Brain regulation of gastric secretion: influence of neuropeptides

Bombesins: A New Frontier in Hybrid Compound Development

Recently, bombesin (BN) and its analogs have attracted much attention as excellent anticancer agents because they interact with specific receptors widely distributed on the surface of various cancer cells. However, their biological properties proceed far beyond this, given a broad spectrum of activity. Bombesin receptor ligands are effective drugs for the treatment of rheumatoid arthritis or gastrointestinal diseases. However, most diseases are complex, and the use of polytherapy may lead to pharmacokinetic and pharmacodynamic drug-drug interactions, resulting in side effects. Therefore, there is a need to develop effective compounds that also contain BN or its analogs, which are combined with other structural entities, thus generating a so-called hybrid drug. Hybrid drugs that contain bombesin pharmacophore(s) may be proposed as a solution to the problem of polytherapy or the lack of an effective cure. Such structures have now demonstrated the desired efficacy, though information on these aforementioned compounds is relatively scarce. Therefore, our paper aims to encourage researchers to focus on bombesins. Herein, we indicate that the hybrid approach should also be firmly applied to bombesins and the BN receptor family. This paper's structure is divided into two main sections demonstrating bombesins and their properties, as well as recent data on bombesin-based hybrid compounds and their potential usefulness in medicine. Overall, it refers to the discovery and synthesis of modified bombesin-based hybrid compounds.

The microbiota-gut-brain axis and neurodevelopmental disorders

The gut microbiota has been found to interact with the brain through the microbiota-gut-brain axis, regulating various physiological processes. In recent years, the impacts of the gut microbiota on neurodevelopment through this axis have been increasingly appreciated. The gut microbiota is commonly considered to regulate neurodevelopment through three pathways, the immune pathway, the neuronal pathway, and the endocrine/systemic pathway, with overlaps and crosstalks in between. Accumulating studies have identified the role of the microbiota-gut-brain axis in neurodevelopmental disorders including autism spectrum disorder, attention deficit hyperactivity disorder, and Rett Syndrome. Numerous researchers have examined the physiological and pathophysiological mechanisms influenced by the gut microbiota in neurodevelopmental disorders (NDDs). This review aims to provide a comprehensive overview of advancements in research pertaining to the microbiota-gut-brain axis in NDDs. Furthermore, we analyzed both the current state of research progress and discuss future perspectives in this field.

A preliminary study for the clinical effect of one combinational physiotherapy and its potential influence on gut microbial composition in children with Tourette syndrome

Introduction

Tourette syndrome (TS) is a chronic neuropsychiatric disorder with unknown causes and inadequate therapies. Inspired by the important roles of gut microbiota in some mental illnesses, the interactions between gut microbiota and TS via the gut-brain axis have gained more and more attention. This study aimed to characterize the gut microbial profiles in children with TS, and explore the clinical effects of one combinational physiotherapy and its potential influence on gut microbial composition.

Methods

The gut microbial profiles were depicted based on the sequence data of 32 patients and 29 matched health children by 16S rDNA amplicon pyrosequencing. Thirty of thirty-two patients underwent uninterrupted two 10-day courses of combinational physiotherapy, which included a 60-minute cranial electrotherapy stimulation (CES) training followed by a 30-minute biofeedback training per session, 2 sessions a day.

Results

Our results indicated that the gut microbial composition in children with TS was different from that in healthy controls. Multiple GBM neurotransmitter modules obtained through Picrust2 functional predictive analysis were significantly increased in patients, including Histamine degradation, Dopamine degradation, and DOPAC synthesis. Moreover, this combinational physiotherapy could significantly diminish tic activity, whose positive effects were first reported in children with TS. Lastly, different gut microbial compositions and predictive metabolic pathways were also observed between patients before and after this treatment, with lower abundances of the genera (e.g., Dorea) and significant decreases of GBM neurotransmitter modules (e.g. dopamine degradation) in patients after this treatment, indicating that improved clinical symptoms might be accompanied by an improvement of intestinal microenvironment.

Discussion

Children with TS showed a cognizable gut microbial profile, and certain enriched bacteria with pro-inflammatory potential might induce neuroinflammatory responses. This combinational physiotherapy could significantly diminish tic activity, and the gut microbial compositions in patients after this treatment were different from those without any treatment, indicating the existence of bidirectional communication of the gut-brain axis in TS. But studies on the gut microbial characteristics in TS patients, the influences of gut microbiota on tic severity, the efficacy and safety of this treatment, and the bidirectional regulatory mechanism between brain signals and gut microbiota in TS still need to be explored.

Brain-gut axis and psychiatric disorders: A perspective from bibliometric and visual analysis

BACKGROUND

The Brain-Gut Axis, a bidirectional signaling pathway that connects the intestinal and central nervous systems, plays an important role in the development of psychiatric disorders. However, the overall research trends in this field are unclear. This study explored the patterns of research on the brain-gut axis and psychiatric disorders from a bibliometric perspective.

METHODS

Relevant data were retrieved from the Web of Science Core Collection, with search terms on psychiatric disorders and the brain-gut axis. R (version 4.2.0), VOSviewer (version 1.6.17), CiteSpace software, and the online bibliometric platform were used in the data analysis.

