause any modification of alpha-MSH release. In contrast, infusion of a depolarizing concentration of K+ induced a robust stimulation of alpha-MSH secretion. These results indicate that, in the lizard L. vivipara, the neuropeptide TRH does not stimulate pituitary melanotrophs.

Distribution of neuropeptide Y-like immunoreactivity in the brain and hypophysis of the cloudy dogfish, Scyliorhinus torazame

Using a specific antiserum raised against synthetic neuropeptide Y, we examined the localization of immunoreactivity in the brain and hypophysis of the cloudy dogfish, Scyliorhinus torazame, by the peroxidase-antiperoxidase method. Immunoreactive perikarya were demonstrated in the ganglion of the nervus terminalis, the dorsocaudal portions of the pallium dorsale, the basal telencephalon, and the nucleus lateralis tuberis and the nucleus lobi lateralis in the hypothalamus. Labeled perikarya were also found in the tegmentum mesencephali, the corpus cerebelli, and the medulla oblongata. Some of the immunoreactive neurons in the hypothalamus were of the CSF-contacting type. The bulk of the labeled fibers in the nervus terminalis ran toward the basal telencephalon, showing radial projections and ramifications. Large numbers of these fibers coursed into the nucleus septi caudoventralis and the nucleus interstitialis commissurae anterioris, where they became varicose and occasionally formed fine networks or invested immunonegative perikarya. In the diencephalon, immunoreactive fibers were observed throughout the hypothalamus, e.g., in the pars neurointermedia of the hypophysis, the subependymal layer of the lobus inferior hypothalami, and in the neuropil of the posterior (mammillary) recess organ. Labeled fibers were scattered throughout the rest of the brain stem and were also seen in the granular layer of the cerebellum. These results suggest that, in the dogfish brain, neuropeptide Y or a related substance is involved in a variety of physiological processes in the brain, including the neuroendocrine control of the hypophysis.

Co-localization of tyrosine hydroxylase, GABA and neuropeptide Y within axon terminals innervating the intermediate lobe of the frog Rana ridibunda

Possible co-existence of gamma-aminobutyric acid (GABA), catecholamines, and neuropeptide Y (NPY) in the same nerve terminals of the frog intermediate lobe was investigated by immunocytochemistry at the electron microscopic level. Co-localization of GABA and tyrosine hydroxylase (TH) was studied by using a double immunogold labeling procedure. Co-localization of glutamate decarboxylase (GAD) and NPY was studied by combining, respectively, the peroxidase-antiperoxidase method and a radioimmunocytochemical labeling procedure. Catecholamines and GABA were systematically co-localized in nerve endings of the pars intermedia. Most of the NPY-immunoreactive fibers also contained GAD-like immunoreactivity. However, a few NPY-positive nerve terminals were not immunoreactive for GAD. These data provide evidence for co-existence of a regulatory peptide (NPY) and several neurotransmitters (i.e., GABA and catecholamines) within the same axon terminals in the intermediate lobe. Since GABA, dopamine, and NPY have all been shown to inhibit the activity of frog melanotrope cells, the present findings suggest that these neuroendocrine factors may interact either at the pre-synaptic or post-synaptic level.

[The intermediate lobe of the pituitary, model of neuroendocrine communication]

