Neuromedin B is a major bombesin-like peptide in rat brain: regional distribution of neuromedin B and neuromedin C in rat brain, pituitary and spinal cord

Blood-brain barrier transport kinetics of the neuromedin peptides NMU, NMN, NMB and NT

The neuromedin peptides are peripherally and centrally produced, but until now, it is generally believed that they only function as locally acting compounds without any quantitative knowledge about their blood-brain barrier (BBB) passage. Here, we characterize the transport kinetics of four neuromedins (NMU, NMN, NMB and NT) across the BBB, as well as their metabolization profile, and evaluate if they can act as endocrine hormones. Using the in vivo mouse model, multiple time regression (MTR), capillary depletion (CD) and brain efflux studies were performed. Data was fitted using linear (NMU, NT and NMB) or biphasic modeling (NMU and NMN). Three of the four investigated peptides, i.e. NMU, NT and NMN, showed a significant influx into the brain with unidirectional influx rate constants of 1.31 and 0.75 μL/(g × min) for NMU and NT respectively and initial influx constants (K1) of 72.14 and 7.55 μL/(g × min) and net influx constants (K) of 1.28 and 1.36 × 10(-16) μL/(g×min) for NMU and NMN respectively. The influx of NMB was negligible. Only NMN and NT showed a significant efflux out of the brain with an efflux constant (kout) of 0.042 min(-1) and 0.053 min(-1) respectively. Our results indicate that locally produced neuromedin peptides and/or fragments can be transported through the whole body, including passing the BBB, and taken up by different organs/tissues, supporting the idea that the neuromedins could have a much bigger role in the regulation of biological processes than currently assumed.

Insights into bombesin receptors and ligands: Highlighting recent advances

This following article is written for Prof. Abba Kastin's Festschrift, to add to the tribute to his important role in the advancement of the role of peptides in physiological, as well as pathophysiological processes. There have been many advances during the 35 years of his prominent role in the Peptide field, not only as editor of the journal Peptides, but also as a scientific investigator and editor of two volumes of the Handbook of Biological Active Peptides [146,147]. Similar to the advances with many different peptides, during this 35 year period, there have been much progress made in the understanding of the pharmacology, cell biology and the role of (bombesin) Bn receptors and their ligands in various disease states, since the original isolation of bombesin from skin of the European frog Bombina bombina in 1970 [76]. This paper will briefly review some of these advances over the time period of Prof. Kastin 35 years in the peptide field concentrating on the advances since 2007 when many of the results from earlier studies were summarized [128,129]. It is appropriate to do this because there have been 280 articles published in Peptides during this time on bombesin-related peptides and it accounts for almost 5% of all publications. Furthermore, 22 Bn publications we have been involved in have been published in either Peptides [14,39,55,58,81,92,93,119,152,216,225,226,231,280,302,309,355,361,362] or in Prof. Kastin's Handbook of Biological Active Peptides [137,138,331].

Expression and regulation of neuromedin B in pituitary corticotrophs of male melanocortin 2 receptor-deficient mice

The hypothalamic-pituitary-adrenal (HPA) axis is a major part of the neuroendocrine system that controls responses to stress, and has an important function in the regulation of various body processes. We previously created a mouse line deficient in the melanocortin 2 receptor (MC2R). MC2R-deficient mice (MC2R(-/-) mice) have high adrenocorticotropic hormone (ACTH) levels because of undetectable corticosterone levels. Increased neuromedin B (NMB) expression was recently reported in the pituitary gland of adrenalectomized mice, a model for acute adrenal insufficiency. To investigate gene expression in the pituitary gland under chronic adrenal deficiency, we examined the pituitary gland of MC2R(-/-) mice, a model of chronic adrenal insufficiency. To understand the molecular background of pituitary cells under chronic adrenal deficiency, we first performed DNA microarray analyses using the pituitary glands of the MC2R(-/-) mice. The DNA microarray analysis and real-time polymerase chain reaction showed that NMB expression was higher in the MC2R(-/-) than in the wild-type (WT) mice. We detected NMB expression in the MC2R(-/-) pituitary corticotrophs by immunohistochemistry using the specific antibodies for ACTH and NMB. In addition, the plasma NMB concentration was significantly higher in the MC2R(-/-) mice than in the WT mice. Subcutaneous implantation of a sustained-release corticosterone pellet decreased the expression of NMB mRNA as well as pituitary proopiomelanocortin mRNA. In isolated anterior pituitary cells, NMB mRNA expression was increased by the administration of corticotropin-releasing hormone (CRH) and was suppressed by dexamethasone treatment. In this study, we first demonstrate NMB expression in corticotrophs and its regulation by CRH and glucocorticoids. Furthermore, corticotrophs seemed to secrete NMB into the systemic circulation.

Autocrine effects of neuromedin B stimulate the proliferation of rat primary osteoblasts

Neuromedin B (NMB) is a mammalian bombesin-like peptide that regulates exocrine/endocrine secretion, smooth muscle contraction, body temperature, and the proliferation of some cell types. Here, we show that mRNA encoding Nmb and its receptor (Nmbr) are expressed in rat bone tissue. Immunohistochemical analysis demonstrated that NMB and NMBR colocalize in osteoblasts, epiphyseal chondrocytes, and proliferative chondrocytes of growth plates from mouse hind limbs. Then, we investigated the effect of NMB on the proliferation of rat primary cultured osteoblasts. Proliferation assays and 5-bromo-2'-deoxyuridine incorporation assays demonstrated that NMB augments the cell number and enhances DNA synthesis in osteoblasts. Pretreatment with the NMBR antagonist BIM23127 inhibited NMB-induced cell proliferation and DNA synthesis. Western blot analysis showed that NMB activates ERK1/2 MAPK signaling in osteoblasts. Pretreatment with the MAPK/ERK kinase inhibitor U0126 attenuated NMB-induced cell proliferation and DNA synthesis. We also investigated the effects of molecules that contribute to osteoblast proliferation and differentiation on Nmb expression in osteoblasts. Real-time PCR analysis demonstrated that 17β-estradiol (E2) and transforming growth factor β1 increase and decrease Nmb mRNA expression levels respectively. Finally, proliferation assays revealed that the NMBR antagonist BIM23127 suppresses E2-induced osteoblast proliferation. These results suggest that NMB/NMBR signaling plays an autocrine or paracrine role in osteoblast proliferation and contributes to the regulation of bone formation.

