Inhibitory Effect Of CCK-8 Research Articles

Inhibitory Effect of CCK-8 on Methamphetamine-Induced Apoptosis.

To investigate the inhibitory effect of cholecystokinin octapeptide (CCK-8) binding to cholecystokinin 2 receptor (CCK2R) on methamphetamine (METH)-induced neuronal apoptosis, and to explore the signal transduction mechanism of β-arrestin 2 in CCK-8 inhibiting METH-induced neuronal apoptosis. SH-SY5Y cell line was cultured, and HEK293-CCK1R and HEK293-CCK2R cell line were constructed by lentivirus transfection. Small interfering RNA (siRNA) was used to knockdown the expression of β-arrestin 2. Annexin Ⅴ-FITC/PI staining and flow cytometry were used to detect the apoptotic rate of cells, and Western blotting was used to detect the expression of apoptosis-related proteins. The apoptosis of SH-SY5Y cells was induced by 1 mmol/L and 2 mmol/L METH treatment, the number of nuclear fragmentation and pyknotic cells was significantly increased, and the expression of apoptosis-related proteins Bax and cleaved caspase-3 were increased. CCK-8 pre-treatment at the dose of 0.1 mmol/L and 1 mmol/L significantly reversed METH-induced apoptosis in SH-SY5Y cells, and inhibited cell nuclear fragmentation, pyknosis and the changes of apoptosis-related proteins induced by METH. In lentivirus transfected HEK293-CCK1R and HEK293-CCK2R cells, the results revealed that CCK-8 had no significant effect on METH-induced changes of apoptosis-related proteins in HEK293-CCK1R cells, but it could inhibit the expression level of apoptosis-related proteins in HEK293-CCK2R cells induced by METH. The inhibitory effect of CCK-8 on METH-induced apoptosis was blocked by the knockdown of β-arrestin 2 expression in SH-SY5Y cells. CCK-8 can bind to CCK2R and exert an inhibitory effect on METH-induced apoptosis by activating the β-arrestin 2 signal.

Cholecystokinin-8 attenuates methamphetamine-induced inflammatory activation of microglial cells through CCK2 receptor

Methamphetamine (METH) exposure reportedly promotes microglial activation and pro-inflammatory cytokines secretion. Sustained inflammation in abusers of psychostimulant drugs further induces neural damage. Cholecystokinin-8 (CCK-8) is a gut-brain peptide which exerts a wide range of biological activities in the gastrointestinal tract and central nervous system. We previously found that pre-treatment with CCK-8 inhibited behavioural and histologic changes typically induced by repeated exposure to METH. Here, we aimed to estimate the effects of CCK-8 on METH-induced neuro-inflammation, which is markedly characterized by microglia activation and increased pro-inflammatory cytokines production in vivo and in vitro. Moreover, we assessed the subtypes of the CCK receptor mediating the regulatory effects of CCK-8, and the changes in the NF-κB signalling pathway. We found that CCK-8 inhibited METH-induced microglial activation and IL-6 and TNF-α generation in vivo and in vitro in a dose-dependent manner. Furthermore, co-treatment of CCK-8 with METH significantly attenuated the activation of the NF-κB signalling pathway by activating the CCK2 receptor subtype in N9 cells. In conclusion, our findings indicated the inhibitory effect of CCK-8 on METH-induced neuro-inflammation in vivo and in vitro, and suggested the underlying mechanism may involve the activation of the CCK2 receptor, which downregulated the NF-κB signalling pathway induced by METH stimulation.

The sympathoinhibitory effects of systemic cholecystokinin are dependent on neurons in the caudal ventrolateral medulla in the rat

