Caerulein, a cholecystokinin-related peptide, depresses somatic function via the vagal afferent system

Mechanisms of cancer-related fatigue

Cancer-related fatigue (CRF) is one of the most prevalent symptoms patients with cancer experience, both during and after treatment. CRF is pervasive and affects patients' quality of life considerably. It is important, therefore, to understand the underlying pathophysiology of CRF in order to develop useful strategies for prevention and treatment. At present, the etiology of CRF is poorly understood and the relative contributions of the neoplastic disease, various forms of cancer therapy, and comorbid conditions (e.g., anemia, cachexia, sleep disorders, depression) remain unclear. In any individual, the etiology of CRF probably involves the dysregulation of several physiological and biochemical systems. Mechanisms proposed as underlying CRF include 5-HT neurotransmitter dysregulation, vagal afferent activation, alterations in muscle and ATP metabolism, hypothalamic-pituitary-adrenal axis dysfunction, circadian rhythm disruption, and cytokine dysregulation. Currently, these hypotheses are largely based on evidence from other conditions in which fatigue is a characteristic, in particular chronic fatigue syndrome and exercise-induced fatigue. The mechanisms that lead to fatigue in these conditions provide a theoretical basis for future research into the complex etiology of this distressing and debilitating symptom. An understanding of relevant mechanisms may offer potential routes for its prevention and treatment in patients with cancer.Disclosure of potential conflicts of interest is found at the end of this article.

Ceruletide, a CCK-like peptide, attenuates dopamine release from the rat striatum via a central site of action

Ceruletide (CLT), a cholecystokinin-like peptide was given subcutaneously or via the perfusate to rats to clarify the site of action (peripheral vs. central location) of CLT, using in vivo microdialysis techniques. Striatal dopamine (DA) release induced by haloperidol (HPD) was significantly inhibited by subcutaneously administered CLT (160 micrograms/kg) when given with a perfusate containing 15 mM K+. Subdiaphragmatic vagotomies failed to block the inhibitory effect of CLT. CLT (10(-15)-10(-11) M) locally applied, via a dialysis tube, produced an inhibitory effect on HPD-induced DA release in the striatum in a dose-dependent manner. The inhibitory effect of CLT given subcutaneously on DA release was antagonized by both locally applied proglumide and systemically administered L-365,260. These findings suggest that systemically administered CLT can directly act on the striatal neurons via CCK-B receptors and produce an inhibitory effect on DA release in the striatum under appropriate depolarization.

Changes in motor activity and forebrain [propionyl-3H]propionylated-CCK-8 binding in mice after repeated administration of drugs affecting cholecystokinin receptors

The effects of acute or repeated treatment of male albino BKW mice with caerulein, a cholecystokinin octapeptide (CCK-8) agonist, and with devazepide (MK-329) and L-365,260, antagonists at CCKA ('peripheral') and CCKB ('central') receptors respectively, on motor activity and [propionyl-3H]propionylated-CCK-8 ([3H]pCCK-8) binding were studied. Acute treatment with a large dose of caerulein (100 micrograms/kg s.c.) suppressed motor activity (line crossings and rearings) whereas devazepide (2 mg/kg i.p.) had the opposite action. L-365,260 (2 mg/kg i.p.) increased only the number of rearings. Tolerance developed to the locomotor effects of caerulein and devazepide when these same doses were administered once daily (caerulein) or twice daily (devazepide) for 10 days. Twice daily administration of L-365,260 (2 mg/kg) for 10 days did not significantly alter the locomotor activity of mice. The sedative effect of caerulein (20 micrograms/kg s.c.) was markedly reduced in mice receiving repeated injections of either a larger amount of caerulein (100 micrograms/kg) or devazepide but not after L-365,260. The stimulant effect of (+)-amphetamine (2 mg/kg s.c.) on motor activity was increased by subchronic administration of either devazepide or caerulein, but not by L-365,260. All three compounds (caerulein, devazepide and L-365,260) increased the number of [( 3H]pCCK-8 binding sites in mouse forebrain but the increase was only significant after L-365,260. The effects of long-term treatment with caerulein are probably related to the stimulation of CCKA receptors, whereas the paradoxically similar action of devazepide may be linked to the blockade of both subtypes of the CCK-8 receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-lasting inhibitory action of caerulein on climbing fiber system in the cerebellum of the rat

Caerulein caused a marked decrease in levels of guanosine 3',5'-cyclic monophosphate (cGMP) in the cerebellum in rats. This effect was observed to be dose-dependent after the intraperitoneal administration of caerulein for doses over 20 micrograms/kg and lasted for about 4 hr in doses of 100 micrograms/kg. However, in vagotomized rats, caerulein failed to alter the level of cGMP in the cerebellum. Caerulein suppressed harmaline-induced increases in cGMP in the cerebellum for more than 30 hr. In contrast, the increases in levels of cGMP in the cerebellum, induced by treatment with methamphetamine, apomorphine and picrotoxin, were not inhibited by pretreatment with caerulein. These results suggest that the peripheral administration of caerulein can inhibit the activity of climbing fibers for a long period of time in the cerebellum of the rat through the stimulation of the abdominal vagus nerves.