Intrathecal bombesin is sympathoexcitatory and pressor in rat

Bombesin, a 14 amino-acid peptide, is pressor when administered intravenously in rat and pressor and sympathoexcitatory when applied intracerebroventricularly. To determine the spinal effects of bombesin, the peptide was administered acutely in the intrathecal space at around thoracic spinal cord level six of urethane-anesthetized, paralyzed, and bilaterally vagotomized rats. Blood pressure, heart rate, splanchnic sympathetic nerve activity (sSNA), phrenic nerve activity, and end-tidal CO(2) were monitored to evaluate changes in the cardiorespiratory systems. Bombesin elicited a long-lasting excitation of sSNA associated with an increase in blood pressure and tachycardia. There was a mean increase in arterial blood pressure of 52 ± 5 mmHg (300 μM; P < 0.01). Heart rate and sSNA also increased by 40 ± 4 beats/min (P < 0.01) and 162 ± 33% (P < 0.01), respectively. Phrenic nerve amplitude (PNamp, 73 ± 8%, P < 0.01) and phrenic expiratory period (+0.16 ± 0.02 s, P < 0.05) increased following 300 μM bombesin. The gain of the sympathetic baroreflex increased from -2.8 ± 0.7 to -5.4 ± 0.9% (P < 0.01), whereas the sSNA range was increased by 99 ± 26% (P < 0.01). During hyperoxic hypercapnia (10% CO(2) in O(2), 90 s), bombesin potentiated the responses in heart rate (-25 ± 5 beats/min, P < 0.01) and sSNA (+136 ± 29%, P < 0.001) but reduced PNamp (from 58 ± 6 to 39 ± 7%, P < 0.05). Finally, ICI-216,140 (1 mM), an in vivo antagonist for the bombesin receptor 2, attenuated the effects of 300 μM bombesin on blood pressure (21 ± 7 mmHg, P < 0.01). We conclude that bombesin is sympathoexcitatory at thoracic spinal segments. The effect on phrenic nerve activity may the result of spinobulbar pathways and activation of local motoneuronal pools.

Pharmacology and selectivity of various natural and synthetic bombesin related peptide agonists for human and rat bombesin receptors differs

The mammalian bombesin (Bn)-receptor family [gastrin-releasing peptide-receptor (GRPR-receptor), neuromedin B-receptor (NMB receptor)], their natural ligands, GRP/NMB, as well as the related orphan receptor, BRS-3, are widely distributed, and frequently overexpressed by tumors. There is increased interest in agonists for this receptor family to explore their roles in physiological/pathophysiological processes, and for receptor-imaging/cytotoxicity in tumors. However, there is minimal data on human pharmacology of Bn receptor agonists and most results are based on nonhuman receptor studies, particular rodent-receptors, which with other receptors frequently differ from human-receptors. To address this issue we compared hNMB-/GRP-receptor affinities and potencies/efficacies of cell activation (assessing phospholipase C activity) for 24 putative Bn-agonists (12 natural, 12 synthetic) in four different cells with these receptors, containing native receptors or receptors expressed at physiological densities, and compared the results to native rat GRP-receptor containing cells (AR42J-cells) or rat NMB receptor cells (C6-glioblastoma cells). There were close correlations (r=0.92-99, p<0.0001) between their affinities/potencies for the two hGRP- or hNMB-receptor cells. Twelve analogs had high affinities (≤ 1 nM) for hGRP receptor with 15 selective for it (greatest=GRP, NMC), eight had high affinity/potencies for hNMB receptors and four were selective for it. Only synthetic Bn analogs containing β-alanine(11) had high affinity for hBRS-3, but also had high affinities/potencies for all GRP-/hNMB-receptor cells. There was no correlation between affinities for human GRP receptors and rat GRP receptors (r=0.131, p=0.54), but hNMB receptor results correlated with rat NMB receptor (r=0.71, p<0.0001). These results elucidate the human and rat GRP-receptor pharmacophore for agonists differs markedly, whereas they do not for NMB receptors, therefore potential GRP-receptor agonists for human studies (such as Bn receptor-imaging/cytotoxicity) must be assessed on human Bn receptors. The current study provides affinities/potencies on a large number of potential agonists that might be useful for human studies.

Regulation of pituitary gene expression by adrenalectomy

Excessive secretion of adrenal hormones, such as glucocorticoid and mineralocorticoid, leads to metabolic syndrome, including insulin resistance, obesity, and hypertension. These metabolic abnormalities are ameliorated by adrenalectomy (ADX). To identify pituitary mediators for ADX-induced physiological alterations, such as weight loss and hypotension, we investigated the effect of ADX on the pituitary transcriptome using serial analysis of gene expression (SAGE). SAGE method is based on isolation of short sequence tags, which usually correspond to unique mRNA species. The SAGE libraries were constructed from pituitary gland of intact (n = 51) and ADX (n = 12) mice. Thirty-one transcripts were differentially expressed between intact and ADX. Three transcripts encoding for proopiomelanocortin and three other transcripts involved in regulation of hormone secretion (neuromedin B, proprotein convertase subtilisin/kexin type 2, and IA-2) were induced by ADX. In addition, ADX increased the expression levels of genes encoding for cation extracellular matrix (matrix gamma-carboxyglutamate protein) and transport (solute carrier family 22 member 17). Conversely, ADX downregulated two transcripts involved in mitochondrial oxidative phosphorylation (nicotinamide adenine dinucleotide (NADH) dehydrogenase 3 and cytochrome c oxidase 3). Moreover, ADX significantly modulated the expression levels of one gene with uncharacterized function and 20 novel transcripts. This study reveals alterations of pituitary gene expressions that may be associated with ADX-induced physiological changes including weight loss.

