The CCK(-like) receptor in the animal kingdom: functions, evolution and structures

In this review, the cholecystokinin (CCK)(-like) receptors throughout the animal kingdom are compared on the level of physiological functions, evolutionary basis and molecular structure. In vertebrates, the CCK receptor is an important member of the G-protein coupled receptors as it is involved in the regulation of many physiological functions like satiety, gastrointestinal motility, gastric acid secretion, gall bladder contraction, pancreatic secretion, panic, anxiety and memory and learning processes. A homolog for this receptor is also found in nematodes and arthropods, called CK receptor and sulfakinin (SK) receptor, respectively. These receptors seem to have evolved from a common ancestor which is probably still closely related to the nematode CK receptor. The SK receptor is more closely related to the CCK receptor and seems to have similar functions. A molecular 3D-model for the CCK receptor type 1 has been built together with the docking of the natural ligands for the CCK and SK receptors in the CCK receptor type 1. These molecular models can help to study ligand-receptor interactions, that can in turn be useful in the development of new CCK(-like) receptor agonists and antagonists with beneficial health effects in humans or potential for pest control.     

食用菌产业发展需要科学研究的强力支撑

我国是世界食用菌产业大国,产量占全球总产80%,拥有全球最多的食用菌基础科学和应用技术研究者,近年来在这两个领域都取得了显著成绩,但仍远远不能满足产业发展的科学需求。我国食用菌产业的发展需要科学研究的强力支持。本专刊集结了食用菌的资源与利用、遗传育种、组学分析、生理栽培、加工技术、活性成分、保健功效评价等方面的论文共计32篇。本刊论文还涉及了食用菌与病原菌的互作研究、野生菌的种类产地鉴定等方面的研究。     

Minireview. The ascent of cholecystokinin (CCK) - from gut to brain

Cholecystokinin (CCK), a classical gastrointestinal polypeptide hormone, appears to have an equally important role as a brain neurotransmitter. CCK is widely distributed throughout both the central and peripheral nervous system. Of the known brain peptides, only CCK and VIP are predominately cerebral cortical peptides. In the pituitary, CCK is found in the posterior pituitary, while gastrin-like peptides are present in the anterior and intermediate lobes. Phylogenetically, gastrin-CCK-like peptides arose extremely early in evolution being present in the primitive nerve cells of the coelenterate, Hydra. Specific high affinity CCK-receptors have been demonstrated in rat and guinea-pig brains with highest concentrations in the cerebral cortex, caudate nucleus and olfactory bulb. Alterations in CCK binding have been reported during fasting and in genetically obese rats and mice. The low levels of CCK receptors in patients with Huntington's Chorea, the coexistance of CCK with dopamine in the same mesolimbic neurons and the rotational syndrome produced after central administration in rats suggests a potential physiological role for CCK in the regulation of extra-pyramidal function. CCK and/or gastrin have been demonstrated to have a number of effects on anterior pituitary hormones and the high concentrations in the posterior pituitary suggest a possible neuromodulatory role in the regulation of vasopressin and/or oxytocin release. CCK is a putative satiety hormone which appears to produce satiety both by peripheral and central effects. The presence of CCK in the periaqueductal gray and the fact that it produces naloxone reversible analgesia suggest a potential role for CCK in the regulation of pain perception. Central administration of CCK produces hyperglycemia which appears to be partly mediated via an adrenal mechanism. CCK also produces mild hypothermia and appears to be a central nervous system depressant. Present evidence indicating that CCK is a central neurotransmitter or neuromodulator includes its regional distribution with localization within neuronal cell bodies and axons; the demonstration that it can be synthesized in neuronal tissue; the fact that it is released by depolarizing stimuli $\text{in vitro}$; the presence of specific, high affinity receptors for CCK in the brain; and the finding that it can activate isolated neurons. The high concentrations of CCK in the cerebral cortex suggest that future studies will produce further surprises concerning the physiological role of this gall-bladder contracting hormone which came of age with the discovery of its wide distribution in the central nervous system.     

Cholecystokinin synthesizes and secretes leptin in isolated canine gastric chief cells

It is well recognized that a product of obese (ob) locus and body weight control hormone, leptin, acts on both short-term satiety for meal-induced termination of food intake (gastric phase) and long-term satiety for energy expenditure via the hypothalamus. The considerable sources of leptin are chief cells for gastric phase and adipocytes for the long-term satiety. The objective of this study was to demonstrate if CCK enhances leptin synthesis and secretion in isolated canine gastric chief cells. Confocal immunofluorescence studies showed that the CCK-A receptor and leptin were colocalized in the endoplasm. Western blotting demonstrated that canine chief cells expressed the leptin peptide and its protein level was enhanced by CCK treatment. An ELISA further showed that CCK dose-dependently secreted leptin from isolated canine chief cells. This was reproduced by the high-affinity CCK-A receptor agonist, CCK-OPE. These results indicate that canine chief cells synthesize and secrete leptin in response to CCK via the high-affinity state of the CCK-A receptor.     

