Cholecystokinin modulates both the development and the expression of behavioral sensitization to amphetamine in the rat

Rationale: Repeated administration of psychostimulants such as amphetamine (AMPH) produces an enduring augmentation of their locomotor effects. Previous research suggests that this phenomenon, termed sensitization, is related to changes within the mesolimbic dopamine (DA) system. Objectives: The present experiments were designed to investigate the contribution of endogenous cholecystokinin (CCK), a neuropeptide co-localized with DA in the mesolimbic system, to the development (experiment 1) and the expression (experiment 2) of locomotor sensitization to AMPH. Methods: In experiment 1, rats were injected (IP) with the CCK_A antagonist devazepide (0, 0.001, 0.01, or 0.1 mg/kg) or the CCK_B antagonist L-365,260 (0, 0.001, 0.01, 0.1, or 1.0 mg/kg) followed by AMPH (1.5 mg/kg) once daily for seven days. Following 10 days withdrawal, rats were administered AMPH (0.75 mg/kg) and their locomotor activity recorded. In experiment 2, rats were administered AMPH (1.5 mg/kg) once daily for 7 days. Following 10 days withdrawal, rats were injected with devazepide (0, 0.0001, 0.001, 0.01, 0.1, or 1.0 mg/kg) or L-365,260 (0, 0.001, 0.01, or 0.1 mg/kg) followed 30 min later by AMPH (0.75 mg/kg) and their locomotor activity recorded. Results: When administered during the AMPH pretreatment phase of experiment 1, the two highest doses of L-365,260 attenuated, and the lowest dose of L-365,260 potentiated, the sensitized locomotor response to AMPH challenge. When administered prior to the AMPH challenge phase of experiment 2, devazepide attenuated the sensitized locomotor response to AMPH. Conclusions: These results suggest that CCK_B and CCK_A receptors modulate the development and the expression of behavioral sensitization to AMPH, respectively. Received: 27 August 1999 / Accepted: 29 February 2000     

Behavioral effects of CCKB receptor ligands in a validated simulation of panic anxiety in rats

Animals or human subjects receiving brain stimulation in the dorsal periaqueductal gray matter (dPAG) show sudden fear-suggestive behavioral reactions and physical signs of autonomic activation which are reminiscent of the symptom profile characterizing a panic attack. An experimental situation in rats measuring dPAG stimulation self-interruption thresholds has been validated as realistically simulating several aspects of panic anxiety with objective signs of symptomatic and predictive validity using established antipanic and panicogenic agents; it was utilized here to evaluate the effects of various cholecystokinin B receptor ligands. A dose-dependent increase in self-interruption thresholds (antipanic-like effect) was recorded following injection of L-365,260 (3.2, 10 and 32 mg/kg i.p.), a CCK_B receptor antagonist with good brain penetration, whereas no significant changes in thresholds were recorded following CI-988 (3.2, 10 and 32 mg/kg i.p.), a dipeptoid CCK_B receptor antagonist with poor brain penetration. Latencies for self-interruption were not modified, suggesting that motor functions remained intact. No significant changes in self-interruption thresholds were recorded following peripheral administration of the CCK_B receptor agonists CCK₄ (0.03 to 0.32 mg/kg i.v.; 0.01 to 3.2 mg/kg i.p.) or the metabolically stabilized analog Boc-CCK₄ (0.1 to 10 mg/kg i.p.). Systemic administration of the panicogenic compounds caffeine and yohimbine enhance acute anxiety in this model. These data indicate that, in the dPAG simulation of panic anxiety, central CCK_B receptor blockade by L-365,260 induces antiaversive effects analogous to those observed following benzodiazepine receptor activation by clonazepam or alprazolam. Potency and efficacy of L-365,260 were lower than those of clonazepam or alprazolam, suggesting modest, but nonetheless authentic, antiaversive properties for this CCK_B receptor antagonist. Lack of effects observed following peripheral administration of the agonists CCK₄ and Boc-CCK₄ or of the dipeptoid antagonist CI-988 is likely to reflect restricted brain penetration of those compounds in rats; it furthermore excludes a contribution of peripheral gastrin and CCK_A receptors to the antipanic-like properties of selective CCK_B receptor antagonists such as L-365,260.     