Effect of cerulein on in vivo release of acetylcholine from the rat striatum

An effect of cerulein on in vivo release of acetylcholine (ACh) from the rat striatum was examined by means of intracerebral dialysis. Intraperitoneal administration of cerulein (25-200 micrograms/kg) enhanced a spontaneous release of ACh in a dose-dependent manner. Intraperitoneal administration of cerulein (100 micrograms/kg) also enhanced the K+-evoked (30 mM) release of ACh. Bilateral subdiaphragmatic vagotomy reduced the increase of both K+-evoked and that of spontaneous release of ACh induced by cerulein administration. Pretreatment with haloperidol (0.5 mg/kg, i.p.) had no effect on increase in spontaneous release of ACh brought about by cerulein administration (100 micrograms/kg, i.p.). These results suggested that peripherally administered cerulein stimulated striatal cholinergic neurons, that its stimulatory effect on striatal ACh release was not mediated by striatal dopamine D2 receptors and that the action of cerulein was, in part, mediated via vagal afferent impulses.

Inhibitory effect of ceruletide on haloperidol-induced catalepsy in rats

Ceruletide (CLT: 160 micrograms/kg, SC) produced a relatively long-lasting inhibition of haloperidol (HPD: 2 mg/kg, PO) catalepsy in rats. Neither bilateral vagotomies nor hypophysectomy abolished the anticataleptic effect of CLT. However, (-)-L-364,718 and proglumide blocked the effect of CLT. CLT (160 micrograms/kg) significantly inhibited HPD (2 mg/kg)-induced increase in dopamine (DA) release from the rat striatum. This effect of CLT was also antagonized by proglumide. These results suggest that CLT (160 micrograms/kg) primarily acts on cholecystokinin-A receptor in the brain, exerts some modulatory influence on HPD binding to striatal DA receptors via unknown neural pathways and, consequently, inhibits HPD catalepsy.

Ceruletide suppresses endogenous dopamine release via vagal afferent system, studied by in vivo intracerebral dialysis

Ceruletide, a cholecystokinin-related decapeptide, has been reported to have some therapeutic effects on tardive dyskinesia and other involuntary movement disorders. In order to clarify the effects of ceruletide on dopaminergic activity in the rat striatum, we measured the release of endogenous dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) after intraperitoneal administration of ceruletide (2, 20, 200 micrograms/kg) using in vivo intracerebral dialysis techniques. After administration of ceruletide (200 micrograms/kg), extracellular DA decreased significantly (P less than 0.05) for 0.5-3 h. The maximal reduction of extracellular DA (by 29%) was observed for 2-2.5 h. Extracellular DA was reduced (21%) by 20 but not by 2 micrograms/kg ceruletide. DOPAC and HVA did not change at any dose of ceruletide. We also demonstrated that bilateral subdiaphragmatic vagotomy blocked this inhibitory effect of ceruletide on DA release. These findings indicate that peripherally administered ceruletide suppresses endogenous DA release via the vagal afferent system.

An analysis of cholecystokinin-induced increase in acetylcholine output from cerebral cortex of the rat

The effect of colecystokinin (CCK-8) on the release of ACh from the cerebral cortex was studied in urethane-anaesthetized rats with the cortical cup technique. The increase in output of ACh brought about by the administration of CCK-8 1.5 micrograms/kg (i.p.) was prevented by pretreatment with haloperidol (1 mg/kg i.p.) and by lesions of the nucleus basalis magnocellularis and substantia nigra but it was reduced only slightly by bilateral vagotomy. Conversely, none of the treatments abolished the decrease in output of ACh brought about by CCK-8 at a dose of 10 micrograms/kg (i.p.). Local injection of CCK-8 into the nucleus basalis had no effect. Therefore, CCK-8 appears to increase cortical cholinergic activity by indirectly stimulating the cholinergic neurones of the nucleus basalis through dopaminergic neurones.

Comparison of motor depressant effects of caerulein and N-propylnorapomorphine in mice

The motor depressant effects of caerulein and N-propylnorapomorphine (NPA) were compared in male mice. Caerulein (1-50 micrograms/kg SC) in a dose dependent manner depressed the exploratory activity, whereas NPA in lower doses (0.5-10 micrograms/kg SC) decreased the motor activity, but in higher doses (over 50 micrograms/kg) had stimulating effect on the exploratory behavior. In mice selected according to their motor response after administration of 100 micrograms/kg NPA to weak and strong responders, the low dose of NPA (1 microgram/kg) similarly suppressed motor activity in both selected groups, while the effect of caerulein (2 micrograms/kg) was apparently higher in weak responders. Destruction of catecholaminergic terminals by 6-hydroxydopamine (60 micrograms ICV) reversed completely the motor depressant effect of NPA, whereas degeneration of serotoninergic terminals (5,7-dihydroxytryptamine 60 micrograms ICV or p-chloroamphetamine 2 X 15 mg/kg IP) enhanced the sedative effect of NPA. The motor depressant effect of caerulein remained unchanged after lesions of monoaminergic terminals in forebrain. Subchronic haloperidol (0.25 mg/kg IP, twice daily during 14 days) treatment, reducing significantly the density of high-affinity dopamine2- and serotonin2-receptors, decreased the motor depressant action of caerulein. It is possible that motor depressant effect of caerulein, differently from the action of NPA, is mediated through the high-affinity dopamine2-receptors and in lesser extent through the high-affinity serotonin2-receptors.