Loxiglumide, a CCK-A receptor antagonist, stimulates calorie intake and hunger feelings in humans

Exogenous cholecystokinin (CCK) induces early satiety when infused into humans. Whether alimentary CCK (CCK-A) receptor blockade stimulates food intake in humans is, however, uncertain. The aim of the present investigation was, therefore, to establish the effect of CCK-A receptor blockade on satiety and eating behavior in healthy volunteers. To further explore the role of endogenous CCK, the effects of the specific CCK-A receptor antagonist loxiglumide (Lox; 22 micromol. kg(-1). h(-1)) on satiety and eating behavior were investigated in healthy men and compared with saline infusions (as placebo) in a series of randomized, double-blind, placebo-controlled, crossover studies. Lox produced a slight (7%), but not significant (P = 0.104), increase in food intake that was accompanied by a modest (10%), but significant (P < 0.004), increase in calorie intake. Fluid ingestion was not affected by Lox. Subjects experienced more hunger and delayed fullness during Lox infusion than during saline infusion (P < 0.05). This study provides further evidence that CCK is an endogenous physiological satiety signal acting through CCK-A receptor-mediated mechanisms. Repeated-dose studies comparing hunger and satiety responses after CCK-A receptor blockade in healthy subjects and patients with eating disorders may help clarify the possible involvement of endogenous CCK in these conditions.     

Central and peripheral proglumide administration and cholecystokinin-induced satiety

Peripheral (50 mg/ml) or central (50 micrograms/microliter) injections of proglumide were made into Sprague-Dawley rats which displayed satiety-like responses after the peripheral (100 micrograms/kg) or central (50 ng in 1 microliter) administration of cholecystokinin (CCK). The satiety produced by CCK injection into the lateral hypothalamus, area postraema and ventromedial hypothalamus was significantly reversed by proglumide injections into these areas during a 4 h food intake test. Peripheral injection of proglumide after central or peripheral CCK injection did not modify this type of CCK-induced satiety. Central proglumide injection produced a reliable decrease in water intake and this is compatible with previous findings which describe the stimulation of water intake after central gastrin administration. These results suggest that various central and peripheral mechanisms which are involved in the regulation of appetite may function independently as a 'failsafe' system.     

The endogenous CCK mediation of electroacupuncture stimulation-induced satiety in rats

A major satiety hormone, cholecystokinin (CCK) is well known to be released by electroacupuncture (EA) stimulation at certain body sites which elicits profound psychophysiological responses. Previous clinical and animal studies have shown that EA stimulation reduces food intake and body weight in both normal and obese subjects. The aim of the present study was to elucidate the satiety effect of EA stimulation and its mechanism related to CCK in rats. Here we show that EA stimulation at "Zusanli" (ST36) acupoint significantly reduced 30-min and 60-min food intake in 48-h fasted Sprague-Dawley rats, and such effect was reversed by a lorglumide (CCK-1 receptor antagonist, 10mg/kg, i.p.) pretreatment. The ST36 EA stimulation-induced satiety was not observed in CCK-1 receptor knockout, Otsuka Long-Evans Tokushima Fatty rats, but in their controls, Long-Evans Tokushima Otsuka rats. Subdiaphragmatic vagotomy also blocked the satiety effect of ST36 EA stimulation in Sprague-Dawley rats. These results suggest that ST36 EA stimulation elicits satiety in rats and this is mediated by the endogenous CCK signaling pathway.     

Evidence for a functional role of cholecystokinin receptors in the rat thyroid gland.

The aim of the present study was to examine the role of cholecystokinin (CCK) and/or cholecystokinin receptors subtypes (CCK1R and CCK2R) in the regulation of the thyroid gland structure and function. Animals were autopsied after 6 days of treatment with CCK or CCK receptor-specific antagonists (CCK1a--PD 140,548 or CCK2a--PD 135,158) solely or in combination with CCK. Results suggest that CCK exerts a stimulatory effect on follicular thyroid cells manifested by increased epithelium/colloid volume fraction ratio (E/C). Application of selective antagonists of CCK receptor subtypes has demonstrated that CCK acts through the CCK1 receptor subtype at the level of pituitary TSH. The model of endogenous hormone action reveals that thyroid CCK1 is responsible for the thyroid growth. It can be concluded that the physiological activity of CCK1 receptor plays a significant role in a complex interrelationship between TSH, vagal system and CCK1-dependent function of the thyroid gland.     

