Presence Of Cholecystokinin Research Articles

Visuoauditory Associative Memory Established with Cholecystokinin Under Anesthesia Is Retrieved in Behavioral Contexts.

Plastic change in neuronal connectivity is the foundation of memory encoding. It is not clear whether the changes during anesthesia can alter subsequent behavior. Here, we demonstrated that in male rodents under anesthesia, a visual stimulus (VS) was associated with electrical stimulation of the auditory cortex or natural auditory stimulus in the presence of cholecystokinin (CCK), which guided the animals' behavior in a two-choice auditory task. Auditory neurons became responsive to the VS after the pairings. Moreover, high-frequency stimulation of axon terminals of entorhinal CCK neurons in the auditory cortex enabled LTP of the visual response in the auditory cortex. Such pairing during anesthesia also generated VS-induced freezing in an auditory fear conditioning task. Finally, we verified that direct inputs from the entorhinal CCK neurons and the visual cortex enabled the above neural plasticity in the auditory cortex. Our findings suggest that CCK-enabled visuoauditory association during anesthesia can be translated to the subsequent behavior action.SIGNIFICANCE STATEMENT Our study provides strong evidence for the hypothesis that cholecystokinin plays an essential role in the formation of cross-modal associative memory. Moreover, we demonstrated that an entorhinal–neocortical circuit underlies such neural plasticity, which will be helpful to understand the mechanisms of memory formation and retrieval in the brain.

Glucagon-like peptide-2 promotes gallbladder refilling via a TGR5-independent, GLP-2R-dependent pathway

ObjectiveGlucagon-like peptides (GLPs) are secreted from enteroendocrine cells in response to nutrients and bile acids and control metabolism via actions on structurally-related yet distinct G protein coupled receptors. GLP-1 regulates gut motility, appetite, islet function, and glucose homeostasis, whereas GLP-2 enhances intestinal nutrient absorption. GLP-1R agonists are used to treat diabetes and obesity, and a GLP-2R agonist is approved to treat short bowel syndrome. Unexpectedly, reports of gallbladder disease have been associated with the use of both GLP-1R and GLP-2R agonists and after bariatric surgery, although the mechanisms remain unknown. MethodsWe investigated whether GLP-1 or GLP-2 acutely controls gallbladder (GB) volume and whether GLP-2 regulates GB muscle activity in mice. The expression of Tgr5, Glp2r, and Glp1r was assessed in mouse GB, and the effects of GLP-2 on hepatic bile acid (BA) flow, intestinal and liver BA uptake, and GB gene expression were determined. GLP-2 regulation of GB volume was assessed in wildtype, Glp2r−/− and Tgr5−/− mice. The effect of GLP-2 on GB smooth muscle (GBSM) calcium transients was characterized ex vivo. ResultsAcute administration of the GLP-1R agonist exendin-4 lowered glucose but had no effect on GB volume in mice. In contrast, GLP-2 rapidly enhanced GB filling in a dose-dependent manner, actions maintained in the presence of cholecystokinin, and mediated through the canonical GLP-2R. GLP-2 also rapidly induced immediate early gene expression in GB, consistent with detection of the endogenous Glp2r in GB RNA. The ability of GLP-2 to increase GB volume was not abrogated by systemic administration of hexamethonium, propranolol, a vasoactive peptide receptor antagonist or N-Nitroarginine methyl ester, and was maintained in Tgr5−/− mice. In contrast, lithocholic acid, a Tgr5 agonist, increased GB filling in Glp2r−/− but not in Tgr5−/− mice. GLP-2 had no effect on ileal uptake or hepatic clearance of taurocholic acid or on hepatic bile flow, yet reduced the frequency of spontaneous calcium transients in murine GBSM ex vivo, in a tetrodotoxin-sensitive manner. ConclusionsOur data extend endocrine concepts of regulation of GB filling beyond FXR-FGF15/19 and the direct effects of BA via Tgr5, to encompass a novel BA-Tgr5-L cell GLP-2 axis providing nutrient-mediated feedback from BA to terminate meal-related GB contraction. These findings have implications for conditions characterized by elevated circulating levels of GLP-2 such as after bariatric surgery and the development and use of agents that promote Tgr5 activation, L cell secretion, or GLP-2R agonism for the treatment of metabolic disease.