Different targets involved in the effect of cholecystokinin on respiration

Respiratory and cardiovascular effects of intravenous administration of cholecystokinin octapeptide (CCK-8) (0.3 to 20 micrograms/kg) were compared in different cat preparations: chronically implanted and decerebrate vagotomized or decerebrate non-vagotomized. In all preparations CCK-8 induced an immediate drop in blood pressure (between 44.0 and 58.1%) and heart rate (between 25.1 and 62.5%) which had completely recovered 5 min after the end of the injection. During cardiovascular modifications tidal volume decreased in non-vagotomized cats and was associated with a decrease in respiratory frequency in decerebrate cats and with an increase in respiratory frequency in chronically implanted animals. Only an increase of tidal volume occurred in vagotomized cats. After cardiovascular conditions had returned to normal, tidal volume remained significantly modified: decreased in chronically implanted (-39%), in decerebrate non-vagotomized (-34%) and increased in vagotomized cats (+27.7%). However, modifications of frequency persisted only in chronically implanted preparations (+69.2%). Recovery from respiratory modifications occurred 30 min after injection. These effects were not produced by systemic administration of non-sulfated CCK-8. The cardiorespiratory modifications induced by CCK-8 are discussed in relation to the different targets which can be reached by the octapeptide in each preparation.

Antistereotypic effects of cholecystokinin octapeptide (CCK-8), ceruletide and related peptides on apomorphine-induced gnawing in sensitized mice

Cholecystokinin octapeptide (CCK-8), ceruletide (caerulein, CER) and 7 analogues of ceruletide, were studied for antagonism of stereotyped gnawing and cage climbing, induced by apomorphine in mice that were sensitized by either administration of scopolamine (1 mg/kg, s.c., 15 min before) or teflutixol (5 mg/kg, i.p., 4 days before). Three neuroleptics (haloperidol, trifluoperazine and teflutixol) served as reference drugs. All peptides reduced or abolished the fully developed gnawing activity and were (on a molar basis) often more potent than the reference drugs. In contrast to the neuroleptics, the peptides did not antagonize the climbing activity. In mice pretreated with scopolamine, the peptides were more potent than in mice pretreated with teflutixol. With the neuroleptics, the influence of the sensitizing pretreatments was converse, and this applied also to the anticlimbing effect. The relationships between peptide structure and antistereotypic effect were different from those found previously in a study on the antagonism of gnawing induced by methylphenidate.

CONCLUSIONS

CCK-like peptides are able to antagonize stereotyped behaviour caused by direct and indirect dopaminergic agonists; the mechanism of action of the peptides differs from that of the reference neuroleptics.

Caerulein and its analogues: neuropharmacological properties

The decapeptide from the frog Hyla caerulea, caerulein (caerulein diethylammonium hydrate, ceruletide, CER) is chemically closely related to the C-terminal octapeptide of cholecystokinin (CCK-8). Like CCK-8, CER and some of its analogues produce many behavioural effects in mammals: inhibition of intake of food and water; antinociception; sedation; catalepsy; ptosis, antistereotypic, anticonvulsive and tremorolytic effects; inhibition of self-stimulation. Effects of CER in man comprise sedation, satiety, changes in mood, analgesia and antipsychotic effects. A modulation of central dopaminergic functions appears to be one possible mechanism of CER and its analogues. A common denominator for all effects of CER is, at present, not evident.

Ceruletide, ceruletide analogues and cholecystokinin octapeptide (CCK-8): effects on isolated intestinal preparations and gallbladders of guinea pigs and mice

The smooth muscle stimulatory effects of cholecystokinin octapeptide (CCK-8), ceruletide (CER), ten analogues of CER, and carbachol were studied in isolated organs of the guinea pig and the mouse (stomach, ileum, duodenum, colon and gallbladder). On a molar basis, CCK-8 and CER had in all organs except stomach greater potency (lower EC50) than carbachol. The effectiveness (Emax) of CCK-8 and CER was in the gut less than that of carbachol, in the guinea pig gallbladder equal with and in the mouse gallbladder superior to that of carbachol. The alteration of peptide structure was virtually without influence on effectiveness; however, it greatly modified the potency and the organ selectivity of the effect. There was no clear-cut correlation between the potency to stimulate smooth muscle and to alter the behavior of the mouse.