Cholecystokinin, a satiety signal in newborn infants?

This study was undertaken in order to describe circulating glucose and cholecystokinin (CCK) concentrations in relation to the spontaneous feeding behavior of the human newborn infant. Eighty-three, healthy, 3-days-old infants were studied in connection with breast feeding. Blood samples from the infants were cross-sectionally collected before feeding, 5 and 10 min after the start of sucking, and after the infants had sucked ad libitum. Before feeding, the infants presented a typical "hunger behavior", which changed in connection with breast feeding into a pattern associated with satiety. A significant increase in the plasma CCK concentration was found, 5 min (P = 0.004) and 10 min (P = 0.02) after the start of sucking, as well as after feeding (P = 0.04). Furthermore, a positive correlation between the CCK concentration and the volume of ingested milk was found 10 min after the start of sucking, when 91% of of the volume of milk had been ingested; Rs = 0.51, n = 19, P < 0.02. However, no change was found in the glucose concentration in connection with breast feeding. It is concluded that CCK may be important as a satiety factor in the regulation of food intake in the newborn infant.     

Postprandial profiles of CCK after high fat and high carbohydrate meals and the relationship to satiety in humans

ContextCCK is understood to play a major role in appetite regulation. Difficulties in measuring CCK have limited the potential to assess its profile in relation to food-induced satiety. Improvements in methodology and progress in theoretical understanding of satiety/satiation make it timely for this to be revisited.ObjectiveFirst, examine how physiologically relevant postprandial CCK8/33(s) profiles are influenced by fat (HF) or carbohydrate (HCHO) meals. Second, to examine relationships between postprandial CCK and profiles of satiety (hunger/fullness) and satiation (meal size).Participants and designSixteen overweight/obese adults (11 females/5 males) participated in a randomised-crossover study (46 years, 29.8 kg/m²) in a university research centre. Plasma was collected preprandially and for 180 min postprandially. Simultaneously, ratings of hunger/fullness were tracked for 180 min before an ad libitum lunch was provided.ResultsCCK8/33(s) levels increased more rapidly and reached a higher peak following HF compared to HCHO breakfast (F_(1,15) = 14.737, p < 0.01). Profiles of hunger/fullness did not differ between conditions (F_(1,15) = 0.505, p = 0.488; F_(1,15) = 2.277, p = 0.152). There was no difference in energy intake from the ad libitum meal (HF-3958 versus HCHO-3925 kJ; t₍₁₄₎ = 0.201, p = 0.844). CCK8/33(s) profiles were not associated with subjective appetite during early and late phases of satiety; nor was there an association between CCK8/33(s) and meal size.ConclusionsThese results demonstrate CCK levels were higher after HF meal compared to HCHO isocaloric meal. There was no association between CCK levels and intensity of satiety, or with meal size. Under these circumstances, CCK does not appear to play a unique independent role in satiety/satiation. CCK probably acts in conjunction with other peptides and the action of the stomach.     

Interaction between CCK and a preload on reduction of food intake is mediated by CCK-A receptors in humans

Cholecystokinin (CCK) interacts with neural signals to induce satiety in several species, but the mechanisms are unclear. We therefore tested the hypothesis that alimentary CCK (CCK-A) receptors mediate the interaction of CCK with an appetizer on food intake in humans. CCK octapeptide (CCK-8, 0.75 microgram infused over 10 min) or saline (placebo) with concomitant infusions of saline (placebo) or loxiglumide, a specific CCK-A antagonist, was infused into 16 healthy men with use of a double-blind, four-period design. All subjects received a standard 400-ml appetizer (amounting to 154 kcal) but were free to eat and drink thereafter as much as they wished. The effect of these infusions on feelings of hunger and satiety and on food intake was quantified. CCK-8 induced a reduction in calorie intake (P < 0.05) compared with saline. Furthermore, a decrease in hunger feelings (P < 0.05, saline-CCK-8 vs. all other treatments) and an increase in fullness were observed. These effects were antagonized for hunger and fullness by loxiglumide. We conclude that CCK-8 interacts with an appetizer to modulate satiety in humans. These effects are mediated by CCK-A receptors.     

