Species differences in the response to cholecystokinin

Cholecystokinin-A receptors are involved in food intake suppression in rats after intake of all fats and carbohydrates tested

The hypothesis of these studies was that all fats and carbohydrates suppress food intake, at least in part, via cholecystokinin-A receptors (CCKAR). Fat (coconut oil, beef tallow, olive and safflower oil) and carbohydrate (cornstarch, sucrose, glucose and fructose) preloads were given intragastrically (1 g/4 mL) 30 min before feeding. Devazepide (0.25 mg/kg), a CCKAR antagonist, was given intraperitoneally at 60 or 30 min before or with each of the macronutrient preloads. Devazepide reversed food intake suppression caused by all fat and carbohydrate sources, but the effect was not consistently related to the time of devazepide administration or to any specific feeding interval. Among the fats, coconut and olive oil were most responsive to devazepide. The effect of all carbohydrates on food intake was decreased by devazepide. We conclude that CCKAR play a role in food intake suppression caused by all fats and carbohydrates, but their role is dependent upon the composition of the fat or carbohydrate.

Postprandial neuronal activation in the nucleus of the solitary tract is partly mediated by CCK-A receptors

CCK-A receptors and neurons of the nucleus of the solitary tract (NTS) are involved in the regulation of food intake, and in rats, there is evidence for involvement of an intestinal vagal afferent pathway. Studies investigating the role of CCK-A receptors in activation of NTS neurons using highly selective CCK-A receptor agonists and antagonists have yielded conflicting data. In the present study, we investigated CCK-induced and postprandial activation of NTS neurons, together with food intake studies, in CCK-A receptor-deficient Otsuka Long-Evans Tokushima fatty (OLETF) rats. Activated NTS neurons were detected using immunohistological staining for c-Fos protein. Exogenous CCK increased the number of c-Fos protein-positive cells in the NTS of Sprague-Dawley and CCK-A receptor-intact Long-Evans Tokushima Otsuka (LETO) rats but had no effect in CCK-A receptor-deficient OLETF rats. Food intake-induced c-Fos protein expression in NTS neurons was significantly reduced in CCK-A receptor-deficient OLETF rats compared with Sprague-Dawley or LETO rats. Postprandial c-Fos protein expression in the NTS was also significantly decreased after pretreatment with the CCK-A receptor antagonist MK329 after both short- and long-term fasting periods. Exogenous CCK decreased cumulative food intake in Sprague-Dawley and LETO rats but not in OLETF rats. These data demonstrate that CCK-A receptors are involved in the CCK- and food-induced c-Fos protein expression in the NTS. Taken together with the results of the food intake studies, this suggests that activation of CCK-A receptors is involved in the postprandial activation of NTS neurons and in the regulation of food intake.

Examining the effects of lipopolysaccharide and cholecystokinin on water ingestion: comparing intake and palatability

Lipopolysaccharide (LPS) and cholecystokinin (CCK) have been shown to have anorectic properties in a variety of species. The present study examined the effects of LPS and CCK, both alone and in combination, on two different aspects of water ingestion, water intake and palatability. On test days, animals were first injected intraperitoneally (i.p.) with either LPS (200 microg/kg) or NaCl vehicle, and 2 h later received a second injection of either CCK (8 microg/kg) or NaCl vehicle. In Experiment 1, water intake was monitored for 1 h on 3 separate test days 72 h apart; while in Experiment 2, water palatability was assessed using the taste reactivity test (TRT), on two separate test days 72 h apart. Both LPS and CCK significantly (p<0.05) reduced water intake, with the effects of combined LPS with CCK being more pronounced than either agent injected alone. Rats developed a rapid tolerance to the effects of LPS on water intake on subsequent exposures to LPS. Results from the TRT indicated that LPS enhanced water palatability (p<0.05), as evidenced by a high level of ingestive responding, whereas CCK produced a pattern of responding indicative of satiety. LPS plus CCK reduced ingestive responding on the first test day, but these responses were significantly increased on the second test day (p<0.05). These results demonstrate that although LPS reduces water intake, it enhances water palatability. The results further underscore the necessity for examining palatability changes in addition to intake measures when studying the regulation of feeding and drinking.

