Differential cataleptogenic and antistereotypic effects of caerulein and haloperidol

Differentiation of potencies of Agaricus muscarius by experimental catalepsy

Agaricus m., administered orally to rats subjected to restraint to induce catalepsy, enhanced the cataleptic state. The higher the potency the longer its duration of peak action and the longer did it take to reach the peak effect. The action of atropine sulphate which diminishes catalepsy, was suppressed by Agaricus m. The degree of suppresion increased with the increase in potency of Agaricus m. Since restraint-induced catalepsy is mediated by cholinergic-dopaminergic interactions in the brain, Agaricus m. is thought to produce its effect by influencing those systems. The work provides a scientific proof for the action of potentized homœopathic drugs and for the principle of the minimum dose. Further, it introduces an animal model for testing homœopathic drugs.

Cholecystokinin and morphine-induced hypothermia

The effects of cholecystokinin-8 sulfate (CCK-8), cholecystokinin-8 unsulfate (CCK-8U), cholecystokinin-4 (CCK-4), caerulein and morphine on mice core body temperature have been studied in the present work. Subcutaneous injection of different doses of caerulein (0.05, 0.1 and 0.5 mg/kg), CCK-8 (0.05, 0.1 and 0.25 mg/kg) and morphine (10, 20 and 30 mg/kg) induced hypothermia. CCK-8U and CCK-4 did not elicit any response. The hypothermic response induced by caerulein, a CCK-related decapeptide but not morphine was decreased by selective CCK(A) receptor antagonist MK-329. However, the hypothermia induced by morphine but not caerulein was reduced by opioid antagonist naloxone. When morphine plus caerulein was administered a higher hypothermia was induced. Pretreatment of animals with L-365 260, a selective CCK(B) receptor antagonist did not alter the hypothermia induced by the drugs. The response induced by combination of the both drugs was decreased by MK-329. Administration of CCK antagonists MK-329 and L-365 260 to mice did not exert any effect on temperature. It is concluded that the CCK(A) receptor mechanism may be involved in the hypothermic effect of CCK agonists or morphine, while opioid receptor mechanism is not involved in CCK receptor agonists' response.

Contrasting effects on methamphetamine sensitization of ceruletide, a cholecystokinin-like decapeptide, and haloperidol

Ceruletide, a cholecystokinin-like decapeptide, and haloperidol show neuroleptic actions through inhibition of dopamine release and blockade of dopamine receptors, respectively. In this study, the effects of both drugs on methamphetamine sensitization were assessed by means of ambulation in mice. The enhancement in ambulation increase caused by five repeated administrations of methamphetamine (2 mg/kg, SC) at 3- to 4-day intervals was dose-dependently reduced when it was administered simultaneously with ceruletide (0.01-0.1 mg/kg, SC) or haloperidol (0.03-0.3 mg/kg, SC). However, only haloperidol could inhibit the induction of methamphetamine sensitization as assessed by challenge with methamphetamine alone. Post-treatment with ceruletide (0.03 mg/kg) 3 h after each methamphetamine accelerated, whereas such post-treatment with ceruletide (0.1 mg/kg) or haloperidol (0.03-0.3 mg/kg) delayed, the induction of methamphetamine sensitization. On the other hand, mice given five pretreatments with ceruletide (0.01-0.1 mg/kg) or haloperidol (0.03-0.3 mg/kg) at 3- to 4-day intervals did not exhibit any significant change in the sensitivity to methamphetamine. The present results suggest that, in contrast to the dose-dependent inhibition of methamphetamine sensitization in the simultaneous administration and post-treatment schedules, although both drugs can antagonize the acute stimulant effect of methamphetamine.