The gastrointestinal hormone CCK inhibits a subset of presympathetic neurons in the rostroventrolateral medulla (RVLM) that may be responsible for driving the sympathetic vasomotor outflow to the gastrointestinal circulation. We tested the hypothesis that the central neurocircuitry of this novel sympathoinhibitory reflex involves a relay in the caudal ventrolateral medullary (CVLM) depressor area. Blood pressure and greater splanchnic sympathetic nerve discharge (SSND) or lumbar sympathetic nerve discharge (LSND) were monitored in anesthetised, paralyzed male Sprague-Dawley rats. The effects of phenylephrine (PE, 10 microg/kg iv; baroreflex activation), phenylbiguanide (PBG, 10 microg/kg iv; von Bezold-Jarisch reflex) and CCK (4 or 8 microg/kg iv) on SSND or LSND, were tested before and after bilateral injection of 50-100 nl of the GABAA agonist muscimol (1.75 mM; n=6, SSND; n=7, LSND) or the excitatory amino acid antagonist kynurenate (55 mM; n=7, SSND) into the CVLM. PE and PBG elicited splanchnic and lumbar sympathoinhibitory responses that were abolished by bilateral muscimol or kynurenate injection into the CVLM. Similarly, the inhibitory effect of CCK on SSND was abolished after neuronal inhibition within the CVLM. In contrast, CCK-evoked lumbar sympathoexcitation was accentuated following bilateral CVLM inhibition. In control experiments (n=7), these agents were injected outside the CVLM and had no effect on splanchnic sympathoinhibitory responses to PE, PBG, and CCK. In conclusion, neurons in the CVLM are necessary for the splanchnic but not lumbar sympathetic vasomotor reflex response to CCK. This strengthens the view that subpopulations of RVLM neurons supply sympathetic vasomotor outflow to specific vascular territories.

Effect of cholecystokinin octapeptide on diacylglycerol-PKC signaling pathway in rat pulmonary interstitial macrophages stimulated by lipopolysaccharide1

To investigate the effect of cholecystokinin octapeptide (CCK-8) on the diacylglycerol-protein kinase C (DAG-PKC) signaling pathway in rat pulmonary interstitial macrophages (PIM) stimulated by lipopolysaccaride (LPS). The PIM from rat lung tissues were isolated using the collagenase digestion method combined with alveolar lavage and pulmonary vessel perfusion. DAG content and PKC activity were measured by radioenzymatic assay. The translocation of PKCzeta was determined by semi-quantitative immunoblot analysis. CCK-8, at high concentrations (1 x 10(-6) - 1 x 10(-5) mol/L), decreased DAG content and inhibited PKC activity and PKCzeta translocation compared with that in rat resting PIM of a control group (P< 0.01). LPS increased DAG content, and promoted PKC activity and PKCzeta translocation (P< 0.01). CCK-8 decreased LPS-induced DAG content and inhibited LPS-induced PKC activity and PKCzeta translocation significantly at 1 x 10(-8) - 1 x 10(-5) mol/L (P< 0.01). This inhibitory effect of CCK-8 could be abrogated partly by proglumide (non-selective CCK receptor antagonist), CR-1409 (selective CCK-A receptor antagonist), and CR-2945 (selective CCK-B receptor antagonist) in a concentration-dependent manner (P< 0.01). CCK-8 was a negative modulator of the DAG-PKC signaling pathway in rat resting PIM, which is very important for maintaining body homeostasis. It significantly inhibited LPS-induced DAG content, PKC activity and PKCzeta translocation in a concentration-dependent manner. The CCK receptor, especially the CCK-A receptor, might play a major role in this process.

Exogeneous and endogenous CCK inhibit ethanol ingestion in Sardinian alcohol-preferring rats

Ethanol ingestion, like food ingestion, stimulates release of the signaling molecule cholecystokinin (CCK) from the small intestine. Here, we investigated the possibility that ethanol-induced CCK release might be a negative-feedback control of ethanol ingestion, similar to its function as part of the mechanism by which ingested food produces meal-ending satiation. We used Sardinian alcohol-preferring (sP) and Marchesian Sardinian (msP) alcohol-preferring rats, two apparently identical substrains that spontaneously ingest pharmacologically relevant amounts of ethanol, as well as their background strain, Wistar (W) rats. We demonstrated that: (1) intraperitoneal (IP), but not intracerebroventricular, injections of 0.5–4 μg/kg CCK-8 produced transient, dose-related reductions in 10% ethanol ingestion; (2) this inhibitory effect of CCK-8 on ethanol intake appeared behaviorally similar to its inhibitory action on ingestion of sucrose solutions; (3) the inhibitory effect of IP CCK-8 on ethanol ingestion occurred without evidence of tolerance when tests were repeated on consecutive days; (4) IP CCK-8 reduced ethanol intake despite simultaneously reducing blood ethanol levels (BALs); and (5) antagonism of CCK 1 receptors with devazepide increased ethanol intake, indicating that endogenous CCK normally limits the size of bouts of ethanol ingestion. These results implicate peripheral CCK in the control of ethanol ingestion in sP and msP alcohol-preferring rats.