C-fos protein expression in the nucleus of the solitary tract correlates with cholecystokinin dose injected and food intake in rats

C-fos protein expression was investigated in the nucleus of the solitary tract (NTS) in response to increasing cholecystokinin (CCK) doses and food intake in rats by counting the number of c-fos protein positive cells in the NTS. C-fos protein expression in the NTS dose-dependently increased in response to CCK, the lowest effective dose being 0.1 microg/kg. The ED(50) for c-fos protein expression in the NTS in response to CCK was calculated to be 0.5 to 1.8 microg/kg, depending on the anatomical level of the NTS investigated. Food intake increased c-fos protein expression in the NTS, the maximum number of c-fos protein positive cells being reached at 90 min after the start of food intake. Regression analysis identified a positive correlation between c-fos protein expression and the amount of food intake. Our data indicate that subpopulations of the NTS that are activated by CCK or food intake are involved into the short-term regulation of food intake and the neural control of feeding by the caudal brainstem.

Differential effects of lipopolysaccharide and cholecystokinin on sucrose intake and palatability

The differential effects of CCK and lipopolysaccharide (LPS) on sucrose intake and palatability were examined. Rats were injected with LPS (200 microg/kg ip) or NaCl (0.9%, vehicle) and 2 h later received a second injection of either CCK (8 microg/kg ip) or NaCl. In experiment 1, sucrose (0.3 M) intake was monitored for 1 h on three different test days 72 h apart, while in experiment 2, palatability was assessed by means of the taste reactivity test (TRT) on two separate days (72 h apart). In the TRT, orofacial and somatic responses to brief (30 s) intraoral infusions of sucrose were recorded and analyzed for response frequency. Singly, LPS and CCK reduced sucrose intake, with a more pronounced effect from combined LPS and CCK. LPS by itself did not alter sucrose palatability, as evidenced by continuous high levels of ingestive responding. In contrast, CCK-treated rats displayed a pattern of responding indicative of satiety, as did the combined LPS-CCK-treated rats. These results suggest that LPS does not induce hypophagia by altering palatability.

Food for thought: a critique on the hypothesis that endogenous cholecystokinin acts as a physiological satiety factor

This review evaluates the various lines of evidence supporting the hypothesis that cholecystokinin (CCK) released from the small intestine during feeding plays a physiological satiety. Issues considered include, the effects of systemic injection of CCK on consummatory and operant feeding, the role of the vagus nerve, the effects of CCKB receptor antagonists, and the neuroendocrine responses to exogenous CCK. A critical appraisal of this research indicates that while it is clearly demonstratable that exogenous peripheral CCK can alter food intake by acting on CCKA receptors, the mechanism involved may be more closely related to the induction if aversion and nausea, rather than satiety. With regard to peripheral endogenous CCK, the available evidence also does not seem to support a role for the hormone in satiety. In particular, it is doubtful whether plasma concentrations of CCK following a meal are sufficiently high to inhibit feeding. Moreover, CCKA receptor antagonist which do not cross the blood brain barrier fail to increase meal size, as would be expected if peripheral CCK was an effective satiety factor. In addition, the recent literature concerned with the possibility that CCK may have a direct action within the brain in the control of food intake has been reviewed. These studies show that CCK administered intracerebroventicularly, or by micoinjection into discrete brain regions, also inhibits feeding via a CCKA receptor mechanism. However, the physiological relevance of these findings have yet to be determined.