RESULTS

A total of 2,298 articles published between 1993 and 2022 were identified, showing an increasing trend over time. China (1,859; 20.70%) was the country that contributed the most publications. The journal Nutrients (95; 4.13%) published the most publications. Cryan JF (153; H-index=73) and University College Cork (559; 22.54%) were the most influential author and the most productive institution, respectively. The high-frequency keywords were clustered into six themes, including neurodegenerative diseases, stress-related diseases, immune, brain behavior, depression, and probiotic-related topics; of which, depression (880; 2019), anxiety (207; 2018) and autism (191; 2019) were the most studied psychiatric disorders in the past 5 years. "Depressive symptom" (2019-2020) and "probiotic treatment" (2019-2020) were the main areas addressed in recent years.

CONCLUSION

Research on the brain-gut axis and psychiatric disorders has attracted increasing attention in the past decade, with most publications originating from high-income level countries. This study provides a useful perspective on understanding the research trends, key hot topics, and research gaps in this expanding field.

Impact of Environmental Pollutants on Gut Microbiome and Mental Health via the Gut–Brain Axis

Over the last few years, the microbiome has emerged as a high-priority research area to discover missing links between brain health and gut dysbiosis. Emerging evidence suggests that the commensal gut microbiome is an important regulator of the gut–brain axis and plays a critical role in brain physiology. Engaging microbiome-generated metabolites such as short-chain fatty acids, the immune system, the enteric nervous system, the endocrine system (including the HPA axis), tryptophan metabolism or the vagus nerve plays a crucial role in communication between the gut microbes and the brain. Humans are exposed to a wide range of pollutants in everyday life that impact our intestinal microbiota and manipulate the bidirectional communication between the gut and the brain, resulting in predisposition to psychiatric or neurological disorders. However, the interaction between xenobiotics, microbiota and neurotoxicity has yet to be completely investigated. Although research into the precise processes of the microbiota–gut–brain axis is growing rapidly, comprehending the implications of environmental contaminants remains challenging. In these milieus, we herein discuss how various environmental pollutants such as phthalates, heavy metals, Bisphenol A and particulate matter may alter the intricate microbiota–gut–brain axis thereby impacting our neurological and overall mental health.

The Effect of a Probiotic Complex on the Gut-Brain Axis: A Translational Study

BACKGROUND

The gut-brain axis refers to the network of connections that involve multiple biologic systems, allowing bidirectional communication between the gut and the brain. This communication is mainly mediated by gut microbiota, thanks to its ability to modulate several processes like the production of neurotransmitters. As such, keeping a balanced gut microbiota through probiotic intake could be a valid solution in supporting the right gut-brain communications.

METHODS

A two-step in vitro screening of five different probiotic strains was carried out to select the best performers in the modulation of stress markers. A first selection on SK-N-DZ neuronal cell lines was performed to evaluate the inhibition of the epigenetic enzyme LSD1, promotion of GABA, and expression of serotonin. Three out of five strains were tested for their ability to promote serotonin synthesis in the Caco2 cell line. As a result, Limosilactobacillus reuteri PBS072 and Bifidobacterium breve BB077 were selected as the best performing strains. To confirm their effects in humans, a proof-of-concept trial was carried out to evaluate stress-related parameters for 28 days of product intake in a group of 30 stressed students.

RESULTS

A significant improvement of cognitive functions, in terms of short-term memory, attention, and executive performance, as well as of psychophysiological markers, such as salivary cortisol level, skin conductance, sleep quality, and anxiety, were observed.

CONCLUSIONS

According to the results, L. reuteri PBS072 and B. breve BB077 are potential probiotic candidates for improving stress resilience, cognitive functions, and sleep quality.

Changes of Gastric Secretion after Bolus and Slow Intravenous Administration of Bombesin and Neurotensin

Objectives:The aim of the present study was to evaluate the changes caused by intravenous administration of regulatory peptides, bombesin (BBS) and neurotensin (NT), on gastric secretion, serum gastrin, and plasma levels of bombesin-1ike immunoreactivity (BLI) and neurotensin. Materials and methods: Fourteen dogs underwent an upper gastrointestinal tract operation and a Pavlov pouch for the concentration of gastric fluids was formed. The experimental animals were divided into two groups. Peptides were given one month after the second operation and after fasting for 12 hours. In group A, the effects of BBS were studied after a rapid 1 ìg/kg body weight dose and a slow 30´ 0.5 ìg/kg body weight dose administration intravenously. Correspondingly to group B the effects of NT were studied in the same way. Results:The rapid intravenous infusion of BBS caused a very significant increase in gastrin levels, BLI in plasma, volume and HCl of the gastric fluids. The same results, plus a significant decrease in gastric pH, were observed following slow intravenous infusion of BBS. Concerning the NT, rapid administration caused a significant decrease in the volume of gastric fluids. Slow NT administration of caused a significant reduction in gastric fluid volume and in HCl. On the contrary, pH was significantly increased. Conclusion:Bombesin increases plasma gastrin levels and HCl secretion. Neurotensin administration causes a decrease in HCl secretion without affecting gastrin levels in plasma.

