Influences of cholecystokinin and analogues on memory processes

Evidence is reviewed to assign the role of cholecystokinins in the cognitive and memory processes. Rat brain contains about 550 ng of CCK-8. When injected, icv or sc, in doses of less than 100 ng of CCK or caerulein, these peptides prevent experimental amnesia and prolong extinction of the already-learned tasks. Caerulein is nearly 10 times as potent as CCK-8, and the effects of both peptides are long-lasting. Pretreatment with these peptides also prevents scopolamine-induced amnesia, and reverses the ACh depletion in the frontal and temporal cortices as well as in the hippocampus. CCK-8 antagonists in small doses produce complete amnesia, further supporting the hypothesis that endogenous CCK-8 modulates the memory processes in the brain. Neurochemical data suggest participation of the NMDA receptors, protein kinase C, and protein synthesis in the action of CCK-8 and caerulein. Sub-diaphragmatical vagotomy abolishes the memory-enhancing effects of these peptides when administered peripherally. Thus, CCK-8 and caerulein are likely to affect not only the receptors localized in the CNS, but also to stimulate peripheral receptors associated with the vagus. Alternatively, the vagus may be the major pathway for CCK transport from the visceral organs to the brain.     

Errata

The effect of novel potent CCK-8 antagonists on a one-trial passive avoidance response was investigated in the rat. Intracerebroventricular administration of L-364,718 and CR 1409 in doses of 10 ng per rat or more and proglumide in doses of 100 ng per rat or more completely attenuated the passive avoidance response, when examined 24 hr after the injection. The effective doses of these antagonists did not cause any motility change, as tested by an open-field situation at the same period of time after the central administration. The present findings, together with our previous results on an active avoidance response, suggests that endogenous CCK-8 may be involved in memory processes.     

侧脑室注射八肽胆囊收缩素及其受体拮抗剂对吗啡依赖大鼠戒断症状的影响

目的观察侧脑室给予八肽胆囊收缩素(CCK-8)及其受体拮抗剂慢性干预对吗啡依赖大鼠戒断症状的影响,并在体外观察CCK-8对μ阿片受体结合反应的影响,初步探讨CCK-8对吗啡依赖过程的影响及其相关受体机制。方法建立大鼠吗啡依赖及纳络酮催促戒断模型,侧脑室注射CCK-8及CCK1受体拮抗剂devazepide、CCK2受体拮抗剂LY-288,513慢性干预,观察其对戒断症状的影响;应用放射配基结合实验体外检测CCK-8对μ阿片受体结合特征的影响。结果①吗啡注射前10 min侧脑室注射CCK-8和CCK受体拮抗剂devazepide、LY-288,513慢性干预均能降低吗啡依赖大鼠的戒断症状评分,并可明显改善体重下降、跳跃、齿颤、流涎等戒断症状,与戒断组相比差异均有显著性(P<0.01);②10-8～10-6 mol.L-1 CCK-8可以剂量依赖性地抑制大鼠脑组织中μ阿片受体与其配基的结合(P<0.01),降低μ阿片受体结合反应的Bmax值,而对Kd值无影响;且此抑制作用可被CCK1及CCK2受体拮抗剂翻转(P<0.01)。结论 CCK-8及其受体拮抗剂慢性干预均能减轻吗啡依赖大鼠戒断症状;CCK-8通过抑制μ阿片受体与其配基的结合,降低μ阿片受体的Bmax值,发挥其"抗阿片作用"。     

CCK-A and CCK-B selective receptor agonists and antagonists modulate olfactory recognition in male rats

Modulation of learning and memory is one of the physiological roles that the neuropeptide cholecystokinin (CCK-8) may play. We have used a behavioural model of olfactory recognition among rats to test this hypothesis and to explore the relationship between CCK-A and CCK-B receptors and memory retention. Adult male rats form a transient memory of a juvenile congenere as indicated by a reduction in the duration of investigatory behaviour upon re-exposure 30 min after an initial exposure, but not when re-exposure is delayed until 120 min afterwards. In the present study, rats were treated after the first contact with various compounds; inhibition and facilitation of olfactory recognition were evaluated as the persistence in investigation 30 min and the decrease in investigation 120 min after pharmacological manipulations, respectively. Systemic injection of CCK-8, of a selective CCK-A agonist, or of non-peptide CCK-B antagonists (CI-988 and LY-262691) enhanced olfactory recognition. In contrast, the CCK-B selective agonist BC 264 and the tetrapeptide CCK-4 both disrupted it. Taken together with previous evidence of the detrimental effect of the non-peptide CCK-A antagonist devazepide on olfactory recognition, these results confirm and extend the hypothesis that there is a balance between CCK-A-mediated facilitative effects and CCK-B-mediated inhibitory effects on memory retention.     