PKC-mediated inhibitory feedback of the cholecystokinin 1 receptor controls the shape of oscillatory Ca²⁺ signals.

Translation of extracellular hormonal input into cellular responses is often mediated by repetitive increases in cytosolic free Ca(2+) concentration ([Ca(2+) ]c ). Amplitude, duration and frequency of these so-called [Ca(2+) ]c oscillations then carry information about the nature and concentration of the extracellular signalling molecule. At present, there are different hypotheses concerning the induction and control of these oscillations. Here, we investigated the role of agonist-induced receptor phosphorylation in this process using Chinese hamster ovary cells stably expressing a variant of the cholecystokinin 1 receptor (CCK1R) lacking the four consensus sites for protein kinase C (PKC) phosphorylation and deficient in CCK-induced receptor phosphorylation (CCK1R-mt cells). In the presence of cholecystokinin-(26-33)-peptide amide (CCK-8), these cells displayed Ca(2+) oscillations with a much more pronounced bursting dynamics rather than the dominant spiking dynamics observed in Chinese hamster ovary cells stably expressing the wild-type CCK1R. The bursting behaviour returned to predominantly spiking behaviour following removal of extracellular Ca(2+) , suggesting that CCK-8-induced, PKC-mediated CCK1R phosphorylation inhibits Ca(2+) influx across the plasma membrane. To gain mechanistic insight into the underlying mechanism we developed a mathematical model able to reproduce the experimental observations. From the model we conclude that binding of CCK-8 to the CCK1R leads to activation of PKC which subsequently phosphorylates the receptor to inhibit the receptor-mediated influx of Ca(2+) across the plasma membrane. Receptor-specific differences in this feedback mechanism may, at least in part, explain the observation that different agonists evoke [Ca(2+) ]c oscillations with different kinetics in the same cell type.

Immunohistochemical study on the neuroendocrine system of the digestive tract of turbot, Scophthalmus maximus (L.), infected by Enteromyxum scophthalmi (Myxozoa)

In recent years a new parasite, causing severe losses, has been detected in farmed turbot, Scophthalmus maximus (L.), in Northwestern Spain. Dead fish showed emaciation and cachexia caused by severe necrotizing enteritis, which affected all areas of the digestive tract. The parasite was classified as a myxosporean and named Enteromyxum scophthalmi. This study was designed to assess the response of the turbot neuroendocrine system against E. scophthalmi infection. Immunohistochemical tests were applied to sections of the gastrointestinal tract of uninfected and E. scophthalmi-infected turbot, and the presence of cholecystokinin (CCK-8), serotonin (5-HT), substance P (SP), calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP) were documented. A higher abundance of both endocrine epithelial cells (ECs) and nerve cell bodies and fibres for CCK-8, 5-HT and SP were recorded in the gastrointestinal tract of infected turbot, whereas VIP-like substance decreased. The results indicate that E. scophthalmi infection in turbot induced changes in the neuroendocrine system, which may cause alterations in gut motility, electrolyte and fluid secretion, and vascular and immune functions.

Leptin and CCK modulate complementary background conductances to depolarize cultured nodose neurons

We have previously reported that intraceliac infusion of leptin induces a reduction of meal size that depends on intact vagal afferents. This effect of leptin is enhanced in the presence of cholecystokinin (CCK). The mechanisms by which leptin and CCK activate vagal afferent neurons are not known. In the present study, we have begun to address this question by using patch-clamp electrophysiological techniques to examine the mechanisms by which leptin and CCK activate cultured vagal afferents from adult rat nodose ganglia. We found that leptin depolarized 41 (60%) of 68 neurons. The magnitude of membrane depolarization was dependent on leptin concentration and occurred in both capsaicin-sensitive and capsaicin-insensitive neurons. We also found that a majority (16 of 22; 73%) of nodose neurons activated by leptin were also sensitive to CCK. CCK-induced depolarization was primarily associated with the increase of an inward current (11 of 12), whereas leptin induced multiple changes in background conductances through a decrease in an outward current (7 of 13), an increase in an inward current (3 of 13), or both (3 of 13). However, further isolation of background currents by recording in solutions that contained only sodium or only potassium revealed that both leptin and CCK were capable of increasing a sodium-dependent conductance or inhibiting a potassium-dependent conductance. Our results support the hypothesis that vagal afferents are a point of convergence and integration of leptin and CCK signaling for control of food intake and suggest multiple ionic mechanisms by which leptin and CCK activate vagal afferent neurons.