The intermediate lobe of the pituitary is composed of a homogeneous population of endocrine cells, the melanotrophs, which secrete several bioactive peptides including alpha-melanocyte-stimulating hormone (alpha-MSH) and beta-endorphin. In contrast to most endocrine glands which are richly vascularized, the intermediate lobe of the pituitary contains very few blood vessels; in some species, the pars intermedia is virtually totally avascular. In contrast, pituitary melanotrophs are richly supplied by nerve fibers originating from the hypothalamus. The pars intermedia thus appears as a pure model of neuroendocrine communication, i.e. it is an archetype of the mode of transducing interface between the central nervous system and endocrine effectors. In mammalian species, different types of nerve terminals containing dopamine, norepinephrine, gamma-aminobutyric acid (GABA) and serotonin have been identified. In lower vertebrates, particularly in fish and amphibians, the pars intermedia is also innervated by peptidergic fibers which are though to take part in regulation of the secretory activity of the melanotroph. In these animals, the pars intermedia is regarded as a major center of neuroendocrine integration and an exceptional model to investigate the process of communication between the brain and the endocrine glands. The purpose of the present review is to summarize our current knowledge on the synthesis, processing and release of peptide hormones from pars intermedia cells and to survey the multiple regulatory mechanisms which are involved in the control of the activity of pituitary melanotrophs. Proopiomelanocortin, a multifunctional precursor. Pituitary melanotrophs synthetise a major precursor protein called proopiomelanocortin (POMC) which generates through proteolytic cleavage several biologically active peptides including adrenocorticotropic hormone (ACTH), endorphins and MSHs. In lower vertebrates, alpha-MSH is generally considered as the major hormone secreted by melanotrophs, in that it is involved in the process of skin colour adaptation. The post-translational processing of POMC, which yields to the mature hormones released by melanotrophs, includes a number of steps: glycosylation, phosphorylation, tissue-specific proteolytic cleavage, amidation and acetylation. Some of these posttranslational modifications can be regulated by neuroendocrine factors. For instance, in frogs, it has been shown that dopamine inhibits acetylation of alpha-MSH and thus reduces the secretion of the biologically active form of the peptide. The intermediate lobe of the pituitary: a model of neuroendocrine integration. In most vertebrate species, the intermediate lobe of the pituitary is innervated by catecholamine-containing fibers. In particular, the presence of dopaminergic nerve fibers has been observed in the pars intermedia of mammals and poikilotherms.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of melanotropin-release-inhibiting factor (melanostatin) from frog brain: homology with human neuropeptide Y

A polypeptide was purified from frog brain extracts on the basis of its ability to inhibit alpha-melanotropin release from perifused frog neurointermediate lobes. Based on Edman degradation, amino acid analysis, and peptide mapping, the primary structure of this frog melanotropin-release-inhibiting factor (melanostatin) was determined to be H-Tyr-Pro-Ser-Lys-Pro-Asp-Asn-Pro-Gly-Glu-Asp-Ala-Pro-Ala-Glu-Asp-Met- Ala-Lys-Tyr-Tyr-Ser-Ala-Leu-Arg-His-Tyr-Ile-Asn-Leu-Ile-Thr-Arg-Gln-Arg- Tyr-NH2 . Frog melanostatin belongs to the pancreatic polypeptide/neuropeptide Y/peptide YY family, and the structure of this peptide differs from that of human neuropeptide Y by only one amino acid substitution in position 19. A synthetic replicate of frog melanostatin is coeluted with the native peptide on HPLC and is highly potent in inhibiting alpha-melanotropin secretion in vitro (IC50 = 60 nM).

Effect of acetylcholine on the electrical and secretory activities of frog pituitary melanotrophs

The activity of melanotroph cells of the amphibian pars intermedia is regulated by multiple factors including classical neurotransmitters and neuropeptides. In this study, we have examined the possible involvement of acetylcholine (ACh) in the regulation of electrical and secretory activities of frog pituitary melanotrophs. Electrophysiological recordings were conducted on cultured cells by using the patch-clamp technique in the whole-cell configuration. In parallel, alpha-MSH release from acutely dispersed pars intermedia cells was studied by means of the perifusion technique. In all cells tested in the current-clamp mode, superfusion with ACh (10(-6) M) gave rise to a depolarization associated with an enhanced frequency of action potentials. Administration of ACh (10(-6) M) to perifused cells also induced stimulation of alpha-MSH release. These results indicate that the neurotransmitter ACh exerts a direct stimulatory effect on pituitary melanotrophs. The action of ACh on electrical and secretory activities was mimicked by muscarine (10(-5) M), while ACh-induced alpha-MSH secretion was completely abolished by the muscarinic antagonist atropine (10(-6) M). The depolarizing effect of muscarine was suppressed by the specific M1 muscarinic antagonist pirenzepine (10(-5) M), indicating the existence of a M1 subtype muscarinic receptor in frog pars intermedia cells. In addition, using a monoclonal antibody against calf muscarinic receptors, we have visualized, by the immunofluorescence technique, the presence of muscarinic receptor-like immunoreactivity in cultured intermediate lobe cells. Electrophysiological recordings showed that nicotine (10(-5) M) induces membrane depolarization associated with an increase of the frequency of action potentials.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization and characterization of neuropeptide Y in the brain of Microcebus murinus (Primate, Lemurian)