Memory impairments induced by peripherally administered cholecystokinin a-type receptor antagonists in rats

Intraperitoneal injection of cholecystokinin (CCK) A-type receptor antagonists, L-364,718 and CR 1409, caused dose-dependent memory impairments in passive and active avoidance responses and in Morris water pool test in rats. These antagonist effects were significant at a dose of 1 mg/kg, while with proglumide, 50–100 mg/kg were required to produce a similar memory deficit. The results suggest that loss of biologically active CCK octapeptide (CCK-8), not only in the brain but also in the peripheral tissues, causes memory impairmets in rats. © 1992 Wiley-Liss, Inc.     

CCK-8及其受体拮抗剂对吗啡戒断大鼠额叶皮质、尾壳核、海马μ阿片受体的影响

目的通过观察CCK-8及其受体拮抗剂对吗啡戒断大鼠额叶皮质、尾壳核、海马μ阿片受体的影响,初步探讨CCK-8对吗啡戒断症状的影响及其受体机制。方法建立大鼠吗啡慢性依赖及纳络酮催促戒断模型,观察CCK-8及CCK1受体拮抗剂L-364,718、CCK2受体拮抗剂LY-288,513慢性干预对戒断症状的影响,并采用放射配基结合法测定额叶皮质、尾壳核、海马μ阿片受体的结合活性,即受体数量(Bmax)及结合力(Kd)。结果①给予吗啡前腹腔注射CCK-8及CCK受体拮抗剂慢性干预均可减轻吗啡戒断症状;②慢性吗啡作用后,额叶皮质和海马μ阿片受体数量及结合力下降,而尾壳核μ阿片受体数量无变化,仅结合力降低;戒断后,额叶皮质、尾壳核μ阿片受体数量及结合力升高,而海马μ阿片受体数量无变化,仅结合力升高;③CCK-8及其受体拮抗剂慢性干预后,使吗啡戒断大鼠尾壳核μ阿片受体结合力降低、海马μ阿片受体数量增加,但是对额叶皮质μ阿片受体的结合活性无影响。结论 CCK-8及其受体拮抗剂可通过调节μ阿片受体减轻吗啡戒断症状,并具有脑区特异性。     

Bilateral 6-OHDA lesions to the hippocampus attenuate the facilitatory effect of CCK-8 us and caerulein on memory in rats.

The involvement of dopaminergic projection to the hippocampus in the facilitatory effect of cholecystokinin-unsulphated octapeptide (CCK-8 us) and caerulein (CER) on memory motivated affectively was investigated in male rats. CCK-8 us and CER were given subcutaneously at the doses of 10 microg kg(-1)and 0.5 microg kg(-1), respectively, immediately after a single learning trial in a passive avoidance situation, after bilateral 6-OHDA lesions to the dentate gyrus of the hippocampus. In order to protect noradrenergic neurones against destruction by neurotoxin, 30 min before surgery rats were pre-treated intraperitoneally with 25 mg kg(-1)of desmethylimipramine, an inhibitor of noradrenaline uptake. Bilateral 6-OHDA lesions to the hippocampus significantly attenuate the facilitatory effect of CCK-8 us and CER on retention of passive avoidance behaviour evaluated 24 h after the learning trial. Neither, destruction of dopaminergic endings in the hippocampus, nor application of CCK-8 us and CER changed the spontaneous psychomotor activity of rats estimated in an 'open field' test. These results may indicate that the facilitatory effect of CCK-8 us and CER on memory motivated affectively is, in part, mediated by dopaminergic projection from the ventral tegmental area to the dentate gyrus of the hippocampus. 2000 Academic Press@p$hr Copyright 2000 Academic Press.     

Mediation by CCKB receptors of the CCK-evoked hyperaemia in rat gastric mucosa.