Hormone replacement modifies cholecystokinin-induced changes in sucrose palatability in ovariectomized rats

The taste reactivity test was used to examine the effect of CCK-octapeptide (CCK-8) on the palatability of a sucrose solution in ovariectomized rats either receiving hormonal replacement (estradiol and progesterone; OVX + HRT), or treated with vehicle only (OVX + VEH). Statistical analyses revealed that the OVX + HRT rats treated with CCK-8 exhibited a robust decrease in ingestive responses, and an increase in aversive responses and passive drips to the intraoral sucrose infusions, relative to treatment with the NaCl vehicle. In contrast, a weak effect of CCK-8 on ingestive responses, no significant effect on the frequency of aversive responses, and a reduced effect on passive drips was observed in the OVX + VEH rats. These results show that CCK-8 modifies sucrose palatability, and that this effect is modulated by gonadal hormone levels.

Cholecystokinin analogs with suppressed central activities

Several analogs of Boc-protected C-terminal heptapeptide of cholecystokinin (Boc-CCK-7) with modified C-end Phe were pharmacologically characterized. The influence of the number of methyl groups on aromatic side chain of Phe was investigated in following tests: binding to pancreatic and brain membrane receptors, gall bladder contraction, amylase secretion, anorexia, sedation and analgesia. Two analogs seem to be promising selective anorectic agents with strongly protracted effect: Boc-[Phe(triMe)7]CCK-7 and Boc-[Phe(pentaMe)7]CCK-7. The first analog exhibits the same spectrum of activities as CCK-8, however partially decreased central effects, the second one shows partially decreased peripheral activities and totally suppressed central ones. Our study supports the idea that C-terminal residue of CCK is more important for biological potency than for binding to CCK receptors.

Effect of L364.718 during suckling on the sensitivity to the hypophagic effect of cholecystokinin in adult rats

1. In the present study it was investigated whether drugs acting at the cholecystokinin (CCK)-A receptor given to rat pups may result in long-lasting changes in body weight or regulation of food intake controlled by CCK. 2. From day 3 to day 10 of life, male and female Wistar rat pups were treated with the CCK-A receptor antagonist L-364.718 and the CCK-A + B agonist CCK-8S. 3. In adult rats, treated with L364.718 during suckling, the sensitivity to the acute hypophagic action of CCK-8S was weaker or abolished compared to adults treated with saline during suckling. In adult rats given CCK-8S during suckling acute treatment with CCK-8S reduced food intake to the same extent as in the group treated with saline postnatally. 4. These data show that early postnatal treatment with the CCK-A receptor antagonist L364.718 has an impact on the hypophagic response to CCK-8S in later life.

Nutritional response in a Drosophila yolk protein gene promoter

The yolk protein genes (yps) of Drosophila melanogaster are only expressed in the ovary and fat body of female flies if they are supplied with proteinaceous food. This nutritional response is specific to the yp genes. We have used transgenic flies transformed with a series of constructs bearing deletions in the upstream region of the yp1 and yp2 genes attached to a reporter gene to search for DNA sequences responsible for the nutritional induction specific for yp1 and yp2 genes. Several regions were shown independently of each other to confer nutritional regulation on the expression of the yp1 and yp2 genes. This regulation can be induced both on the yp promoter and the heterologous Drosophila heat-shock 70 (hsp 70) promoter. The redundancy of sequences conferring a nutritional response on the yp genes is similar to that observed for the female specificity of these genes and suggest that several DNA binding proteins interact to provide the correct regulation of these genes. These results suggest that nutrition acts to modify the level of a trans-acting factor in the fat body. Northern blot analysis showed that the transcript levels from the dsx gene are not affected by nutrition, indicating that the response is not mediated via the dsx gene.