Synchronizing Our Clocks as We Age: The Influence of the Brain-Gut-Immune Axis on the Sleep-Wake Cycle Across the Lifespan

The microbes that colonize the small and large intestines, known as the gut microbiome, play an integral role in optimal brain development and function. The gut microbiome is a vital component of the bi-directional communication pathway between the brain, immune system, and gut, also known as the brain-gut-immune axis. To date there has been minimal investigation into the implications of improper development of the gut microbiome and the brain-gut-immune axis on the sleep-wake cycle, particularly during sensitive periods of physical and neurological development, such as childhood, adolescence, and senescence. Therefore, this review will explore the current literature surrounding the overlapping developmental periods of the gut microbiome, brain, and immune system from birth through to senescence, while highlighting how the brain-gut-immune axis affects maturation and organisation of the sleep-wake cycle. We also examine how dysfunction to either the microbiome or the sleep-wake cycle negatively affects the bidirectional relationship between the brain and gut, and subsequently the overall health and functionality of this complex system. Additionally, this review integrates therapeutic studies to demonstrate when dietary manipulations, such as supplementation with probiotics and prebiotics, can modulate the gut microbiome to enhance health of the brain-gut-immune axis and optimize our sleep-wake cycle.

The Microbiota-Gut-Brain Axis

The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators of gut-brain function and has led to the appreciation of the importance of a distinct microbiota-gut-brain axis. This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans. Many factors can influence microbiota composition in early life, including infection, mode of birth delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and host genetics. At the other extreme of life, microbial diversity diminishes with aging. Stress, in particular, can significantly impact the microbiota-gut-brain axis at all stages of life. Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Animal models have been paramount in linking the regulation of fundamental neural processes, such as neurogenesis and myelination, to microbiome activation of microglia. Moreover, translational human studies are ongoing and will greatly enhance the field. Future studies will focus on understanding the mechanisms underlying the microbiota-gut-brain axis and attempt to elucidate microbial-based intervention and therapeutic strategies for neuropsychiatric disorders.

Microbes and mental health: A review

There is a growing emphasis on the relationship between the microorganisms inhabiting the gut (gastrointestinal microbiota) and human health. The emergence of a microbiota-gut-brain axis to describe the complex networks and relationship between the gastrointestinal microbiota and host reflects the major influence this environment may have in brain health and disorders of the central nervous system (CNS). Bidirectional communication between the microbiota and the CNS occurs through autonomic, neuroendocrine, enteric, and immune system pathways. Potential neurobiological mechanisms through which disruptions in this network may impact health and disease include hypothalamic-pituitary-adrenal (HPA)-axis activation, and altered activity of neurotransmitter and immune systems. Perturbations of the gut microbial community have already been implicated in multiple host diseases such as obesity, diabetes, and inflammation, while recent evidence suggests a potential role of the microbiota-gut-brain axis in neuropsychiatric disorders, such as depression and anxiety. Here, we review the current literature related to the influence of the gut microbial community on central nervous system function, with a specific focus on anxiety and depressive symptoms. The role of stress and stress-mediated changes in autonomic, neuroendocrine, immune, and neurotransmitter systems are examined, followed by a discussion of the role of the microbiota in novel gastrointestinal-based treatment options for the prevention and treatment of brain-based disorders such as anxiety and depression.

Neuromedin: An insight into its types, receptors and therapeutic opportunities

Neuropeptides are small protein used by neurons in signal communications. Neuromedin U was the first neuropeptide discovered from the porcine spinal and showed its potent constricting activities on uterus hence was entitled with neuromedin U. Following neuromedin U another of its isoform was discovered neuromedin S which was observed in suprachiasmatic nucleus hence was entitled neuromedin S. Neuromedin K and neuromedin L are of kanassin class which belong to tachykinin family. Bombesin family consists of neuromedin B and neuromedin C. All these different neuromedins have various physiological roles like constrictive effects on the smooth muscles, control of blood pressure, pain sensations, hunger, bone metastasis and release and regulation of hormones. Over the years various newer physiological roles have been observed thus opening ways for various novel therapeutic treatments. This review aims to provide an overview of important different types of neuromedin, their receptors, signal transduction mechanism and implications for various diseases.

Amiloride but not memantine reduces neurodegeneration, seizures and myoclonic jerks in rats with cardiac arrest-induced global cerebral hypoxia and reperfusion

It has been reported that both activation of N-methyl-D-aspartate receptors and acid-sensing ion channels during cerebral ischemic insult contributed to brain injury. But which of these two molecular targets plays a more pivotal role in hypoxia-induced brain injury during ischemia is not known. In this study, the neuroprotective effects of an acid-sensing cation channel blocker and an N-methyl-D-aspartate receptor blocker were evaluated in a rat model of cardiac arrest-induced cerebral hypoxia. We found that intracisternal injection of amiloride, an acid-sensing ion channel blocker, dose-dependently reduced cerebral hypoxia-induced neurodegeneration, seizures, and audiogenic myoclonic jerks. In contrast, intracisternal injection of memantine, a selective uncompetitive N-methyl-D-aspartate receptor blocker, had no significant effect on cerebral hypoxia-induced neurodegeneration, seizure and audiogenic myoclonic jerks. Intracisternal injection of zoniporide, a specific sodium-hydrogen exchanger inhibitor, before cardiac arrest-induced cerebral hypoxia, also did not reduce cerebral hypoxia-induced neurodegeneration, seizures and myoclonic jerks. These results suggest that acid-sensing ion channels play a more pivotal role than N-methyl-D-aspartate receptors in mediating cerebral hypoxia-induced brain injury during ischemic insult.