Ceruletide, a cholecystokinin-like decapeptide, differentially reduces the stimulant effect of MK-801 and ketamine: evaluation by discrete shuttle avoidance in mice

The non-competitive NMDA antagonist, MK-801 (dizocilpine: 0.03-0.3 mg/kg i.p.), a dissociative anesthetic, ketamine (1-20 mg/kg s.c.) and a CNS stimulant, methamphetamine (0.1-1 mg/kg s.c.), dose dependently increased the response rate in mice trained to discrete shuttle avoidance. MK-801 (0.1 mg/kg), ketamine (10 mg/kg) and methamphetamine (0.3 mg/kg) were almost equipotent. The cholecystokinin-like decapeptide, ceruletide, 0.1 micrograms/kg s.c., completely attenuated the response-increasing effect of MK-801 (0.1 mg/kg), although at this dose ceruletide alone did not produce any significant change in the avoidance response. Up to 10 micrograms/kg of ceruletide, which itself decreased the response rate, was required to reduce significantly the response-increasing effect of ketamine (10 mg/kg) and methamphetamine (0.3 mg/kg). On the other hand, haloperidol (0.01-0.1 mg/kg s.c.) decreased both the response rate and the % avoidance dose dependently, and inhibited the response-increasing effects of MK-801, ketamine and methamphetamine to almost the same degree. The present results suggest that comparatively lower doses of ceruletide inhibit selectively the stimulant effect of MK-801. Inhibition of dopamine release from the stored site in the nucleus accumbens may be mainly involved in this interaction.

Effects of ceruletide, administered singly and in combination with central-acting drugs, on discrete shuttle avoidance response in mice

The single administration of ceruletide at 10-300 micrograms/kg, i.p., slightly but significantly decreased the response rate (frequency of shuttles) under a discrete avoidance task in mice. Over 10 micrograms/kg of ceruletide attenuated the increase in the response rate induced by methamphetamine (0.5 mg/kg, s.c.). However, ceruletide, at 1-300 micrograms/kg, did not significantly enhance the response- and/or avoidance-decreasing effects of chlorpromazine (1 mg/kg, s.c.), haloperidol (0.1 mg/kg, s.c.), pilocarpine (4 mg/kg, s.c.) and N6-(L-2-phenylisopropyl)-adenosine (0.1 mg/kg, s.c.), but rather tended to reduce the avoidance-decreasing effect of chlorpromazine and pilocarpine at 1-100 micrograms/kg.

Effects of caerulein and cholecystokinin-octapeptide on acetylcholine and choline contents in the brains of intact and vagotomized mice

The effects of caerulein (CLN; 0.5, 5, and 50 micrograms/kg, IP) and cholecystokinin-octapeptide (CCK-8; 5, 50, and 400 micrograms/kg, IP) on the acetylcholine and choline contents in the discrete brain regions were examined, 30, 60, and 120 min after injection into intact and vagotomized mice. In all of the discrete brain regions of the intact mice. CLN and CCK-8 was found to have a complex effect on the acetylcholine and choline contents depending on the brain region, dosage and treatment time. On the other hand, the effect of CLN was abolished completely in the vagotomized mice. Thus, the present study indicates that peripherally administered CLN and CCK-8 have an effect on the central cholinergic system, mainly mediated via the vagus.

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

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

Acute and long-lasting effects of peripheral injection of caerulein and CCK-8 on the central GABAergic system in mice

Acute and long-lasting effects of peripheral injection of caerulein (CLN) and cholecystokinin octapeptide (CCK-8) on the gamma-aminobutylic acid (GABA) content and the GABA accumulation by aminooxyacetic acid (AOAA) in the discrete brain regions of mice were examined. The content and accumulation of GABA in the striatum, hypothalamus, and frontal cortex was measured with high performance liquid chromatography with electrochemical detection (HPLC-ECD). The GABA content slightly decreased in the striatum 60 min after CLN and CCK-8 were administered, whereas it slightly increased in the hypothalamus and frontal cortex. Moreover, with CLN and CCK-8, the GABA accumulation after AOAA treatment decreased in the striatum and hypothalamus 30 min after injection. Meanwhile, when administering CLN, the GABA content as well as the GABA accumulation after AOAA treatment increased in the striatum and frontal cortex 1 day after injection, and continued to increase the second and third day in the striatum. These results showed that peripheral injection of CLN and CCK-8 had effects on the central GABAergic system with local specific actions, and also the long-lasting and time-dependent biphasic effects of CLN.