International Union of Pharmacology. LXVIII. Mammalian bombesin receptors: nomenclature, distribution, pharmacology, signaling, and functions in normal and disease states

The mammalian bombesin receptor family comprises three G protein-coupled heptahelical receptors: the neuromedin B (NMB) receptor (BB(1)), the gastrin-releasing peptide (GRP) receptor (BB(2)), and the orphan receptor bombesin receptor subtype 3 (BRS-3) (BB(3)). Each receptor is widely distributed, especially in the gastrointestinal (GI) tract and central nervous system (CNS), and the receptors have a large range of effects in both normal physiology and pathophysiological conditions. The mammalian bombesin peptides, GRP and NMB, demonstrate a broad spectrum of pharmacological/biological responses. GRP stimulates smooth muscle contraction and GI motility, release of numerous GI hormones/neurotransmitters, and secretion and/or hormone release from the pancreas, stomach, colon, and numerous endocrine organs and has potent effects on immune cells, potent growth effects on both normal tissues and tumors, potent CNS effects, including regulation of circadian rhythm, thermoregulation; anxiety/fear responses, food intake, and numerous CNS effects on the GI tract as well as the spinal transmission of chronic pruritus. NMB causes contraction of smooth muscle, has growth effects in various tissues, has CNS effects, including effects on feeding and thermoregulation, regulates thyroid-stimulating hormone release, stimulates various CNS neurons, has behavioral effects, and has effects on spinal sensory transmission. GRP, and to a lesser extent NMB, affects growth and/or differentiation of various human tumors, including colon, prostate, lung, and some gynecologic cancers. Knockout studies show that BB(3) has important effects in energy balance, glucose homeostasis, control of body weight, lung development and response to injury, tumor growth, and perhaps GI motility. This review summarizes advances in our understanding of the biology/pharmacology of these receptors, including their classification, structure, pharmacology, physiology, and role in pathophysiological conditions.

Characterization of the bombesin-like peptide receptor family in primates

In mammals, bombesin-like peptides mediate a broad range of physiological functions through binding to three highly conserved G-protein-coupled receptors: the neuromedin B-preferring, the gastrin-releasing peptide-preferring, and the bombesin-receptor subtype 3. Selective modulation of these receptors presents opportunities for the development of novel therapeutics. To ascertain if rhesus monkey could serve as a surrogate animal model for the development of modulators of bombesin-like receptor function, we undertook a search for additional receptor family members and studied the expression profiles of the three known bombesin-related receptors. We found no evidence for additional receptor family members in mammals, suggesting that the expression of the previously described bombesin-receptor subtype 4 is limited to amphibians. We studied the distribution of the three receptors in a broad array of human and rhesus monkey tissues. Based on the similarity between the human and the rhesus expression profiles, we conclude that the rhesus monkey may be a suitable animal model to evaluate the clinical efficacy and potential side effects of bombesin-like peptide ligands.

The distribution of the orphan bombesin receptor subtype-3 in the rat CNS

Bombesin receptor subtype 3 (BRS-3) is an orphan G-protein coupled receptor that shares between 47 and 51% homology with other known bombesin receptors. The natural ligand for BRS-3 is currently unknown and little is known about the mechanisms regulating BRS-3 gene expression. Unlike other mammalian bombesin receptors that have been shown to be predominantly expressed in the CNS and gastrointestinal tract, expression of the BRS-3 receptor in the rat brain has previously not been observed. To gain further understanding of the biology of BRS-3, we have studied the distribution of BRS-3 mRNA and protein in the rat CNS. The mRNA expression pattern was studied using reverse transcription followed by quantitative polymerase chain reaction. Using immunohistological techniques, the distribution of BRS-3 protein in the rat brain was investigated using a rabbit affinity-purified polyclonal antiserum raised against an N-terminal peptide. The BRS-3 receptor was found to be widely expressed in the rat brain at both mRNA and protein levels. Particularly strong immunosignals were observed in the cerebral cortex, hippocampal formation, hypothalamus and thalamus. Other regions of the brain such as the basal ganglia, midbrain and reticular formation were also immunopositive for BRS-3. In conclusion, our neuroanatomical data provide evidence that BRS-3 is as widely expressed in the rat brain as other bombesin-like peptide receptors and suggest that this receptor may also have important roles in the CNS, mediating the functions of a so far unidentified ligand.

Neuromedin B

Neuromedin B (NMB) is one of the bombesin (BN)-related peptides in mammals. It was originally purified from pig spinal cords, and it has been shown to be present in central nervous system as well as in gastrointestinal tract. BN and its related peptides have various physiological effects. These include regulation of exocrine and endocrine secretions, smooth muscle contraction, feeding, blood pressure, blood glucose, body temperature and cell growth. NMB exerts its effect by binding to the cell surface receptor. A high affinity receptor, NMB receptor (NMB-R) has been identified. This is a G-protein coupled receptor with seven membrane-spanning regions. Upon agonist binding, several intracellular signaling cascades including phospholipase activation, calcium mobilization and protein kinase C (PKC) activation lead to expression of several genes, DNA synthesis or cellular effects such as secretion. Existence of NMB-R has been demonstrated in several brain regions, notably in olfactory and thalamic regions, and in gastrointestinal tracts. Recent analysis using NMB-R-deficient mice, generated by gene-targeting technique, enables to distinguish functional properties of NMB-R from GRP-R. In this review, molecular characterization, anatomical distribution and pharmacological properties of NMB and NMB-R will be presented. Moreover, physiological roles of NMB and its receptor demonstrated by the analysis of NMB-R-deficient mice will be reported. Comparison with GRP/GRP-R system will provide important information about BN-like peptide systems in mammals.