Opposite effects of CCKB agonists in grooming behaviour in rats: further evidence for two CCKB subsites

1. The hypothesis of the existence of two CCK_B receptor subsites, CCK_B1 and CCK_B2 corresponding probably to different coupling states of CCK_B receptors, was studied by measuring grooming behaviour in rats.
2. The B1 receptor agonist, BC197 (300 μg kg⁻¹, i.p.) produced a 45–50% decrease in grooming activity, which was prevented by both the CCK_B receptor antagonists CI-988 (20 μg kg⁻¹ i.p.) and L-365,260 (200 μg kg⁻¹, i.p.).
3. In contrast, 3, 10 and 30 μg kg⁻¹, i.p., of the potent B2 receptor agonist, BC264, enhanced grooming (150–190%). This effect was prevented by previous injection of 75 μg kg⁻¹ of L-365,260 while higher doses (200 μg kg⁻¹, i.p.) produced only a partial antagonism. Moreover, CI-988 (20 μg kg⁻¹, i.p.), showed an opposite effect in potentiating the responses induced by BC264. However, 200 μg kg⁻¹ of CI-988 tended to suppress the increase of grooming induced by BC264.
4. The effects of BC264 were prevented by the D₁ receptor (SCH 23390) and D₂ receptor (sulpiride) antagonists, while those of BC197 were only antagonized by sulpiride, emphasizing the existence of a link between peptidergic (CCK) and dopaminergic systems.
5. This study brings additional evidence for the existence of the two CCK_B receptor subsites and suggests that particular attention should be focused on the selectivity of CCK_B receptor agonists, notably to explain the fact that some compounds such as Boc-CCK4 induce anxiogenic-like effects while others, including BC264, are devoid of these effects.

     

Evaluation of the discriminative stimulus effects of the novel sedative-hypnotic CL 284,846

CL 284,846,N-[3-(3-cyanopyrazolo[1, 5-a]pyrimidin-7-yl)phenyl)]-N-ethylacetamide, is a novel non-benzodiazepine sedative-hypnotic with benzodiazepine-like sedative effects, but with less apparent liability for accompanying undesired side effects. In an effort to further characterize its pharmacological activity, CL 284,846 (3.0 mg/kg, IP, 30 min pretreatment) was established as a discriminative stimulus (DS) in rats (n=7). CL 284,846 (0.3–10.0 mg/kg) showed a dose-related increase in drug-appropriate responding up to the training dose and a dose-related decrease in response rate. The benzodiazepine agonist triazolam (0.1–1.0 mg/kg), the benzodiazepine partial agonist Ro 17-1812 (0.3–3.0 mg/kg) and the triazolopyridazine CL 218,872 (1.0–3.0 mg/kg) substituted for CL 284,846 in all rats, whereas the imidazopyridines zolpidem (3.0–10.0 mg/kg) and alpidem (10.0–30.0 mg/kg), the benzodiazepine partial agonist bretazenil (0.03–10.0 mg/kg) and the novel putative anxiolytic CL 273,547 (10.0–56.0 mg/kg) substituted in most, but not all, rats. Ro 17-1812, bretazenil, and CL 218,872 had no effect on response rate while the other drugs showed a concomitant decrease in rate. The 5-HT_1A agonist buspirone (1.0–10.0 mg/kg) and the barbiturate pentobarbital (3.0–17.0 mg/kg) failed to substitute for CL 284,846 up to rate-decreasing doses. The benzodiazepine antagonist flumazenil (3.0–10.0 mg/kg) blocked the DS effects of CL 284,846 in most rats with no effect on response rate. Taken together, these results suggest that the DS effects of CL 284,846 are mediated via benzodiazepine receptors; however, the DS profile of CL 284,846 remains distinct from both benzodiazepine and non-benzodiazepine sedative-hypnotic drugs.     

Opposite effects mediated by CCKA and CCKB receptors in behavioural and hormonal studies in rats