Cholecystokinin-Induced Antinociception is Not Blocked by CCK-A or CCK-B Receptor Antagonists

Williams, C. L., G. C. Rosenfeld and T. F. Burks. Cholecystokinin-induced antinociception is not blocked by CCK-A or CCK-B receptor antagonists. Peptides 18(3) 409–414, 1997.—To determine the relative importance of CCK-A, CCK-B, and opioid receptors in mediating the antinociceptive actions of cholecystokinin, we evaluated the actions of selective agonists and antagonists in the mouse hot plate assay. The agonists used were CCK (1–30 nmol ICV), a CCK-A receptor agonist (SNF9019; 0.3–10 nmol ICV), and a CCK-B receptor agonist (SNF9007; 0.3–10 nmol ICV). The antagonists used were the CCK-A receptor antagonist, L364,718 (12.5 nmol ICV), CCK-B receptor antagonist, L365,260 (2.5–25 nmol ICV), and the nonselective opioid receptor antagonist naloxone (1 mg/kg SC). CCK and its receptor-selective analogues, SNF9019 and SNF9007, resulted in antinociception that was blocked by naloxone, but was not antagonized by L364,718 or L365,260. In contrast, in positive control experiments, the inhibitory effects of CCK, SNF9019, and SNF9007 on gastrointestinal propulsion in mice were antagonized by identical ICV doses of L364,718 and L365,260. We conclude that centrally administered CCK produces antinociception in the mouse hot plate assay via opioid receptors, but independent of CCK-A or CCK-B receptors. It is necessary to speculate that other CCK receptors, not antagonized by currently available selective antagonists, may exist.

Central and no-mediated mechanisms are involved in the inhibitory effects of CCK on the chicken cecorectal area

In chickens CCK-8s induces defecation and causes an inhibition of rectal electrical activity (EA) and an increase in cecal motility. In contrast, CCK-4 inhibits the motility of both rectum and ceca. The cecorectal responses to CCK-8s and CCK-4, given intravenously (i.V.), were studied in conscious chickens prepared with electrodes for electromyography; the influence of atropine, phentolamine plus propranolol, hexamethonium and L-NAME on such responses was determined. Atropine and phentolamine plus propranolol did not cause any change in the response to CCK-8s or CCK-4 in the cecorectal area. Hexamethonium only induced a significant decrease in the number of defecations (ND) induced by CCK-8s. L-NAME slightly modified the decrease in rectal EA due to CCK-8s. The effects of intracerebroventricular (i.c.v.) administration of CCK-Ss and CCK-4 were also studied. CCK-8s and CCK-4, given i.c.v., caused, in conscious chickens, a slight decrease in cecal EA, in the 15 minutes following administration. This effect was similar to that seen after i.v. administration of CCK-4. In conclusion, our results suggest that the inhibitory action of CCK on chicken rectum is mediated, at least in part, through nitric oxide release. In addition, nicotinic receptors mediate the increase in the ND caused by CCK-8s. Ganglionic, muscarinic, adrenergic and nitrergic blockade were not able to modify the excitatory cecal response to CCK-8s, which may indicate that the receptor mediating this effect is located on the cecal smooth muscle. Finally, the inhibitory action of i.v. CCK-4 on chicken cecum seems to be centrally mediated, as suggested by the fact that i.c.v. administration of either CCK-8s or CCK-4 induce a similar effect.

Inhibitory effects of cholecystokinin on rat's geniculate activity can be blocked by GABA-antagonists

Cholecystokinin applied iontophoretically as the sulfated octapeptide (CCK-8S) or as highly selective CCKA- and CCKB-agonists induced excitatory as well as inhibitory effects on dorsal lateral geniculate unit activity. Inhibitory effects of CCK could be abolished by administration of GABAergic antagonists, especially bicuculline. Therefore, interneurons seem to be largely excited by CCK, and in this way, they appear to mediate the inhibition of the discharge rate in geniculate relay cells induced by CCK.

The stimulation of cholecystokinin receptors in the rostral nucleus accumbens significantly antagonizes the EEG and behavioural effects induced by phencyclidine in rats.

The influence of cholecystokinin (CCK), bilaterally injected into the rostral nucleus accumbens, on the EEG and behavioural effects induced by phencyclidine (PCP) has been studied in rats. CCK (10 ng) significantly inhibited PCP-induced EEG effects (increase of spectral power with respect to pre-drug tracing; increase of relative power distribution in the slowest frequency bands), and behavioural effects (circling and ataxia). The inhibitory effects of CCK were completely antagonized by 1 ng PD 135-158, a selective CCKB receptor antagonist, but not by lorglumide (1 microgram), a selective CCKA receptor antagonist. Since the effects induced by PCP in rodents have been proposed to be an experimental correlate of the psychotic symptoms it induces in humans, these results indicate that CCK may act as a neuroleptic. They also suggest that CCKB receptors located in the rostral nucleus accumbens may be involved in the neuroleptic-like activity of CCK.