Capsaicin-sensitive fibers are required for the anorexic action of systemic but not central bombesin

Bombesin (BN) suppresses food intake in rats whether given centrally or systemically. Although the brain BN-sensitive receptors are known to be essential for the anorexic effect of systemic BN, the mode of communication between the gut and the brain remains unclear. This study assessed whether the anorexic effect of systemic BN is mediated humorally or via neural circuits. Afferent neurons were lesioned using capsaicin (50 mg/kg sc) on postnatal day 2, and responses to BN were assessed during adulthood. Capsaicin treatment decreased body weight gain significantly from postnatal age 4-7 wk. Peripheral BN (4-16 micrograms/kg ip) dose dependently suppressed food intake in control animals. However, this effect was completely blocked in capsaicin-treated rats. In contrast to systemic effects, feeding-suppressant effects of centrally administered BN (0.01-0.5 microgram icv) were not affected by capsaicin treatment. This research suggests that peripheral BN communicates with the brain via a neuronal system(s) whose afferent arm is constituted of capsaicin-sensitive C and/or Adelta-fibers, whereas the efferent arm of this satiety- and/or anorexia-mediating circuitry is capsaicin resistant.

Breast cancer cell-associated endopeptidase EC 24.11 modulates proliferative response to bombesin

We have investigated the production, growth and inactivation of gastrin-releasing peptide (GRP)-like peptides in human breast cancer cell lines. Radioimmunoassay detected GRP-like immunoreactivity (GRP-LI) in T47D breast cancer cells but not in the conditioned medium, indicating rapid clearance. No GRP-LI was found in the ZR-75-1 or MDA-MB-436 cells or their conditioned medium. High-performance liquid chromatography (HPLC) analysis of the GRP-LI in the T47D cells revealed a major peak, which co-eluted with GRP(18-27), and a minor more hydrophilic peak. In vitro stimulation of T47D cell growth by bombesin (BN) was enhanced to 138% of control levels (bombesin alone) by the addition of the selective endopeptidase EC 3.4.24.11 inhibitor phosphoramidon (0.1 ng ml(-1)). Fluorogenic analysis using whole cells confirmed low levels of this phosphoramidon-sensitive enzyme on the T47D cells. This enzyme, previously unreported in human breast cancer cells, significantly modulates both T47D growth and its response to BN-induced growth.

Binding of nickel(II) and copper(II) to the N-terminal sequence of human protamine HP2

A potentiometric and spectroscopic (UV/vis and CD) study of Cu(II) and Ni(II) binding to the N-terminal pentadecapeptide of human protamine HP2 (HP2(1-15)) was performed. The results indicate that the N-terminal tripeptide motif Arg-Thr-His is the exclusive binding site for both metal ions at a metal to HP2(1-15) molar ratio not higher than 1. The very high value of protonation-corrected stability constant (log *K) for Ni(II)-HP2(1-15) complex, -19.29, indicates that HP2 has the potential to sequester Ni(II) from other peptide and protein carriers, including albumin. The same is likely for Cu(II) (log *K = -13.13). The CD spectra of Cu(II) and Ni(II) complexes of HP2(1-15) indicate that the N-terminal metal binding affects the overall conformation of the peptide that, in turn, may alter interaction of HP2 with DNA. These results imply HP2 as a likely target for the toxic metals Ni(II) and Cu(II).

Pituitary neuromedin B content in experimental fasting and diabetes mellitus and correlation with thyrotropin secretion

Fasting and diabetes mellitus in the rat model have been associated with abnormalities of thyrotropin (TSH) secretion. Neuromedin B is a bombesin-like peptide highly concentrated in the pituitary gland that has been shown to have inhibitory action on TSH secretion, acting as an autocrine/paracrine factor. Here, we aimed to determine if the pituitary content of neuromedin B would change in fasted rats (1, 2, 3, and 4 days of food deprivation) and streptozotocin (55 mg/kg body weight)-diabetic rats. The total pituitary content of neuromedin B was decreased in fasted rats, except at 2 days of fasting, as was the total protein content in the gland; however, the concentration of the peptide (femtomoles per milligram protein) did not significantly change until the fourth day of food deprivation, when an abrupt decrease in total protein happened and therefore neuromedin B concentration increased. In rats after 20 days of diabetes induction, pituitary neuromedin B increased. Serum thyroxine (T4) and triiodothyronine (T3) decreased in both disorders, whereas serum TSH was normal or decreased in 4-day fasted rats. Therefore, the caloric deprivation of diabetes and fasting changed the pituitary neuromedin B content and concentration, by mechanisms that remain to be elucidated. Since neuromedin B has been shown to act as a local inhibitor of TSH release, the results raise the possibility that increased neuromedin B concentration might be involved in the altered TSH secretion of diabetes mellitus and fasting.

Effect of thyroid hormones on pituitary neuromedin B and possible interaction between thyroid hormones and neuromedin B on thyrotropin secretion

Neuromedin B (NB), a bombesin-like peptide, has been recently characterized as a physiological paracrine/autocrine inhibitor of thyrotropin (TSH) secretion. We hypothesized on the basis of our prior experiments that thyroid hormones stimulate pituitary NB secretion which mediates, at least in part, the TSH-suppressive effect of thyroid hormone. Here, we evaluated the time-course of the effect of thyroid hormones administration to eu- and hypothyroid rats on the anterior pituitary content of NB and on serum TSH. As previously reported, the pituitary content of NB increased in hyperthyroidism and decreased in hypothyroidism. Chronic treatment of hypothyroid rats with a physiological dose of thyroxine (0.8 microgram/100 g b.w. s.c, for 3 or 5 days) normalized pituitary NB content, while 5 days of treatment with a pharmacological dose of thriiodothyronine (0.4 microgram/100 g b.w.) induced an increase above that of normal pituitaries. Thyroxine and triiodothyronine injected once, s.c., into hypothyroid rats required 30 min to normalize NB content, which reached higher than normal values in 3-6 h. At these times, the increment in NB preceded or was simultaneous with the suppression of serum TSH. This rapid and marked effect on pituitary neuromedin B content, associated in time with TSH suppression, is in agreement with the hypothesis that neuromedin B may mediate at least in part, the acute suppression of TSH release by thyroid hormone, a hypothesis that still needs further verification.