红细胞生成素受体研究进展

红细胞生成素受体是促红细胞生成素的作用受体 ,属于细胞因子超家族的成员。近年来 ,由于其克隆表达技术的应用使人们在对造血机制、EPO的信号转导机制 ,及利用其受体筛选 EPO类似物方面的研究有了新的进展。本文综合近年来有关文献对 EPO受体的研究作一概括性介绍。     

Cholecystokinin/dopamine/GABA interactions in the nucleus accumbens: biochemical and functional correlates.

The present article reviews our recent biochemical and microdialysis studies showing the evidence for an antagonistic CCK(B)/D(2) receptor interaction in the regulation of dopaminergic transmission in the nucleus accumbens and GABAergic transmission in the ipsilateral ventral pallidum. Since the nucleus accumbens plays a crucial role in regulating the output from the limbic system and consequently motivation, it may be speculated that a dysregulation of this receptor interaction may have consequences in a wide range of central nervous system disorders.     

Low-affinity CCK-A receptors are coexpressed with leptin receptors in rat nodose ganglia: implications for leptin as a regulator of short-term satiety

The paradigm for the control of feeding behavior has changed significantly. Research has shown that leptin, in the presence of CCK, may mediate the control of short-term food intake. This interaction between CCK and leptin occurs at the vagus nerve. In the present study, we aimed to characterize the interaction between CCK and leptin in the vagal primary afferent neurons. Single neuronal discharges of vagal primary afferent neurons innervating the gastrointestinal tract were recorded from rat nodose ganglia. Three groups of nodose ganglia neurons were identified: group 1 responded to CCK-8 but not leptin; group 2 responded to leptin but not CCK-8; group 3 responded to high-dose CCK-8 and leptin. In fact, the neurons in group 3 showed CCK-8 and leptin potentiation, and they responded to gastric distention. To identify the CCK-A receptor (CCKAR) affinity states that colocalize with the leptin receptor OB-Rb, we used CCK-JMV-180, a high-affinity CCKAR agonist and low-affinity CCKAR antagonist. As expected, immunohistochemical studies showed that CCK-8 administration significantly potentiated the increase in the number of c-Fos-positive neurons stimulated by leptin in vagal nodose ganglia. Administration of CCK-JMV-180 eliminated the synergistic interaction between CCK-8 and leptin. We conclude that both low- and high-affinity CCKAR are expressed in nodose ganglia. Many nodose neurons bearing low-affinity CCKAR express OB-Rb. These neurons also respond to mechanical distention. An interaction between CCKAR and OB-Rb in these neurons likely facilitates leptin mediation of short-term satiety.     

The effects of proglumide on cholecystokinin-, bombesin-, and glucagon-induced satiety in the rat

Intraperitoneal (IP) administration of the glutaramic acid derivative proglumide inhibited satiety induced by all IP doses of cholecystokinin octapeptide (CCK-OP) in 3-hour food-deprived intact rats. Proglumide did not influence satiety when administered alone and did not inhibit satiety induced by IP glucagon. While proglumide did not inhibit satiety induced by low doses of IP bombesin, it partially and significantly inhibited the satiety effects produced by high doses of this peptide. Since bombesin is a known secretagogue for CCK in several species, these results indicate that while bombesin and CCK act independently to induce satiety, the effect induced by high doses of bombesin is mediated, in part, by the release of endogenous CCK or a structurally related peptide. Furthermore, these results illustrate that proglumide is a specific antagonist of CCK-induced satiety and is, therefore, a potentially useful tool for investigating the physiologic role of this peptide in the control of food intake.     

Time-resolved quantitative analysis of CCK1 receptor-induced intracellular calcium increase

Cholecystokinin (CCK) is a gastrointestinal hormone, which regulates many physiological functions such as satiety by binding to the CCK receptor (CCKR). Molecules, which recognize this receptor can mimic or block CCK signaling and thereby influence CCKR-mediated processes. We have set up a quantitative heterologous assay with CHO cells over-expressing the rat CCK1 receptor to screen for such candidate molecules. Receptor activation, induced by agonist binding, is followed by an intracellular calcium increase, which was monitored using a fluorescent sensor dye. For quantification of the calcium increase, a population average technique using a fluorescence plate reader was optimized and subsequently compared with a single-cell approach using confocal microscopy. With both strategies, dose-response curves were generated for the natural agonist CCK-8S, the partial agonist JMV-180 as well as the antagonist lorglumide. Significant differences were found between the ligands and a strong correspondence was observed between both methods in terms of maximum response and median effect concentrations. Both highly sensitive methods proved complementary: whereas the plate reader assay allowed faster, high throughput screening, the confocal microscopy identified single-cell variations and revealed factors that reduce specificity and sensitivity.     