Arachidonic Acid Modulates the Spatiotemporal Characteristics of Agonist-evoked Ca2+ Waves in Mouse Pancreatic Acinar Cells

In pancreatic acinar cells analysis of the propagation speed of secretagogue-evoked Ca2+ waves can be used to examine coupling of hormone receptors to intracellular signal cascades that cause activation of protein kinase C or production of arachidonic acid (AA). In the present study we have investigated the role of cytosolic phospholipase A2 (cPLA2) and AA in acetylcholine (ACh)- and bombesin-induced Ca2+ signaling. Inhibition of cPLA2 caused acceleration of ACh-induced Ca2+ waves, whereas bombesin-evoked Ca2+ waves were unaffected. When enzymatic metabolization of AA was prevented with the cyclooxygenase inhibitor indomethacin or the lipoxygenase inhibitor nordihydroguaiaretic acid, ACh-induced Ca2+ waves were slowed down. Agonist-induced activation of cPLA2 involves mitogen-activated protein kinase (MAPK) activation. An increase in phosphorylation of p38(MAPK) and p42/44(MAPK) within 10 s after stimulation could be demonstrated for ACh but was absent for bombesin. Rapid phosphorylation of p38(MAPK) and p42/44(MAPK) could also be observed in the presence of cholecystokinin (CCK), which also causes activation of cPLA2. ACh-and CCK-induced Ca2+ waves were slowed down when p38(MAPK) was inhibited with SB 203580, whereas inhibition of p42/44(MAPK) with PD 98059 caused acceleration of ACh- and CCK-induced Ca2+ waves. The spreading of bombesin-evoked Ca2+ waves was affected neither by PD 98059 nor by SB 203580. Our data indicate that in mouse pancreatic acinar cells both ACh and CCK receptors couple to the cPLA2 pathway. cPLA2 activation occurs within 1-2 s after hormone application and is promoted by p42/44(MAPK) and inhibited by p38(MAPK). Furthermore, the data demonstrate that secondary (Ca2+-induced) Ca2+ release, which supports Ca2+ wave spreading, is inhibited by AA itself and not by a metabolite of AA.

The third intracellular loop of the rat and mouse cholecystokinin-A receptors is responsible for different patterns of gene activation.

It has previously been reported that the cholecystokinin analog JMV-180 behaves differently on the rat and the mouse cholecystokinin-A receptor (CCK-AR). In mice this analog acts as an agonist on low- and high-affinity sites of the CCK-AR, whereas in rats this compound acts as an agonist on high-affinity sites and as an antagonist on low-affinity sites. In an attempt to understand why the same compound behaves differently on these two CCK-A receptors, we cloned the cDNA encoding the mouse CCK-AR. We then investigated a cellular model able to mimic the effect that was observed in rats and mice. HeLa cells were transiently cotransfected with plasmids leading to expression of the rat or mouse CCK-AR in the presence of pFos-Luc as reporter plasmid; such a plasmid placed the regulatory part of the human c-Fos gene upstream from the firefly luciferase structural gene (Luc). We then observed that the two CCK-A receptors behaved differently, not only in the presence of compound JMV-180 but also in the presence of cholecystokinin or even in absence of ligand; the rat CCK-AR was 2 to 3 times more potent than the mouse CCK-AR in inducing the reporter protein, whatever the ligand studied. This result was confirmed using the same kind of experiment with the reporter plasmid p(TRE)(3)-tk-Luc. Using various mutated receptors, we investigated the role of the putative third intracellular loop. We concluded that both the primary structure of the receptor and the cellular context are in part responsible for the differential behavior of these CCK-A receptors.

