Growth hormone release in man induced by galanin, a new hypothalamic peptide

Spexin-expressing neurons in the magnocellular nuclei of the human hypothalamus

Neuropeptides are involved in numerous brain activities being responsible for a wide spectrum of higher mental functions. The purpose of this concise, structural and qualitative investigation was to map the possible immunoreactivity of the novel neuropeptide spexin (SPX) within the human magnocellular hypothalamus. SPX is a newly identified peptide, a natural ligand for the galanin receptors (GALR) 2/3, with no molecular structure similarities to currently known regulatory factors. SPX seems to have multiple physiological functions, with an involvement in reproduction and food-intake regulation recently revealed in animal studies. For the first time we describe SPX expressing neurons in the supraoptic (SON) and paraventricular (PVN) nuclei of the human hypothalamus using immunohistochemical and fluorescent methods, key regions involved in the mechanisms of osmotic homeostasis, energy expenditure, consummatory behaviour, reproductive processes, social recognition and stress responses. The vast majority of neurons located in both examined neurosecretory nuclei show abundant SPX expression and this may indirectly implicate a potential contribution of SPX signalling to the hypothalamic physiology in the human brain.

Effects of temperature on the transcriptomes of pituitary and liver in Golden Pompano Trachinotus blochii

Fish growth can be modulated dynamically through the brain-pituitary-liver regulation axis. In the present study, whole transcriptomes of the pituitary and liver from Golden Pompano Trachinotus blochii were sequenced in seawater at 20 °C (T_low) and 25 °C (T_high). A total of 187,277,583 paired-end reads were assembled to obtain 100,495 transcripts, corresponding to 83,974 genes. These reads were mapped to T. blochii transcripts, and the mapping accuracy ranged from 80.4 to 94.9%. Two lists of differentially expressed genes were obtained by comparisons of pituitary and liver T_low versus T_high groups, comprising 458 and 205 genes, respectively. Of these, 33 differentially expressed genes were common between the two lists. Twelve GO terms were overrepresented for the 458 differentially expressed genes in the pituitary, and it is noteworthy that the GO term galanin receptor activity (GO: 0004966) related to the modulation of appetite and metabolism, whose genes made up half of all assembled genes in the term. For the 205 differentially expressed genes in the liver, 19 overrepresented GO terms were mainly related to immune regulation, digestion, and protein metabolism. Among the common differentially expressed genes, there were 32 genes that had identical changing trends in both pituitary and liver comparisons. Furthermore, two GO terms inorganic diphosphatase activity and MHC protein complex were overrepresented. These results indicate that the brain could regulate pituitary function through galanin signal mechanism and that the metabolism of liver was further optimized to modulate immunity and growth under different temperatures.

Preclinical Analgesic and Safety Evaluation of the GalR2-preferring Analog, NAX 810-2

The potential clinical utility of galanin peptidic analogs has been hindered by poor metabolic stability, lack of brain penetration, and hyperglycemia. In addition to possessing potent anticonvulsant efficacy, galanin analogs are analgesic in various assays. The purpose of these studies was to evaluate the lead galanin receptor type 2 (GalR2)-preferring analog, NAX 810-2, in various pain assays, as well as determine any potential for insulin inhibition, growth hormone stimulation, and cognitive impairment. NAX 810-2 was evaluated in mouse (carrageenan, formalin, tail flick, plantar incision) and rat pain models (partial sciatic nerve ligation). NAX 810-2 dose-dependently increased paw withdrawal latency following plantar administration of carrageenan (ED₅₀ 4.7 mg/kg). At a dose of 8 mg/kg, NAX 810-2 significantly attenuated nociceptive behaviors following plantar administration of formalin, and this was observed for both phase I (acute) and phase II (inflammatory) components of the formalin behavioral response. NAX-810-2 was active at higher doses in the mouse tail flick model (ED₅₀ 20.2 mg/kg) and similarly, reduced mechanical allodynia following plantar incision in mice at a dose of 24 mg/kg. NAX 810-2 also reduced mechanical allodynia in the partial sciatic nerve ligation model at a dose of 4 mg/kg. In addition, NAX 810-2 did not impair insulin secretion at doses of 2.5 and 8 mg/kg (acutely) or at a dose of 8 mg/kg given daily for 5 days. Similarly, 8 mg/kg (twice daily, 5 days) of NAX 810-2 did not increase growth hormone levels. These results demonstrate that NAX 810-2 possesses a favorable pre-clinical profile as a novel and first-in-class analgesic.

Comparative Anterior Pituitary miRNA and mRNA Expression Profiles of Bama Minipigs and Landrace Pigs Reveal Potential Molecular Network Involved in Animal Postnatal Growth

The anterior pituitary is the most important endocrine organ modulating animal postnatal growth, mainly by controlling growth hormone (GH) gene transcription, synthesis, and secretion. As an ideal model for animal postnatal growth studies, the Bama minipig is characterized as having a lower growth performance and fewer individual differences compared with larger pig breeds. In this study, anterior pituitaries from Bama minipig and Landrace pig were used for miRNA and mRNA expression profile analysis using miRNA microarrays and mRNA-seq. Consequently, a total of 222 miRNAs and 12,909 transcripts were detected, and both miRNAs and mRNAs in the two breeds showed high correlation (r > 0.97). Additionally, 41 differentially expressed miRNAs and 2,254 transcripts were identified. Pathways analysis indicated that 32 pathways significantly differed in the two breeds. Importantly, two GH-regulation-signalling pathways, cAMP and inositol 1, 4, 5-triphosphate (IP3), and multiple GH-secretion-related transcripts were significantly down-regulated in Bama minipigs. Moreover, TargetScan and RNAHybrid algorithms were used for predicting differentially expressed miRNAs (DE miRNAs) and differentially expressed mRNAs (DE mRNAs) interaction. By examining their fold-changes, interestingly, most DE miRNA-DE mRNA target pairs (63.68-71.33%) presented negatively correlated expression pattern. A possible network among miRNAs, mRNAs, and GH-regulation pathways was also proposed. Among them, two miRNA-mRNA interactions (Y-47 targets FSHB; ssc-miR-133a-3p targets GNAI3) were validated by dual-luciferase assay. These data will be helpful in understanding the possible molecular mechanisms involved in animal postnatal growth.

Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity

Galanin was first identified 30 years ago as a "classic neuropeptide," with actions primarily as a modulator of neurotransmission in the brain and peripheral nervous system. Other structurally-related peptides-galanin-like peptide and alarin-with diverse biologic actions in brain and other tissues have since been identified, although, unlike galanin, their cognate receptors are currently unknown. Over the last two decades, in addition to many neuronal actions, a number of nonneuronal actions of galanin and other galanin family peptides have been described. These include actions associated with neural stem cells, nonneuronal cells in the brain such as glia, endocrine functions, effects on metabolism, energy homeostasis, and paracrine effects in bone. Substantial new data also indicate an emerging role for galanin in innate immunity, inflammation, and cancer. Galanin has been shown to regulate its numerous physiologic and pathophysiological processes through interactions with three G protein-coupled receptors, GAL1, GAL2, and GAL3, and signaling via multiple transduction pathways, including inhibition of cAMP/PKA (GAL1, GAL3) and stimulation of phospholipase C (GAL2). In this review, we emphasize the importance of novel galanin receptor-specific agonists and antagonists. Also, other approaches, including new transgenic mouse lines (such as a recently characterized GAL3 knockout mouse) represent, in combination with viral-based techniques, critical tools required to better evaluate galanin system physiology. These in turn will help identify potential targets of the galanin/galanin-receptor systems in a diverse range of human diseases, including pain, mood disorders, epilepsy, neurodegenerative conditions, diabetes, and cancer.