(68)Ga-labeled bombesin analogs for receptor-mediated imaging

Targeted receptor-mediated imaging techniques have become crucial tools in present targeted diagnosis and radiotherapy as they provide accurate and specific diagnosis of disease information. Peptide-based pharmaceuticals are gaining popularity, and there has been vast interest in developing (68)Ga-labeled bombesin (Bn) analogs. The gastrin-releasing peptide (GRP) family and its Bn analog have been implicated in the biology of several human cancers. The three bombesin receptors GRP, NMB, and BRS-3 receptor are most frequently ectopically expressed by common, important malignancies. The low expression of Bn/GRP receptors in normal tissue and relatively high expression in a variety of human tumors can be of biological importance and form a molecular basis for Bn/GRP receptor-mediated imaging. To develop a Bn-like peptide with favorable tumor targeting and pharmacokinetic characteristics for possible clinical use, several modifications in the Bn-like peptides, such as the use of a variety of chelating agents, i.e., acyclic and macrocyclic agents with different spacer groups and with different metal ions (gallium), have been performed in recent years without significant disturbance of the vital binding scaffold. The favorable physical properties of (68)Ga, i.e., short half-life, and the fast localization of small peptides make this an ideal combination to study receptor-mediated imaging in patients.

Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour

Recent years have witnessed the rise of the gut microbiota as a major topic of research interest in biology. Studies are revealing how variations and changes in the composition of the gut microbiota influence normal physiology and contribute to diseases ranging from inflammation to obesity. Accumulating data now indicate that the gut microbiota also communicates with the CNS--possibly through neural, endocrine and immune pathways--and thereby influences brain function and behaviour. Studies in germ-free animals and in animals exposed to pathogenic bacterial infections, probiotic bacteria or antibiotic drugs suggest a role for the gut microbiota in the regulation of anxiety, mood, cognition and pain. Thus, the emerging concept of a microbiota-gut-brain axis suggests that modulation of the gut microbiota may be a tractable strategy for developing novel therapeutics for complex CNS disorders.

Intracisternal administration of glibenclamide or 5-hydroxydecanoate does not reverse the neuroprotective effect of ketogenic diet against ischemic brain injury-induced neurodegeneration

PRIMARY OBJECTIVE

To investigate the role of ATP-sensitive potassium (K(ATP)) channels in the neuroprotective effects of a ketogenic diet against cardiac arrest-induced cerebral ischemic brain injury-induced neurodegeneration.

RESEARCH DESIGN

Male Sprague Dawley rats were randomly divided into three groups and were fed with a ketogenic diet for 25 days before being subjected to a cardiac arrest-induced cerebral ischemia for 8 minutes 30 seconds. Four hours before cardiac arrest-induced cerebral ischemia, one group was intracisternally injected with glibenclamide, a plasma membrane K(ATP) channel blocker. The second group was injected with 5-hydroxydecanoate, a mitochondrial K(ATP) channel blocker. The third group was without the pre-treatment with K(ATP) channel antagonist. Nine days after the cardiac arrest, rats were sacrificed. Fluoro-jade (FJ) staining was used to evaluate cerebral ischemic neurodegeneration in the rat brain sections.

MAIN OUTCOMES AND RESULTS

The number of FJ-positive degenerating neurons in the CA1 area of the hippocampus, the cerebellum and the thalamic reticular nucleus of the ketogenic diet-fed rats with or without glibenclamide or 5-hydroxydecanoate pre-treatment before cardiac arrest-induced cerebral ischemia is zero.

CONCLUSIONS

The results suggest that K(ATP) channels do not play a significant role in the neuroprotective effects of the ketogenic diet against cardiac arrest-induced cerebral ischemic injury-induced neurodegeneration.

Bombesin and the brain-gut axis

Bombesin is the first peptide shown to act in the brain to influence gastric function and the most potent peptide to inhibit acid secretion when injected into the cerebrospinal fluid (CSF) in rats and dogs. Bombesin responsive sites include specific hypothalamic nuclei (paraventricular nucleus, preoptic area and anterior hypothalamus), the dorsal vagal complex as well as spinal sites at T9-T10. The antisecretory effect of central bombesin encompasses a variety of endocrine/paracrine (gastrin, histamine) or neuronal stimulants. Bombesin into the CSF induces an integrated gastric response (increase in bicarbonate, and mucus, inhibition of acid, pepsin, vagally mediated contractions) enhancing the resistance of the mucosa to injury through autonomic pathways. The physiological significance of central action of bombesin on gastric function is still to be unraveled.