Distribution of bombesin-like immunoreactivity in the nucleus of the solitary tract and dorsal motor nucleus of the rat and human: colocalization with tyrosine hydroxylase

Bombesin is a peptide neurotransmitter/neuromodulator with important autonomic and behavioral effects that are mediated, at least in part, by bombesin-containing neurons and nerve terminals in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV). The distribution of bombesin-like immunoreactive nerve terminals/fibers and cell bodies in relation to a viscerotopically relevant subnuclear map of this region was studied by using an immunoperoxidase technique. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gelatinous, central, and rostral commissural subnuclei and the periventricular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissural and dorsal subnuclei had light bombesin fiber/terminal staining, as did the intermediate, interstitial, ventral, and ventrolateral subnuclei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal commissural, intermediate, interstitial, ventral, and ventrolateral subnuclei. Bombesin-like immunoreactive neurons were found in numerous other areas of the brain, including the ventrolateral medulla, the parabrachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreactive neurons were labeled in a number of subnuclei, with clusters of neurons labeled in the dorsal and ventrolateral subnuclei. Double immunofluorescence studies in rat demonstrated that bombesin colocalizes with tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other location in the brain. In conclusion, the distribution of bombesin in the NTS adheres to a viscerotopically relevant map. This is the anatomical substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic similarities between human and rat suggest that bombesin has similar functions in the visceral neuraxis of these two species. Bombesin coexists with catecholamines in neurons in the dorsal subnucleus, which likely mediate, in part, the cardiovascular effects of bombesin.

Neuromedin B stimulates arachidonic acid release, c-fos gene expression, and the growth of C6 glioma cells

The effects of neuromedin B (NMB) on C6 glioma cells were investigated. NMB bound with high affinity (IC50 = 1 nM) to C6 cells whereas BN and GRP were less potent (IC50 = 40 and 100 nM). NMB (1 nM) elevated cytosolic Ca2+ in individual C6 cells and the increase in cytosolic Ca2+ was reversed by 1 microM [D-Arg1, D-Pro2,D-Trp7.9,Leu11]substance P [APTTL]SP, a broad spectrum antagonist. NMB stimulated [3H]arachidonic acid release from C6 cells and the increase in [3H]arachidonic acid release was reversed [APTTL]SP. NMB increased transiently c-fos gene expression in C6 cells. NMB increased the number of C6 colonies in soft agar and the increase in growth caused by NMB was reversed by [APTTL]SP. These data suggest that NMB receptors may regulate the proliferation of C6 cells.

Investigations on the acute effects of neuropeptides on the pituitary-adrenocortical function in normal and cold-stressed rats. I. Bombesin and neuromedin B

The effects of a subcutaneous bolus injection of 2 micrograms bombesin (BM) or neuromedin B (NMB) on the function of the hypothalamo-pituitary-adrenocortical (HPA) axis were investigated in both normal and cold-stressed rats. The blood concentrations of ACTH, corticosterone (B) and aldosterone (ALDO) were measured by specific radioimmunoassays 1, 2 or 4 h after the neuropeptide administration. Cold stress strikingly enhanced plasma levels of ACTH, B and ALDO, and these rises lasted unchanged until 4 h. BM and NMB significantly elevated plasma concentrations of ACTH and B in both normal and stressed animals. In both groups of rats the level of circulating ALDO was not apparently affected by neuropeptides. In light of these findings the following conclusions can be drawn: (i) BM and NMB acutely activate the HPA axis, probably by acting via the same receptor; (ii) the mechanism underlying this effect of BM and NMB is independent of that involved in the cold stress-induced activation of the HPA axis; and (iii) the well-known acute ALDO secretagogue effect of ACTH is probably counteracted by a direct inhibitory action of BM and NMB on adrenal zona glomerulosa.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Expression of the genes encoding bombesin-related peptides and their receptors in anterior pituitary tissue

The bombesin-related peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) have been demonstrated in the anterior pituitary (AP) on an immunological basis. We studied the presence of mRNAs for these peptides and for their receptors by RNAse protection assay using fresh adult male rat AP, AP cell reaggregates cultured in the presence of estradiol and the rat AP derived GH3 cell line. In total RNA from fresh AP we detected high amounts of NMB mRNA and much smaller amounts of GRP mRNA, while finding a weak signal for GRP-receptor (GRP-R) and NMB-receptor (NMB-R) mRNAs. In total RNA from the reaggregate cell cultures we detected high levels of NMB mRNA as well as a strong signal for GRP-R mRNA. Finally, in GH3 cells, high levels of NMB mRNA and GRP-R mRNA were found, while GRP mRNA and NMB-R mRNA remained undetectable even in high amounts (200 micrograms) of total RNA. We conclude that mRNAs encoding both bombesin-related peptides and each of the mRNAs encoding their receptors are expressed in rat AP tissue. NMB mRNA is more prominent than GRP mRNA in all AP-like tissues examined (fresh AP, estradiol-treated reaggregate AP cell cultures and GH3 cells). NMB-R mRNA and GRP-R mRNA are both present in low levels in fresh AP whereas the GRP-R mRNA is predominant in GH3 cells and estradiol treated AP reaggregate cell cultures. Compared to fresh AP tissue, NMB mRNA and GRP-R mRNA expression is enhanced in estradiol-treated reaggregate cell cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiological effects of pressure-ejected bombesin-like peptides on hamster suprachiasmatic nucleus neurons in vitro