Novel galanin receptors in teleost fish: identification, expression and regulation by sex steroids

In fish, the onset of puberty, the transition from juvenile to sexually reproductive adult animals, is triggered by the activation of pituitary gonadotropin secretion and its timing is influenced by external and internal factors that include the growth/adiposity status of the animal. Kisspeptins have been implicated in the activation of puberty but peripheral signals coming from the immature gonad or associated to the metabolic/nutritional status are also thought to be involved. Therefore we hypothesize the importance of the galinergic system in the brain and testis of pre-pubertal male sea bass as a candidate to translate the signals leading to activation of testicular maturation. Here, the transcripts for four galanin receptors (GALR), named GALR1a, 1b, 2a and 2b, were isolated from European sea bass, Dicentrarchus labrax. Phylogenetic analysis confirmed the previously reported duplication of GALR1 in teleost fish, and unravelled the duplication of GALR2 in teleost fish and in some tetrapod species. Comparison with human showed that the key amino acids involved in ligand binding are present in the corresponding GALR1 and GALR2 orthologs. Transcripts for all four receptors are expressed in brain and testes of adult fish with GALR1a and GALR1b abundant in testes and hardly detected in ovaries. In order to investigate whether GALR1 dimorphic expression was dependent on steroid context we evaluated the effect of 11-ketotestosterone and 17β-estradiol treatments on the receptor expression in brain and testes of pre-pubertal males. Interestingly, steroid treatments had no effect on the expression of GALRs in the brain while in the testes, GALR1a and GALR1b were significantly up regulated by 11KT. Altogether, these results support a role for the galaninergic system, in particular the GALR1 paralog, in fish reproductive function.

Identification and characterization of the chicken galanin receptor GalR2 and a novel GalR2-like receptor (GalR2-L)

In mammals, the neuropeptide galanin exerts a variety of physiological roles in the neuroendocrine system through its interactions with three galanin receptor subtypes (GalR1, GalR2 and GalR3). However, little is known about the characteristics of galanin receptors in birds, and it is only recently that avian GalR1 and a novel GalR1-like receptor were first identified in chickens. In this study, we report the cDNA cloning and characterization of the other two chicken galanin receptors, the galanin type II receptor (cGalR2) and a novel GalR2-like receptor (GalR2-L), which share high degrees of similarity in sequence identity, gene structure and signaling properties. cGalR2 and cGalR2-L cDNAs encode two putative receptors of 371 and 370 amino acids, in which they show considerable amino acid sequence identities (65-67%, and 53-55%, respectively) with the mammalian GalR2. RT-PCR assays revealed that cGalR2 and cGalR2-L mRNA were widely expressed in the adult chicken tissues including the whole brain, intestine, lung, ovary, pituitary and different regions of the oviduct. As assayed with different luciferase reporter systems, chicken galanin (cGal 1-29) and human galanin-like peptide (hGALP 1-60) were demonstrated to stimulate the luciferase activities in Chinese hamster ovary cells expressing cGalR2 and cGalR2-L through the activations of cAMP/PKA, Ca(2+)/calcineurin and MAPK/ERK signaling pathways, hence suggesting that both receptors are functionally coupled to the G(s) and G(q) proteins. Furthermore, the previously identified cGalR1 and cGalR1-L were found to be solely coupled to the G(i/o) proteins, and the hGALP (1-60) exhibited only a low potency to cGalR1, cGalR1-L, cGalR2 and cGalR2-L activations.

Galanin and its three receptors in human pituitary adenoma

Galanin, a 29-aminoacid peptide (30 in humans), is widely distributed in the nervous and endocrine systems and exerts its actions via three G-protein-coupled receptors, GalR1-3. The galanin system has, among others, been associated with tumorigenesis. Our objective was to assess the expression of galanin and its receptors in pituitary tumors. Transcript levels of galanin and galanin receptors 1-3 (GalR1-3) were measured using quantitative real-time PCR (q-PCR) in pituitary tumors, surgically removed from thirteen patients, and twelve post mortem pituitaries. Galanin, GalR1 and GalR2 mRNA, but not GalR3 mRNA, were found in the twelve human post-mortem pituitaries. Expression of GalR1 was relatively increased in most, whereas GalR2 was decreased in some tumors. High levels of GalR3 were only found in tumors of five patients, who all relapsed shortly after surgical intervention. The results suggest that GalR3, a receptor for the neuroendocrine peptide galanin, is a potential marker for relapsing pituitary tumors. Thus, galanin receptors may play an important role in pituitary tumors, also for surgical outcome and prognosis, and may serve as a diagnostic tool. The association of GalR3 with tumor relapse suggests that antagonists to this receptor represent a potential therapeutic approach to treatment of pituitary tumors.

Characterization of the chicken galanin type I receptor (GalR1) and a novel GalR1-like receptor (GalR1-L)

Galanin is a multi-functional neuropeptide that is widely distributed in the mammalian central nervous system and peripheral tissues. It exerts multiple physiological functions through interaction with 3 known G protein-coupled receptors (GPCR), namely, galanin type I, II and III (GalR1, 2 and 3) receptors, which have only been identified in mammals. In this study, we reported the cloning and characterization of chicken galanin type I receptor (GalR1) and a novel galanin receptor with considerable homology to chicken GalR1, which herein is designated as galanin type I-like receptor (GalR1-L). Chicken GalR1 and GalR1-L full-length cDNAs were cloned from chicken brain and small intestine tissue, respectively. The former encodes a protein of 357 amino acids that shares 84-86% amino acid sequence identities with its mammalian counterparts, whereas the latter encodes a 363-amino acid protein with comparatively lower identities (55-56%) to the mammalian GalR1. Using reverse transcription (RT)-PCR assays, we examined the expression of both receptors in adult chicken tissues. Both receptors were found to be widely distributed in the tissues examined, including brain, small intestine, kidney, ovary, pancreas, pituitary and spleen. Interestingly, cGalR1 expression was detected in different regions of chicken oviduct, while cGalR1-L expression was restricted to the vagina. Using a pGL3-CRE luciferase reporter system, chicken galanin peptide (1-29) was demonstrated to inhibit both basal and forskolin-stimulated luciferase activities, in dose-dependent manners, through the cAMP-mediated signaling pathway in Chinese hamster ovary (CHO) cells expressing either cGalR1 or cGalR1-L, thus suggesting the functional couplings of both receptors to G(i) proteins. Together, the characterization of chicken GalR1 and GalR1-L provides a better understanding of the physiological roles of galanin in avian species.

Chronic increase of circulating galanin levels induces obesity and marked alterations in lipid metabolism similar to metabolic syndrome

OBJECTIVE

Galanin (GAL) has a role in the regulation of food intake by way of acting on the central nervous system in rodents. High serum GAL levels have been observed in obese human subjects, suggesting that peripheral GAL has a role in the regulation of energy balance and that elevated circulating GAL levels contribute to the development of obesity and obesity-associated metabolic impairments. Currently, it is not known how chronically increased levels of circulating GAL affect energy balance. The purpose of this study is to clarify the importance of chronically increased levels of circulating GAL on energy balance in a transgenic mouse model.

RESEARCH DESIGN AND METHODS

Male wild-type and homozygous galanin transgenic (GAL-Tg) mice were used to study the peripheral effects of a 10-fold increase in circulating GAL on food intake, body weight, lipid metabolism, hepatic steatosis, glucose homeostasis and energy expenditure.