1. Cholecystokinin octapeptide (CCK-8) and gastrin-17 augment gastric mucosal blood flow in the rat. The present study examined whether the gastric vasodilator effect of these peptides is mediated by CCKA or CCKB receptors. 2. Intravenous injection of CAM-1481 (1 mg kg-1), a dipeptoid antagonist of CCKA receptors, or CAM-1028, a dipeptoid CCKB receptor antagonist (1 mg kg-1), had no effect on basal gastric mucosal blood flow as determined by the clearance of hydrogen in urethane-anaesthetized rats. 3. Intravenous infusion of CCK-8 or gastrin-17 (8-200 pmol min-1) increased gastric mucosal blood flow in a dose-dependent fashion. The CCKB receptor antagonist, CAM-1028, significantly attenuated the hyperaemic response to CCK-8 and gastrin-17 whereas the CCKA receptor antagonist, CAM-1481, did not antagonize CCK-8 but caused a slight attenuation of the vasodilator response to gastrin-17. 4. The selectivity of the two antagonists was proved by the findings that CAM-1028, but not CAM-1481, inhibited gastric acid secretion evoked by CCK-8 or gastrin-17 (CCKB receptor assay) while CAM-1481, but not CAM-1028, inhibited the CCK-8-induced contraction of guinea-pig isolated gall bladder strips (CCKA receptor assay). 5. These data show that the actions of CCK-8 and gastrin-17 to increase mucosal blood flow in the rat stomach are primarily mediated by CCKB receptors.     

Antagonism of cholecystokinin-like peptides by opioid peptides, morphine or tetrodotoxin

Morphine, beta-endorphin, Met-enkephalin, and Leu-enkephalin antagonized intestinal actions of cholecystokinin octapeptide (CCK-8), caerulein, and pentagastrin in a manner partly suggesting physiologically competitive antagonism. Further, these acidic peptides (CCK-8, caerulein, pentagastrin) were much more sensitive to the actions of opioids than was angiotensin. Tetrodotoxin also caused changes in the concentration-effect curves, but these were different from the shifts due to the opioids and differentiated between CCK-8, caerulein, and pentagastrin. Naloxone did not modify the response to CCK-8 and caerulein, but completely abolished the antagonistic influence of the opioids. The potencies of morphine and the opioid peptides as antagonists of CCK-8, were of nearly the same order of magnitude. This and the presence in gut and brain of both CCK-like and opioid peptides suggests the hypothesis that these two groups of peptides interact on both myenteric and central nervous system receptors, and thus are directly involved in the regulation of both intestinal motility and satiety.     

DOPAMINERGIC PROJECTION TO THE CENTRAL AMYGDALA MEDIATES THE FACILITATORY EFFECT OF CCK-8US AND CAERULEIN ON MEMORY IN RATS

The involvement of dopaminergic projection to the central amygdala in the facilitatory effect of cholecystokinin unsulphated octapeptide (CCK-8US) and caerulein (CER) on memory motivated affectively was investigated in male rats. CCK-8US and CER were administered subcutaneously at the doses of 10 micrograms kg-1and 0.5 microgram kg-1, respectively, immediately after a single learning trial in a passive avoidance situation, after bilateral 6-OHDA lesions to the central amygdala. Bilateral 6-OHDA lesions to the central amygdala totally abolished the facilitatory effect of CCK-8US and CER on retention of passive avoidance behaviour evaluated 24 h after the learning trial. These results may indicate that the facilitatory effect of CCK-8US and CER on memory motivated affectively is mediated by dopaminergic projection from ventral tegmental area to the central amygdala.     

Environmental mimic of receptor interaction: conformational analysis of CCK-15 in solution

CCK-15, a peptide derived from the 115-membered CCK preprohormone, was the object of a comparative conformational analysis by NMR spectroscopy and molecular modeling methods. NMR data in several solvents demonstrate that the propensity of the peptide to fold into a helical conformation is intrinsic, not merely a consequence of the interaction with phosphatidylcholine micelles or with a putative receptor, as suggested by a previous study on CCK-8 (Pellegrini, M.; Mierke, D. Biochemistry 1999, 38, 14775-14783.). The prevailing CCK-15 conformer in a mixture 1,1,1,3,3,3-hexafluoroacetone/water reveals that the residues common to CCK-15 and CCK-8 assume very similar conformations. Our CCK-15 structure is consistent with the model of receptor interaction proposed by Pellegrini and Mierke and discloses possible novel interactions that involve a larger area of the putative receptor. The consensus structure between CCK-15 and CCK-8 shows a good superposition of the side chains of residues 12-14 with crucial moieties of two non-peptidic CCK-A antagonists.     