Brain histamine mediates the bombesin-induced central activation of sympatho-adrenomedullary outflow

Intracerebroventricular (i.c.v.) administration of bombesin (0.3 nmol) increased plasma levels of both adrenaline and noradrenaline in urethane anesthetized rats. These bombesin-induced increases were inhibited by i.c.v. pretreatment with pyrilamine, an H1-receptor antagonist. Ranitidine, an H2-receptor antagonist also inhibited the increase of adrenaline, however, its effective dose was much larger than that of pyrilamine. Furthermore, the bombesin-induced increase of noradrenaline was not effectively inhibited by ranitidine. In the next series, turnover of histamine was assessed by measuring accumulation of tele-methylhistamine (t-MH), a major metabolite of brain histamine. I.c.v. administration of bombesin (0.3-3 nmol) increased turnover of hypothalamic histamine, while its intravenous administration was without effect. The present results suggest that the bombesin-induced central activation of sympatho-adrenomedullary outflow is probably, at least in part, mediated through brain histaminergic neurons.

Bombesin affects the central nervous system to produce sodium intake inhibition in rats

Bombesin (BN) elicits in the rat important behavioural modifications, including inhibition of food and of water intake. Recently, it has been observed that the peptide also inhibits the intake of sodium chloride. To state whether BN possesses a selective antinatriorexic effect or it elicits only an aspecific depression of ingestive behaviour, we studied the effects of this peptide on the intake of sodium, water or sucrose of Wistar rats after injections into the fourth brain ventricle or into selected brain areas involved in the control of sodium intake, containing BN-like peptides and/or their precursors or specific receptors. We observed that: a) BN (100-200 ng/rat) injected into the fourth brain ventricle inhibits not only the intake of 2% NaCl of sodium depleted rats but also that of water and of 5% sucrose; b) BN (5-50 ng/rat) administered into the nucleus of the solitary tract and the medial amygdala does not influence the intake of these fluids and c) BN (5-50 ng/rat) injected into the paraventricular nucleus does not influence the intake of water and 5% sucrose but potently inhibits that of 2% NaCl. We concluded that the inhibitory effect elicited on salt intake by intracranial administration of BN is selective for this behaviour and is not the expression of an aspecific depression of ingestive behaviour.

Central administration of PACAP stimulates gastric secretion mediated through the vagal pathway in anesthetized rats

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide that was originally isolated from ovine hypothalamic tissue. The peptide has two amidated forms, PACAP38 and PACAP27. In this study, we examined the effects of centrally administered PACAP38 and PACAP27 on gastric secretion in anesthetized rats. Centrally administered PACAP stimulated gastric acid and pepsin secretion in a dose-dependent manner. PACAP38 was 1.5-2 times more potent than PACAP27 on gastric secretion. By contrast, intravenously administered PACAP38 had no effect on basal or pentagastrin-stimulated gastric secretion. PACAP6-38, a PACAP antagonist, by itself at high doses also stimulated gastric and pepsin secretion, but at lower doses had no effect. Centrally administered PACAP6-38 at a dose that had no effect on gastric secretion, atropine pretreatment, or vagotomy pretreatment, suppressed the stimulatory effect of PACAP38. It is concluded that centrally administered PACAP may have a regulatory effect on gastric secretion through PACAP receptors and the vagal pathway.

Inhibition of gastric acid secretion by stress: a protective reflex mediated by cerebral nitric oxide

Moderate somatic stress inhibits gastric acid secretion. We have investigated the role of endogenously released NO in this phenomenon. Elevation of body temperature by 3 degrees C or a reduction of 35 mmHg (1 mmHg = 133 Pa) in blood pressure for 10 min produced a rapid and long-lasting reduction of distension-stimulated acid secretion in the rat perfused stomach in vivo. A similar inhibitory effect on acid secretion was produced by the intracisternal (i.c.) administration of oxytocin, a peptide known to be released during stress. Intracisternal administration of the NO-synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) reversed the antisecretory effect induced by all these stimuli, an action prevented by intracisternal coadministration of the NO precursor, L-arginine. Furthermore, microinjection of L-NAME into the dorsal motor nucleus of the vagus nerve reversed the acid inhibitory effects of mild hyperthermia, i.v. endotoxin, or i.c. oxytocin, an action prevented by prior microinjection of L-arginine. By contrast, microinjection of L-NAME into the nucleus tractus solitarius failed to affect the inhibitory effects of hyperthermia, i.v. endotoxin, or i.c. oxytocin. Immunohistochemical techniques demonstrated that following hyperthermia there was a significant increase in immunoreactivity to neuronal NO synthase in different areas of the brain, including the dorsal motor nucleus of the vagus. Thus, our results suggest that the inhibition of gastric acid secretion, a defense mechanism during stress, is mediated by a nervous reflex involving a neuronal pathway that includes NO synthesis in the brain, specifically in the dorsal motor nucleus of the vagus.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

Correlation between the effects of bombesin antagonists on cell proliferation and intracellular calcium concentration in Swiss 3T3 and HT-29 cell lines

Bombesin (BN) acts as an autocrine mitogen in various human cancers. Several pseudononapeptide BN-(6-14) analogs with a reduced peptide bond between positions 13 and 14 have been shown to suppress the mitogenic activity of BN or gastrin-releasing peptide (GRP) when assessed by radioreceptor or proliferation assays and may have significant clinical applications. The search for potent and safe BN antagonists requires the evaluation of a large series of analogs in radioreceptor and proliferation assays. In this paper, we report that the ability of BN analogs to inhibit BN-induced calcium transients in Swiss 3T3 cells shows a high correlation with their inhibitory potency as evaluated by classical proliferation tests. The assay of calcium transients allows a rapid characterization of new BN analogs (in terms of minutes rather than days) and can be adapted as a labor and cost-effective screening step in the selection of potentially relevant BN antagonists for further characterization in cell proliferation systems. We also observed that results from the assay of calcium transients in Swiss 3T3 cells can be correlated with the results of the proliferative response in HT-29 cells, a cell line that does not seem to use the same early transmembrane ionic signal system. This result suggests that the calcium pathway is not mandatory for triggering cell division by the BN receptor.