Cholecystokinin reduces ingestive taste reactivity responses to water in fluid-replete but not fluid-deprived rats

The effects of hydrational factors on the ability of cholecystokinin (CCK) to alter taste reactivity responses to intraoral water infusions was assessed in fluid-replete and fluid-deprived rats. Naive male rats were injected with CCK (8 micrograms/kg, IP), or physiological saline (1 ml/kg, IP) and taste reactivity responses elicited by brief (30 s) intraoral water infusions at 2, 4, 6, 8, and 10 min postinjection were measured. One week later and following a 24 h water deprivation period, taste reactivity responses to intraoral water infusions were measured again. Exogenous administration of CCK was found to produce a significant decrease in the frequency of ingestive responses accompanied by a significant increase in passive drip during oral water infusions in fluid-replete rats. In contrast, CCK was found to have no effect on the frequency of taste reactivity responses when rats were subjected to a period of water deprivation. These results demonstrate that the rat's state of hydration interacts with the ability of CCK to alter taste reactivity responses to intraoral water infusions.

Exogenous cholecystokinin octapeptide in broiler chickens: satiety, conditioned colour aversion, and vagal mediation

Intraperitoneal injections of 3.5, 7.0, 14.0, and 28.0 micrograms/kg of CCK-8 into free-feeding broiler chickens significantly reduced food intake and delayed feeding (p < 0.05). To determine whether CCK can condition preference or aversion and to investigate the latency and the reversal of the effect, a low (2 micrograms/kg) and a high (14 micrograms/kg) dose of CCK-8 were administered using the coloured food paradigm. One colour, the conditioning stimulus (CS+), was paired with injections of CCK-8; the other colour was paired with injections of saline (CS-). The 2 micrograms/kg dose of CCK-8 neither reduced food intake nor conditioned a colour aversion. The 14 micrograms/kg dose significantly reduced food intake and conditioned a colour aversion (p < 0.05). When vagotomy was performed, the 14 micrograms/kg dose of CCK suppressed feeding in sham-operated birds (p < 0.05) but not in vagotomized birds (p > 0.05). A significant aversion for the food paired with CCK was obtained in sham-operated birds (p < 0.001) but not in vagotomized birds (p > 0.05). It was concluded that IP injections of CCK-8 reduce food intake in broiler chickens and that chicks can learn to associate the colour of the food with injections of CCK, developing an aversion. It was also shown that the vagus nerve mediates the CCK satiety effects and that aversion conditioning to CCK is dependent upon intact vagal innervation of the viscera.

Biological actions of cholecystokinin

Cholecystokinin (CCK) has emerged as an important mammalian neuropeptide, localized in peripheral organs and in the central nervous system. This review presents an overview of the molecular aspects of CCK peptides and CCK receptors, the anatomical distribution of CCK, the neurophysiological actions of CCK, release of CCK and effects of CCK on release of other neurotransmitters, and the actions of CCK on digestion, feeding, cardiovascular function, respiratory function, neurotoxicity and seizures, cancer cell proliferation, analgesia, sleep, sexual and reproductive behaviors, memory, anxiety, and dopamine-mediated exploratory and rewarded behaviors. Human clinical studies of CCK in feeding disorders and panic disorders are described. New findings are presented on potent, nonpeptide CCK antagonists, selective for the two CCK receptor subtypes, which demonstrate that endogenous CCK has biologically important effects on physiology and behavior.

Localization of cholecystokinin binding sites in the adult and developing Brazilian opossum brain

Cholecystokinin (CCK) is now recognized as one of the most abundant peptides in the mammalian central nervous system. We have previously used immunohistochemistry to localize CCK in the adult and developing Brazilian opossum brain. However, little is known about the distribution of CCK binding sites in the developing mammalian brain. Therefore, to further our knowledge of the sites of action for CCK during development, we initiated a series of studies to localize CCK binding sites in the adult and developing Brazilian opossum. This species was chosen because pups are born in a fetus-like state. Receptor autoradiography was performed on coronally sectioned brains of 1 to 60 day postnatal (PN) animals and adults with 125I-Bolton Hunter-CCK-8 as the radioligand. Binding is evident in the 1PN opossum brainstem and is observed in the developing forebrain by 5PN. Region-specific binding increases during development, and binding in the 35PN brain resembles the adult pattern. Binding is evident prior to the detection of CCK-like immunoreactivity in many areas. The facial motor nucleus is identifiable and exhibits high levels of binding in Brazilian opossum pups of 10 to 35 days of age. However, binding is undetectable in the facial motor nucleus of 45 and 60PN pups. In general, the binding patterns for CCK in the adult opossum resemble those of other mammals and likely mediate similar physiological functions. However, some cholecystokininergic pathways appear to be unique to neonatal mammals.