We compared the influence of two cholecystokinin (CCK) antagonists, devazepide and L,365,260 [3R-(+)-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1 H-1,4-benzodiazepine-3y1)-N-(3-methyl-phenyl)urea], upon two distinct phenomena, behavioural and hormonal effects of caerulein (5 g/kg s.c.), and unselective CCK agonist, in rats. Behavioural effects were assessed in the elevated plusmaze and open field tests. In separate experiments, effects on thyrotropin (TSH), prolactin (PRL) and growth hormone (GH) levels in serum of male rats were studied.Caerulein inhibited the exploratory behaviour in the plus-maze. Time spent in the open part, the number of line crossings and closed arm entries were significantly decreased, whereas the ratio of failed attempts/closed arm entries was increased. The anti-exploratory effect of caerulein was antagonized by the pretreatment with L-365,260 (10 g/kg), a preferential antagonist at CCK_B receptors, but was increased by devazepide (1–100 g/kg), a preferential CCK_A antagonist. L-365,260 (1–100 /kg) and devazepide (1–100 Fig/kg) given alone did not change the behaviour of rats in the plusmaze test. Caerulein (5 g/kg) itself did not modify the locomotor activity of rats in open field. However, the concomitant administration of caerulein with devazepide (1–10 g/kg) reduced the frequency of line crossings and rearings. In the hormonal studies caerulein significantly decreased the cold-induced increase of TSH levels in serum. GH and PRL levels were not markedly affected by caerulein. Pretreatment with devazepide (100 g/kg) antagonized, while Lr365,260 (100 Ng/kg) even increased, the suppressing effect of caerulein on TSH levels. The concomitant administration of L-365,260 and caerulein reduced the levels of GH, whereas the combination of CCK agonist with devazepide caused the opposite effect. L-365,260 and devazepide alone did not change the levels of hormones in serum.The results support the idea that CCK_A and CCK_B receptors exert an opposite influence not only upon the exploratory behaviour in rats (CCK_A receptor activation mediates an increase, CCK_B receptor activation a decrease) but also upon the secretion of two anterior pituitary hormones, TSH and probably GH (CCK_A receptor activation mediates a decrease, CCK_B receptor activation an increase). Correspondence to: P. T. Mannisto at the above address     

The effects of CCK-4 on dopamine D1 agonist-induced grooming are blocked by a CCKA receptor antagonist: Evidence for a novel CCK receptor subtype?

The neuropeptide cholecystokinin (CCK) has been shown to interact with dopamine in various ways, including attenuation of dopamine D₁ receptor-mediated vacuous chewing and grooming. While we have demonstrated a clear role for the CCK_A receptor in the attenuation of dopamine D₁ agonist-induced vacuous chewing, studies of grooming yielded anomolous results. We examined the effects of selective CCK receptor antagonists on the attenuation of SKF 38393-induced grooming by the CCK_B agonist CCK-4. Administration of SKF 38393 (5 mg/kg s.c.) to male Sprague-Dawley rats resulted in a significant increase in grooming which was reduced to control levels by CCK-4 (20 mg/kg i.p.). Pretreatment with either the CCK_A receptor antagonist devazepide or the CCK_B receptor antagonist L-365,260 significantly attenuated this effect over a range of doses (20, 100, 500 μg/kg i.p.). The suppression of dopamine D₁ agonist-induced grooming by CCK-4 does not appear to reflect a non-specific effect of anxiogenesis, as it was unaffected by the anxiolytic diazepam. The CCK receptor antagonists alone were without behavioural effect. Taken together with previous studies in models of anxiety and analgesia, our findings lend further support to the hypothesis that CCK-4 may act at a novel receptor subtype.     

Differential profile of the CCKB receptor antagonist CI-988 and diazepam in the four-plate test

The cholecystokinin_B receptor antagonist CI-988 ([R-(R*,R*)]-4-[[2-[[3-(1H-indol-3-yl)-2-methyl-1-oxo-2-[[(tricyclo[3.3.1. 1^3,7]dec-2-yloxy)carbonyl]amino]-propyl]amino]-1-phenylethyl]amino]-4-oxobbutanoic acid compound with 1-deoxy-1-(methylamino)-D-glucitol (1:1)) and the benzodiazepine receptor agonist diazepam were tested for potential anxiolytic effects on punished exploratory behavior in the four-plate test using mice. Diazepam (0.31–5 mg/kg PO) increased the number of shocks taken in a dose-dependent manner, an effect blocked by the benzodiazepine receptor antagonist flumazenil. CI-988 (0.00001–1 mg/kg PO) tended to increase the number of delivered shocks over the chosen dose range; this effect was, however, not dose-related or as large as that produced by diazepam. A limited testing of the 5-hydroxytryptamine₃ receptor antagonist ondansetron (0.1 and 1 mg/kg PO) suggested an effect similar to CI-988. These results indicate that distinct and contrasting dose-response profiles exist for these classical and atypical drugs in an animal model of anxiety based on electric shock.     