Relative importance of the dopaminergic system in haloperidol-catalepsy and the anticataleptic effect of antidepressants and methamphetamine in rats

The mechanisms involved in haloperidol (HPD)-catalepsy in rat and the effect of antidepressants and methamphetamine (MA) were studied. HPD-catalepsy, as measured by high bar test, lasted for 6-8 min. MA, imipramine (IMP), nomifensine (NOM) and mianserin (MIAN) reduced the duration of catalepsy on IP injection. Electrolytic lesion of the caudate-putamen (CP) and nucleus accumbens (ACC) extensively reduced HPD-catalepsy. Microinjection of MA and NOM into ACC had a similar effect. In the medial amygdala and CP, only MA displayed anticataleptic activity. Zimelidine did not reduce the duration of catalepsy. These results suggest that dopaminergic systems play a key role in mediating HPD-catalepsy and the anticataleptic activity of MA and NOM.

Drug effects on active immobility responses: what they tell us about neurotransmitter systems and motor functions

The literature reviewed indicates that active immobility can be promoted by systemic injections of various neurotransmitter systems, as follows: (1) Dopaminergic blockade of both D1 and D2 receptor subtypes. (2) Cholinergic agonism of both muscarinic and nicotinic receptors. (3) Noradrenergic agonism of both alpha-1 and alpha-2 receptors (but these agonists may interfere with haloperidol- and reserpine-induced catalepsy). (4) GABA agonism. (5) Histamine agonism, particularly at the H1 receptor. (6) Opiate agonism, including action of many endogenous opiate peptides, particularly those affecting mu and delta receptors. (7) Agonism by certain other peptides (neurotensin, cholecystokinin). Among the major interactions of neurotransmitter systems that regulate immobility, are the following: (1) Cholinergic-dopaminergic (cholinolytics disrupt catalepsy of dopaminergic blockade and dopaminergic agonists tend to disrupt cholinomimetic catalepsy). (2) Opiate-induced catalepsy is antagonized by the dopamine agonist, apomorphine, but is enhanced by amphetamine. It is also antagonized by certain alpha-2 adrenergic agonists, while it does not seem to be antagonized by anticholinergics. (3) Numerous other interactions have been reported, involving opiates and MSH, serotonin and dopamine mimetics, serotonin and ketamine, GABA and neuroleptics, neurotensin and anticholinergics and histamine. The significance of the multiple neurotransmitter systems is unknown. One possible explanation is that the various neurotransmitter systems participate in mediating the sensory inputs that are involved in triggering immobility and regulate the higher-order limbic and basal ganglia processing reactions that engage a final motor output pathway from the brainstem. The brain is assumed to contain two sets of systems, each with its own, or possibly overlapping, set of neurotransmitter systems, that promote either active immobility or locomotion. The systems reciprocally inhibit each other. Another view, not mutually exclusive, is that output from the locomotor-promoting system provides a negative feedback, via the active immobility pathways, to act as a "brake" on movement, while at the same time maintaining the muscular tonus that is characteristic of active immobility.

Cholecystokinin

1. CCK-peptides are distributed throughout the whole brain with the exception of the cerebellum. 2. There is strong evidence that they act as neuromodulators on the noradrenergic, opioid and mainly dopaminergic system. 3. CCK reduces food-intake. However, tolerance occurs, when chronically given. Thus, potential benefits in the treatment of obesity seem unlikely. 4. CCK increases threshold and tolerance to electrically and thermally induced cutaneous pain. CCK yields relief of pain in colic and ischaemic pain. 5. To date, results about CCK-content in CSF and post-mortem-brain in various psychiatric and neurological diseases related to the dopaminergic system are equivocal. 6. Treatment studies do not provide evidence for beneficial effects of CCK-peptides in schizophrenia.

Differential effects of proglumide on mesolimbic and nigrostriatal dopamine function

Cholecystokinin octapeptide (CCK-8) is prevalent as a co-transmitter in the mesolimbic dopamine pathway. The effect of proglumide, a CCK-8 antagonist, on two acute and one chronic behavioral models of dopamine function was tested. First, haloperidol was used to inhibit stereotypies induced by apomorphine in rats. Pre-administration of proglumide significantly shifted the haloperidol dose response curve to the left. Second, rats were injected in the left caudate nucleus with kainic acid. Three weeks later, haloperidol was used to inhibit apomorphine-induced circling. Pre-administration of proglumide had no effect on this haloperidol dose response curve. Third, either proglumide, haloperidol, or combined treatment was administered to rats for 2 weeks. In proglumide-treated animals, a significant increase in 3H-spiperone binding sites in the nucleus accumbens was observed.