Pharmacological characterization of new cholecystokinin analogues

New analogues of cholecystokinin-7 (CCK-7) modified at amino acid residues 5 and 7 were assayed for their effect on gall bladder, pancreatic secretion, food intake (anorectic activity), amount of rearing (sedative activity) and analgesia, as well as their ability to inhibit 125I-CCK-8 binding to pancreatic cell membrane receptors and brain membrane receptors. The results were compared to the activities of standard compounds, CCK-8, cerulein, BOC-CCK-7 (BOC = tertbutyloxycarbonyl) and BOC-[Nle2,Nle5]CCK-7. All analogues exhibited agonistic effects. Their anorectic activity was significantly prolonged.

Differential interaction of cholecystokinin with morphine and phencyclidine: effects on operant behavior in pigeons

To extend previous operant research in rats with morphine and cholecystokinin (CCK), these two substances were given alone and in combination to pigeons. In one component of a multiple schedule, responding of pigeons (key pecking) was reinforced under a fixed-ratio (FR 50) schedule of food presentation. In the other component, responding had no programmed consequence (timeout). Each session consisted of four 10-min timeout components alternating with four 5-min FR components. In Experiment 1, cumulative dose-effect curves for morphine were obtained by giving an IM injection before each of four FR components; successive injections increased the cumulative dose by 1/4 log-unit steps. In general, as the cumulative dose of morphine increased, the overall response rate in each FR component decreased. Dose-dependent decreases in response rate also occurred when single noncumulative doses of CCK were administered alone 20 min prior to the start of the session. This effect of CCK alone diminished as the session progressed. When CCK was given as a pretreatment before cumulative doses of morphine, the morphine dose-effect curve for response rate shifted to the left. At intermediate doses of CCK, the "potentiation" was so complete that two of three subjects failed to respond during any of the four FR components (i.e., the dose-effect curve for morphine had shifted approximately 1 log-unit to the left). In order to evaluate the pharmacological specificity of this effect, cumulative doses of phencyclidine were administered in combination with CCK (Experiment 2). Unlike the interaction between morphine and CCK, the interaction between phencyclidine and CCK was reciprocal.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cholecystokinin on morphine-elicited hyperactivity in hamsters

The effects of the octapeptide cholecystokinin (CCK) on hamster locomotor activity were investigated in three experiments. In Experiment 1, the effect of CCK (25, 50, 75 micrograms/kg) on morphine (2.5 mg/kg)-elicited hyperactivity was studied. Results indicated that CCK antagonized morphine-elicited hyperactivity and that CCK alone elicited hypoactivity. There were no effects of dose of CCK. In Experiment 2, the effects of intraperitoneal (IP) and subcutaneous (SC) routes of administration of CCK (25 micrograms/kg) on locomotor activity were studied. Compared to saline controls, CCK induced hypoactivity that was of greater magnitude and of longer duration when administered IP than SC. Experiment 3 was designed to replicate the route of administration effect observed in Experiment 2 and to determine whether sensitization to CCK-induced hypoactivity develops over the course of a few injections. Results indicated that CCK-induced hypoactivity was greater after IP than SC administration but that sensitization was not detectable. It is concluded that CCK antagonizes morphine-elicited hyperactivity in the hamster by acting, in part, independently of morphine to produce opposite behavioral effects.