Evaluation of the Specificity and Potency of a Series of Cholecystokinin-B/Gastrin Receptor Antagonists in vivo

Abstract: The potency and specificity of five proposed cholecystokinin-B receptor antagonists, YM022, RP73870, L-740,093, L-365,260 and LY288513, were studied in rats and mice. Gastrin activates rat stomach histidine decarboxylase via cholecystokinin-B/gastrin receptors. To examine cholecystokinin-B receptor-mediated effects of the five drugs, they were infused intravenously to fasted rats and the histidine decarboxylase activity in the oxyntic mucosa was determined. While YM022, RP73870, L-740,093 and L-365,260 failed to activate histidine decarboxylase, they dose-dependently antagonized the gastrin-induced histidine decarboxylase activation. LY288513 had no effect in the doses tested. The maximal inhibitory effect of L-365,260, L-740,093, RP73870 and YM022 on histidine decarboxylase, activated by the intravenous infusion of an ED₅₀ dose of gastrin (0.4 nmoles/kg/hr), was seen at doses of 3, 0.3, 0.1 and 0.1 μmoles/kg/hr, respectively; the corresponding ID₅₀ values were 0.4, 0.02, 0.007 and 0.004 μmoles/kg/hr. In a follow-up study, YM022 and RP73870 were found to produce a rightward shift of the gastrin dose-response curve, which is consistent with competitive inhibition. The effect of the five drugs on a cholecystokinin-A receptor-mediated response was examined by studying gastric emptying in mice. Cholecystokinin-8s, given by a subcutaneous bolus injection, dose-dependently inhibits gastric emptying. The specific cholecystokinin-A receptor antagonist devazepide (given intravenously as a bolus injection) antagonized the effect of cholecystokinin-8s in a dose-dependent manner, with an ID₅₀ value of 28 nmoles/kg. None of the drugs inhibited the gastric emptying or prevented the cholecystokinin-8s-induced effect at the doses tested. The results indicate that YM022, RP73870, L-740,093 and L-365,260 act as cholecystokinin-B receptor antagonists in vivo, being without measurable agonistic activity. Furthermore, they do not interact with cholecystokinin-A receptors at the doses tested. Among the cholecystokinin-B receptor antagonists studied YM022 and RP73870 are superior, the rank order of potency being YM022±RP73870>L-740,093>L-365,260.     

Effect of intracerebroventricular and systemic injections of caerulein,a CCK analogue,on electrical self-stimulation and its interaction with the CCKA receptor antagonist,L-364,718 (MK-329)

Systemic administration of caerulein (10–100 µg/kg SC), a potent analogue of cholecystokinin, caused a profound dose-related depression of variable-interval self-stimulation, followed by progressive recovery within 60 min. Intracerebroventricular injection of caerulein (3–1000 ng) was not more effective than systemic injection, while injections into the nucleus accumbens (3–100 ng bilaterally) were without detectable effect. Systemic injections of L-364,718 (70–700 µg/kg IP), a specific competitive antagonist of CCK_A (peripheral-type) receptors, had no effect on self-stimulation when given alone. When given in combination with caerulein, L-364,718 (200 µg/kg IP) significantly reduced the inhibitory effect of caerulein (30 µg/kg SC); however, this dose, and higher doses of L-364,718, failed to confer complete protection. It is concluded that self-stimulation performance may be subject to modulation by CCK receptors distributed predominantly in the peripheral nervous system and that some but not all of these receptors are CCK_A receptors.     

A comparison of the effects of the novel muscarinic receptor agonists L-689,660 and AF102B in tests of reference and working memory

Four experiments compared the CNS effects of a novel M₁/M₃ receptor agonist L-689,660 with those of the M₁/M₃ muscarinic receptor agonist AF102B. In the mouse tail-flick test of antinociception (TF) the minimum effective doses to increase tail-flick latency (MED) of L-689,660 and AF102B were 0.03 mg/kg and 10.0 mg/kg, respectively. In a rat conditioned-suppression-of-drinking (CSD) test of reference memory, doses of 0.3 and 1.0 mg/kg L-689,660 and a dose of 5.0 mg/kg AF102B reversed a scopolamine-induced deficit in performance (0.6 mg/kg). Although there was a tendency for L-689,660 to reverse the scopolamine-induced (0.4 mg/kg) performance deficit in a rat delayed-matching-to-position (DMTP) test, the difference failed to reach statistical significance. In contrast, a 5.0 mg/kg dose of AF102B potentiated the scopolamine-induced deficit in choice accuracy and the number of trials completed on this task. In a response sensitivity (RS) test, chain-pulling rates were significantly decreased by L-689,660 (MED=0.03 mg/kg) and by AF102B (MED=5.0 mg/kg). These results suggest that L-689,660 and AF102B may ameliorate or reverse a scopolamine-induced deficit, but only at doses that also reduce chain-pulling rates on operant schedules of reinforcement.     