Transgenic CCK-B/gastrin receptor mediates murine exocrine pancreatic secretion

Background & Aims: The presence of cholecystokinin (CCK)-B/gastrin receptors in the pancreas of higher mammals including humans has been shown, but their physiological function in the normal pancreas is unknown. The aim of this study was to investigate whether they couple to the secretory machinery of normal acinar cells. Methods: A transgenic mouse strain expressing the human CCK-B/gastrin receptor in the exocrine pancreas was created. The transgenic construction used the promoter region of the elastase I gene and the human CCK-B/gastrin receptor gene. Analysis of ElasCCKB mice included polymerase chain reaction and receptor autoradiography. Molecular and binding features of the CCK-B/gastrin receptor were determined by Western blot and radioligand binding studies. Amylase secretion and inositol phosphate production assays were used in functional characterization. Results: The CCK-B/gastrin receptor was expressed in the exocrine pancreas and had typical molecular and binding features. CCK and sulfated gastrin stimulated enzyme secretion with identical potencies and efficacies. They activated phospholipase C, but CCK was 60-fold less potent than sulfated gastrin. Conclusions: The data show that the CCK-B/gastrin receptor mediates exocytosis in acinar cells and can differentially couple to phospholipase C depending on the agonist. The ElasCCKB mice provide a useful model to study phospholipase C–dependent and –independent intracellular transduction pathways leading to pancreatic exocrine secretion. GASTROENTEROLOGY 1998;115:988-996

Facilitating effect of CCK on nicotinic neurotransmission in cat pancreatic ganglion.

Previous studies have demonstrated the presence of cholecystokinin (CCK)-like peptides in nerve terminals surrounding ganglion neurons of the cat pancreas. The present study was undertaken to determine the effect of cholecystokinin octapeptide (CCK-8) on ganglionic transmission. Recordings were made intracellularly in vitro from ganglion neurons in isolated pieces of the pancreas. Sulfated CCK-8 (S-CCK-8) and nonsulfated CCK-8 initiated or increased ongoing fast excitatory postsynaptic potential (fEPSP) activity, an effect antagonized by hexamethonium. Superfusion of S-CCK-8 in concentrations ranging from 10(-11) to 10(-8) M significantly augmented the amplitude of nerve-evoked subthreshold fEPSPs without a significant change in either membrane potential or membrane input resistance. S-CCK-8 (10(-8)M) also increased the quantal content and quantal size of nerve-evoked fEPSPs and increased the response to exogenously applied acetylcholine (ACh). Concentrations of S-CCK-8 higher than 10(-8)M caused depolarization and an increase in membrane input resistance, an effect unaltered by a low-Ca+, high-Mg2+ solution. It was concluded that S-CCK-8 potentiated nicotinic transmission by facilitating release of ACh from preganglionic nerve terminals and by increasing the postsynaptic membrane sensitivity to ACh.

NOS is present in the brain of Triatoma infestans and is colocalized with CCK.

Immunohistochemistry was used to establish the presence of nitric oxide synthase (NOS) in the central nervous system of Triatoma infestans which is the main vector for Chagas' disease in Argentina and neighbouring countries. In addition, we have investigated the presence of cholecystokinin (CCK) and studied the possible coexistence of these molecules. The results show NOS-like immunoreactivity (LI) in neurones of the soma rind of the protocerebrum, the optic lobe and in the lateral part of the sensory deutocerebrum with a few cells in the suboesophageal and the prothoracic ganglia. The distribution of CCK-LI was similar to that of NOS-LI and in several areas both molecules coexisted in neurones and fibres. The results suggest that nitric oxide may act as a neurotransmitter in the brain of insects.

Immunohistochemical Differentiation of Gastrin and Cholecystokinin in Gastrointestinal Tract of Chickens

The presence of cholecystokinin (CCK) in the gastrointestinal tract of chickens has not been well demonstrated, although immunological and chromatographic techniques have shown the presence of intestinal gastrin-CCK-like factors. Recently, a new peptide, structurally related to mammalian CCK, but with a gastrin-like activity, has been isolated from the digestive tract of chickens. The objective of this work has been: 1) to study the presence of gastrin-CCK-like immunoreactivity (IMR) in the digestive tract of chickens; 2) to distinguish chicken gastrin from CCK; and 3) to establish their distribution using specific antibodies. Tissue specimens from the proventriculus, gizzard, pylorus, duodenum, jejunum, ileum, ceca, and rectum were studied using indirect immunofluorescence procedures. The antibodies used were: 1) an antibody specific against the C-terminal pentapeptide common to gastrin and CCK; 2) one specific against CCK-33; and 3) one specific against chicken gastrin. Their use allowed the differentiation of two cellular populations which showed different affinities for the antibodies, indicating the presence of a gastrin-like peptide in the antrum and another CCK-like peptide in the small intestine, with the highest concentration in the proximal ileum. Immunoreactivity was not found in any other studied area. Two different peptides of the gastrin-CCK family are present in the chicken’s gastrointestinal tract. However their differentiation and identification are more difficult than in mammals due to the greater structural similarities of these peptides in birds.