RESULTS

In the absence of an orexigenic effect, GAL-Tg mice had increased body weight, visceral adiposity, total serum cholesterol, total serum triglycerides and hyperinsulinemia, as well as impaired glucose tolerance. Compared with wild-type mice, the obese phenotype observed in the GAL-Tg mice was attributed to decreased oxygen consumption and carbon dioxide production, and this effect was independent of any changes in food intake or horizontal activity. In this obese model, GAL contributed to the development of fatty liver disease, which was associated with impaired glucose tolerance, as well as a reduction in heat production and metabolic rate.

CONCLUSIONS

Chronically elevated GAL may regulate body weight, metabolic rate, and lipid and carbohydrate metabolism through a mechanism that is independent of feeding regulation. The obese phenotype in the GAL-Tg mice is related to the reduced energy expenditure and insulin resistance. These findings support the hypothesis that increased circulating GAL levels contribute to the development of metabolic syndrome.

Effects of galanin-monoaminergic interactions on vasopressin secretion in rat neurohypophyseal cell cultures

The effects of dopamine (DA), serotonin (5-HT), histamine (HA), adrenaline (ADR), noradrenaline (NADR) and K(+) administration on vasopressin (VP) secretion were studied in 13-14-day cultures of rat neurohypophyseal (NH) cells, and it was examined whether galanin (GAL) can modify the VP release enhancement induced by these monoaminergic compounds. An enzymatic dissociation technique was used to make the rat NH cell cultures. The VP contents of the supernatants of 14-day cultures were determined by radioimmunoassay. Following the administration of 10(-6) M GAL, the VP secretion into the supernatant media decreased. DA, 5-HT, ADR or NADR treatment increased the VP level substantially, while the enhancing effect of HA was more moderate. GAL administration before DA, ADR and NADR treatment prevented the VP concentration increase induced by DA, ADR or NADR. Preincubation with GAL reduced the 5-HT- or HA-induced VP level increases; the VP concentrations of the supernatant media remained above the control level. The GAL blocking effect was prevented by previous treatment with the GAL receptor antagonist galantid (M15). GAL had no effect on the VP level increase induced by K(+), which causes a non-specific hormone secretion. The results indicate that the changes in VP secretion induced by the monoaminergic system can be directly influenced by the GAL-ergic system. The interactions between the monoaminergic and GAL-ergic systems regarding VP secretion occur at the level of the posterior pituitary.

Targeted disruption of the galanin gene attenuates inflammatory responses in murine skin

The release of neuropeptides from primary sensory nerve fibers has been implicated in the modulation of local immune responses in surface tissues, such as the skin and the gastrointestinal mucosa, thereby inducing neurogenic inflammation, which is characterized by plasma extravasation and vasodilatation. In addition, cytokines, either alone or in conjunction with neuropeptides, initiate recruitment of immunocompetent cells such as neutrophils during the initial phases of inflammation. Growing evidence suggests that the neuropeptide galanin plays an important role in skin immune defense and pathophysiology. In this paper, we report that adult mice carrying a loss-of-function mutation in the galanin gene (galanin knockout, Gal KO) demonstrate an absence of the normal neurogenic inflammatory response, upon treatment of the skin either with the vanilloid receptor 1 agonist capsaicin or noxious heat. Furthermore, a lack of an acute inflammatory edema induced by coinjection of substance P and calcitonin gene-related peptide was observed. In addition, Gal KO animals also exhibit a deficit in neutrophil accumulation in the skin after exposure to noxious heat, carrageenin, or tumor necrosis factor alpha. These data indicate that Gal KO mice demonstrate abnormal neurogenic inflammatory responses in murine skin compared to strain-matched wild-type mice.

Galanin-like peptides exert potent vasoactive functions in vivo

The cutaneous vasculature plays a key role in the pathophysiology of inflammatory skin diseases. The vascular activity is under the control of the peripheral nervous system that includes locally released neuropeptides. Recently, we detected receptors for the neuropeptide galanin in association with dermal blood vessels, suggesting a role of the galanin-peptide-family in the regulation of the cutaneous microvasculature. Therefore, we have investigated galanin and galanin-like peptide (GALP), a neuropeptide previously only considered to be involved in metabolism and reproduction in the central nervous system, for vaso-modulatory activity in the murine skin in vivo. Picomole amounts of intradermally injected galanin and GALP decreased cutaneous blood flow and inhibited inflammatory edema formation. Both the full-length GALP (1-60) and the putative smaller proteolytic fragment GALP (3-32) showed similar effects. These activities are most likely mediated by galanin receptors galanin receptor subtype 2 (GalR2) and/or galanin receptor subtype 3 (GalR3), because reverse transcription-PCR analysis of murine skin revealed messenger RNA (mRNA) expression of GalR2 and GalR3 but not of galanin receptor subtype 1. The lack of galanin receptor mRNAs in endothelial and smooth muscle cells indicates a neuronal localization of these receptors around the vessels. These results indicate functional activity of GALP in the periphery in vivo and suggest a potential role as an inflammatory modulator.

Homodimerization and internalization of galanin type 1 receptor in living CHO cells

Galanin is a 29- to 30-aa-long neuropeptide affecting feeding, cognitive, and sexual behavior. It exerts its effects through galanin receptors 1, 2 and 3, which are all seven transmembrane domain G-protein coupled receptors (GPCRs). The GPCRs have been shown to function as monomers, homodimers, heterodimers and oligomers. In this study, we examined the extent of galanin receptor 1 (GalR1) dimerization and internalization in living CHO cells using fluorescence resonance energy transfer (FRET) and time lapse confocal imaging. Ratio imaging analysis and emission spectral analysis revealed substantial homodimerization of GalR1. In addition, internalization of GalR1 after 1h of agonist stimulation with the GalR1 agonist galanin (1-29) was observed with time lapse fluorescence imaging, whereas stimulation with the GalR2 specific agonist galanin (2-11) did not lead to internalization. Treatment of GalR1 transfected cells with the non-selective adenylyl cyclase activator forskolin influenced the rate of internalization when administered together with galanin (1-29). These results indicate that GalR1 can act as a dimer on the cell surface and that receptor desensitization and internalization was observed after stimulation with the agonist galanin (1-29). Western blots further confirm the FRET data that GalR1-XFP dimerizes and can be detected in the cell as a monomer or dimer using antibodies to XFP. Internalization and dimerization of GalR1 is shown, contributing to the regulation of galanergic signaling.

Inhibitory effects of different galanin compounds and fragments on osmotically and histamine-induced enhanced vasopressin secretion in rats

The effects of rat, porcine and human galanin, and the human 1-16 and human 16-30 terminal galanin fragments on vasopressin secretion were studied in rat. The plasma vasopressin level was determined by radioimmunoassay (RIA). There were no changes in the basal vasopressin secretion after galanin administration. A significant increase in vasopressin concentration was detected following 2.5% NaCl or histamine administration. I.c.v. injected rat, porcine or human galanin or the 1-16 N-terminal galanin fragment prevented the plasma vasopressin level enhancement. Following the i.v. administration of rat galanin or the i.c.v. injected 16-30 C-terminal galanin fragment, the vasopressin concentration did not return to the normal level. Administration of the galanin antagonist galantid (M15) i.c.v. before the rat galanin i.c.v. injection prevented the inhibitory effect on the increased plasma vasopressin level following 2.5% NaCl solution or histamine administration. The results indicate that there is no significant difference in the inhibitory effect of rat, porcine or human galanin or the 1-16 galanin fragment on the enhanced plasma vasopressin secretion induced by hyperosmosis or histamine administration. Our findings suggest that galanin, as a peptide modulator, is physiologically involved in the regulation of vasopressin release following different forms of stimulation: an osmotic response or histamine administration.