Endogenous cholecystokinin reduces feeding in young rats

The hypothesis that endogenous cholecystokinin (CCK) released from the small intestine during feeding causes satiety was tested in rat pups, 9 to 12 days old. Intragastric administration of soybean trypsin inhibitor, a procedure that releases CCK from the small intestine, decreased the subsequent intake of a test meal. This effect was reversed by prior treatment with MK-329, a selective antagonist of CCK at alimentary-type CCK (CCK-A) receptors. Thus, endogenous, small intestinal CCK can cause satiety in the neonatal rat and this effect involves CCK-A receptors.

Centrally administered CCK-8 suppresses activity in mice by a "peripheral-type" CCK receptor

Cholecystokinin octapeptide (CCK-8) administered either systemically (IP) or centrally (ICV) suppresses several types of behavior in mice including exploratory locomotion, rearing and grooming. At doses equimolar to those active for CCK-8, neither desulfated CCK-8 (CCK-8-DS), nor the protected C-terminus tetrapeptide fragment, BOC-CCK-4, is behaviorally active when administered either centrally or systemically. A potent and selective antagonist to the peripheral type (Type A) CCK receptor, A-65186, when given systemically, blocked the effects of systemically administered CCK-8, but failed to block the effects of ICV administered CCK-8. Central administration of A-65186 blocked the effects of ICV administered CCK-8. These results demonstrate that administration of exogenous CCK-8 to mice can suppress exploratory locomotion by acting either centrally or peripherally and that in either case the demonstrated behavioral effects are mediated via a "peripheral" type (Type A) CCK receptor.

The effect of neuropeptide Y on drinking in mice

Neuropeptide Y (NPY) when administered intracerebroventricularly is a potent stimulator of feeding and drinking in rats. In these studies we demonstrated that, in contrast, in mice NPY inhibits drinking induced by water deprivation and that associated with food intake. In addition, we found that mice failed to respond to the rat dipsogen angiotensin II. Old mice demonstrated hypodipsia compared to young mice and NPY failed to inhibit drinking in older mice. Monosodium glutamate (MSG) administered neonatally produces lesions of the arcuate nucleus, an area rich in NPY cell bodies. NPY inhibited drinking and enhanced feeding in MSG treated mice. NPY also significantly inhibited the intake of water flavored with 8% sucrose and 0.1% quinine. NPY failed to alter ingestion of 0.2% or 5% saline. These studies support the contention that marked species differences exist in the regulation of water intake between rats and mice.

The effect of peripheral administration of peptides on food intake, glucose and insulin in wolf pups

In the studies reported here we demonstrate that bombesin decreases food intake in wolf (Canis lupus) pups without altering glucose or insulin levels. A high dose of cholecystokinin-octapeptide (CCK, 5 micrograms/kg) decreased food intake. CCK produced a transient increase in insulin, without altering glucose. Glucagon (0.5 mg/kg) failed to decrease food intake despite producing a marked hyperglycemia and hyperinsulinemia. Calcitonin was ineffective at decreasing food intake, although it did decrease the time spent feeding. These studies suggest a potential role for peripheral peptides in food regulation in the wolf.

Oxytocin secretion in response to cholecystokinin and food: differentiation of nausea from satiety

Administration of cholecystokinin (CCK) to rats caused a dose-dependent increase in plasma levels of the neurohypophyseal hormone oxytocin (OT). The OT secretion was comparable to that found in response to nausea-producing chemical agents that cause learned taste aversions. The effect of CCK on OT secretion was blunted after gastric vagotomy, as was the inhibition of food intake induced by CCK. Food ingestion also led to elevated plasma OT in rats, but CCK and aversive agents caused even greater OT stimulation. Thus, after administration of large doses of CCK, vagally mediated activation of central nausea pathways seems to be predominantly responsible for the subsequent decrease in food intake. Despite their dissimilar affective states, both nausea and satiety may activate a common hypothalamic oxytocinergic pathway that controls the inhibition of ingestion.