Prevention of experimental amnesia by peripherally administered cholecystokinin octapeptide in the rat

The effect of subcutaneously injected cholecystokinin octapeptide (CCK-8) on amnesia induced by electroconvulsive shock (ECS), CO₂ inhalation, or cycloheximide injection was investigated in rats. In normal rats, single administration of CCK-8 had no significant effect on the passive avoidance response. Treatment with ECS, CO₂, or cycloheximide markedly decreased the latency of the passive avoidance response, but CCK-8 in doses from 0.1 to 10 μg/kg could prevent the induced amnesia when injected 30 min before the training trials, immediately after foot shock or amnesic treatments, and 30 min before the first retention test. The results indicate that peripheral administration of CCK-8 is effective in preventing amnesia in the rat.     

Cholecystokinin octapeptide prevents extinction of active avoidance behavior in the rat

The effect of cholecystokinin octapeptide (CCK-8) on the performance of platform-jumping avoidance behavior was investigated in the rat. CCK-8 was injected subcutaneously once in different doses immediately after training trials. The number of avoidance responses remained high 5 and 10 days after the CCK-8 administration and the greatest effect was observed with doses of 10 and 100 ng/kg, while in control saline group the number of responses decreased after 5 days. Larger doses of CCK/8 were less effective, probably due to a sedative action.     

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.     

Further analysis of the effects of cholecystokinin octapeptides on avoidance behaviour in rats

Experiments were performed to examine the acute effects of cholecystokinin octapeptides and fragments on the active and passive avoidance behaviour of rats following peripheral and central administration. Both the sulphated (CCK-8-SE) and non-sulphated cholecystokinin octapeptide (CCK-8-NS) and also the COOH-terminal tetra-, penta-, hexa- and heptapeptides of cholecystokinin octapeptide facilitated the extinction of active avoidance behaviour and retention of passive avoidance behaviour. This latter effect of cholecystokinin octapeptides was reversed by anxiolytic chlordiazepoxide pretreatment, showing that in these test situations cholecystokinin octapeptides are able to modify fear-motivation or arousal of the animals; their effect is at least partly similar to that of the neuroleptic substance haloperidol. Subcutaneous treatment with CCK-8-SE or CCK-8-NS appeared to be 3-10 times more effective than intraperitoneal treatment. Following intracerebroventricular administration, 100-300 times lower doses were needed to cause a behavioural effect similar to that after subcutaneous injection. Microinjection of CCK-8-SE or CCK-8-NS in the fmol dose range into the nucleus accumbens facilitated the extinction of active avoidance behaviour and attenuated the retention of passive avoidance behaviour, while microinjection of these peptides into the central amygdaloid nucleus caused opposite effects on these behavioural tests. It seems that the neuroleptic-like effects of cholecystokinin octapeptides are mediated through the nucleus accumbens, and the opposite action (non neuroleptic-like) through the central amygdaloid nucleus.     

In rats, the behavioral profile of CCK-8 related peptides resembles that of antipsychotic agents

The action of some CCK-8 related peptides, desulphated CCK-8 (CCK-DS), the sulphated form of CCK-8 (CCK-8-S) and ceruletide was explored in a number of test procedures with rats, in which antipsychotic agents are active. Following injection into the nucleus accumbens, all three peptides antagonized the hypolocomotion induced by low doses of apomorphine (10 ng). Ceruletide appeared to be the most potent in this respect (ED50: approximately 5 pg). The increased locomotion observed following injection of relatively high doses of apomorphine (10 micrograms) into the nucleus accumbens was antagonized by local pretreatment with CCK-8-S, but not with CCK-8-DS or ceruletide. None of these CCK-8 related peptides affected the stereotyped sniffing response elicited by treatment with apomorphine or amphetamine (10 micrograms) given into the nucleus caudatus. Passive avoidance behavior was facilitated following subcutaneous administration of 10 micrograms of CCK-8-related peptides 1 h before the retention test. The same periods given into the nucleus accumbens (0.3 pg) however attenuated passive avoidance behavior. intraventricular injection with CCK-8-DS and CCK-8-S induced a positive effect in various 'grip tests'. Given subcutaneously, the CCK-8-related peptides decreased the rate of ambulation and rearing especially in the middle of the open field. These results indicate that CCK-8 related peptides, especially CCK-8-DS and ceruletide, exhibit behavioral effects that are similar to those observed following treatment with gamma-type endorphins and that resemble the effects of antipsychotic agents. Very low doses of CCK-8 related peptides exert behavioral effects following injection into the nucleus accumbens, indicating that this brain area is extremely sensitive to the action of these peptides. It is postulated that certain peptides which are either present in neurons (like CCK-8-related peptides) or generated by brain endorphin systems (like gamma-type endorphins) control the activity of specific neurons of the mesolimbic dopaminergic pathways. This may be of relevance for the purported antipsychotic action of these peptides.     