Centrally applied bombesin increases nerve activity of both sympathetic and adrenal branch of the splanchnic nerves

We reported that centrally applied bombesin probably excites both the gastric sympathetic and adrenomedullary systems and thus induces inhibition of gastric acid secretion. In the present study, therefore, we examined whether or not centrally applied bombesin directly affects sympathetic nerve activities in rats anesthetized with urethane. Intracerebroventricular administration of bombesin (0.3 and 3.0 nmol) increased discharge rates of the sympathetic branch as well as those of the adrenal branch of preganglionic greater splanchnic nerves. These effects were not secondary to changes in arterial blood pressure by bombesin. In conclusion, centrally applied bombesin directly activates both the sympathetic and adrenomedullary systems.

Inhibition of gastric acid secretion and ulcers by calcitonin [correction of calciton] gene-related peptide

A central action of CGRP to inhibit gastric acid secretion, demonstrated in rats and dogs, is mediated at least in rats through modulation of parasympathetic outflow to the stomach. The centrally mediated protective effects of CGRP against ethanol-induced lesions is unique to this peptide and not shared by other centrally acting inhibitors of gastric function. It may be related to the increase in gastric mucosal blood flow induced by central CGRP. The presence of CGRP-like immunoreactivity and receptors in medullary nuclei receiving visceral information and influencing vagal outflow suggests a possible role of the peptide in the central regulation of gastric function. Peripheral injection of CGRP is well established to inhibit acid secretion in rats, dogs, rabbits, and humans. Its antisecretory effect is unlikely to be related to a direct action on the parietal cells. It involves specific and marked release of gastric somatostatin through an interaction with CGRP receptors characterized on D cells and coupled with cAMP. In addition, CGRP induces a decrease in acetylcholine transmission in the enteric nervous system, which may contribute to the inhibition of acid. The rich innervation of the stomach with CGRP-like immunoreactivity, which forms the major component of gastric sensory fibers, along with peptide release by sensory stimulation and potent actions on gastric secretions suggests a role of the peptide in the regulation of gastric function.

Central and peripheral actions of calcitonin gene-related peptide on gastric secretory and motor function

CGRP exerts a potent central action to inhibit gastric acid secretion in rats and dogs and gastric emptying, contractility and ulcer formation in rats. The site of action to inhibit acid secretion has been localized in the dorsal vagal complex. The inhibition of acid secretion is related primarily to the decrease in vagal efferent activity whereas the inhibition of gastric motor functions involves increases in sympathetic outflow. The central action of CGRP to prevent ethanol-induced lesions is unique to this peptide and not shared by other centrally acting inhibitors of gastric function. It may be related to the increase in gastric mucosal blood induced by central CGRP. The presence of CGRP-like immunoreactivity and receptors in medullary nuclei receiving visceral information and influencing vagal outflow suggests a possible role of the peptide in the vagal regulation of gastric secretion. Peripheral injection of CGRP also inhibits acid secretion when administered peripherally in rats, dogs, rabbits and humans. Its antisecretory effect is unlikely to be related to a direct action on the parietal cells. It involves specific and marked release of gastric somatostatin through an interaction with CGRP receptors characterized on D cells and coupled with cAMP. In addition, CGRP induces a decrease in acetylcholine transmission in the enteric nervous system which may contribute to the inhibition of acid. Peripheral CGRP inhibits gastric emptying and motility by a direct action on smooth muscles through receptors linked with cAMP. The release of CGRP from spinal afferents innervating the stomach in response to stimulation of capsaicin-sensitive fibers suggests a role of the peptide in the regulation of gastric function.

Changes in gastric secretion after intracerebroventricular infusion of bombesin in dogs

Synthetic bombesin (BBS) was infused intracerebroventricularly in 14 mongrel dogs, to study the effects of the peptide on gastric secretion and on gastrin and neurotensin levels. The infusion was performed with a specific apparatus, and gastric fluid was collected with a Pavlov pouch. BBS was given in two series of experiments: as a bolus intracerebroventricular injection of 308.6 pmol/kg and as a continuous intracerebroventricular infusion at a rate of 617.3 pmol/kg/h for 30 min. The bolus injection caused a very significant decrease of gastric fluid volume, a significant decrease of HCl output, and a significant increase of its pH, while serum immunoreactive gastrin increased significantly. The continuous infusion of BBS caused similar changes in gastric secretion. The plasma neurotensin levels did not change. In conclusion, the intracerebroventricular administration of BBS increases the serum gastrin levels, decreases the volume and HCl content of gastric fluid, and increases its pH.