Galanin in the brain: chemoarchitectonics and brain cartography--a historical review

We present a review of galanin in the brain from a historical perspective of the development of "chemoarchitectonics" and "brain cartography" accomplished in the Histopharmacology Section at the National Institutes of Health. It was the mapping of potential brain neuroregulators that served as a springboard of ideas from which behavioral studies emanate. The integration of the known localization of neurotransmitter/neuromodulatory nerves ("chemoarchitectonic maps") and receptor binding sites with biochemical data derived from brain micropunches coupled with behavioral analysis at the level of discrete brain allows one to define the anatomical circuits which support behavioral changes and which ultimately will improve our understanding of mental disorders.

Galanin in pituitary adenomas

Tumor galanin content was measured in extracts from human pituitary adenomas using a specific RIA method for monitoring human galanin. Twenty-two out of twenty-four tumors contained galanin with notably high levels in corticotroph adenomas, varying levels in clinically inactive tumors, and low levels in GH secreting adenomas. Tumor galanin and ACTH contents were closely correlated in all tumors. In four young patients with microadenomas and highly active Mb Cushing tumor galanin was inversely related to tumor volume. The molecular form of tumor galanin, studied with reverse-phase HPLC, was homogeneous with the majority of tumor galanin coeluting with standard human galanin. In the tumors analysed with in situ hybridization there was a good correlation between galanin peptide levels and galanin mRNA expression. In some tumors galanin mRNA and POMC levels coexisted, in others they were essentially in different cell populations. Levels of plasma galanin-LI were not related to tumor galanin concentration, and galanin levels were in the same range in sinus petrosus close to the pituitary venous drainage as in peripheral blood. Corticotrophin releasing hormone injections in two patients caused ACTH, but no detectable galanin release into sinus petrosus. Our results demonstrate that corticotroph, but not GH adenomas, express high levels of galanin, in addition to ACTH, and that in some tumors both polypeptides are synthesised in the same cell population. However, galanin levels in plasma were not influenced by the tumor galanin content.

Inhibitory effect of galanin on dopamine-induced enhanced vasopressin secretion in rat neurohypophyseal tissue cultures

The effect of galanin (GAL) on vasopressin (VP) secretion was studied in 13-14-day cultures of isolated rat neurohypophyseal (NH) tissue. The VP content of the supernatant was determined by radioimmunoassay (RIA) after a 1- or 2-h incubation. A significantly decreased content of VP was detected following the administration of 10(-6)-10(-9) M doses of GAL. Dopamine (DA) and the DA-active drugs apomorphine (APM) and Pro-Lys-Gly (PLG) (10(-6) M in each medium) increased the VP level of NH tissue cultures. This VP concentration elevation could be blocked by the administration of GAL together with DA, APM or PLG. The DA-blocking effect of GAL was prevented by previous treatment with the GAL receptor antagonist galantid (M15). The results indicate that VP release is directly influenced by the GAL-ergic system. The GAL-ergic control of VP secretion from NH tissue in rats can occur independently of the hypothalamus, at the level of the posterior pituitary.

Distribution of Galanin mRNA Containing Cells and Galanin Receptor Binding Sites in Human and Rat Hypothalamus

The distribution of cells containing galanin mRNA and that of galanin receptor binding sites were investigated using in situ hybridization histochemistry and receptor autoradiography in male rat hypothalamus and in postmortem hypothalamic tissues from control human brains. Oligonucleotide probes labelled with 32P were used for hybridization experiments. The specificity of the hybridization signal was ascertained using several probes, competition assays and Northern blot analysis. High levels of hybridization were found in the paraventricular, supraoptic and arcuate nuclei of rat and human hypothalamus. Human intermediate nuclei and scattered cells of the posterior perifornical nucleus also contained galanin mRNA. Galanin mRNA was also found in the dorsomedial nucleus of the rat. The distribution of galanin receptor sites was investigated by receptor autoradiography using 125I-labelled porcine galanin. The specificity of the binding was assessed by competition with different neuropeptides. While galanin blocked the binding at nanomolar concentrations, the other neuropeptides examined were ineffective at 10-7 M concentrations. The highest densities of galanin binding sites were seen in the preoptic area, ventromedial and lateral nuclei, of rat and human hypothalamus. In contrast, very low densities of binding sites were observed in the paraventricular, supraoptic and arcuate nuclei. Our results show that the distribution of neurons expressing galanin is complementary to that of galanin receptors in the rat and human hypothalamus. This suggests that receptors for galanin are not located on the cell bodies of galaninergic neurons, but are probably presynaptic on or postsynaptic to the processes of these cells.

Evaluation of the circadian profile of peripheral plasma galanin concentrations in normal subjects

Galanin administration can influence pituitary function principally resulting in an increase in GH secretion. However, the role of circulating GAL levels in human endocrine function is still unknown. In the present study we simultaneously measured the circadian profiles of GAL, ACTH and GH in peripheral blood of ten adult subjects. Plasma samples were collected through an intravenous catheter at 0800, 1200, 1600, 2000, 2200, 2400, 0200, 0400 hours. The results were statistically evaluated by the cosinor analysis technique. A significant circadian rhythm of both plasma ACTH (p < 0.001) and GH levels (p < 0.03) was found with acrophases occurring at 0753 hrs and 0131 hrs for ACTH and GH, respectively. On the contrary, no significant rhythm was found in plasma GAL levels, indicating that no correlations exist between GAL and either GH or ACTH circadian profiles. Furthermore, the simultaneous assay of both GAL and GH plasma levels during a nocturnal frequent sampling performed in four volunteers showed the presence of peaks in GAL levels which, however, were not concomitant to the peaks in GH levels. These data demonstrate the lack of rhythmicity in the circadian profile of plasma GAL levels in healthy human subjects. The role of GAL in human endocrine function remains unknown and these results suggest that, in spite of the well documented increase in plasma GH concentrations following the intravenous administration of GAL, physiologically circulating levels of GAL are likely not involved in the regulation of GH secretion.

Galanin immunoreactive innervations of the anterior pituitary in the monkey and the dog

As we know, the anterior pituitary is regulated by hypothalamic hormones via the portal system. However, our recent studies have demonstrated the presence of a substantial amount of substance P (SP)- and calcitonin gene-related peptide (CGRP)-containing nerve fibers in the anterior pituitary. In the present paper, the existence of a considerable amount of galanin (GAL)like immunoreactive (ir) nerve fibers with numerous of varicosities in the anterior pituitaries of the Macaca mulatta monkey and the dog were reported. In the monkey, GAL-ir nerve fibers with a large amount of varicosities were mainly located in the medial part of the gland, dominantly in its dorso-posterior regions. A great majority of varicosities were found to be closely related to the glandular tissue although some were located along the walls of blood sinus. GAL-ir nerve fibers were traced to enter the pars distalis of the anterior pituitary from the stalk as well as from the meningeal sheath covering the upper part of the anterior pituitary. Numerous GAL-ir cells presented in the pars distalis and the pars intermedia of the adenohypophysis. In the dog pituitary, GAL-ir nerve fibers were mainly located in the tail part and some in oral region. A majority of GAL-ir nerve fibers were at the periphery of the gland, especially in the medial planes, although some could be found deep in the gland. They appeared in individual fibers or in patches. Many GAL-ir nerve fibers and fiber fascicles existed in the median eminence and the sheath covering the tail and the oral part of the pituitary.