Antinociceptive effect of centrally administered caerulein and cholecystokinin octapeptide (CCK-8)

When injected into the brain (periaqueductal gray (PAG), caudate nucleus, ventromedial thalamus) or subarachnoidal space of the lumbar spinal cord of rats, caerulein and CCK-8 produced a long-lasting (2 h) inhibition of the tail-flick response to thermal stimulation. The effective dose range for caerulin was from 1 to 5 ng per rat, for CCK-8 from 10 to 40 ng, and for morphine from 1 to 20 μg. On a molar basis and dependent upon the site of administration, caerulein was 4000–7000 times and CCK-8400-700 times more potent than morphine. Unsulphated caerulein (injected into the PAG) was less active than caerulin by a factor of 9. Sedation was seen after intracerebral, but not after spinal administration of the peptides; it was not observed after morphine or unsulphated caerulin. Naloxone (0.5 mg/kg i.p.) abolished the antinociceptive but not the sedative effect. It is concluded that caerulin and CCK-8 are very potent in reducing nociception by acting at both spinal and supraspinal levels.     

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.     

Effect of cholecystokinin octapeptide antagonists on the extinction of an active avoidance task in the rat

Cholecystokinin octapeptide (CCK-8) has been shown to be involved in memory processes. For example, in the absence of endogenous CCK-8 in the brain, memory processes are imparied. In order to extend the understanding of this relationship, the present study observed the effect of novel potent CCK-8 antagonists, L-364,718 and CR 1409, on active avoidance responding in the rat. These antagonists caused marked impairment in the performance of the learned task when administered intracerebroventricularly immediately after the learning trials. The results suggest that CCK-8 is indispensable for memory processes.     

Naltrexone-insensitive facilitation and naltrexone-sensitive inhibition of passive avoidance behavior of the ACTH-(4-9) analog (ORG 2766) are located in two different parts of the molecule

Subcutaneous injection of the ACTH-(4-9) analog (OG 2766) in ng amounts prior to the retention test facilitated, while microgram doses attenuated passive avoidance behavior. The inhibitory effect could easily be overcome by treatment with ACTH-(1-10) either before or after ORG 2766 administration. Thus, inhibition of passive avoidance behavior by ORG 2766 probably was not due to competition with ACTH-like peptides or a functional antagonistic influence on brain structures sensitive to ACTH-like peptides. Intracerebroventricular administration of ACTH-(4-10) in a wide dose range (0.5-10.0 micrograms) and of ORG 2766 in low doses (0.5-1.0 ng) facilitated passive avoidance behavior, whereas 'high' doses of ORG 2766 (5.0 and 10.0 ng) and graded doses of COOH terminal tripeptide of ORG 2766 (Phe-D-Lys-Phe; PDLP; 0.5-10.0 ng) attenuated passive avoidance behavior. The NH2 terminal tetrapeptide of ORG 2766 (H-Met/O2/-Glu-His-Phe) facilitated passive avoidance behavior, whereas the NH2 terminal tripeptide (H-Met/O2/-Glu-His) was ineffective. Naltrexone pretreatment antagonized the attenuating effect of ORG 2766 and PDLP. Following pretreatment with this opiate antagonist both 'low' and 'high' doses of ORG 2766 and the NH2 terminal tetrapeptide of ORG 2766 induced facilitation of passive avoidance behavior, while PDLP was ineffective in the presence of naltrexone. Thus, ORG 2766 exerts a dual effect on passive avoidance behavior. The facilitating effect of ORG 2766 resides in the NH2 terminal part and is unrelated to naltrexone-sensitive brain opiate receptor sites, whereas the inhibiting influence is located in the COOH terminal part of the peptide and depends on naltrexone-sensitive brain opiate receptor sites.     