Antistereotype effects of ceruletide and some neuroleptics differentiated by interactions with clonazepam, muscimol, scopolamine and clonidine

Compulsive gnawing was produced in mice by administration of either methylphenidate or (after sensitizing pretreatment with the neuroleptic, tetflutixol) apomorphine. Drugs which antagonise stereotypy, such as ceruletide (CER, a sulphated decapeptide related to cholecystokinin octapeptide), haloperidol, zuclopenthixol and fluphenazine were applied in equipotent doses (reducing stereotypy by 80%). Clonazepam, muscimol, clonidine and scopolamine (but not methylscopolamine) antagonized to a different extent the antistereotype effect of ceruletide and the neuroleptics. The ED50s for clonazepam and other drugs, were determined; clonazepam had the greatest potency. Regarding the antagonism of the antistereotype effect, ceruletide was similar to but by no means congruent with haloperidol. The antagonism of the antistereotype effect was specific because other effects of ceruletide and cholecystokinin octapeptide (inhibition of exploratory rearing activity, ptosis, antinociception, hypothermia) were not antagonized by clonazepam and only weakly modified by scopolamine. Methylscopolamine was ineffective throughout, indicating a central site for the mechanism of the actions studied of scopolamine. In conclusion, the antistereotype effect of ceruletide is different from that of conventional neuroleptic drugs and functionally independent of other behavioural effects of the cholecystokinin-like peptides.

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 stereotyped 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.

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.

Inhibition of feeding by the C-terminal tetrapeptide fragment of cholecystokinin in a novel environment

Several doses of the C-terminal tetrapeptide fragment of cholecystokinin octapeptide (CCK-5-8) were injected intraperitoneally (ip.) and intracerebroventricularly (icv.), and their effects on the feeding of 24-hr food-deprived rats in familiar and novel environments were studied. In the familiar environment, CCK-5-8 ip. or icv. had no effect on the food intake of the rats. In the novel environment (i.e. in an open field), CCK-5-8 showed merely slight effects on the main open-field parameters: only ip. administered CCK-5-8 enhanced the incidence of grooming. Of the feeding parameters tested in the open field, mainly the food intake/approach to food ratio was depressed by CCK-5-8 ip. or icv. The 24 mumole/kg ip. dose of CCK-5-8 decreased the food intake, while the 8 pmole icv. dose increased the number of approaches to food. After the treatments found to be the most effective, the latency to first bite was also enhanced. The results suggest that CCK-5-8 can amplify the arousal enhancement elicited by novelty through a central mechanism.

Prolonged cataleptogenic effects of potentized homoeopathic drugs

The four homoeopathic drugs, Gelsemium, Cannabis Indica, Graphites and Agaricus Muscarius, administered orally in 30th and 200th potencies on white rats, enhanced restraint-induced catalepsy in a similar manner to the two standard drugs pilocarpine and haloperidol (IP injection at 5 mg/kg). All the drugs tested differed from each other in the duration of cataleptogenic effect, which was more prolonged with Cannabis, Graphites and Agaricus than with Gelsemium and the two non-homoeopathic drugs used. The 200th potency of any homoeopathic drug tested acted longer than its 30th potency.

Cataleptogenic and anticataleptic activity produced by cholecystokinin octapeptides in mice

The catalepsy induced by subcutaneously (sc.) and intracerebroventricularly (icv.) administered cholecystokinin octapeptide sulfate ester (CCK-8-SE) and desulfated cholecystokinin octapeptide (CCK-8-NS), and the effects of CCK-8-SE and CCK-8-NS on haloperidol-induced catalepsy, were investigated in mice. The results demonstrate the bimodal effect of CCK octapeptides in a catalepsy test. With sc. administration CCK-8-SE in the doses of 0.4 or 0.8 mumole/kg, but not CCK-8-NS at any dose, induced catalepsy. Furthermore, the catalepsy induced by CCK-8-SE was of short duration. With icv. administration only 40 pmole CCK-8-NS induced significant catalepsy. When 0.2, 0.4 and 0.8 mumole/kg sc. doses of CCK-8-NS or 0.4 pmole icv. dose of CCK-8-SE or CCK-8-NS was given in combination with intraperitoneal (ip.) administration of 1.0 mg/kg haloperidol, the total duration of catalepsy was suppressed. Finally, CCK-8-SE sc. when given in combination with haloperidol ip., exerted a biphasic, synergistic-antagonistic effect on the haloperidol-induced catalepsy.