The distribution of neuropeptide Y (NPY) in the brain of the lemur Microcebus murinus was determined by immunocytochemistry with the aid of a highly specific antiserum against synthetic porcine NPY. When compared with previous immunohistochemical data obtained in primates and other mammalian species, the localization of NPY-immunoreactive (IR) structures in the Microcebus murinus brain revealed particular features. (1) Numerous NPY-IR perikarya and a dense network of IR nerve terminals were found in the supraoptic and suprachiasmatic nuclei, respectively. The occurrence of NPY-IR perikarya in the supraoptic nucleus, also reported in the squirrel monkey, seems to be specific to primates. In the squirrel monkey, the suprachiasmatic nucleus exhibits only a moderate innervation, whereas in humans it appears totally devoid of NPY-IR fibers. (2) IR perikarya and axon processes were observed in many upper brainstem areas, in particular in the interpeduncular, raphe pontine, dorsal tegmental, parabrachial, and dorsal raphe nuclei, in the locus coeruleus, the nucleus of the solitary tract, and the reticular formation; in this latter area, the occurrence of two categories of NPY-IR neurons was demonstrated on the basis of their morphology and localization, suggesting that they may play distinct roles. (3) NPY-IR nerve processes could be traced over a long distance. (4) For the first time, numerous NPY-IR terminals were observed close to the lumen of the various cerebral ventricles. The immunoreactive NPY-like peptide was characterized by combining high performance liquid chromatography (HPLC) analysis and radioimmunoassay quantification. The dilution curves obtained with synthetic porcine NPY and serial dilutions of occipital cortex, paraventricular and supraoptic hypothalamus, posterior hypothalamus, medulla oblongata, or preoptic area extracts were parallel. The highest amounts of NPY were measured in the hypothalamus and telencephalon. HPLC analysis resolved a single peak of NPY-like immunoreactivity that exhibited the same retention time as synthetic porcine NPY. The distribution of NPY in the lemurian brain is discussed with respect to phylogeny and putative functions.

Neuropeptide Y: localization in the central nervous system and neuroendocrine functions

Neuropeptide Y (NPY) is a 36-amino acid peptide first isolated and characterized from porcine brain extracts. A number of immunocytochemical investigations have been conducted to determine the localization of NPY-containing neurons in various animal species including both vertebrates and invertebrates. These studies have established the widespread distribution of NPY in the brain and in sympathetic neurons. In the rat brain, a high density of immunoreactive cell bodies and fibers is observed in the cortex, caudate putamen and hippocampus. In the diencephalon, NPY-containing perikarya are mainly located in the arcuate nucleus of the hypothalamus; numerous fibers innervate the paraventricular and suprachiasmatic nuclei of the hypothalamus, as well as the paraventricular nucleus of the thalamus and the periaqueductal gray. At the electron microscope level, using the pre- and post-embedding immunoperoxidase techniques, NPY-like immunoreactivity has been observed in neuronal cell body dendrites and axonal processes. In nerve terminals of the hypothalamus, the product of the immunoreaction is associated with large dense core vesicles. In lower vertebrates, including amphibians and fish, neurons originating from the diencephalic (or telencephalic) region innervate the intermediate lobe of the pituitary where a dense network of immunoreactive fibers has been detected. At the ultrastructural level, positive endings have been observed in direct contact with pituitary melanotrophs of frog and dogfish. These anatomical data suggest that NPY can act both as a neurotransmitter (or neuromodulator) and as a hypophysiotropic neurohormone. In the rat a few NPY-containing fibers are found in the internal zone of the median eminence and high concentrations of NPY-like immunoreactivity are detected in the hypothalamo-hypophyseal portal blood, suggesting that NPY may affect anterior pituitary hormone secretion. Intrajugular injection of NPY causes a marked inhibition of LH release but does not significantly affect other pituitary hormones. Passive immunoneutralization of endogenous NPY by specific NPY antibodies induces stimulation of LH release in female rats, suggesting that NPY could affect LH secretion at the pituitary level. However, NPY has no effect on LH release from cultured pituitary cells or hemipituitaries. In addition, autoradiographic studies show that sites for 125I-labeled Bolton-Hunter NPY or 125I-labeled PYY (2 specific ligands of NPY receptors) are not present in the adenohypophysis, while moderate concentrations of these binding sites are found in the neural lobe of the pituitary. It thus appears that the inhibitory effect of NPY on LH secretion must be mediated at the hypothalamic level.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain neuropeptide Y in the control of adrenocorticotropic hormone secretion in the dog