Effect of CCK-8 on myoelectrical activity of the gastrointestinal tract in the conscious miniature pig.

In conscious miniature pigs, with implanted electrodes in the wall of the antrum pylori, duodenum, jejunum, and ileum, the influence of IV infusions of CCK-8 (17.5 and 175 pM/kg/min) on gastrointestinal myoelectrical activity was measured. Although both doses under study induced a decrease in antral spike activity. only the higher dose resulted in an overall decrease in integrated myoelectrical activity. In the ileum both doses augmented spiking activity during the infusion, but inhibited electrical activity after the end of the infusion. No response was observed in the duodenum and jejunum. The experiments demonstrate the overall inhibitory effect of CCK-8 on antral electrical activity and its stimulatory influence on ileal smooth muscle.

Putrescine Uptake in Rat Pancreatic Acini

Polyamines [putrescine (Put), spermidine, and spermine] are normal cellular constituents that can modulate cellular proliferation and differentiation in a number of tissue and cell types. Transport is one of the mechanisms that control intracellular polyamine content. The present investigation explores the influence of cholecystokinin (CCK), other secretagogues [carbachol, bombesin, vasoactive intestinal polypeptide (VIP)], insulin, insulin-like growth factor 1 (IGF-1), and epidermal growth factor (EGF) on Put uptake in rat pancreatic acini. Insulin, IGF-1, and EGF stimulated Put uptake by 30-40%. Insulin did not enhance intracellular metabolism of Put. In contrast, CCK and the other secretagogues inhibited this transport system by 40-50% of control (VIP by 23% only). Further investigations of the inhibitory effect of CCK revealed that the maximal uptake rate of Put (Vmax) shifted from 346 pmol [14C]Put/mg DNA-min (control) to 265 pmol [14C]Put/mg DNA-min (100 pM CCK), whereas the Km was only moderately influenced. Augmented Put efflux as well as increased production of endogenous Put (possibly induced by CCK) did not contribute to this change in transport kinetics. In addition, the inhibition of Put uptake induced by CCK was specific and dose dependent up to 100 pM. CCK at 1,000 pM exerted only minor inhibition (20% of control). Incubation with the Ca-ionophore A 23187 did not influence Put accumulation, whereas treatment with the phorbol ester phorbol 12-myristate-13-acetate led to enhanced Put uptake (30-40%). Pretreatment of the acini with 1 mM ouabain led to a reduction of Put uptake by 43%.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of the satiety effect of cholecystokinin by estradiol

Data obtained from a wide variety of mammalian species indicate that feeding behavior can be influenced by changes in endogenous estrogens and by exogenous estrogenic treatments. The present experiment represents an initial investigation of the hypothesis that the suppression of food intake by estradiol is mediated by an enhancement of the satiety effect of cholecystokinin (CCK). Twenty-four female rats were ovariectomized and implanted either with a 5% estradiol silastic capsule or an empty capsule on the day of surgery. Three weeks later, animals received IP injections of CCK-octapeptide (5.0 or 10.0 μg/kg) or saline after 24-h food deprivation. Food and water intake were measured 60 min after treatment. Although CCK suppressed feeding in all subjects, the effects on food intake were greater in estradiol-treated females. CCK injections also reduced water intake, but there was no interaction between estradiol and CCK on drinking. These findings indicate that the inhibitory effect of CCK on food intake is enhanced in females treated with a physiological dose of estradiol, and suggest that the effects of estradiol on feeding behavior may be mediated by a potentiation of the satiety effect of CCK.

Inhibitory effect of CCK-8 and ceruletide on glutamate-induced rises in intracellular free calcium concentrations in rat neuron cultures