The suprachiasmatic nuclei (SCN) of the rodent hypothalamus function as a light entrainable circadian pacemaker. The SCN contain moderate to high concentrations of a number of neuropeptides including peptides showing structural homology with the amphibian derived tetradecapeptide, bombesin (BN), called bombesin-like peptides (BNLPs). BNLPs include the 27 amino acid peptide, gastrin releasing peptide (GRP1-27), a smaller decapeptide (GRP18-27) and another decapeptide with less structural homology, neuromedin B (NmB). Immunoreactivity for BN and receptors for BNLPs have been demonstrated in the region of the rat SCN receiving photic input. We studied the effects of local pressure ejections of BNLPs dissolved in saline/1% bovine serum albumin (BSA) vehicle on the extracellularly recorded firing rates of Syrian hamster SCM neurons in a hypothalamic slice preparation. In one study, an ejecting electrode containing BN (10(-8) to 10(-4) M) was positioned 20 to 60 microm from a recording electrode. Of 74 cells tested with BN, 50 (67.6%) showed significant increases in firing rate, while 3 of 29 cells (15.8%) tested with vehicle ejections were activated. In a second study, a single electrode was used for both recordings and pressure ejections. Of 48 cells tested, BN (10(-6) to 10(-4) M) activated 30 (62.5%) and suppressed firing in 4 (8.3%). Of 208 cells tested with GRP1-27 (10(-9) to 10(-4) M), 105 (50.5%) were activated and 2 (1.0%) were suppressed. The percentage of cells responding increased with the concentration of GRP1027 used in the electrode. No circadian variation in responsiveness to GRP1-27 was detected. GRP18-27 (5 x 10(-5) to 10(-4) M) activated 10 out of 18 cells tested (55.6%), while NmB (10(-4) M) activated 2 out of 30 cells tested (6.7%) and vehicle ejections activated 1 out of 36 cells tested (2.8%). GRP1-27, GRP18-27 and BN, the BNLPs showing the greatest degree of structural homology, activate approximately 50% of SCN cells, apparently via the BN/GRP-preferring receptor subtype, and may play a role in photic entrainment.

Scratching behavior induced by bombesin-related peptides. Comparison of bombesin, gastrin-releasing peptide and phyllolitorins

Bombesin and 10 bombesin-related peptides were administered intracerebroventricularly to conscious and freely moving rats. All peptides tested were found to elicit excessive grooming, especially scratching behavior. Bombesin itself had the most potent and long-lasting activity in eliciting scratching behavior. Naturally occurring peptides such as neuromedin B and gastrin-releasing peptide (GRP)-(18-27) were short-acting compared with exogenous peptides such as bombesin and synthesized analogs. Two phyllolitorins, a new bombesin subfamily, were also examined in this study. [Leu8]phyllolitorin induced more scratching than [Phe8]phyllolitorin and proved to be virtually equipotent to bombesin. Corticotropin-releasing factor (CRF) and substance P induced considerable excessive grooming, but both peptides were strikingly weak in inducing scratching behavior. It is suggested that (1) scratching represents a specific behavior commonly induced by bombesin-related peptides and (2) the relative potency to induce scratching behavior reflects the metabolic stability of the peptide, e.g. endogenous versus exogenous, shorter versus longer sequences, or chemical protection of N-terminus.

Effects of neonatal blockade of bombesin (BN) receptors with [D-Phe6, phi Leu13-Cpa14]BN(6-14) on adult behavior and sensitivity to BN

Long-term consequences of neonatal blockade of bombesin (BN) receptors were examined in the present study. Rat pups were injected twice daily with [D-Phe6, phi Leu13-Cpa14]BN(6-14), a BN receptor antagonist, at either high (10 mg/kg; HD group) or low (5 mg/kg; LD group) doses from postnatal day 1 through 8. Their behavioral responses to a variety of conditions were compared to those of rats neonatally injected with saline (SAL group) or animals handled but not injected during infancy (UNT group). Adult HD rats entered and spent more time on the open arms of the elevated plus maze than LD, SAL, or UNT animals. Under the conditions of a water deprivation schedule, neither central nor peripheral injections of BN differentiated the neonatally pretreated groups as determined by measures of grooming, feeding, and drinking behaviors. These results indicate that at the dosage regimen employed, neonatal injections of [D-Phe6, phi Leu13-Cpa14]BN(6-14) had little effect on adult sensitivity to BN, but that such treatments could alter activity on the elevated plus maze through as yet unknown mechanisms.

Distinct distributions of two bombesin receptor subtypes in the rat central nervous system

We have previously demonstrated the presence of two distinct bombesin receptor subtypes in the rat CNS and distinguished them as bombesin/gastrin-releasing peptide (BBS/GRP) and neuromedin B (NMB)-preferring binding sites. In the present study, we conducted a complete evaluation of the distribution of these binding sites throughout the rat brain using in vitro receptor autoradiography. The BBS/GRP-preferring binding sites were characterized as those that bound 125I-(Tyr4)BBS but not 125I-(D-Tyr0)NMB. At these sites 125I-(Tyr4)BBS binding was inhibited in the presence of 100 nM BBS but not by the same concentration of NMB. In contrast, NMB-preferring sites bound both radioligands and binding at these sites was inhibited in the presence of 100 nM NMB. Our results indicate that the distributions of BBS/GRP and NMB-preferring binding sites are widespread and distinct at all levels of the rat brain suggesting these peptides mediate separate functions in the rat central nervous system.

Isolation and sequence of a cDNA encoding the precursor of a bombesinlike peptide from brain and early embryos of Xenopus laevis

A cDNA encoding the precursor of a bombesinlike peptide was isolated from brain of Xenopus laevis. The predicted end product resembles neuromedin B, which was originally isolated from mammalian spinal cord. The mRNA for this precursor was also present in gastrointestinal tract and in ovaries. Moreover, it could be detected in early embryos (stage 2 and stage 10) of X. laevis. These findings suggest novel roles for peptides of the bombesin family in oocyte maturation and early amphibian development.