Devazepide,a CCKA receptor antagonist,impairs the acquisition of conditioned reward and conditioned activity

Cholecystokinin (CCK) is co-localized with dopamine (DA) in portions of the mesolimbic system, where it may facilitate the function of DA through the CCK_A receptor subtype. DA has been implicated in the acquisition of conditioned incentive learning, raising the possibility of a role for endogenous CCK in this learning process. This hypothesis was tested using two complementary behavioral paradigms. Experiment 1 examined the effects of systemic administration of the CCK_A receptor selective antagonist, devazepide (0, 0.001, 0.01, 0.1 mg/kg), on the acquisition of conditioned reward. Two novel levers were presented to drug-free animals in a test session; depression of the conditioned reward (CR) lever produced a light-tone stimulus previously paired with food availability while depression of the non-CR lever produced no programmed consequence. Animals receiving vehicle pretreatment in the food-CS conditioning sessions responded more frequently on the CR lever during the test session. However, pre-treatment with devazepide (0.1 mg/kg but not 0.001 or 0.01 mg/kg) in the conditioning sessions blocked the acquisition of conditioned reward. In contrast, experiment 2 showed that the development of conditioned reward was not affected by similar administration of the CCK_B selective antagonist, L-365,260 (0, 0.001, 0.01 or 0.1 mg/kg). The possibilities that devazepide (0.1 mg/kg) impaired the development of conditioned reward by decreasing the amount of food consumed or by inducing a conditioned taste aversion to the food were ruled out in experiments 3 and 4. The effects of devazepide on the acquisition of conditioned activity induced by amphetamine were assessed in experiment 5. During four conditioning sessions, rats received devazepide (0, 0.001, 0.01, 0.1 or 1.0 mg/kg) treatment prior to amphetamine-environment pairings. The conditioned activity effect was demonstrated if on the subsequent drug-free test day the environment alone elicited increased locomotion. Devazepide (0.1 or 1.0 mg/kg) attenuated the development of conditioned activity. Together, these results provide converging evidence that intact CCK_A function may be necessary for the development of conditioned incentive learning.     

CCKB antagonists protect against anxiety-related behaviour produced by ethanol withdrawal, measured using the elevated plus maze

The effects of the CCK_B antagonists, CAM1028 and CI988 and a CCK_A antagonist, CAM1481, were studied on the anxiety-related behaviour produced by withdrawal from chronic ethanol treatment, using the elevated plus maze. Cessation of chronic ethanol administration produced a profile, in both mice and rats, consistent with increase in anxiety-related behaviour. In mice, SC administration of CAM1028 or CI988 reduced the decrease in the time spent on the open arms, the number of entries into these arms and the increases in the latencies to first open arm entry, after withdrawal from the ethanol treatment. The increases in stretched attend postures and head dips from the closed arms and the central square seen during the withdrawal phase, were also decreased by the CCK_B antagonists, but the decreases in the number of rears and in general activity were unaffected. The doses of CAM1028 and CI988 tested were 0.1 and 1 mg/kg; for some of the withdrawal-induced changes in behaviour only the 1 mg/kg dose was effective. In contrast, the CCK_A antagonist, CAM1481, at the same doses, had little effect on the anxiety-related behaviour produced by withdrawal from chronic ethanol treatment, although it did decrease the changes in the number of rears and the head dipping behaviour. In rats, the majority of the changes produced by withdrawal from chronic ethanol treatment were decreased by CAM1028 at 1 mg/kg, although the decreases in open arm entries, rearing behaviour and in overall activity were unaffected. CAM1028, CI988 and CAM1481 had no effects on the behaviour of control mice or rats in the plus-maze. The results show that CCK_B antagonists were effective in decreasing the majority of the anxiogenic effects of withdrawal from chronic ethanol treatment. Received: 7 May 1997/Final version: 24 October 1997     

Failure of CCK receptor ligands to modify anxiety-related behavioural suppression in an operant conflict paradigm in rats

The effects of cholecystokinin (CCK) receptor ligands were studied in the rat safety signal withdrawal conflict procedure, an operant paradigm sensitive to both anxiolytic and anxiogenic compounds. In this procedure, behavioural suppression of lever pressing for food was induced by the withdrawal of a conditioned signal for safety without the usual presentation of a conditioned signal for danger. The compounds tested were selective CCK-B antagonists [CI-988 (0.01–1 mg/kg SC), L-365,260 (0.004–2 mg/kg IP) and LY 262,691 (0.001–1 mg/kg SC)], CCK-B agonists [CCK-4 (0.01–1 mg/kg SC) and BC 264 (0.004–1 mg/kg IP)] and CCK-A antagonists [devazepide (0.001–1 mg/kg SC) and lorglumide (0.01–1 mg/kg SC)]. None of these drugs induced the expected behavioural effects, i.e. an anxiolytic-like release of the behavioural suppression with CCK-B and, possibly, CCK-A antagonists and/or a further reduction of lever pressing with CCK-B agonists, indicative of an anxiogenic-like potential. In contrast, the established anxiolytic lorazepam (0.06–0.25 mg/kg IP), as well as diazepam (2 mg/kg IP) and buspirone (0.25 mg/kg SC) used as positive control drugs, released the suppression of pressing for food during the period associated with the safety signal withdrawal, whereas picrotoxin (1 mg/kg IP), used as an anxiogenic control, further reduced responding during this conflict period. The present results contrast with a series of published data suggesting the involvement of CCK processes in anxiety-related behaviour in rodent models such as the elevated plus-maze or the light:dark two compartment test, and in panic disorders in humans. They indicate that the behavioural effects of one category of drugs might vary considerably, depending on the experimental situation. Furthermore, they allow the conclusion that anticipatory anxiety generated by withdrawal of conditioned signals for safety does not involve CCK-related processes.     