To study the mechanism by which cholecystokinin octapeptide (CCK-8) and its potent analogue, ceruletide, prevent glutamate-induced neuronal cell death in rat neuron cultures, we examined the effect of both peptides on glutamate-induced increases in the intracellular free calcium concentrations ([Ca 2+] i), which are known to be a crucial trigger of the neurodegeneration induced by glutamate. CCK-8 itself did not alter [Ca 2+] i in rat neuron cultures. Glutamate increased [Ca 2+] i in neuron cultures rapidly and markedly. CCK-8 and ceruletide significantly suppressed the increases in [Ca 2+] i induced by glutamate. The maximum inhibitory effects of CCK-8 and ceruletide at 10 −6 M reached 43 and 46% of the response to glutamate, respectively. Gastrin-I and CCK-4 also significantly attenuated the increases in [Ca 2+] i induced by glutamate. The inhibitory effect of CCK-8 was completely blocked by the selective antagonist for CCK-B receptors, (+)L-365,260, but not by (−)L-364,718, which is a selective antagonist for CCK-A receptors. CCK-8 significantly suppressed [Ca 2+] i response to kainate and high concentrations of extracellular K +, but not to N- methyl- d-aspartate . With cultured astrocytes, CCK-8 did not inhibit the increment of [Ca 2+] i induced by glutamate. These findings clearly demonstrated that CCK-8 and ceruletide inhibit glutamate-induced increases in [Ca 2+] i in neuron cultures through CCK-B receptors, suggesting that CCK-8 may participate in the central actions of glutamate.

Gastric motility and food intake in rats after lesions of hypothalamic paraventricular nucleus.

Systemic administration of cholecystokinin (CCK) or LiCl inhibits gastric motility and food intake in rats. Brain stem-projecting oxytocin (OT) neurons in the hypothalamic paraventricular nucleus (PVN) have been proposed to mediate the inhibitory effects of CCK and LiCl on gastric motility and food intake. In the present studies, we found that basal gastric motility was elevated in rats 12-20 h after knife-cut lesions of the PVN; however, this effect disappeared 3 days later. Furthermore, CCK and LiCl inhibited gastric motility at 12-20 h, 3 days, and 3 wk after PVN lesions, although their effects were blunted. Injection of the local anesthetic lidocaine into the PVN had effects similar to acute PVN lesions. In rats with PVN lesions, the inhibitory effects of CCK and LiCl on food intake were indistinguishable from those in sham-lesioned rats. We conclude that the PVN tonically inhibits gastric motility and that it participates in, but is not essential for, the inhibitory effects of CCK and LiCl on gastric motility and food intake in rats.

Cholecystokinin inhibits DNA alkylation induced by N-nitrosobis (2-oxopropyl)amine (BOP) in hamster pancreas

Cholecystokinin (CCK) inhibits pancreatic cancer but not hepatic tumor induction by N-nitrosobis (2-oxopropyl) amine (BOP) in hamsters when administered with or shortly before BOP. In this study, we evaluated the capability of sulfated CCK-8 to inhibit DNA alkylation in the hamster pancreas. We examined the pattern of O 6-methylguanine (G 6-Me) and N 7-methylguanine (G 7-Me) in pancreatic ductal, acinar and liver tissues from Syrian hamsters treated with a single dose of BOP (20 mg/kg s.c.) and with five s.c. injections of CCK-8 (200 pM/kg, 30 min apart). The first CCK injection was given either 90 min before, or together, or 3 h after POP administration. The amount of G 6-Me in liver DNA did not differ significantly. We observed a decrease of G 7-Me in the liver of the group treated with CCK together with POP as compared to POP alone (P < 0.005). Lower amounts of G 6-Me were found in ductal preparations (P < 0.01) of the animals treated with CCK before POP as compared to POP alone. CCK also modified the pattern of alkylation in the acinar tissue, but without a clear relationship with the timing of adminstration. The results suggest that the inhibitory effect of CCK-8 on pancreatic carcinogenicity of BOP could be related to its capability to modify DNA alkylation by yet unknown mechanisms.

Intracellular mechanisms involved in short-term regulation of net protein synthesis in pancreatic acini

The mechanisms regulating the net synthesis of digestive enzymes during short-term stimulation by agonists were examined in pancreatic acini isolated from the rat. Dispersed pancreatic acini were stimulated for up to 60 min with various concentrations of cholecystokinin octapeptide (CCK-OP), carbachol, A23187, 4β-phorbol 12-myristate 13-acetate (PMA). The effects of these agonists on net protein synthesis was determined by measuring the incorporation of [ 3H]leucine or [ 35S]methionine into protein. Carbachol, PMA, A23187 and concentrations of CCK-OP of 100 pM and greater caused inhibition of protein synthesis. Fluorography of [ 35S]methionine labeled acinar cell proteins separated by one-dimensional SDS-polyacrylamide gel electrophoresis demonstrated that the agonists inhibited the synthesis of the digestive enzymes. Northern blot analysis using cDNA probes revealed that CCK-OP, carbachol and PMA did not alter the cellular content of amylase, lipase and elastase mRNA. The protein kinase C inhibitors 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) and staurosporine failed to reverse the inhibitory effects of CCK-OP, carbachol and PMA on protein synthesis. CCK-OP and PMA activated phospholipase A (PLA) which liberated lysophosphatidylcholine (LPC) and free fatty acids from membrane phosphatidylcholine. Exogenously added PLA 2 ( Naja naja venom) inhibited protein synthesis and increased LPC to a similar extent as CCK and PMA. The results suggest that the inhibitory effects of CCK and carbachol on net protein synthesis are due to their effects on intracellular calcium and PLA-mediated breakdown of phosphatidylcholine rather than protein kinase C activation.