Expression of cholecystokinin, enkephalin, galanin and neuropeptide Y is markedly changed in the brain of the megencephaly mouse

Megencephaly, enlarged brain, is a major sign in several human neurological diseases. The mouse model for megencephaly (mceph/mceph) has an enlarged brain, presumably due to brain cell hypertrophy, and exhibits neurological and motor disturbances with seizure-like activity, as well as disturbances in the insulin-like growth factor system. Here, we report that expression of the neuropeptides cholecystokinin, enkephalin, galanin and neuropeptide Y is dramatically changed in mceph/mceph brains compared to wild type, as revealed by in situ hybridization and immunohistochemistry. The changes were confined to discrete brain regions and occurred in a parallel fashion for peptides and their transcripts. For cholecystokinin, mceph/mceph brains had region-specific up- and down-regulations in several layers of the hippocampal formation and increased levels in, especially ventral, cortical regions. Enkephalin messenger RNA expression was up-regulated in the dentate gyrus granular layer and in ventral cortices, but down-regulated in the CA1 pyramidal layer. Enkephalin-like immunoreactivity was elevated in mossy fibers of the hippocampus and the ventral cortices. Galanin expression was increased in several layers and interneurons of the hippocampal formation, as well as in ventral cortices. Galanin-like immunoreactivity was reduced in nerve terminals in the forebrain. Neuropeptide Y expression was increased in the hippocampal formation and ventral cortices. Whether the mainly increased peptide levels contribute to the excessive growth of the brain or represent a consequence of this growth and/or of the neurological and motor disturbances remains to be elucidated.

An immunocytochemical study of intrapancreatic ganglia, nerve fibres and neuroglandular junctions in Brockmann bodies of the tompot blenny (Blennius gattoruggine), a marine teleost

The innervation of the Brockmann bodies in the teleost fish, Blennius gattoruggine, was studied using immunocytochemical techniques at both the light and electron microscopy levels. Islet innervation consisted of intrapancreatic ganglia, generally localized inside the rim of the exocrine tissue of the Brockmann bodies, in proximity to the islet, nerve fibres and nerve terminals with synaptic complexes. The intrapancreatic ganglia were of variable size, with different numbers of ganglionic cells, that appeared unipolar in section. The cell bodies showed immunoreactivity to galanin, oxytocin, peptide tyrosine tyrosine and glucagon. The extrinsic and intrinsic nerve fibres passed through the exocrine parenchyma and crossed the connectival septa and islet connectival sheath, penetrating into the islets, where they became increasingly thinner. They terminated on the endocrine cells with dilated nerve terminals. At least three types of terminals were detected, depending on the different vesicle content: peptidergic, cholinergic or adrenergic. They presented specialized synaptic structures, the neuroglandular junctions, some of which contained neurosecretory granules immunogold labelled by galanin antiserum. This new finding confirms the role of galanin as a neurotransmitter. This rich supply of innervation may be important in the regulation and integration of islet secretion.

Modulation of hippocampal excitability and seizures by galanin

Previous studies have shown that the expression of the neuropeptide galanin in the hippocampus is altered by seizures and that exogenous administration of galanin into the hippocampus attenuates seizure severity. To address the role of endogenous galanin in modulation of hippocampal excitability and its possible role in seizure mechanisms, we studied two types of transgenic mice: mice with a targeted disruption of the galanin gene (GalKO) and mice that overexpress the galanin gene under a dopamine-beta-hydroxylase promoter (GalOE). GalKO mice showed increased propensity to develop status epilepticus after perforant path stimulation or systemic kainic acid, as well as greater severity of pentylenetetrazol-induced convulsions. By contrast, GalOE mice had increased resistance to seizure induction in all three models. Physiological tests of hippocampal excitability revealed enhanced perforant path-dentate gyrus long-term potentiation (LTP) in GalKO and reduced LTP in GalOE. GalKO showed increased duration of afterdischarge (AD) evoked from the dentate gyrus by perforant path simulation, whereas GalOE had increased threshold for AD induction. Depolarization-induced glutamate release from hippocampal slices was greater in GalKO and lower in GalOE, suggesting that alterations of physiological and seizure responses in galanin transgenic animals may be mediated through modulation of glutamate release. Our data provide further evidence that hippocampal galanin acts as an endogenous anticonvulsant and suggest that genetically induced changes in galanin expression modulate both hippocampal excitability and predisposition to epileptic seizures.

Acromegaly associated with a granular cell tumor of the neurohypophysis: a clinical and histological study. Case report

Acromegaly is usually caused by a growth hormone (GH)-secreting pituitary adenoma, and hypersecretion of GH-releasing hormone (GHRH) from a hypothalamic or neuroendocrine tumor accounts for other cases. The authors report on the unusual association of acromegaly with a granular cell tumor of the neurohypophysis. A 42-year-old woman with a 10-year history of acral enlargement, headache, and menstrual abnormalities was referred to our department for a suspected GH-secreting pituitary adenoma. The patient's basal GH levels were mildly elevated at 4.8 microg/L, were not suppressed in response to an oral glucose tolerance test, and increased paradoxically after administration of thyrotropin-releasing hormone. The patient's insulin-like growth factor-1 (IGF-1) level was elevated at 462 microg/L, whereas a magnetic resonance image of the sella turcica revealed an intra- and suprasellar lesion that was compatible with a diagnosis of pituitary adenoma. A transsphenoidal approach to remove the lesion, which was mainly suprasellar, was successful during a second operative attempt, resulting in the clinical and biochemical regression of the patient's acromegaly. Four months postoperatively, the patient's basal GH level was 0.9 microg/L and her IGF-1 level was 140 microg/L. Histological analysis of the operative specimen demonstrated a granular cell tumor of the neurohypophysis, which when stained proved negative for pituitary hormones and GHRH. This case represents the first reported association between a granular cell tumor of the neurohypophysis and acromegaly. Granular cell tumor of the neurohypophysis could be added to the restricted list of neoplastic causes of acromegaly secondary to hypersecretion of a GH-releasing substance.

The differential effects of galanin-(1-30) and -(3-30) on anterior pituitary hormone secretion in vivo in humans

Intravenous injection of galanin increases plasma growth hormone (GH) and prolactin (PRL) concentrations. In the rat, the effects of galanin on GH appear to be mediated via the hypothalamic galanin receptor GAL-R(1), at which galanin-(3-29) is inactive. In contrast, the effect of galanin on PRL is mediated via the pituitary-specific galanin receptor GAL-R(W), at which galanin-(3-29) is fully active. We investigated the effects of an intravenous infusion of human galanin (hGAL)-(1-30) and -(3-30) on anterior pituitary hormone levels in healthy females. Subjects were infused with saline, hGAL-(1-30) (80 pmol. kg(-1). min(-1)), and hGAL-(3-30) (600 pmol. kg(-1). min(-1)) and with boluses of gonadotropin-releasing hormone, thyrotropin-releasing hormone, and growth hormone-releasing hormone (GHRH). Both hGAL-(1-30) and -(3-30) potentiated the rise in GHRH-stimulated GH levels [area under the curve (AUC), saline, 2,810 +/- 500 vs. hGAL-(1-30), 4,660 +/- 737, P < 0.01; vs. hGAL-(3-30), 6, 870 +/- 1,550 ng. min. ml(-1), P < 0.01]. In contrast to hGAL-(1-30), hGAL-(3-30) had no effect on basal GH levels (AUC, saline, -110 +/- 88 vs. hGAL 1-30, 960 +/- 280, P < 0.002; vs. hGAL-(3-30), 110 +/- 54 ng. min. ml(-1), P = not significant). These data suggest that the effects of galanin on basal and stimulated GH release are mediated via different receptor subtypes and that the human equivalent of GAL-R(W) may exist.