An immunoneutralization technique with specific antibodies was used to explore the role of endogenous neuropeptide Y (NPY) in the adrenocorticotropic hormone (ACTH) release after hypoglycemic stress in the dog. Dogs received injections of rabbit antihuman NPY gamma-globulin (anti-NPY) or normal gamma-globulin (NGG) into the third cerebral ventricle, which was followed by i.v. injection of insulin. Hypoglycemia of a 40% fall in systemic glucose levels occurred in anti-NPY-treated dogs as well as NGG-treated animals. An intraventricular administration of anti-NPY significantly inhibited the ACTH and cortisol release to hypoglycemia, but had no effect on the pancreatic polypeptide (PP) response. These findings suggest involvement by endogenous NPY in the ACTH secretion induced by hypoglycemia.

Quantitative autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites in rat brain. Comparison with [125I]peptide YY receptor sites

The autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites was quantified in rat brain. The highest level of [125I]Bolton-Hunter neuropeptide Y binding sites was seen in the hippocampus (ventral stratum radiatum, CA3 subfield: 6029 +/- 250 fmol/g tissue). The distribution of these sites was clearly laminated, being particularly concentrated in the oriens layer (dorsal CA3 subfield: 2562 +/- 147 fmol/g tissue) and stratum radiatum (dorsal CA3 subfield: 2577 +/- 95 fmol/g tissue). Lower levels of sites were seen in the pyramidal cell layer (1708 +/- 105 fmol/g tissue) and the molecular layer (1155 +/- 116 fmol/g tissue). The cortical distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites was also laminated, being particularly enriched in superficial laminae (occipital cortex, layers I-II, 4038 +/- 148 fmol/g tissue; layers III-IV, 1392 +/- 97 fmol/g tissue and layers V-VI, 1522 +/- 138 fmol/g tissue). Other areas containing high amounts of sites included the anterior olfactory nuclei (ventral part, 4935 +/- 119 fmol/g tissue; lateral part, 4530 +/- 149 fmol/g tissue; dorsal part, 3378 +/- 140 fmol/g tissue and medial part, 2601 +/- 150 fmol/g tissue); anteromedial (5168 +/- 211 fmol/g tissue), medial (4611 +/- 107 fmol/g tissue) and lateral posterior thalamic nuclei (4465 +/- 189 fmol/g tissue); medial mammillary nucleus (5555 +/- 241 fmol/g tissue); medial geniculate nucleus (4747 +/- 56 fmol/g tissue); claustrum (4123 +/- 235 fmol/g tissue); posteromedial cortical amygdaloid nucleus (3524 +/- 138 fmol/g tissue), tenia tecta (2540 +/- 195 fmol/g tissue); lateral septum (1785 +/- 90 fmol/g tissue); suprachiasmatic hypothalamic nucleus (1604 +/- 115 fmol/g tissue), and substantia nigra, pars compacta (1846 +/- 142 fmol/g tissue) and pars lateralis (1750 +/- 165 fmol/g tissue). Areas moderately enriched with [125I]Bolton-Hunter neuropeptide Y binding sites included the zonal layer of the superior colliculus (1347 +/- 71 fmol/g tissue); anterior pretectal nucleus (1172 +/- 113 fmol/g tissue); ventral tegmental area (1090 +/- 97 fmol/g tissue); periventricular fibre system (1026 +/- 48 fmol/g tissue); core of nucleus accumbens (948 +/- 29 fmol/g tissue) and area postrema (799 +/- 87 fmol/g tissue). These results are discussed with regard to some of the suggested biological effects of neuropeptide Y in the central nervous system such as effects on learning, locomotion and circadian rhythms. Moreover, we also compared the distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites with that of [125I]peptide YY sites in rat brain. The resolution of the autoradiographic image is better with [125I]peptide YY most likely because of higher affinity and percentage of specific labelling.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y inhibits thyrotropin-releasing hormone-induced stimulation of melanotropin release from the intermediate lobe of the frog pituitary