Marked increase in cholecystokinin b receptor messenger RNA levels in rat dorsal root ganglia after peripheral axotomy

It is now well established that the expression of peptides in rat primary sensory neurons is dramatically changed in response to peripheral nerve injury. Thus, as first shown by Jessell et al. 15 peripheral axotomy causes a decrease in substance P levels in the dorsal horn of the corresponding spinal cord segments, and this is due to down-regulation of peptide synthesis in dorsal root ganglion neurons. 22 In contrast, other peptides such as vasoactive intestinal polypeptide and peptide histidine isoleucine, 27 galanin 12 and neuropeptide Y 32 are all markedly upregulated in the rat L4 and L5 dorsal root ganglia after sciatic nerve sectioning. The levels of another peptide, cholecystokinin and its messenger RNA are normally very low or undectable in rat primary sensory neurons, 5,20,24,25,26 but after peripheral axotomy approximately 30% of the ganglion neurons express cholecystokinin messenger RNA. 30 During the last few years a number of peptide receptors have been cloned, and they all belong to the family of G-protein coupled receptors with seven membrane spanning segments, 21 among them the two cholecystokinin receptors cholecystokinin A and cholecystokinin B. 17,23,34 Ghilardi et al. 11 have recently described presence of cholecystokinin B binding sites in rat dorsal root ganglia neurons. In the present study we report that the messenger RNA for the cholecystokinin B receptor is present at very low levels in normal dorsal root ganglia of the rat, but axotomy causes a very marked increase in the number of sensory neurons of all sizes expressing cholecystokinin B receptor messenger RNA, suggesting an increased sensitivity to cholecystokinin for many primary sensory neurons of different modalities after lesion.

Cells in the intestinal system of holoturians (echinodermata) express cholecystokinin-like immunoreactivity

The presence of cholecystokinin (CCK), originally isolated from porcine small intestine, has been reported in a diversity of invertebrates ranging, from cnidarians to protochordates, but so far, not in echinoderms. We have used immunohistochemical techniques to demonstrate the presence of cells expressing CCK-like immunoreactivity in the intestine of three species of sea cucumber: Holothuria mexicana, H. glaberrima, and Stichopus badionotus. The immunoreactivity was observed within the cytoplasm of these cells, in what appeared to be granular or vesicle-like structures. The cell bodies were present in the outer connective tissue layer of the intestine and had a neuronal appearance, sending an axon-like structure into the circular muscle and internal connective tissue. A plexus of fibers expressing CCK-like immunoreactivity was found overlying the muscle layer. Contractility of H. mexicana intestinal strips was studied under partially isometric conditions. CCK and related peptides induced relaxation of the basal muscle tension, and of tension induced by ACh application, suggesting a role for this agent in the intestinal physiology of holothurians.

The localization of cholecystokinin immunoreactivity in the rat ovary and uterine tube

The presence of cholecystokinin (CCK) immunoreactive nerve fibres in the rat ovary and uterine tubes was detected using the peroxidase antiperoxidase (PAP) technique. The antibody used was anti CCK 4562 which reacts with CCK-4, CCK-8, CCK-12 and CCK-33 (Larsson and Rehfeld, 1977). CCK-immunoreactive nerve fibres were found between the interstitial cells of the ovary, along blood vessels, and close to smooth muscle fibres in the ovary and tubal wall. A possible role of CCK-nerves in modulation of the sensitivity of the ovarian components to other humoral and nervous stimuli is discussed. The possible control of CCK over smooth muscle fibres in the ovary and the uterine tube and its role in ovulation is a matter of further studies.

P-456 - The presence of cholecystokinin B receptors in rat pituitary gland and GH3, a rat anterior pituitary tumor cell line.

P-456 - The presence of cholecystokinin B receptors in rat pituitary gland and GH3, a rat anterior pituitary tumor cell line.

Neurotrophic effect of cholecystokinin on ventral spinal cord in culture.