Cholecystokinin contracts isolated human and monkey iris sphincters; a study with CCK receptor antagonists.

The contractile effects of cholecystokinin (CCK) on iris sphincter and ciliary muscles from monkey and human eyes were studied using an isolated smooth muscle bath. The ability of the CCKA receptor antagonists, lorglumide and loxiglumide, to inhibit CCK-8s-induced contraction was also examined. Various neuropeptides reported to be present in capsaicin-sensitive sensory neurons were also screened for contractile effect. CCK contracted isolated human and monkey iris sphincters at nM concentrations. Both antagonists caused a rightward shift of the dose-response curve for CCK-8s on the monkey iris sphincter. The ciliary muscle from both species failed to contract in response to CCK-8s. Of the eight other neuropeptides screened on the monkey iris sphincter, only [Arg8]vasopressin elicited a weak contraction when used in microM concentrations. These results indicate that the primate iridial sphincter muscle exhibits a high sensitivity to CCK, and that CCKA receptor antagonists effectively block the CCK-induced contraction.     

Preventive effect of cholecystokinin octapeptide on scopolamine-induced memory impairment in the rat

In a passive avoidance response, intraperitoneal administration of scopolamine (0.5 mg/kg) at 15 min before the training trials produced a marked impairment of memory in the rat. However, pretreatment with cholecystokinin octapeptide (CCK-8) either given subcutaneously or intracerebroventriculary (i.c.v.) prevented the scopolamine-induced amnesia. Continuous i.c.v. infusion of CCK-8 (1 ng/day) for 7 days significantly prevented the amnesia. The results support our previous findings that CCK-8 has a protective effect against experimental amnesia in the rat.     

Ethological analysis of cholecystokinin (CCKA and CCKB) receptor ligands in the elevated plus-maze test of anxiety in mice

The literature on the effects of CCK receptor manipulations in animal models of anxiety is rife with inconsistency, and the data subject to a variety of methodological and interpretative difficulties. In the present paper, the effects of a range of CCK receptor ligands on anxiety in male mice have been assessed using an ethological version of the elevated plusmaze test. Compounds selected for study were the agonists, CCK-4 and CCK-8s (12.5–100µg/kg), and the antagonists, devazepide, L-365, 260 and PD 135158 (1.0 µg/kg–1.0mg/kg). CCK-4 failed to produce any significant behavioural effects over the dose range tested, while treatment with the sulphated octapeptide, CCK-8s, induced signs of behavioural inhibition at 100 µ/kg without altering anxiety-related indices. Furthermore, in contrast to the clear anxiolytic profile of diazepam (1 mg/kg), and despite the comprehensive behavioural profiles yielded by ethological analysis, all three CCK receptor antagonists studied (devazepide, L-365, 260 and PD 135158) were found to be without significant effect under present test conditions. Together, present findings provide little support for the involvement of CCK receptor mechanisms in anxiety and, in particular, the form of anxiety evoked in mice by exposure to a plus-maze.     

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.     

Combined dose-ratio analysis of cholecystokinin receptor antagonists, devazepide, lorglumide and loxiglumide in the guinea-pig gall bladder.

1. Interactions between cholecystokinin octapeptide (CCK-8) and CCKA-receptor antagonists derived from benzodiazepines (devazepide) and glutamic acid (lorglumide and loxiglumide) have been examined in an improved bioassay using the guinea-pig, isolated, gall bladder preparation. 2. The presence of CCKB-receptors in the assay was provisionally-ruled out on the basis of the low potency of pentagastrin in the assay. By applying analyses of both agonism and antagonism, pentagastrin was shown to behave as a partial agonist at the CCKA-receptor. 3. Devazepide, lorglumide and loxiglumide behaved as simple competitive antagonists of CCKA-receptors and pKB values of 9.98, 7.59 and 7.07 were estimated, respectively. 4. Application of a combined dose-ratio analysis to the interactions between CCK-8 and combinations of devazepide/lorglumide and devazepide/loxiglumide indicated that these molecules behave as syntopic, competitive, antagonists at the CCKA-receptor. 5. We conclude that the guinea-pig gall bladder assay contains a homogeneous population of CCKA-receptors and offer an explanation for the differences between our results and those obtained recently by Maubach et al. (1991) which were taken as preliminary evidence for CCKA-receptor heterogeneity.     