Previous studies have shown that the release of melanotropin from frog neurointermediate lobes is under the control of two neuropeptides: thyrotropin-releasing hormone (TRH) stimulates, while neuropeptide Y (NPY) inhibits alpha-melanocyte-stimulating hormone (alpha-MSH) secretion from intact neurointermediate lobes in vitro. The aim of the present study was to investigate possible interactions between the two regulatory peptides at the pituitary level. Whole neurointermediate lobes or acutely dispersed pars intermedia cells from Rana ridibunda were perifused in vitro for 2 to 7.5 hr and the concentrations of alpha-MSH released into the effluent perifusate were monitored by radioimmunoassay. Administration of TRH (10(-7) M) or NPY (10(-7) M) to dispersed cells induced, respectively, marked stimulation or inhibition of alpha-MSH release. The effects of the two neuropeptides were similar to those observed using intact neurointermediate lobes, suggesting that TRH and NPY act directly on melanotropic cells. Perifused whole neurointermediate lobes were exposed to NPY (10(-8) to 3 x 10(-7) M) for 120 min and a single dose of TRH (10(-8) M) was administered during the prolonged infusion of NPY. Using this procedure, we observed a dose-dependent inhibition of TRH-evoked alpha-MSH release. These data support the concept that TRH and NPY act through a common intracellular pathway to regulate alpha-MSH release.

Characterization, cerebral distribution and gonadotropin release activity of neuropeptide Y (NPY) in the goldfish

The presence of a peptide closely related to porcine NPY has been demonstrated in the goldfish brain and pituitary by means of radioimmunoassay (RIA) and high performance liquid chromatography (HPLC). The RIA data demonstrate that displacement curves of brain extracts are parallel to a porcine NPY standard and that in HPLC a compound present in brain extracts is co-eluted with porcine NPY. The distribution of this NPY-like factor within the central nervous system was studied by radioimmunoassay and immunohistochemistry. The results indicated that NPY has a widespread distribution with the highest concentrations being found in the telencephalon and diencephalon. In the pituitary gland, NPY immunoreactive terminals characterized at the electron microscope level were found in the different lobes and, in particular, in close association with the gonadotrophin (GTH) secreting cells. Using anin vitro perifusion system, it was shown that NPY causes a dose dependent increase of GTH release from anterior lobe fragments.These data indicate for the first time in teleosts that NPY is present and widely distributed in the brain and pituitary, and that among other putative functions, could be implicated in the multihormonal release of GTH from the pituitary.

Neuropeptides regulating the activity of goldfish corticotropes and melanotropes

The goldfish (Carassius auratus) has proven an advantageous model for investigations of the neuroendocrine regulation of pituitary hormone secretion in teleost fishes. Investigations examining the secretion of adrenocorticotropin (ACTH) and melanocyte-stimulating hormone (MSH) from pituitary cellsin vitro have been used to identify neuropeptides influencing goldfish corticotrope and melanotrope activity. Ovine CRF, urotensin I (UI), arginine vasotocin (AVT), isotocin and angiotensins I and II stimulate the release of ACTH from corticotropesin vitro. Thyrotropin-releasing hormone (TRH), oCRF, UI and neuropeptide Y stimulate the release of MSH from melanotropesin vitro. Immunocytochemical studies have revealed the presence of separate CRF- and UI-immunoreactive perikarya in the hypothalamus suggesting the existence of two structurally similar, yet distinct, hypothalamic CRF-UI-like peptides. Interactions of AVT and CRF in the regulation of ACTH secretion is suggested from studies demonstrating the co-localization of AVT- and CRF-immunoreactivities in perikarya of the preoptic-hypophyseal system. These investigations demonstrate that the secretory activity of goldfish corticotropes and melanotropes is influenced by a diversity of neuropeptides of hypothalamic origin.

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.