Studies of the effect of cholecystokinin on organotypic cultures of rat ventral spinal cord revealed that concentrations of 10(-4) to 10(-14) M exert a marked growth-stimulating effect. In the presence of cholecystokinin, the neuritic extension of the ventral spinal cord exceeds control values 3.5-6.5 times. The growth zone of spinal cord explants increases in cholecystokinin-treated cultures. The possible mechanism of the trophic effect of cholecystokinin on the ventral spinal cord is discussed briefly.

Responses of the pancreatic digestive enzyme secretion to various combinations of amino acids and cholecystokinin in chicks ( Gallus domesticus)

1. 1. Effect of amino acid administration on pancreatic secretion of digestive enzymes, amylase, trypsinogen and chymotrypsinogen was studied after wing vein injection of an amino acid (AAs) mixture (Thr, Lys, Phe, Leu, Ile, Glu, Val, His, and Met) or combinations of selected amino acids, i.e. Thr + Phe + Ile, Thr + Phe, Thr + Ile or Phe + Ile, in the presence of cholecystokinin (CCK) in chicks. 2. 2. Time course changes of enzyme output were similar in all treatment groups having a peak within 10–30 min, except for Phe + Ile that resulted in delayed induction of the enzyme release as shown by significant increases in the last 20 min compared with those in the rest. 3. 3. When increases in enzyme outputs for the first 30 min were compared, it was shown that the three enzyme responses brought about by the administration of the AAs mixture was almost entirely accounted for by the combined injection of Thr + Phe. 4. 4. Neither Thr + Ile nor Phe + Ile was as effective as Thr + Phe in inducing the output of these pancreatic enzymes. 5. 5. The present results suggest that Thr and Phe may have a specific regulatory role in the secretion of pancreatic digestive enzymes in chicks when administered simultaneously.

Photoaffinity labeling with GTP-γ-azidoanilide of a cholera toxin-sensitive 40 kDa protein from pancreatic acinar cells

In isolated pancreatic acinar plasma membranes a 40 kDa protein was labeled with the photoreactive GTP-analogue [alpha 32P] GTP-gamma-azidoanilide. Increased incorporation of the photolabel into the 40 kDa protein was obtained in the presence of increasing concentrations of cholecystokinin-octapeptide (10(-8) - 10(-5) M) but not with carbachol. Adenylyl cyclase activating hormones such as vasoactive intestinal polypeptide and secretin had no effect. Pretreatment of plasma membranes with cholera toxin reduced incorporation of GTP-gamma-azidoanilide into the 40 kDa protein by about 30%. This reduction was reversed if ADP-ribosylation by cholera toxin was performed in the presence of cholecystokinin, whereas carbachol had no effect. The data indicate that a cholera toxin-sensitive 40 kDa GTP-binding protein is involved in functionally coupling cholecystokinin- but not muscarinic acetylcholine-receptors to phospholipase C.

Co-existence of cholecystokinin- or gastrin-like peptides with other peptides in the hypophysis and the hypothalamus.

The presence of cholecystokinin and gastrin has been reported in the hypothalamohypophyseal system. These peptides present a peculiar distribution in the hypothalamic nuclei, the median eminence, and the neurohypophysis. CCK and gastrin have close relationships with other peptides like oxytocin, CRF, vasopressin, and the enkephalins; these relationships vary in different projecting areas and in different types of hypothalamic neurons. The functional role of G-CCK in neurosecretion seems to be linked to the role of these closely associated peptides and certainly deserves further investigation.

Localisation of intestinal gastrin in a distinct endocrine cell type

GASTRIN extracted from human intestine has two main molecular forms, little (G17) and big (G34) gastrins1. Both these peptides are also found in antral tissue although their relative proportions differ, G17 being the major component in antral tissue and G34 that in intestinal tissue1. The endocrine cell associated with the production of the immunoreactive gastrin found in the antral tissue is the ultrastructurally classified G cell2. The cellular origin of the immunoreactive gastrin extracted from the intestinal tissue has not been determined. The presence of cholecystokinin (CCK) peptides3,4, closely related to gastrin and sharing with it a C-terminal pentapeptide sequence (see Fig. 1), makes the specific immunological detection of both gastrin and CCK dependent on the use of well characterised and highly specific antibodies. We report here the finding that intestinal gastrin originates in a type of cell totally distinct from the I cell which has recently been identified as the source of CCK5.