Inhibition of haloperidol-induced catalepsy by cholecystokinin octapeptides after central administration to rats

The possible cataleptogenic or anticataleptic effects of cholecystokinin octapeptide sulphate ester (CCK-8-SE) and desulphated CCK-8 (CCK-8-NS) were evaluated in rats after intracerebroventricular (i.c.v.) administration. Neither CCK-8-SE nor CCK-8-NS induced any sign of catalepsy. When haloperidol, in a dose of 1.0 mg/kg (i.p.), and either CCK-8-SE or CCK-8-NS, in doses of 8, 80 or 800 pmol (i.c.v.), were applied at the same time, the peptides significantly decreased the total duration of catalepsy, the 80 pmol dose being the most effective. For the inhibition of catalepsy CCK-8-NS was the more active as it decreased catalepsy scores even 120 min after administration. Both peptides showed only transient effects on the fully developed catalepsy induced by haloperidol.

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.

Potentiation of beta-endorphin effects by proglumide in rats

The effects of proglumide, a cholecystokinin (CCK) receptor antagonist, on the analgesia and catalepsy induced by beta-endorphin were investigated in rats. Proglumide itself produced a slight analgesia but no catalepsy. Combined intracerebroventricular administration of beta-endorphin and proglumide produced marked potentiation of the analgesic and cataleptic effects of beta-endorphin. The results suggest that endogenous CCK may have an antagonistic effect on the actions of beta-endorphin in the brain.

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.

CCK-33 antagonizes apomorphine-induced growth hormone secretion and increases basal prolactin levels in man

Cholecystokinin (CCK-33) (225 Ivy Dog Units intravenously) had no effect on basal growth hormone (GH) secretion but antagonized the GH response to the dopamine receptor agonist, apomorphine HCl (0.5 mg sc) (N = 7), and induced a transient increase in basal prolactin (PRL) secretion (N = 8) in normal men. These findings are similar to those described with neuroleptics and are compatible with an inhibitory effect of CCK-33, or fragments, on dopamine function in man, at least in the hypothalamic-pituitary axis. However, an inhibitory effect of CCK-33 on the release of GH and a stress-induced increase in PRL secretion cannot be excluded.

Effects of naloxone on methamphetamine and apomorphine stereotypy and on haloperidol catalepsy in rats

Pretreatment with the opiate antagonist naloxone, at 1.25-5 mg/kg, increased the intensity of methamphetamine stereotypy, had no effect (over a range of 0.3125-5 mg/kg) on apomorphine stereotypy, and antagonized haloperidol catalepsy in rats at 1.25-5 mg/kg. It is suggested that naloxone, by blocking the opiate receptors located on the nigro-striatal and mesolimbic dopamine (DA) nerve terminals, releases the DA systems from endogenous inhibition, presumably caused by endogenous opiate systems, and thereby potentiates methamphetamine stereotypy and antagonizes haloperidol catalepsy. However, the possibility that naloxone might have affected methamphetamine stereotypy and haloperidol catalepsy by modulating the activity of the central noradrenergic and GABAergic systems, which are reported to influence dopaminergically mediated behaviours, also needs to be considered.

A caerulein-sensitive potentiation of the behavioral effects of apomorphine by dibutyryl-cAMP

The dopaminergic behavioral effects of apomorphine in rats were evaluated using a rating scale. Caerulein, a decapeptide physiologically similar to cholecystokinin, enhanced at lower doses and inhibited at higher doses the behaviors induced by apomorphine. Dibutyryl-cAMP, but not dibutyryl-cGMP, potentiated apomorphine behaviors. This potentiation was inhibited by a high dose of caerulein. These data provide evidence for an opposing effect of cAMP and caerulein or cholecystokinin in modulating dopaminergic systems.