Bombesin improves rats' operant responding maintained by a differential-reinforcement-of-low-rates schedule of food reinforcement

The present study examined rats' responding on a differential-reinforcement-of-low-rates schedule of food reinforcement following intraperitoneal injections of various doses of bombesin (4, 6, 8, 16, 32 micrograms/kg). Analyses indicated that only the 6 micrograms/kg dosage improved DRL responding. The findings are consistent with prior research examining bombesin's effect on operant behavior and support the notion that bombesin induces satiety rather than malaise.

Comparative immunocytochemical study of the catecholaminergic and peptidergic afferent innervation to the dorsal vagal complex in rat and guinea pig

Light and electron microscopic immunocytochemistry was used to study the fine structural organization of the catecholaminergic and hypothalamic peptidergic innervation of the dorsal vagal complex of the medulla oblongata in the rat and guinea pig, the latter of which is known to lack central adrenergic neurons. In the rat, adrenergic fibers immunoreactive to phenylethanolamine-N-methyltransferase were concentrated in the dorsal motor nucleus of the vagus, where they established frequent symmetric synapses with dendrites and perikarya. On the other hand, the density of both oxytocin- and corticotropin-immunoreactive fibers appeared far lower in this nucleus than in the dorsal regions of the nucleus of the tractus solitarius, where they formed asymmetric synapses with small dendrites. In tissue treated for the dual labeling of two neuronal antigens, oxytocin- or corticotropin-reactive fibers were in close contact with adrenergic neurons in this dorsal medullary region. In the guinea pig, unlike the rat, the dorsal motor nucleus of the vagus contained large amounts of oxytocin- and corticotropin-reactive fibers, which formed many symmetric synapses with perikarya and dendrites. Taken together, these data suggest that the control of vagal preganglionic neurons by hypothalamic peptidergic neurons involves a bisynaptic neuronal pathway including adrenergic medullary neurons in the rat, whereas it is direct in the guinea pig, which lacks this adrenergic relay.

Neurobiology of brain-gut interactions. Implications for ulcer disease

Clinical and laboratory evidence indicates that the brain exerts major control on the gastrointestinal tract. Specific brain loci and circuits that send efferent viscerotropic projections to the gut have been described. A variety of aminergic and peptidergic neurotransmitters have been shown to occur along these cerebrogastrointestinal pathways and to influence motor and secretory functions of the gut. Some of the newly identified peptides have been shown to influence the development of gastroduodenal ulcers. Findings with thyrotropin-releasing hormone (TRH) indicate that this endogenous tripeptide induces a full spectrum of gut effects, prominent among which is production of gastric ulcers. By contrast, other peptides including beta-endorphin, neurotensin, and bombesin induce gut effects opposite to those of TRH, namely, inhibition of gastric acid and motility and prevention of experimental ulcers. These laboratory findings suggest that ulcer disease may represent a brain-driven event, which may be the result of a neurochemical imbalance within the brain. Further neurobiological research will generate additional data on brain-gut interactions and will probably disclose new information to explain certain functional and organic disorders of the gut.

Neuroendocrine regulation of canine gastric secretion, emptying and blood flow

Abstract Several peptides have been implicated as central nervous system transmitters regulating various peripheral organ systems. This study examined the central nervous system effects of rat corticotrophin-releasing factor (CRF), salmon calcitonin (CT), beta-endorphin (beta-End), neurotensin (NT), rat calcitonin gene-related peptide (CGRP) and bombesin (BOM) on gastric acid secretion, gastric emptying and left gastric artery flow in conscious dogs. All of these peptides, injected into the third cerebral ventricle, significantly inhibited gastric acid secretion but not plasma gastrin concentrations stimulated by a liquid protein meal. Ganglionic blockade with chlorisondamine abolished the gastric inhibitory action of CRF, CT, beta-End and NT but not of CGRP and BOM. Truncal, subdiaphragmatic vagotomy prevented the gastric inhibitory actions of beta-End and NT only, while bilateral adrenalectomy did not affect gastric acid inhibition induced by any of the six peptides. Cerebroventricular administration of CRF, NT and BOM significantly delayed gastric emptying of the protein meal while beta-End, CT and CGRP were not effective. Only BOM significantly increased left gastric artery flow. These results indicate that various neuropeptides alter gastric functions in a differentiated fashion and via distinct pathways. CRF and CT inhibit meal-stimulated gastric acid secretion by activation of sympathetic efferents. beta-End and NT inhibit meal-stimulated acid secretion by inhibition of vagal efferents while the pathways that mediate CT- and CGRP-induced gastric acid inhibition in the dog are unknown. Gastrin, the adrenal glands and changes in gastric emptying or blood flow do not play a role in mediating gastric acid inhibition produced by Cerebroventricular administration of CRF, CT, beta-End, NT, CGRP and BOM.

Intracerebroventricular administration of bombesin inhibits biliary and gastric secretion in the rat

The effect of intracerebroventricular (ICV) bombesin on bile and gastric acid secretion was examined in the rat. ICV bombesin (10 micrograms in 10 microliters) inhibited basal biliary volume by 27% and bile bicarbonate by 52% of control values, while gastric acid secretion was decreased by 75%. These results provide evidence for central mechanisms for the control of gastrointestinal function.