Effect of intranasally administered cholecystokinin on encoding of controlled and automatic memory processes

RATIONALE: The neuropeptide cholecystokinin (CCK) is present in abundance in the central nervous system, where it is involved in the regulation of a wide range of functions. It also takes part in the modulation of memory processes, but its effect on human memory systems and processes is not yet well understood. OBJECTIVE: The present experiment was conducted to examine the influence of CCK when present during encoding on later controlled and automatic recognition memory processes in humans. MATERIALS AND METHODS: A version of the process dissociation procedure was used to separate the contributions of controlled and automatic memory processes to participants' recognition memory performance. Data were analyzed within a multinomial modeling framework. Participants (N = 64) received either 40 mug CCK-8S or placebo intranasally. The learning and test phases began 30 min after substance application. Behavioral, physiological, and self-report control variables were measured at three points of time during the experiment. RESULTS: Compared to placebo, CCK increased the automatic, familiarity-based recognition memory component, while the parameter representing controlled, retrieval-based processes did not differ between groups. Also, in the exclusion condition of the test phase, the guessing parameter was reduced by CCK. None of the control variables were affected by the peptide. CONCLUSIONS: This result-the enhancement of the automatic recognition memory component when CCK is applied before encoding (and thus present during encoding and retrieval)-complements earlier results indicating that CCK decreases controlled, recollection-based recognition memory when applied during consolidation. The possible neuronal systems and processes mediating these effects are discussed.     

Cholecystokinin-8S increases dynorphin B, aspartate and glutamate release in the fronto-parietal cortex of the rat via different receptor subtypes

The effect of sulphated cholecystokinin-8 (CCK-8S) on extracellular dynorphin B, aspartate, glutamate and GABA levels in the rat fronto-parietal cortex was investigated with in vivo microdialysis. The peptide was infused through the microdialysis probe trying to mimic local CCK-8S release. Basal levels of dynorphin B were around 20pM, aspartate 100nM, glutamate 600nM and GABA 30nM. CCK-8S (10μM) induced a ≈3-fold increase in extracellular dynorphin B, aspartate and glutamate levels, while GABA levels were only slightly increased. The effect of CCK-8S was restricted to the stimulated neocortex. Systemic pretreatment with the CCK_B antagonist, L-365, 260, but not with the CCK_A antagonist, L-364, 718, significantly antagonised the effect of CCK-8S on cortical dynorphin B and aspartate release. However, both CCK_A and CCK_B antagonists inhibited the increase in cortical glutamate levels. Thus, the present results indicate that cortical CCK release exerts a stimulatory modulation on cortical dynorphin B and aspartate release via the CCK_B receptor subtype, and on glutamate release via both CCK_A and CCK_B receptor subtypes. Considering electrophysiological evidence that CCK increases neuronal firing rates in many brain regions, it may be suggested that CCK represents a stimulatory system modulating the function of the neocortex. Received: 25 September 1996 / Accepted: 25 January 1997     

Alzheimer's Disease Drugs: An Application of the Hormetic Dose-Response Model

This article provides an evaluation of the dose-response features of drugs that are intended to improve memory, some of which have been used in the treatment of Alzheimer's disease (AD). A common feature of these drugs is that they act via an inverted U-shaped dose response, consistent with the hormetic dose response model. This article assesses historical foundations that lead to the development of AD drugs, their dose-response features and how the quantitative features of such dose responses affected drug discovery and development, and the successes and possible failures of such agents in preclinical and clinical settings. This story begins about 150 years ago with the discovery of an active agent in the Calabar bean plant called physostigmine, its unfolding medical applications, and its implications for dose-response relationships, memory enhancement, and improved drug discovery activities. The article also demonstrates the occurrence of U-shaped dose responses for memory with numerous endogenous agonists including neurosteroids, various peptides (e.g., vasopressin, CCK-8, neuropeptide Y), and other agents (e.g., epinephrine, antagonists for platelet activity factor and nicotinic receptors), supporting the generalizability of the hormetic biphasic dose response. Finally, the significance of the U-shaped dose response is critical for successful clinical application, since it defines the therapeutic window.