Memory-enhancing effect of a cerulein analogue following peripheral administration in the rat

Our previous studies demonstrated that cerulein (CER) has a potent preventive action on amnesia induced by electroconvulsive shock, administration of scopolamine, puromycin, anisomycin, NMDA receptor antagonists, and protein kinase C inhibitors. The present study was aimed at finding more effective CER analogues which could enhance memory processes. Five CER analogues were synthesized and the potencies in passive and active avoidance responses and in the Morris water pool test were examined in the rat. Among the preparations, des-Gln²-[Leu⁵, Nle⁸]-CER was found to possess particularly potent effects on memory acquisition and/or storage. The effects were apparent in less than 1 μg/kg single subcutaneous (s.c.) injection for at least 120 hr in passive avoidance response and 15 days in active avoidance response. Memory impairments induced by scopolamine and puromycin were well improved in passive avoidance response. In the Morris water maze test, disordered behaviors caused by scopolamine and protein kinase C inhibitor were totally restored to the normal state by s.c. injection of this CER analogue. © 1992 Wiley-Liss, Inc.     

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.     

Neuroleptic activity of the neuropeptide beta-LPH62-77 ([Des-Tyr1]gamma-endorphin; DT gamma E).

In contrast to β-endorphin, α-endorphin, β-LPH_61–69 and Met-enkephalin which delay extinction of pole-jumping avoidance behavior (De Wied et al., 1978), γ-endorphin given either subcutaneously (30 ng/rat) or intraventricularly (0.3 ng/rat) facilitated extinction. Removal of the N-terminal amino acid residue tyrosine — yielding the neuropeptide [Des-Tyr¹]γ-endorphin (DTγE) — which destroys the opiate-like activity as determined on the electrically driven guinea pig ileum, potentiated the facilitating effect of γ-endorphin on pole-jumping avoidance behavior. Observations on passive avoidance behavior gave essentially the same results. Whereas α-endorphin facilitated this behavior. DTγE attenuated passive avoidance behavior. Amounts of γ-endorphin and DTγE which were highly active on extinction of pole-jumping avoidance behavior (0.3 μg s.c. per rat) were without effect on gross behavior in an open field. Much higher amounts (10–50 μg s.c. per rat) also failed to affect the rate of ambulation in an open field. In relatively high doses (20 μg i.v.t. or 50 μg s.c. per rat), γ-endorphin and in particular DTγE were positive in the various “grip tests”. Haloperidol given s.c. (0.03–0.1 μg/rat) facilitated extinction of pole-jumping avoidance behavior and attenuated passive avoidance behavior. The same amounts decreased ambulation in an open field. In higher doses haloperidol was active in the “grip tests” but in addition caused severe immobility, ptosis and extension of the lower limbs. Intraventricularly administered morphine or β-endorphin induced wide open eyes, exophthalmus, rigidity and reduced reflexes, in contrast to γ-endorphin and DTγE which did not produce such effects. These results are interpreted to indicate that DTγE or a closely related peptide is an endogenous neuroleptic. It may be that a reduced availability as a result of an inborn error in the generation of DTγE is an etiological factor in psychopathological states for which neuroleptic drugs are beneficial.     

Behavioral effects of acetyl-l-carnitine in the male rat

The behavioral activity of carnitine acetylate derivative, acetyl-l-carnitine has been studied in the male rat. Intraperitoneal (IP) injection of acetyl-l-carnitine was followed by an increase in ambulation and rearing items in the open field behavior. Both the number of conditioned avoidance response (CARs) and the percentage of learners in the acquisition of shuttle-box active avoidance behavior appeared to be increased by IP or intracerebroventricular (ICV) injection of the drug at different doses. Subchronic administration of the drug mimicked the effects found after acute injection. The number of CARs in the extinction of shuttle-box active avoidance behavior appeared to be increased after acute IP or ICV injection, and after subchronic administration of acetyl-l-carnitine. The retention of passive avoidance behavior was facilitated by IP injection of the substance. The behavioral effects of acetyl-l-carnitine may involve central mechanisms, e.g., cholinergic neurotransmission in the brain.     

Vasopressin antagonists block peripheral as well as central vasopressin receptors