Differential role of cholecystokinin receptor subtypes in opioid modulation of ongoing maternal behavior.

Cholecystokinin (CCK) can have effects opposite those of opioids. The present study was undertaken to determine whether peripheral injections of antagonists of the CCK1 receptor (lorglumide) and the CCK2 receptor (L-365,260) can influence the effects of morphine on maternal behavior during lactation. A total of 110 female Wistar rats were tested on days 5 and 6 postpartum. Groups were randomly assigned to morphine vehicle (MV-SC) + saline (S-IP), MV + lorglumide (LOR: 1.0 or 10.0 mg/kg), MV + L-365,260 (10 mg/kg), morphine chlorhydrate (MC: 7.0 mg/kg) + S, MC + LOR (1.0 or 10.0 mg/kg), and MC + L-365,260 (1.0 or 10 mg/kg). Maternal behavior testing was started 30 min after the injections, at which time pups were placed in the home cage of their mother. Latencies for retrieval, grouping, and crouching responses were scored. The results show that both lorglumide and L-365,260 potentiated the MC-induced inhibition of maternal behavior. In addition L-365,260 treatment alone inhibited maternal behavior. Blockade of both the CCK1 and CCK2 receptors potentiated the morphine-induced disruption of maternal behavior, while CCK2 antagonism alone also inhibited this behavior. The results suggest that CCK antagonism of opioid-induced disruption of maternal behavior occurs due to the action of CCK on both CCK1 and CCK2 receptor subtypes.     

Characterization of CCK receptors in a novel smooth muscle preparation from the guinea-pig stomach by use of the selective antagonists CI-988, L-365,260 and devazepide.

1. The cholecystokinin receptors mediating motor responses in a novel smooth muscle preparation from the corpus region of the guinea-pig stomach have been characterized by use of five agonist peptides and the antagonists CI-988, L-365,260 and devazepide. 2. Mucosa-denuded strips of circular muscle were contracted in a concentration-dependent manner by the five cholecystokinin (CCK)-related peptides CCK-8S, pentagastrin, gastrin-I, CCK-8US and CCK-4. 3. CI-988 was a powerful antagonist of the response to pentagastrin with an affinity (pKB = 9.49) similar to that obtained in CCKB receptor binding assays. With CCK-8S as the agonist, CI-988 was approximately 1000 fold less powerful as an antagonist. 4. Devazepide powerfully blocked responses to CCK-8S with an affinity (pKB = 9.54) that was in agreement with reported functional data obtained in pancreatic amylase secretion studies, a system exhibiting CCKA receptor activity. Devazepide displayed lower affinity against pentagastrin than against CCK-8S. 5. CI-988 blocked responses to pentagastrin in an insurmountable manner in the presence of 3 nM devazepide; a concentration previously shown to block the CCKA receptor. The nature of the antagonism observed with L-365,260 was unaltered by the presence of devazepide. 6. The guinea-pig stomach corpus smooth muscle preparation contains both subtypes of CCK receptor and will be useful as a pharmacological tool for investigating the functional effects of novel CCK ligands.     