Neuroleptic-like effects of ceruletide and cholecystokinin octapeptide: interactions with apomorphine, methylphenidate and picrotoxin

Haloperidol in low doses antagonized the apomorphine-induced cage-climbing behaviour of mice, whereas ceruletide (CER) and its analogue, Nle8-CER-(4-10) had very weak anticlimbing efficacy; Nle8-CER and diazepam were inactive. The ptosis caused by CER and cholecystokinin octapeptide (CCK-8) was antagonized by apomorphine in doses 27 times smaller than those effective against the haloperidol-induced ptosis. No such differences occurred when either methylphenidate or picrotoxin replaced apomorphine. Low-dose haloperidol was an antagonist to the antiptotic effect of apomorphine versus both CER and CCK-8. The rearing inhibiting effect of CER and haloperidol, in contrast to that of clonazepam, was very resistant to apomorphine. Methylphenidate was weakly effective against clonazepam and haloperidol but inactive versus CER. Picrotoxin was no antagonist to either rearing inhibiting agent. The results taken together suggest presynaptic sites of the dopaminergic system as important for the production of ptosis by CCK-like peptides.

Facilitation of GABA release by cholecystokinin and caerulein in rat cerebral cortex

Cholecystokinin octapeptide and its analogue, caerulein, facilitated the K+-evoked release of 14C-GABA from tissue slices of rat parietal cortex. The effect of caerulein was maximal at 1 nM where an enhancement of 36% was produced. Cholecystokinin octapeptide gave rise to a similar maximal enhancement (29%), but was two orders of magnitude less potent. The enhancement of 14C-GABA release by caerulein was reversed by proglumide, a putative competitive antagonist at the cholecystokinin receptor. The possibility that the cholecystokinin-induced facilitation of GABA release in the cortex is involved in the anticonvulsant properties of cholecystokinin-like peptides is discussed.

State-dependent tardive dyskinesia in manic-depressive illness

We report the occurrence of a drug-resistant tardive dyskinesia coexistent with Parkinsonism-like symptoms in a manic-depressive patient. The tardive dyskinesia completely disappeared during the manic phases and recurred after remission over the course of different mood-cycles.

Cholecystokinin octapeptide (CCK-8), ceruletide and analogues of ceruletide: effects on tremors induced by oxotremorine, harmine and ibogaine. A comparison with prolyl-leucylglycine amide (MIF), anti-Parkinsonian drugs and clonazepam

Cholecystokinin octapeptide (CCK-8), ceruletide (caerulein, CER) and 10 analogues of ceruletide, were studied in mice for antagonism of the tremors induced by harmine (5 mg/kg, s.c.), ibogaine (20 mg/kg, s.c.) and oxotremorine (0.2 mg/kg, s.c.). The following reference drugs were tested for comparison: prolyl-leucylglycine amide (MIF), atropine, haloperidol, biperiden, ethopropazine, trihexyphenidyl, methixene and clonazepam. All treatments were subcutaneous, the antagonists being given 10 min (in some trials 30 min) before the tremorogen. Tremorolytic potency (ED50) was calculated from dose-response curves. Against the tremors induced by either harmine or ibogaine, CCK-8 and ceruletide, as well as many of the analogues of ceruletide had greater tremorolytic potency than the reference drugs. Against oxotremorine, however, ceruletide and its most potent analogue, Nle8-CER (other analogues were not tested) were inactive and MIF showed very little effectiveness. Additional experiments on hypothermia and sedation as well as evaluation of previous studies on other central actions suggested that the tremorolytic effect of CCK-like peptides is independent of other central effects. The CCK-like peptides may play a physiological role in the regulation of extrapyramidal motor activity.

Neuroendocrine evaluation of CCK-peptides on dopaminergic function in man

CCK-33 (225 Ivy Dog Units iv) antagonized the growth hormone response to the dopamine receptor agonist, apomorphine HCl (0.5 mg sc), and increased basal prolactin secretion in normal male volunteers. A stress mediated prolactin effect could not be excluded. CCK-8 (5 ug iv) antagonized the growth hormone response to apomorphine but had no effect on basal prolactin or plasma homovanillic acid. Ceruletide (0.3 ug/kg im) had no effect on basal prolactin or apomorphine-induced growth hormone secretion. CCK-33, CCK-8 and ceruletide had no effect on basal growth hormone secretion which suggests that they do not inhibit the release of growth hormone. These findings are compatible with an inhibitory effect of CCK-33 and CCK-8 (or fragments) on dopaminergic function in man, at least in the hypothalamic-pituitary axis and point to a simple way to study the effect of peptides on dopaminergic function in man including those which may not cross the blood brain barrier.