The aim of the present study was to differentiate between the postulated central behavioral effects of vasopressin and its pressor response, which is mainly mediated by peripheral vascular receptors. Thus, the interaction between the vasopressor antagonists dPTyr(Me)AVP (AAVPa) and d(CH2)5Tyr(Me)AVP (AAVPb) with the effects of [Arg8]vasopressin (AVP-(1-9)) and [pGlu4,Cyt6]AVP-(4-8) (referred to as AVP-(4-8)) was examined using passive avoidance behavior and the pressor response as parameters. AVP-(4-8) was approximately 4 and 200 times more potent than AVP-(1-9) in facilitating passive avoidance behavior after subcutaneous (SC) or intracerebroventricular (ICV) administration respectively. This effect of SC injected AVP-(1-9) and AVP-(4-8) could be prevented by both vasopressor antagonists following SC treatment. A similar antagonistic action was found when AVP-(1-9) or AVP-(4-8) and the antagonist AAVPb were administered ICV. SC injection of AAVPb prevented the behavioral effect of ICV administered AVP-(1-9) while ICV treatment with the antagonist blocked the behavioral action of systemically injected AVP-(1-9) and AVP-(4-8). In contrast to SC injected AVP-(1-9) which dose-dependently increased blood pressure and decreased heart rate, AVP-(4-8) injected SC in identical doses did not affect blood pressure and heart rate, neither did AVP-(1-9) and AVP-(4-8) when injected ICV in behaviorally active doses. A SC, but not an ICV injection of the antagonist AAVPb could prevent the blood pressure increase and bradycardia induced by SC AVP-(1-9).(ABSTRACT TRUNCATED AT 250 WORDS)     

NMDA receptor antagonists antagonize the facilitatory effects of post-training intra-basolateral amygdala NMDA and physostigmine on passive avoidance learning

In the present study, the effects of post-training intra-basolateral amygdala (BLA) injection of an N-methyl-d-aspartate (NMDA) receptor agonist and competitive or noncompetitive antagonists, on memory retention of passive avoidance learning was measured in the presence and absence of physostigmine in rats. Intra-BLA administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) did not affect memory retention, although higher doses of the drug (10(-3), 10(-2) and 10(-1) microg/rat) increased memory retention. The greatest response was obtained with 10(-1) microg/rat of the drug. The different doses of the competitive NMDA receptor antagonist DL-AP5 (1, 3.2 and 10 microg/rat) and noncompetitive NMDA receptor antagonist MK-801 (0.5, 1 and 2 microg/rat) decreased memory retention in rats dose dependently. Both competitive and noncompetitive NMDA receptor antagonists reduced the effect of NMDA (10(-2) microg/rat). In another series of experiments, intra-BLA injection of physostigmine (2, 3 and 4 microg/rat) improved memory retention. Post-training co-administration of lower doses of NMDA (10(-5) and 10(-4) microg/rat) and physostigmine (1 microg/rat), doses which were ineffective when given alone, significantly improved the retention latency. The competitive and noncompetitive NMDA receptor antagonists, DL-AP5 and MK-801, decreased the effect of physostigmine (2 microg/rat). Atropine decreased memory retention by itself and potentiated the response to DL-AP5 and MK-801. It may be concluded that amygdalar NMDA receptor mechanisms interact with cholinergic systems in the modulation of memory.     

Substance P enhancement of passive and active avoidance conditioning in mice

In a series of seven experiments we explored the effects of peripherally administered substance P on passive and active avoidance conditioning in mice of two genotypes. The peripheral post-trial administration of substance P significantly enhanced the retention of a single-trial passive avoidance task. This effect was dose dependent; 1 ng/g of substance P enhanced the retention of this habit, whereas higher and lower doses were either less effective or ineffective. In heterogeneous strain (HS) mice, substance P administered before training on an active avoidance task did not alter the rate at which these animals learned this habit. However, animals that had been trained with substance P were significantly more resistant to extinction than were animals that had been injected with vehicle. Similarly, C57Bl/6J mice that had been treated with substance P immediately after active avoidance training were more resistant to extinction than were mice that had been given control injections. The enhancement of retention of the passive avoidance habit with substance P was reversed in animals that had been pretreated with naltrexone. Substance P enhancement of the retention of the passive avoidance habit, and its reversal with naltrexone, was observed in both sham operated and adrenalectomized mice.     

Anxiogenic-like action of caerulein,a CCK-8 receptor agonist,in the mouse: influence of acute and subchronic diazepam treatment