Modulation of cisplatin sensitivity and growth rate of an ovarian carcinoma cell line by bombesin and tumor necrosis factor-alpha

A twofold change in the cisplatin (DDP) sensitivity of 2008 human ovarian carcinoma cells is sufficient to reduce tumor response in vivo. The DDP sensitivity of these cells can be enhanced by activation of the epidermal growth factor and protein kinase C signal transduction pathways. We report here that two endogenous growth factors, bombesin and tumor necrosis factor alpha (TNF alpha), enhanced DDP sensitivity by factors of 1.7 +/- 0.1 (SD)-fold and 1.8 +/- 0.1 (SD)-fold, respectively. Both agents also produced sensitization in an 11-fold DDP-resistant 2008 subline. Neither bombesin nor TNF alpha changed the accumulation of DDP, glutathione content, or glutathione-S-transferase activity in 2008 cells. However, a 2-h exposure to both bombesin and TNF alpha was sufficient to increase 2008 cloning efficiency by up to 2.6 +/- 0.1 (SD)-fold and 2.2 +/- 0.1 (SD)-fold, and it increased average colony size by 1.35 +/- 0.1 (SD)-fold and 1.55 +/- 0.1 (SD)-fold, respectively. Bombesin increased intracellular free calcium, and this was blocked by the bombesin receptor-specific antagonist SC196, demonstrating that 2008 cells have functional bombesin receptors. These results indicate that bombesin and TNF alpha can enhance sensitivity to DDP in both DDP sensitive and resistant variants of a human ovarian carcinoma and that both agents serve as growth factors for this tumor.

Identification and initial characterization of a putative neuromedin B-type receptor from rat urinary bladder membranes

Receptor binding site(s) on the rat urinary bladder membranes were characterized using a biologically active analog of bombesin, [Tyr4,Leu14]bombesin, and a 50,000 x g total particulate preparation. The binding was specific, reversible, saturable, time- and concentration-dependent. A dissociation curve showed that both bombesin and neuromedin B equally displaced the radioligand in the first 10 min after saturation. From the rate constant of association K + 1 = 7.60 x 10(9) M-1 min-1, and the rate constant of dissociation k-1 = 0.050 min-1, the apparent equilibrium dissociation constant Kd = 6.57 +/- 1.09 pM was determined. A linear Scatchard plot of the specific binding of 125I-[Tyr4,Leu14]bombesin to the membranes revealed that the radioligand bound with high affinity, Kd = 6.38 +/- 0.86 pM, to a single class of sites (Bmax = 2.3 fmol/mg protein). The Hill coefficient of the same binding data was 1.05 +/- 0.21, indicating that the radioligand was binding to a single population of noninteracting binding sites. Both bombesin and neuromedin B displaced the radioligand dose dependently (IC50 = 0.3 nM). Neurokinin A and neurokinin B were less potent (IC50 = 20 and 110 nM, respectively). Substance P, or the specific bombesin receptor antagonists [D-Phe6]bombesin-(6-13) methyl ester, [D-F5Phe6,D-Ala11]bombesin-(6-11) methyl ester, [D-Phe6]bombesin-(6-13) propylamide, [D-Phe6,Leu13psi(CH2NH)Leu14]bombesin or [D-Cpa6,Phe14(psi13-14)]bombesin-(6-14) had an IC50 greater than 1 microM. The results presented suggest the presence of neuromedin B receptor sites on the rat urinary bladder membranes that can be occupied also by some other peptides, notably bombesin, neurokinin A and neurokinin B.(ABSTRACT TRUNCATED AT 250 WORDS)

Bombesin, neuromedin C and neuromedin B given intrathecally facilitate the tail flick reflex in the rat

Evidence from an earlier study suggested that bombesin, neuromedin C and neuromedin B may play a role in spinal nociceptive transmission; iontophoretic administration of these peptides onto dorsal horn neurones in the cat was found to preferentially depress those neurones activated by noxious stimulation. Therefore, to further examine the possible function of these peptides in the spinal cord, the present study compares the effects of intrathecal administration of bombesin, neuromedin C and neuromedin B on reaction time in the tail flick test in the rat. Intrathecal injection of bombesin and neuromedin C to the lower lumbar vertebral level produced a dose-dependent decrease in reaction time which lasted up to 46 min. Similar administration of neuromedin B had a biphasic effect; there was a dose-dependent decrease in reaction time lasting about 6 min followed by a delayed increase in reaction time to above control values at 31-46 min. In addition, administration of these peptides induced behavioral responses such as spontaneous vocalization and vocalization in response to innocuous touch. These results provide physiological evidence for a role of neuromedin C and neuromedin B in sensory transmission at the spinal level. In this model, bombesin was a potent agonist which may selectively activate the neuromedin C receptor.

Neuromedin-induced excessive grooming/scratching behavior is suppressed by naloxone, neurotensin and a dopamine D1 receptor antagonist

Neuromedin B and neuromedin C were tested for their grooming/scratching-inducing effects and the composition of neuromedin-induced grooming was established by calculating the relative contribution of various grooming elements to the total grooming scores. Excessive grooming induced by neuromedins is characterized by a predominant display of scratching. Since neuromedin C is much more potent than neuromedin B to induce excessive grooming/scratching behavior, it is concluded that the carboxyl-terminal heptapeptide of neuromedin C is important for this effect. Furthermore, it is concluded that dopamine D1 receptors and opiate receptors are involved in this effect since the dopamine D1 receptor antagonist, SCH 23390, as well as the opiate receptor antagonist, naloxone, suppresses or attenuates neuromedin C-induced excessive grooming/scratching behavior.

High-affinity receptors for bombesin-like peptides in normal guinea pig lung membranes

The binding of the radiolabelled bombesin analogue [125I-Tyr4]bombesin to guinea-pig lung membranes was investigated. Binding of [125I-Tyr4]bombesin was specific, saturable, reversible and linearly related to the protein concentration. Scatchard analysis of equilibrium binding data at 25 degrees C indicated the presence of a single class of non-interacting binding sites for bombesin (Bmax = 7.7 fmol/mg protein). The value of the equilibrium dissociation constant (KD = 90 pM) agrees with a high-affinity binding site. Bombesin and structurally related peptides such as [Tyr4]bombesin, neuromedin B and neuromedin C inhibited the binding of [125I-Tyr4]bombesin in an order of potencies as follows: [Tyr4]bombesin greater than bombesin greater than or equal to neuromedin C much greater than neuromedin B. These results indicate that guinea-pig lung membranes possess a single class of bombesin receptors with a high affinity for bombesin and a lower one for neuromedin B.