A tyrosine protein kinase activated by bombesin in normal fibroblasts and small cell carcinomas

In Swiss 3T3 fibroblasts, antibodies which recognize a phosphotyrosine residue (P-Tyr antibodies) identify a 115-kDa cell surface protein (p115) that becomes phosphorylated on tyrosine as a response to bombesin stimulation of quiescent cells. The extent of phosphorylation is dose-dependent and correlates with the mitogenic effect induced by bombesin, measured by [3H]thymidine incorporation. Tyrosine phosphorylation of p115 is detectable minutes after addition of bombesin and precedes the activation of c-fos and c-myc gene transcription. Immunocomplexes of phosphorylated p115 with P-Tyr antibodies bind 125I-labeled [Tyr4]bombesin in a specific and saturable manner and display an associated tyrosine protein kinase activity enhanced by bombesin. P-Tyr antibodies also recognize a protein of 115 kDa, phosphorylated at tyrosine, in four human SCLC lines producing bombesin but not in a non-producer "variant" line. Phosphorylation of SCLC p115 does not require the addition of exogenous bombesin. As in the case of the p115 immunoprecipitated from mouse fibroblasts, the SCLC p115 is phosphorylated in an immunocomplex kinase assay. These observations are in agreement with the hypothesis of autocrine activation of bombesin receptors in human small cell lung carcinoma cells.

C-terminal bombesin sequence requirements for binding and effects on protein synthesis in Swiss 3T3 cells

1. Synthetic peptides corresponding to the five, seven, nine and eleven C-terminal amino acids of the tetradecapeptide bombesin as well as bombesin itself and gastrin-releasing peptide have been evaluated in Swiss 3T3 cells in order to define the minimal peptide length needed for biological responsiveness. 2. Gastrin-releasing peptide, bombesin, the undecapeptide and nonapeptide had nearly equipotent abilities to compete for binding of labelled gastrin-releasing peptide to the cell receptors and showed half-maximal competition at 5-10 nM. The heptapeptide and pentapeptide were ineffective. 3. Cross-linking experiments demonstrated specific binding of gastrin-releasing peptide to a 100 kDa receptor subunit. 4. Total cell protein synthesis was stimulated equally by the nonapeptide and longer peptides with a half-maximal effect at 0.5 nM, while a more than 1000-fold higher concentration of the heptapeptide was required to produce a similar response. Comparable results were found when insulin was also present. 5. Neither an inhibition of protein breakdown nor a stimulation of DNA labelling could be demonstrated by bombesin or gastrin-releasing peptide. 6. We conclude that a C-terminal peptide ligand comprising more than seven but no more than nine amino acids is required to achieve high-affinity binding and receptor-mediated responses via the bombesin receptor.

Receptor for bombesin with associated tyrosine kinase activity

The neuropeptide bombesin is known for its potent mitogenic activity on murine 3T3 fibroblasts and other cells. Recently it has been implicated in the pathogenesis of small cell lung carcinoma, in which it acts through an autocrine loop of growth stimulation. Phosphotyrosine (P-Tyr) antibodies have been successfully used to recognize the autophosphorylated receptors for known growth factors. In Swiss 3T3 fibroblasts, phosphotyrosine antibodies identified a 115,000-Mr cell surface protein (p115) that became phosphorylated on tyrosine as a specific response to bombesin stimulation of quiescent cells. The extent of phosphorylation was dose dependent and correlated with the mitogenic effect induced by bombesin, measured by [3H]thymidine incorporation. Tyrosine phosphorylation of p115 was detectable minutes after the addition of bombesin, and its time course paralleled that described for the binding of bombesin to its receptor. Immunocomplexes of phosphorylated p115 and phosphotyrosine antibodies bound 125I-labeled [Tyr4]bombesin in a specific and saturable manner and displayed an associated tyrosine kinase activity enhanced by bombesin. Furthermore, the 125I-labeled bombesin analog gastrin-releasing peptide, bound to intact live cells, was coprecipitated with p115. These data strongly suggest that p115 participates in the structure and function of the surface receptor for bombesin, a new member of the family of growth factor receptors with associated tyrosine kinase activity.

Opioids and opioid receptors in peripheral tissues

Opioid peptides belonging to the enkephalin, beta-endorphin or dynorphin family, acting on specific opiate receptors may be found in peripheral tissues. Enkephalins have a widespread peripheral distribution, while beta-endorphin and dynorphin may be found locally in the enteric nervous system. The peptides of the various families are formed from specific precursor molecules. Apart from the enteric nervous system, opioids are also found in the adrenal medulla as well as in several autonomic ganglia. There is some evidence of three different classes of opioid receptors in peripheral tissues, i.e. mu-, delta- and kappa-receptors. These receptors are not only found on enteric nervous and mucosa cells but also on various cells in the immune system where opioid peptides seem to have important actions and appear to link the neuroendocrine and immune systems to control immunological functions. The physiological as well as the pathophysiological role of opioid peptides in the periphery is gradually being elucidated and, based on such knowledge, new therapeutic implications in gastrointestinal or immune diseases may be developed.