P-454 - Inhibitory effect of CCK-8 and ceruletide on neuronal cell death induced by glutamate and its possible mechanism

P-454 - Inhibitory effect of CCK-8 and ceruletide on neuronal cell death induced by glutamate and its possible mechanism

CCK-8 decreases food intake and gastric emptying after pylorectomy or pyloroplasty.

Specific binding sites for cholecystokinin (CCK) in the gastrointestinal tract of the adult rat are limited to the gastroduodenal region and are concentrated in the circular muscle of the pyloric sphincter. To determine the relationship of these pyloric muscle binding sites to the inhibition by CCK of food intake and of gastric emptying, these inhibitory effects of CCK were investigated in rats that had the pyloric sphincter surgically removed or that had the pyloric sphincter contractile mechanism damaged by a pyloroplasty procedure. CCK-8 decreased food intake and gastric emptying significantly in rats after pylorectomy or pyloroplasty. This demonstrates that an intact pyloric sphincter is not necessary for these inhibitory effects in rats. Because we found autoradiographic evidence for CCK receptors near the gastroduodenal anastomosis, however, the results suggest either that these receptors mediated the inhibition of food intake and emptying by CCK-8 or that these effects depend on CCK receptors in other locations.

Naloxone Potentiation of Effects of Cholecystokinin and Lithium Chloride on Oxytocin Secretion, Gastric Motility and Feeding

Neurohypophyseal secretion of oxytocin (OT) in response to dehydration, hypovolemia, restraint, and parturition in rats is known to be potentiated by the opioid antagonist naloxone. The present studies demonstrated that stimulation of OT secretion by systemic injections of cholecystokinin (CCK) and lithium chloride (LiCl) likewise are potentiated by naloxone pretreatment. Moreover, the inhibitory effects of CCK and LiCl on gastric motility and feeding similarly were enhanced by naloxone. Because neurohypophyseal hormone secretion and inhibition of gastric motility are known to be mediated by oxytocinergic neurons projecting from the paraventricular nucleus of the hypothalamus, this parallel potentiation by naloxone of CCK- and LiCl-induced effects on OT secretion, gastric motility, and food intake suggests that one of the pathways involved in the central control of feeding behavior also may be oxytocinergic. These findings therefore provide evidence in support of an important role of endogenous opioid peptides in regulating OT secretion in a diffuse neuronal system that mediates an integrated neuroendocrine, autonomic, and behavioral response to CCK, LiCl, and perhaps other treatments that similarly affect ingestive behavior in rats.

A behavioral pharmacological study on CCK-8 related peptides in mice

The effects of CCK-8, ceruletide, their non-sulfated forms and CCK-4 on locomotor activity and rearing in mice were examined. CCK-8 and ceruletide, but not their non-sulfated forms and CCK-4, significantly inhibited the behavioral parameters dose-dependently. The inhibitory effects of CCK-8 and ceruletide were similar, but ceruletide acted more slowly and its inhibitory effect continued much longer than CCK-8, suggesting a difference in stability with the chemical structure. The antagonistic effects of ceruletide on behavioral changes induced by DA agonists were also examined. Peripherally injected ceruletide antagonized both methylphenidate- and methamphetamine-induced hyperactivity in mice dose-dependently, whereas it had no dose-related antagonistic effect on methylphenidate-induced stereo-typed behavior. Ceruletide also significantly inhibited apomorphine-induced hyperactivity when injected peripherally. However, no obvious dose-response relationship was observed in either intensity or duration of inhibitory action of ceruletide. These findings suggest that ceruletide does not interfere with dopaminergic transmission due to the blockade of postsynaptic DA receptors in the brain. In conclusion, peripheral injection of CCK-8 and ceruletide may affect directly or indirectly dopamine function producing behavioral changes that resemble those of neuroleptics in some respects.