Aversive properties of bombesin in rats

Aversive properties of bombesin were determined in the conditioned place-preference paradigm in rats and compared with the effects on spontaneous behavior. Bombesin induced excessive grooming and/or scratching behavior at doses of 80 ng, 400 ng, and 2.0 micrograms ICV. In the conditioned place-preference paradigm, doses of 400 ng and 2.0 micrograms ICV induced a profound aversion to the environment in which the animals had received peptide treatment. Eighty ng were partially effective, and 16 ng did not induce a significant change in preference. The grooming/scratching behavior was attenuated by pretreatment with 4 mg/kg morphine-sulfate. These results show that bombesin is strongly aversive at doses that induce grooming/scratching behavior. Although the relationship between these different effects is not known, the similarity in their dose-response relationship suggests that they may be mediated by a common mechanism.

Neuromedin U-like immunoreactivity in rat intestine: regional distribution and immunohistochemical study

Neuromedin U-25 and its C-terminal octapeptide, neuromedin U-8 are related peptides originally identified in porcine brain which elicit potent uterus stimulant activity. Radioimmunoassay using an antiserum raised against porcine neuromedin U-8, indicated that neuromedin U-like immunoreactivity in the rat was far more abundant in the small intestine than the brain. Neuromedin U in the rat is a single, a 23 amino acid peptide (2, 17). Rat neuromedin U has the same 7 residues on its C-terminus as porcine neuromedin U, and the antiserum against porcine neuromedin U-8 is 100% crossreactive with rat neuromedin U. Immunohistochemical analyses using this antiserum revealed that neuromedin U-immunoreactive structures in rat intestine were confined to the enteric nervous system, implying that neuromedin U may be involved in neuronal regulation of gut function.

Structural identification, subcellular localization and secretion of bovine adrenomedullary neuromedin C [GRP-(18-27)]

Bombesin-like immunoreactivity (BLI) was purified from acid (HCl) extracts of bovine adrenal medulla. High performance liquid chromatography (HPLC) on a mu-Bondapak C18 column revealed the presence of five molecular forms of BLI, one coeluting with synthetic gastrin releasing peptide (GRP), the mammalian counterpart of amphibian bombesin, one coeluting with neuromedin C, one coeluting with neuromedin B and the two other ones coeluting with the oxidized forms of neuromedins B and C. The material corresponding to neuromedin C was purified to homogeneity and its amino acid composition and sequence corresponded to those expected for neuromedin C. HPLC analysis on an analytical SP-5PW column of subcellular extracts of bovine adrenal medulla indicated that neuromedin C is almost exclusively localized in secretory granules. The neuropeptide function of neuromedin C and/or other BLI peptides at this level was supported by the stimulatory effect of carbamylcholine (500 microM) on the release of BLI (4.5-fold increase over the basal release of 19 fmol/5 min) from perfused bovine adrenal glands.

Inhibition of serotonin release by bombesin-like peptides in rat hypothalamus in vitro

We investigated the activity of bombesin (BN), neuromedin-C (NM-C) and neuromedin-B (NM-B) on serotonin (5-HT) release and reuptake in rat hypothalamus (HYP) in vitro. BN and NM-C but not NM-B (all 1 microM) decreased K+ evoked 3H-5-HT release from superfused HYP slices by 25%. Bacitracin (BCN, 2 micrograms/ml), a nonspecific peptidase inhibitor, reversed the inhibitory effect of BN on K+ evoked 3H-5-HT release. Phosphoramidon (PAN, 10 microM) an endopeptidase 24.11 inhibitor, abolished the inhibitory effect of BN, but not NM-C, on K+ evoked 3H-5-HT release. The peptidyl dipeptidase A inhibitor enalaprilat (ENP, 10 microM), enhanced both BN and NM-C inhibition of 3H-5-HT release. Bestatin (BST, 10 microM) had no effect on BN or NM-C inhibitory activity on 3H-5-HT release. Neither BN, NM-C nor NM-B affected reuptake of 3H-5-HT into HYP synaptosomes alone or in combination with any of the peptidase inhibitors, nor did these peptides alter the ability of fluoxetine to inhibit 3H-5-HT uptake. These data suggest: a) that BN-like peptides may alter neurotransmission in the HYP by acting presynaptically on the 5-HT release mechanism; b) a similarity in the structural requirements for the BN induced inhibition of 5-HT release and BN evoked thermoregulatory disturbances; and c) that peptidases may selectively augment or reduce pharmacologic activity of BN-like peptides upon CNS administration.

Brain natriuretic peptide-32: N-terminal six amino acid extended form of brain natriuretic peptide identified in porcine brain

Brain natriuretic peptide (BNP) is a newly identified peptide of 26 residues, which has a remarkable homology to but is distinct from atrial natriuretic peptide. The peptide exerts natriuretic-diuretic activity as well as potent chick rectum relaxant activity. By using radioimmunoassay specific to BNP and immunoaffinity chromatography, we have isolated from porcine brain a novel peptide of 32 residues carrying a BNP structure at the C-terminus. The amino acid sequence of this peptide was determined to be: Ser-Pro-Lys-Thr-Met- Arg-Asp-Ser-Gly-Cys-Phe-Gly-Arg-Arg-Leu-Asp-Arg-Ile-Gly-Ser-Leu-Ser-Gly- Leu- Gly-Cys-Asn-Val-Leu-Arg-Arg-Tyr. This peptide is an N-terminal six amino acid extended form of BNP and henceforth is designated BNP-32. BNP and BNP-32 are found to be major forms of BNP family in porcine brain.