Differential involvement of CCK-A and CCK-B receptors in the regulation of locomotor activity in the mouse

The influence of the CCK-A antagonist devazepide and the CCK-B/gastrin antagonist L-365,260 on the locomotor activity of mice was studied. Devazepide and L-365,260 had opposite effects on spontaneous locomotor activity, and on caerulein- and apomorphine-induced hypomotility in the mouse. Devazepide in high doses (0.1-1 mg/kg IP) reduced spontaneous motor activity, whereas L-365,260 at a high dose (1 mg/kg IP) increased the activity of mice. Devazepide (0.1-10 micrograms/kg) moderately antagonized the sedative effect of apomorphine (0.1 mg/kg SC) and caerulein (25 micrograms/kg SC), whereas L-365,260 (1-10 micrograms/kg) significantly potentiated the actions of dopamine and CCK agonists. Concomitant administration of caerulein (15 micrograms/kg SC) and apomorphine (0.1 mg/kg SC) caused an almost complete loss of locomotor activity in the mouse. Devazepide and L-365,260 (0.1-10 micrograms/kg) were completely ineffective against caerulein-induced potentiation of apomorphine hypomotility. Devazepide in high doses (0.1-1 mg/kg), reducing the spontaneous motor activity of mice, counteracted the motor excitation induced by d-amphetamine (5 mg/kg IP). The CCK agonist caerulein (100 micrograms/kg SC) had a similar antiamphetamine effect. Devazepide (1-100 micrograms/kg) and L-365,260 (1 micrograms/kg) reversed completely the antiamphetamine effect of caerulein. The results of present study reflect apparently distinct role of CCK-A and CCK-B receptors in the regulation of motor activity. The opposite effect of devazepide and L-365,260 on caerulein- and apomorphine-induced hypolocomotion is probably related to the antagonistic role of CCK-A and CCK-B receptor subtypes in the regulation of mesencephalic dopaminergic neurons. The antiamphetamine effect of caerulein is possibly linked to the stimulation of CCK-A receptors in the mouse brain, whereas the blockade of both subtypes of the CCK-8 receptor is involved in the antiamphetamine effect of devazepide.     

The cholecystokinin-B receptor antagonist CI-988 failed to affect CCK-4 induced symptoms in panic disorder patients

The effects of the cholecystokinin-B (CCK-B) receptor antagonist CI-988 on symptoms elicited by the cholecystokinin tetrapeptide (CCK₄) were studied in DSM-IIIR patients with panic disorder. The study employed a double-blind, two-period incomplete block design. Patients (n = 14) received two different dosages of CI-988 (50 mg or 100 mg) or placebo 2 h prior to an IV bolus injection of CCK₄ (20 μg) on two separate occasions. The primary efficacy parameter was the total intensity score on the Panic Symptoms Scale (PSS). Secondary parameters were the number of panic symptoms, time to and occurrence of the first panic symptoms, duration of symptoms, intensity of apprehension and the percentage of patients who did not have a panic attack. The PSS failed to show a statistically significant treatment effect on any of these outcome measures. The average panic rate was 50%, 14.3% and 37.5% after placebo, 50 and 100 mg CI-988, respectively. The differences in panic rate were not statistically significant. The results of this study suggest that CI-988 in doses up to 100 mg is not effective in reducing symptoms of panic anxiety induced by CCK₄. Received: 13 May 1996/Final version: 27 September 1996     

Opposite role of CCKA and CCKB receptors in the modulation of endogenous enkephalin antidepressant-like effects

Systemic administration of RB 101, a complete inhibitor of the enkephalin degrading enzymes, has been reported to induce naltrindole-reversed anti-depressant-like effects in the conditioned suppression of motility (CSM) test in mice. The selective CCK_B antagonist L-365,260 also elicits the same naltrindole-blocked responses on CSM. The aim of this study was therefore to investigate the possible modulation of RB 101 induced behavioral responses by activation or blockade of CCK receptors. Thus, the effects induced by RB 101 administered alone or associated with an ineffective dose of a selective CCK_B agonist (BC 264), a CCK_B antagonist (L-365,260) or a CCK_A antagonist (L-364,718), were evaluated on the CSM in mice. RB 101 alone decreased the stress-induced loss of motility, as previously reported. The antidepressant-like effect of RB 101 was potentiated by L-365,260, and suppressed by BC 264 and to a lesser extent by L-364,718. The facilitatory effect induced by L-365,260 on RB 101 responses was blocked by the delta selective antagonist naltrindole. All these effects occurred only in shocked animals. The present results suggest that the activation of CCK_A and CCK_B receptors by endogenous CCK, could play an opposite role in the control of behavioral responses induced by endogenous enkephalins. Delta opioid receptors seem to be selectively involved in this interaction.     

Effects of S-0509, a novel CCKB/gastrin receptor antagonist, on acid secretion and experimental duodenal ulcers in rats

Background:

S-0509, 2-[(tert-butoxycarbonylmethyl) [(m-(carboxy-phenyl)-ureidomethyl-carbonyl]] aminobenzo phenone, was developed as a potent and selective CCK_B/gastrin receptor antagonist that does not affect the central nervous system.