Effects of galanin on growth hormone and prolactin secretion in anorexia nervosa

Galanin (GAL) elicits growth hormone (GH) release in normal subjects through interaction with hypothalamic somatostatin. GAL also stimulates GH-releasing hormone (GHRH) secretion in vitro. In rats, GAL is able to stimulate prolactin (PRL) release, but this effect is not clear in humans. We have thus investigated GAL effects on GH and PRL release in patients with anorexia nervosa (AN), known to have altered regulation of the GH-insulin-like growth factor axis and PRL dynamics, and compared the effects of GHRH and GAL on GH and PRL secretion in AN and normal healthy subjects. Eight women with AN (15 to 27 years; body mass index [BMI], 17 to 19.5 kg/m2) were treated with (1) GHRH 50 microg intravenous (IV) injection, (2) porcine GAL 500 microg infusion from -10 to +30 minutes, and (3) 135-minutes saline infusion as a control, respectively. Both peptides induced a significant increase in plasma GH in AN patients (peak level, 27.41 +/- 5.50 microg/L after GAL and 18.97 +/- 2.67 microg/L after GHRH). When data for AN patients and the control group were compared, GH peak levels after GAL were significantly higher in AN patients (27.41 +/- 5.50 v 13.64 +/- 2.32 microg/L), while GH peak levels after GHRH were not different between the 2 groups (18.97 +/- 2.67 v 15.98 +/- 3.88 microg/L). PRL levels significantly increased after both GHRH (peak, 11.70 +/- 2.80 microg/L) and GAL (peak, 18.02 +/- 5.10 microg/L) treatment in AN patients, but not in normal subjects. We conclude that GAL stimulates exaggerated GH release in AN patients as compared with normal controls, suggesting a dual hypothalamic interaction via both an increase in endogenous GHRH and a decrease in somatostatin secretion. Finally, GAL may act as a PRL secretagogue in AN patients.

Distribution of galanin-1, -2 and -3 receptor messenger RNAs in central and peripheral rat tissues

Galanin is a neuropeptide widely expressed in the central nervous system and periphery. In rat, three galanin-binding receptors have been cloned and characterized. We report the qualitative and quantitative distribution of galanin-1, galanin-2, and galanin-3 messenger RNAs in central and peripheral rat tissues by reverse transcription-polymerase chain reaction and solution hybridization/RNase protection assays, respectively. Galanin-1 messenger RNA was detected exclusively in the central and peripheral nervous system with highest expression in hypothalamus, amygdala, spinal cord and dorsal root ganglia. Galanin-2 messenger RNA was highly expressed in hypothalamus, dorsal root ganglia, and kidney with moderate expression in several other tissues. Galanin-3 messenger RNA was widely distributed at low to moderate levels in many central and peripheral tissues. The observed expression of multiple galanin receptors in several tissues including hypothalamus, anterior pituitary and spinal cord supports earlier pharmacological studies suggesting the presence of more than one receptor subtype in these regions. The presence of multiple galanin receptors in these tissues in conjunction with the detection of a single subtype, galanin-2, in tissues such as heart and intestine, illustrates the potential complexity of galanin-associated actions in rat central nervous system and periphery.

Distribution of galanin immunoreactivity in the sheep diencephalon

Although the physiological role of galanin has been demonstrated in several endocrine regulations in sheep, the anatomical characteristics of this neuronal system has never been studied. The distribution of galanin-containing neurones was described by immunohistochemistry using galanin antiserum in the diencephalon of adult ewes, both ovariectomized or treated with colchicine. Galanin-immunoreactivity was found throughout the diencephalon. In the ovariectomized ewes, galanin-immunoreactive neurones were mainly observed in the medial preoptic area and the infundibular nucleus. The highest density of immunoreactive fibres was found in the external layer of the median eminence. Numerous galanin-immunoreactive fibres were also observed in the preoptic area, the mediobasal hypothalamus, the periphery of the supraoptic and the paraventricular nuclei. With colchicine treatment, the number of labelled neurones increased, and additional galanin-immunoreactive perikarya were observed in the bed nucleus of the stria terminalis, the lateral septum, the supraoptic, the paraventricular and the periventricular nuclei and the paraventricular nucleus of the thalamus. In the caudal part of the diencephalon, the density of labelled neurones was lower in both groups of animals than in other species studied. Regardless of treatment, labelling was not seen in the suprachiasmatic nucleus and only rarely in the ventromedial nucleus. These results describe, for the first time, the distribution of galanin-immunoreactive neurones in the sheep diencephalon. Compared to other species studied, distribution in the sheep diencephalon has several distinct differences. In ovariectomized animals, the medial preoptic area presents more labelled neurones in sheep than in monkeys, whereas in the supraoptic nucleus the density of labelled neurones is lower in sheep than in humans or opossums. After colchicine treatment only very few differences were observed between sheep and rats, but in contrast to other species, the suprachiasmatic nucleus of the sheep does not contain labelled neurones.

The role of galanin in feeding behavior

Galanin inhibits food consumption in satiated rats. Discovered relatively recently, galanin is a 29-amino-acid neuropeptide, not homologous with any other known peptide. Three G-protein-linked galanin receptor subtypes have been cloned. This review summarizes the mechanisms by which exogenously administered galanin may stimulate ingestion, discusses pharmacological and genetic investigations of the role of endogenous galanin on feeding and body weight, and speculates on the therapeutic potential of non-peptide galanin receptor antagonists for the treatment of appetite disorders.

Galanin and galanin receptors

The development of a strain of galanin knockout mice has provided confirmation of a neuroendocrine role for galanin, as well as supporting results of previous physiological investigations indicating a role for galanin in analgesia and neuropathic pain, and potentially in neuronal growth and regeneration processes. Whether elevation of galanin expression in neurodegenerative disorders such as Alzheimer's disease represents a survival response or exacerbates functional deficit in afflicted individuals remains to be determined. More detailed analysis of the phenotype of the galanin knockout mouse should provide insights into the physiological role of galanin in memory and learning processes, as well as in hypothalamic function and other aspects of neuroendocrine regulation. Biochemical and molecular cloning efforts have demonstrated that the multiplicity of actions of galanin is matched by complexity in the distribution and regulation of galanin and its receptors. A focus on characterisation of galanin receptors has resulted in the molecular cloning of three receptor subtypes to date. The distribution and functional properties of these receptors have not yet been fully elucidated, currently precluding assignment of discrete functions of galanin to any one receptor subtype. It is not currently possible to reconcile available pharmacological data using analogs of galanin and chimeric peptides in functional assay systems with the pharmacological properties of cloned receptor subtypes. This highlights the value of further knockout approaches targeting galanin receptor subtypes, but also raises the possibility of the existence of additional receptor subtypes that have yet to be cloned, or that receptor activity may be modulated by regulatory molecules that remain to be identified. The development of receptor subtype-specific compounds remains a high priority to advance work in this area. The ability to selectively modulate the many different actions of galanin, through a clearer understanding of receptor structure-function relationships and neuronal distribution, promises to provide important insights into the molecular and cellular basis of galanin action in normal physiology, and may provide lead compounds with therapeutic application in the prevention and treatment of a range of disorders.