Summary Effects of caerulein, a cholecystokinin octapeptide (CCK-8) receptor agonist, on exploratory activity of mice were investigated. Exploratory and locomotor activity of animals were measured using elevated plus-maze and open field tests. The systemic administration of caerulein at nonsedative doses (100 ng/kg-1 µkg i. p.) resulted in a significant decrease in the exploratory activity of mice. This effect was completely blocked by proglumide, a CCK-8 antagonist (15 mg/kg i. p.), indicating the participation of CCK-8 receptors. Acute treatment with low doses (0.1–0.75 mg/kg i. p.) of diazepam did not attenuate the anxiogenic-like effect of caerulein, but at more high doses of diazepam the coadministration depressed locomotor activity in mice. After subchronic diazepam treatment (2.5 mg/kg once a day, 10 days, i.p.) tolerance was developed toward the sedative effect of diazepam, and 72 h after withdrawal of the drug the animals showed increased anxiety in the plus-maze test. 30 min after the last injection procedure the anxiogenic-like effect of caerulein (500 ng/kg i. p.) on exploration was absent in both diazepam or vehicle groups. However, 72 h after the last pretreatment injection caerulein (500 ng/kg i. p.) reduced significantly the exploratory activity in control group, whereas it was inactive after diazepam withdrawal. The results obtained in this study support the hypothesis that endogenous CCK-8 an CCK-8 receptors are involved in the neurochemistry of anxiety and the anxiolytic action of benzodiazepine tranquillizers. Send offprint requests to: J. Harro at the above address     

Methylatropine blocks the central effects of cholinergic antagonists

These studies were conducted in order to establish the dose dependency and relative peripheral versus central activity of four prototypical cholinergic antagonists on the rodent passive avoidance response, a widely used animal model of retention. Subcutaneous administration of 0.1 to 100mg/kg revealed a potency profile of scopolamine > atropine methylscopolamine >/= methylatropine for the impairment of passive avoidance responding. A series of neurological assessments of the doses used indicated that side effects alone were not sufficient to impair passive avoidance responding. Although inactive when delivered peripherally, methylatropine was able to produce retention deficits at 10nmol (3.66μg) when administered intracerebrally. To further evaluate whether systemic methylatropine could enter the central nervous system, either scopolamine or atropine was administered subcutaneously in mice and rats pretreated with 10-100mg/kg methylatropine. The deficit-producing effects of scopolamine and atropine were abolished with methylatropine. Thus methylatropine is an exclusive peripheral antagonist; its ability to block the deficit-producing effects of scopolamine and atropine may occur through a change in blood-brain barrier permeability or through uncharacterized pharmacokinetic properties.     

Dose-related facilitation and inhibition of passive avoidance behavior by the ACTH 4-9 analog (ORG 2766)

The effects of "low" and "high" doses of the ACTH 4-9 analog (ORG 2766) were studied on passive avoidance behavior of rats compared to ACTH 4-10 and [D-Phe7] ACTH 4-10. All peptides increased avoidance latency in a dose-dependent manner. However, "high" doses of ORG 2766 (500 and 1000 ng/rat) inhibited passive avoidance retention. "High" amounts of ACTH 4-10 and [D-Phe7] ACTH 4-10 still facilitated passive avoidance behavior. "High" doses of ORG 2766 like "low" amounts of this peptide delayed extinction of active avoidance behavior. "High" doses of [D-Phe7] ACTH 4-10 like "low" amounts of this peptide facilitated extinction of active avoidance behavior. The substituted analog apparently carries a dual effect on passive avoidance behavior.     

N alpha-acetyl-[Arg8]vasopressin antagonizes the behavioral effect of [Cyt6]vasopressin-(5-9), but not of vasopressin

It has been found recently that N alpha-acetyl-[Arg8]vasopressin (Ac-VP) is present in the brain of rats. The physiological significance of this peptide is as yet unknown. Therefore, the central nervous system effects of this peptide were investigated, namely, its effects on passive avoidance behavior, exploratory behavior and body temperature. The interaction of Ac-VP with the central nervous system effects of vasopressin (VP) was also studied. Ac-VP had a slight agonistic effect on passive avoidance behavior, i.e. it facilitated passive avoidance behavior at a dose 100 times higher than that of VP. Relatively low doses (3-10 ng) of Ac-VP attenuated passive avoidance behavior, which suggests that Ac-VP interfered with an endogenous compound involved in the control of passive avoidance responding. Ac-VP was also able, albeit in higher doses (30 ng), to competitively antagonize the effect of [Cyt6]VP-(5-9), a highly potent, putative endogenous metabolite of vasopressin in the rat brain. This antagonism could be due to an interaction of Ac-VP with sites other than the V1 vasopressin receptor. Ac-VP had no significant influence on other central nervous system effects of the hormonally active nonapeptide VP, such as exploratory behavior and body temperature. These effects were readily antagonized by the V1 vasopressin receptor antagonist d(CH2)5Tyr(Me)VP. Ac-VP may be competitive antagonist of behaviorally active vasopressin metabolite(s) in the brain.