Methods:

We evaluated the effects of S-0509 on gastric acid secretion and duodenal ulcerogenic and healing responses in rats comparing it with L-365,260, another CCK_B/gastrin receptor antagonist.

Results:

S-0509 (0.1~10 mg/kg, i.d.) was able to dose-dependently decrease basal acid secretion and inhibit the acid secretory responses induced by both pentagastrin (60 μg/kg/h, i.v.) and peptone (10%, i.g.) but not histamine (4 mg/kg/hr, i.v.) or carbachol (60 μg/kg/h, i.v.). L-365,260 (10 and 30 mg/kg, i.d.) caused only partial a suppression of the acid secretory response to pentagastrin but not to other stimuli, including peptone treatment. On the other hand, a duodenal ulcerogen, mepirizole (200 mg/kg, s.c.) caused an increase in acid secretion and resulted in penetrating ulcers in the proximal duodenum, and these ulcers gradually healed over 3 weeks. S-0509 significantly inhibited both the acid secretory (> 1.0 mg/kg, i.d.) and ulcerogenic (> 3 mg/kg, p.o.) responses induced by mepirizole when it was given as a pre-treatment. It also promoted significantly the healing of these ulcers (> 3 × 2 mg/kg, p.o.) when it was given twice daily for 14 days. In contrast, L-365,260 (30 mg/kg) tended to reduce the severity of mepirizole-induced duodenal ulcers, with a slight inhibition of acid secretion, but it caused no influence on the healing response of these ulcers.

Conclusion:

These results confirmed that S-0509 is a selective CCK_B/gastrin receptor antagonist with potent antisecretory action in vivo conditions, and further demonstrated that this agent not only prevents the development of duodenal ulcers but also shows healing promoting action on duodenal ulcers, probably through the blockade of CCK_B/gastrin receptors.

     

Effect of CCK receptor antagonists on the antinociceptive, reinforcing and gut motility properties of morphine.

1. The ability of a selective CCKA receptor antagonist PD 140548 and a selective CCKB receptor antagonist CI-988 (formerly PD 134308) to modulate the various in vivo properties of morphine was investigated in the rat. 2. PD 140548 dose-dependently (0.001-1.0 mg kg-1, i.p.) antagonised the development of conditioned place preference to morphine (2.0 mg kg-1, s.c.). In contrast, CI-988 (0.01-1.0 mg kg-1, i.p.) did not affect this morphine-induced behaviour. Neither of the CCK receptor antagonists blocked or generalised to the morphine (3.0 mg kg-1, i.p.) discriminative stimulus. 3. CI-988 (0.001-10.0 mg kg-1, s.c.) at doses of 0.05 and 0.1 mg kg-1 (s.c.), potentiated the antinociceptive action of a threshold dose of morphine (5.0 mg kg-1, i.p.) in a radiant heat model of acute nociception, the rat tail flick test. Furthermore, at 0.01 mg kg-1 it potentiated the antinociceptive action of morphine (3.0 mg kg-1) during the acute phase of the rat paw formalin test. And at doses of 0.01 and 0.1 mg kg-1 it also potentiated the antinociceptive action of morphine (1.0 mg kg-1) during the tonic phase of the formalin test. However, in both models, higher doses of CI-988 were ineffective. In contrast, PD 140548 (0.001-10 mg kg-1, s.c.) was only active at a dose of 1.0 mg kg-1 (s.c.) and only in the tonic phase of the formalin test. Neither CI-988 nor PD 140548 possessed any intrinsic antinociceptive action in either of the tests. Chronic treatment with CI-988 (0.01 mg kg-1, s.c.) prevented the development of tolerance to morphine antinociception (4 mg kg-1, s.c.) following a 6 day period of twice daily injections of morphine escalating from 1 to 16 mg kg-1 (i.p.). 4. Morphine dose-dependently (1-10 mg kg-1, s.c.) reduced the distance travelled by a charcoal meal in the rat intestine. Neither PD 140548 (0.01-1.0 mg kg-1, i.p.) nor CI-988 (0.01-1.0 mg kg-1, i.p.) potentiated or suppressed this inhibitory action of morphine. 5. In conclusion, the results of the present study indicate that CCKA and CCKB receptors modulate different properties of morphine. Thus, whilst a selective CCKA receptor antagonist blocked the rewarding properties of morphine, a selective CCKB receptor antagonist potentiated the antinociceptive action. However, neither compound displayed a potential for modulating the influence of morphine on gastro-intestinal motility. It is suggested that these findings may have important implications for development of CCK receptor antagonists as analgesic adjuncts to the therapeutic use of morphine.