Neuroendocrine control of growth hormone secretion

The secretion of growth hormone (GH) is regulated through a complex neuroendocrine control system, especially by the functional interplay of two hypothalamic hypophysiotropic hormones, GH-releasing hormone (GHRH) and somatostatin (SS), exerting stimulatory and inhibitory influences, respectively, on the somatotrope. The two hypothalamic neurohormones are subject to modulation by a host of neurotransmitters, especially the noradrenergic and cholinergic ones and other hypothalamic neuropeptides, and are the final mediators of metabolic, endocrine, neural, and immune influences for the secretion of GH. Since the identification of the GHRH peptide, recombinant DNA procedures have been used to characterize the corresponding cDNA and to clone GHRH receptor isoforms in rodent and human pituitaries. Parallel to research into the effects of SS and its analogs on endocrine and exocrine secretions, investigations into their mechanism of action have led to the discovery of five separate SS receptor genes encoding a family of G protein-coupled SS receptors, which are widely expressed in the pituitary, brain, and the periphery, and to the synthesis of analogs with subtype specificity. Better understanding of the function of GHRH, SS, and their receptors and, hence, of neural regulation of GH secretion in health and disease has been achieved with the discovery of a new class of fairly specific, orally active, small peptides and their congeners, the GH-releasing peptides, acting on specific, ubiquitous seven-transmembrane domain receptors, whose natural ligands are not yet known.

Discovery of a receptor related to the galanin receptors

We report the isolation of a cDNA clone named GPR54, which encodes a novel G protein-coupled receptor (GPCR). A PCR search of rat brain cDNA retrieved a clone partially encoding a GPCR. In a library screening this clone was used to isolate a cDNA with an open reading frame (ORF) encoding a receptor of 396 amino acids long which shared significant identities in the transmembrane regions with rat galanin receptors GalR1 (45%), GalR3 (45%) and GalR2 (44%). Northern blot and in situ hybridization analyses revealed that GPR54 is expressed in brain regions (pons, midbrain, thalamus, hypothalamus, hippocampus, amygdala, cortex, frontal cortex, and striatum) as well as peripheral regions (liver and intestine). In COS cell expression of GPR54 no specific binding was observed for 125I-galanin. A recent BLAST search with the rat GPR54 ORF nucleotide sequence recovered the human orthologue of GPR54 in a 3.5 Mb contig localized to chromosome 19p13.3.

Galanin: analysis of its coexpression in gonadotropin-releasing hormone and growth hormone-releasing hormone neurons

Galanin is coexpressed in a subset of gonadotropin-releasing hormone (GnRH) and growth hormone-releasing hormone (GHRH) neurons in the brain and has an important role in the neuroendocrine regulation of gonadotropin and growth hormone secretion. Our overall goal has been to understand the functional significance of galanin as a cotransmitter with GnRH and GHRH in the regulation of these important physiologic processes. To this end, we studied the regulation of galanin's expression in GnRH and GHRH neurons under a variety of physiologic and experimental conditions. Using double-label in situ hybridization and computerized image analysis, we observed that in GnRH neurons, galanin's expression is increased over the course of development in both sexes. Galanin achieves a higher basal expression in GnRH neurons in females, and it is sexually differentiated in the adult as a result of the differential exposure to testosterone during the neonatal critical period. Galanin is induced in GnRH neurons coincident with and subsequent to the proestrous luteinizing hormone surge (reflecting the combined action of estradiol and progesterone) acting indirectly on GnRH neurons through a synaptic relay. Galanin's expression in GnRH neurons is inhibited during lactation, when the neuroendocrine reproductive axis is relatively quiescent. In GHRH neurons, the expression of galanin is also induced over the course of development in both sexes. Galanin's expression in GHRH neurons in the adult is sexually differentiated, but in this case, its expression is higher in males than females, reflecting the stimulatory effect of testosterone on galanin in the male. Galanin's expression in GHRH neurons is induced by growth hormone (GH), whereas the absence of GH leads to a reduction of galanin mRNA in these same cells. On the basis of these observations, we conclude that galanin is an important target for regulation by many hormones, and we postulate that as a cotransmitter, galanin acts presynaptically to modulate the secretion of GnRH and GHRH, possibly by altering their pulsatile release patterns, which in turn influences the release of the gonadotropins and GH from the pituitary.

Influence of galanin and serotonin on the endocrine response to Hexarelin, a synthetic peptidyl GH-secretagogue, in normal women

Hexarelin (HEX) is a synthetic GH-secretagogue (GHS) which acts on specific receptors either at the pituitary or the hypothalamic level to stimulate GH release both in animal and in man. Like other GHS, HEX possesses also PRL-, ACTH- and cortisol (F)-releasing activity but the mechanisms underlying these effects are even less clear. On the other hand, galanin (GAL) and serotonin play an important role in the neural control of GH, PRL and ACTH secretion both in animal and in man. In order to study the interaction between HEX and GAL and to verify whether serotoninergic mechanisms underly the endocrine effects of GHS, in 12 normal young volunteers (24-30 yr) the following tests were performed: group A (N = 5), HEX (2.0 micrograms/kg i.v. at 0 min), GAL (15.0 micrograms/kg i.v. from 0 to 60 min) and HEX + GAL; group B (N = 7), HEX alone and preceeded by cyproeptadine (CYPRO, 8 mg os at -60 min). In group A, the GH response to HEX (1204.2 +/- 312.9 micrograms*min/L) was higher (p < 0.05) than that to GAL alone (305.6 +/- 35.5 micrograms*min/L) and was not modified by GAL co-administration (1021.8 +/- 249.9 micrograms*min/L). PRL secretion was increased to the same extent by HEX and GAL (507.9 +/- 81.1 and 743.0 +/- 164.7 micrograms*min/L) which showed no interaction (603.5 +/- 75.7 micrograms*min/L). HEX elicited an increase in both ACTH and F secretion (924.5 +/- 169.7 pg*min/ml and 6131.3 +/- 616.6 micrograms*min/L) while GAL had no effect when given alone (759.5 +/- 185.5 pg*min/ml and 5350.3 +/- 755.6 micrograms*min/L) and did not modify the effect of HEX (891.3 +/- 159.2 pg*min/ml and 5877.8 +/- 554.4 micrograms*min/L). In group B, the GH response to HEX (1636.4 +/- 267.5 micrograms*min/L) was blunted by CYPRO (1164.8 +/- 212.3 micrograms*min/L) but this difference did not attained statistical significance. On the other hand, CYPRO did not modify the HEX-induced PRL (599.5 +/- 129.2 vs 638.9 +/- 131.9 micrograms*min/L), ACTH (1282.8 +/- 222.0 vs 1330.2 +/- 347.0 pg*min/ml) and F response (4738.3 +/- 355.3 vs 4580.9 +/- 857.3 micrograms*min/L). Our present data demonstrate that Hexarelin has no interaction with galanin; thus thereotically, the stimulatory effect of GHS on GH and PRL secretion could involve, at least partially, a galanin-mediated mechanism. On the other hand, our data demonstrate that serotonin does not mediate the stimulatory effect of GHS on PRL, ACTH and cortisol; the intrinsic anticholinergic property of cyproeptadine could account for the trend toward its blunting effect on the GH response to Hexarelin.

Galanin receptor-mediated inhibition of glutamate release in the arcuate nucleus of the hypothalamus

It is thought that galanin, a 29 amino acid neuropeptide, is involved in various neuronal functions, including the regulation of food intake and hormone release. Consistent with this idea, galanin receptors have been demonstrated throughout the brain, with high levels being observed in the hypothalamus. However, little is known about the mechanisms by which galanin elicits its actions in the brain. Therefore, we studied the effects of galanin and its analogs on synaptic transmission using an in vitro slice preparation of rat hypothalamus. In arcuate nucleus neurons, application of galanin resulted in an inhibition of evoked glutamatergic EPSCs and a decrease in paired-pulse depression, indicating a presynaptic action. The fragments galanin 1-16 and 1-15 produced a robust depression of synaptic transmission, whereas the fragment 3-29 produced a lesser degree of depression. The chimeric peptides C7, M15, M32, and M40, which have been reported to antagonize some actions of galanin, all produced varying degrees of depression of evoked EPSCs. In a minority of cases, C7, M15, and M40 antagonized the actions of galanin. Analysis of mEPSCs in the presence of TTX and Cd2+, or after application of alpha-latrotoxin, indicated a site of action for galanin downstream of Ca2+ entry. Thus, our data suggest that galanin acts via several subtypes of presynaptic receptors to depress synaptic transmission in the rat arcuate nucleus.