Cholinergic-dopaminergic interactions in experimental catalepsy

The 'pinch-induced' model of catalepsy in the mouse was disrupted by atropine sulfate (4 mg/kg IP), confirming an earlier finding, and also by the antinicotinic mecamylamine (4 mg/kg). Either anticholinergic, when given concurrently with haloperidol (5 mg/kg), interfered with the typical haloperidol-induced enhancement of catalepsy. In mice pretreated with a peripheral cholinergic blocker, the cholinomimetic pilocarpine (10 mg/kg) enhanced catalepsy. The dopamine (DA) agonist apomorphine (5 mg/kg) reversed the enhancement that was normally caused by pilocarpine. Apomorphine did not stimulate open field locomotion in mice that were pretreated with pilocarpine. This lack of correlation between catalepsy and open field activity indicates that catalepsy in a unique state that involves more than mere absence of movement. The DA mechanisms, thus, appear to be specifically antagonistic to catalepsy or, conversely, cholinergic mediation of catalepsy involves reduced influence of DA systems.

Ceruletide, ceruletide analogues and cholecystokinin octapeptide (CCK-8): effects on motor behaviour, hexobarbital-induced sleep and harman-induced convulsions

Ten ceruletide analogues and cholecystokinin octapeptide (CCK-8) were compared with ceruletide regarding neuropharmacological effects in mice after subcutaneous administration. The effects under study were catalepsy, prolongation of hexobarbital-induced sleep and delay in onset of harman-induced convulsions. Ceruletide and several analogues were more potent than the reference drugs, diazepam and haloperidol. Desulfation, deamidation and shortening of the peptide chain by five amino acids strongly reduced or abolished the pharmacological activities of ceruletide. Other chemical modulations mostly weakened the efficacy, but to an unequal extent for the three effects, which altered the pharmacological selectivity.

Caerulein and cholecystokinin octapeptide (CCK-8): sedative and anticonvulsive effects in mice unaffected by the benzodiazepine antagonist Ro 15-1788

Cholecystokinin octapeptide (CCK-8), caerulein and diazepam inhibited exploratory rearing activity and harman-induced convulsions in mice. Pretreatment with the selective benzodiazepine receptor antagonist Ro 15-1788, reduced or abolished the sedative and anticonvulsive effects of diazepam, but left the same effects of both peptides unaffected. The peptide-induced ptosis was even increased by Ro 15-1788. The results suggest that the CCK-like peptides do not directly interact with the benzodiazepine receptor.

Anticonvulsant effects of caerulein, cholecystokinin octapeptide (CCK-8) and diazepam against seizures produced in mice by harman, thiosemicarbazide and isoniazid

Caerulein, cholecystokinin octapeptide (CCK-8) and diazepam delayed the onset of seizures produced by harman and thiosemicarbazide (TSC). Caerulein had the potency of diazepam, whereas CCK-8 was less active by a factor of four. The convulsions induced by isoniazid (INH) were very resistant to both caerulein and diazepam; CCK-8 was not tested against isoniazid. Haloperidol did not influence the effect of TSC; it enhanced isoniazid-induced seizures, and antagonized the convulsant effect of harman.

Central effects of ceruletide analogues

Ten ceruletide analogues and cholecystokinin octapeptide (CCK-8) were compared with ceruletide regarding neuropharmacological effects in mice after peripheral administration. The effects under study were inhibition of motor response to noxious stimulation (hot plate), production of ptosis, inhibition of exploratory rearing activity, elevation of threshold for picrotoxin-induced convulsions, and antagonism of methylphenidate-induced gnawing. Desulfation, deamidation and shortening of the peptide chain by five amino acids destroyed all pharmacological activities of ceruletide. Other modifications were of unequal consequences for the pharmacological profile of a given analogue, decreasing some effects while increasing others. Hence, structural changes of the ceruletide molecule resulted in modulations of both potency and selectivity.