Cholecystokinin, vasoactive intestinal peptide and peptide histidine methionine responses to feeding in anorexia nervosa.

Anorexia nervosa (AN) is a syndrome of unknown cause characterized by voluntary starvation. Cholecystokinin has been implicated as a neuroendocrine regulatory factor in control of satiety. Relatively little information is known about gastrointestinal hormone responses to feeding in subjects with anorexia nervosa. In the present studies, we examine fasting and postprandial levels of cholecystokinin (CCK), vasoactive intestinal peptide (VIP) and peptide histidine methionine (PHM) in anorexia nervosa subjects and in control individuals. Results of these studies indicate that plasma CCK response to a liquid meal (Ensure Plus) in untreated AN subjects was distinctly different from that observed in healthy controls, both in terms of temporal pattern of peptide released and the amount of CCK secreted into the circulation. Peak levels of CCK release occurred at 30 min following meal ingestion in AN patients and at 60 min in control subjects. Integrated CCK release in untreated AN patients was approximately twice that measured in control individuals. Renutrition therapy was associated with reversion of the pattern of CCK release to that observed in control subjects. Plasma VIP levels were unchanged following meal ingestion in both control and anorexic subjects. In contrast, PHM levels in AN subjects were significantly greater than that observed in control individuals. The pattern of PHM release following liquid meal ingestion was similar to that observed with plasma CCK; namely, peak release of peptide was observed at 30 min which was significantly greater than corresponding control values (P less than 0.05). In conclusion, these results demonstrate distinctive differences in plasma CCK and PHM levels in response to feeding in AN subjects when compared to control individuals. These findings suggest that the earlier and greater rise in plasma CCK levels in AN subjects following meal ingestion may contribute to the abnormal sensation of satiety in this condition.     

Integrating Professional Skills in Wildlife Student Education

Abstract: Recent articles have called for enhanced quantitative proficiency in wildlife students, arguing that such training will increase scientific rigor and produce wildlife researchers and managers who are better able to remedy current problems and to address future challenges in wildlife management. The idea that better, or more rigorous, science is the panacea for controversial natural resource problems is a cavalier and common presumption in many applied professions and one to which wildlife science and management is not immune. However, science and management are distinct processes and although scientific rigor is important, dialogue between the 2 processes is more critical for successful interaction. Integrated training that exposes students to nontraditional coursework and develops essential professional skills, such as planning, consensus-building, and communication, can help produce graduates to bridge the science—management gap and promote the conservation of natural resources. Changes in the structure and coursework of university wildlife departments can help to develop more effective wildlife professionals.     

The role of segment 32-47 of cholecystokinin receptor type A in CCK8 binding: synthesis, nuclear magnetic resonance, circular dichroism and fluorescence studies.

The segment 32-47 of the N-terminal extracellular domain of the type A cholecystokinn receptor, CCK(A)-R(32-47), was synthesized and structurally characterized in a membrane mimicking environment by CD, NMR and molecular dynamics calculations. The region of CCK(A)-R(32-47) encompassing residues 39-46 adopted a well-defined secondary structure in the presence of DPC micelles, whereas the conformation of the N-terminal region (segment 32-37) could not be uniquely defined by the NOE derived distance constraints because of local flexibility. The conformation of the binding domain of CCK(A)-R(32-47) was different from that found for the Intact N-terminal receptor tail, CCK(A)-R(1-47). To assess whether CCK(A)-R(32-47) was still able to bind the nonsulfated cholecystokinin C-terminal octapeptide, CCK8, a series of titrations was carried out in SDS and DPC micelles, and the binding interaction was followed by fluorescence spectroscopy. These titrations gave no evidence for complex formation, whereas a high binding affinity was found between CCK(A)-R(1-47) and CCK8. The different affinities for the ligand shown by CCK(A)-R(32-47) and CCK(A)-R(1-47) were paralleled by different interaction modes between the receptor segments and the micelles.The interaction of CCK(A)-R(32-47) with DPC micelles was much weaker than that of CCK(A)-R(1-47), because the former receptor segment lacks proper stabilizing contacts with the micelle surface. In the case of SDS micelles CCK(A)-R(32-47] was found to form non-micellar adducts with the detergent that prevented the onset of a functionally significant Interaction between the receptor segment and the micelle. It is concluded that tertiary structure interactions brought about by the 1-31 segment play a key role in the stabilization of the membrane bound, biologically active conformation of the N-terminal extracellular tail of the CCKA receptor.