Inhibition of gastric acid secretion by galanin in rats. Relation to endogenous histamine release

Inhibitory effect of galanin on basal and secretagogs-stimulated gastric acid secretion was investigated in urethane-anesthetized rats. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and either gastric acid or alkaline secretion was determined by titrating the perfusate. Gastric mucosal blood flow (GMBF) was measured by a laser Doppler flowmeter. Intravenous infusion of galanin dose-dependently inhibited the increase of acid secretion induced by pentagastrin and carbachol but not by histamine, without any influence on the GMBF response. Galanin also reduced basal acid secretion while increasing GMBF, but did not evoke any change in basal gastric alkaline secretion. M15, which is a galanin receptor antagonist in the central nervous system but acts as a full agonist in the gastrointestinal smooth muscle, also suppressed pentagastrin-induced acid secretion, similar to galanin. In addition, pentagastrin increased the release of histamine into the gastric lumen, and this response was significantly inhibited by galanin. These results suggest that the inhibitory effect of galanin on acid secretion is mediated by suppression of endogenous histamine release from enterochromaffin-like cells and that the process may be related to the activation of the same subtype of galanin receptors as in the central nervous system and pancreatic beta-cells.

The relationship of galanin immunoreactive nerve fibers to glandular cells in the anterior pituitary in the monkey

The anterior pituitary is known to be regulated by hypothalamic hormones via the portal system. However, our recent studies have demonstrated the presence of a substantial amount of substance P (SP)-, calcitonin gene-related peptide (CGRP)- and galanin (GAL)- immunoreactive (ir) nerve fibers with numerous varicosities in the anterior pituitaries of the Macaca mulatta monkey. The present study investigated the relationship of the GAL-ir nerve fibers to the glandular cells. The M. mulatta monkeys were used and sections of the anterior pituitary were double immunostained. GAL-ir nerve fibers and/or varicosities were found in proximity to contact directly with corticotropes, somatotropes, lactotropes, gonadotropes and thyrotropes without any exception. These findings indicate that a direct neural factor may be involved in the regulation of adenohypophyseal secretion.

Ultrastructural localization of galanin and galanin receptors in the guinea pig median eminence

The aim of this work was to compare the localization of galanin and galanin receptors in the guinea pig median eminence at the light and electron microscopic level. Concerning galanin the highest labeling was shown in the external part of the median eminence. At the ultrastructural level, galanin immunoreactivity was observed only in nerve terminals containing granular vesicles of approximately 120 nm in diameter. Light microscopic autoradiographs of semithin sections exhibited a moderate labeling in the external part of the median eminence. Galanin receptors were labeled in vitro on semithin sections (2 microm) using the highly specific radioligand [125I]galanin. Ultrastructural data showed that most of galanin binding sites overlaid membrane appositions between nerve terminals and also between nerve terminal and tanycyte. By considering the percentages in the distribution of the binding it appeared that galanin receptors were located on some nerve ending membranes. Our observations were not really in favor of a presence of receptors in tanycytes. The presence of galanin nerve endings in the external part suggests that like in the rat the peptide may have a direct hypophysiotrophic role. In contrast, the occurrence of numerous binding sites gives additional arguments in favor of a local action (paracrine and/or autocrine) of galanin occurring via galanin receptors located essentially on the pericapillary nerve terminals in the guinea pig median eminence.

Pituitary cytokine and growth factor expression and action

The complex range of pituitary regulatory mechanisms reviewed here underlies the critical function of the pituitary in sustaining all higher life forms. Thus, the ultimate net secretion of pituitary hormones is determined by signal integration from all three tiers of pituitary control. It is clear from our current knowledge that the trophic hormone cells of the anterior pituitary are uniquely specialized to respond to these signals. Unravelling their diversity and complexity will shed light upon the normal function of the master gland. Understanding these control mechanisms will lead to novel diagnosis and therapy of disordered pituitary function (357).

Evaluation of circulating galanin levels after exercise-induced pituitary hormone secretion in man

The neuropeptide galanin (GAL) is widely distributed in the central and peripheral nervous systems, anterior pituitary, and adrenal medulla. GAL is colocalized with corticotropin (ACTH) in the human pituitary and with epinephrine (E) and norepinephrine (NE) in chromaffin cells of the adrenal medulla. The function of GAL in peripheral tissues is not known, although the presence of the peptide in corticotrophs and the adrenal gland suggest that it participates in stress responses. In the present study, we investigated whether GAL is cosecreted with ACTH during activation of corticotrophs by an acute physical exercise test. Circulating levels of GAL and pituitary hormones were measured in healthy exercise-tested and control male subjects. Blood samples were collected during basal conditions, maximal power output (MPO), and the recovery period. Control subjects were sampled during the resting condition. The pituitary response to exercise was characterized by a significant increase in ACTH plasma levels (peak value 13.28 +/- 2.19 v 6.68 +/- 1.01 pmol/L, P < .05) and growth hormone (GH) serum levels (peak value, 14.53 +/- 5.59 v 0.29 +/- 0.1 microg/L, P < .02), with the peak in hormone levels detected 15 minutes after the end of exercise. No change in circulating prolactin (PRL) levels was detected. An expected significant increase in plasma levels of both E (peak value, 1,574.41 +/- 403.31 v 267.44 +/- 60.03 pmol/L, P < .01) and NE (peak value, 7,275.25 +/- 955.80 v 961.51 +/- 168.40 pmol/L, P < .01) was also observed. Plasma GAL levels were not affected by the acute exercise test, with the levels being comparable to baseline during the exercise test and the recovery phase. At any sample time, GAL values were comparable between exercise-tested and control subjects. These data show that despite the colocalization of GAL and ACTH within the same pituitary cells, the two peptides are not coreleased in response to stress resulting from acute physical exercise. Furthermore, pituitary GAL seems not to be involved in the stimulation of GH secretion in exercise-tested subjects. The results also indicate that GAL is not coreleased with E or NE in response to the exercise-induced stress condition.

Growth hormone inhibits the hypophysectomy-induced expression of galanin in hypothalamic neurons of the toad (Bufo arenarum hensel)

The expression of the neuropeptide galanin was analyzed by immunohistochemistry in magnocellular and preoptic hypothalamic neurons of toads following hypophysectomy (HPX) and pars distalectomy (PDX). There was a marked increase in the galanin-like immunoreactive expression in magnocellular hypothalamic cells 3 days after HPX, followed by a decrease to normal levels after 7 days. No changes in the expression of galanin were detected after PDX in these neurons when compared to controls. Moreover, 7 days after HPX or PDX the number of cells expressing galanin was significantly increased in the preoptic area, where numerous intraependymal cells were intensely immunoreactive. The hypophysis grafts into the hind limb in HPX or PDX animals prevented increased galanin-like immunoreactivity in preoptic cells but not in magnocellular neurons. Similarly, PDX toads given growth hormone showed no GAL-LI in the intraependymal preoptic cells. These results suggest the presence of a region regulation of galanin expression in the preoptic area by hypophyseal hormones, in particular growth hormone.