Repeated treatment with cholecystokinin octapeptide improves maze performance in aged Fischer 344 rats.

Previous studies have shown that sulfated cholecystokinin octapeptide (CCK-8S) can improve learning in adult rodents when administered systemically or into the central nucleus of amygdala. Here we analyzed the effect of repeated intraperitoneal (i.p.) injection of CCK-8S on the performance of 26-month-old Fischer 344 rats in different versions of the Morris water maze and in a rota-rod test of motor coordination. Old rats were injected daily with different doses of CCK-8S (0.32 to 8.0 microg/kg; IP) 10 min before the behavioral tests. Control groups included vehicle-injected old and adult (3-month-old) F 344 rats. To control for a possible development of tolerance to the behavioral effects of repeated CCK-8S administration, groups of aged rats were included which were subjected to an acute rather than a repeated CCK injection schedule. The repeated administration of CCK-8S did not influence the performance of the old rats in the hidden-platform version of the maze. In addition, the acute treatment with CCK-8S failed to modify navigation performance in this task, suggesting that drug-tolerance may not account for the lack of behavioral effects seen after repeated CCK-8S injection. During the "probe trial", the percentage of animals per group, which swam exactly across the former platform site, was markedly increased in aged rats treated repeatedly with 1.6 microg/kg CCK-8S. This might be indicative of improved retention of the prior platform location and/or a higher resistance of the learned escape response to extinction. The specificity of the effect of CCK-8S on processes related to spatial learning and memory is supported by the lack of effect on motor performance.

Lesion of the median raphe nucleus: a combined behavioral and microdialysis study in rats.

The purpose of the present study was to investigate the behavioral consequences and the neurochemical correlates of a 5,7-dihydroxytryptamine (5,7-DHT) lesion of the median raphe nucleus (MRN) in rats. Anxiety-related behavior was assessed in the elevated plus maze test on days 5, 14, and 21 after lesioning. In general, behavior of MRN-lesioned rats was unchanged when compared with sham-lesioned or untreated controls. Neurochemically, microinjection of 5,7-DHT into the MRN resulted in 87.5% depletion of hippocampal 5-HT content. Using the in vivo microdialysis technique, the exposure of 5,7-DHT-lesioned rats to the elevated plus-maze failed to increase extracellular 5-HT release (94%) in the hippocampus, as shown in sham-lesioned (150%) or untreated controls (194%). Moreover, application of fenfluramine (10 mg/kg, i.p.) evoked a 10-fold increase in hippocampal extracellular 5-HT levels in sham-lesioned animals, whereas in 5,7-DHT lesioned rats 5-HT was only slightly increased. The results demonstrate, that a marked reduction of 5-HT release from the MRN is not necessarily accompanied by anxiolytic-like behavior.

Does increased endogenous CCK interact with serotonin to reduce food intake in rats?

The present study was aimed to test the hypothesis that increased endogenous CCK may interact with the anorectic serotonergic agent dl-fenfluramine to reduce food intake in rats. Previous studies, using selective CCK receptor antagonists, could demonstrate CCK-dependent 5-HT-induced anorexia. In the present approach, we used protease inhibitors to increase levels of endogenous CCK instead of blocking CCK receptors by antagonists. The protease inhibitors we used were soybean trypsin inhibitor (STI) and camostate. We hypothesized that combining the anorectic serotonergic drug dl-fenfluramine with either STI or camostate should result in an enhanced hypophagic effect when compared to single drug treatment. All feeding experiments were performed in non-deprived rats during night time feeding. Given alone, STI (500 mg/kg, po), camostate (200 mg/kg po) and also fenfluramine (1-9 mg/kg ip) reduced significantly food intake, with a more pronounced effect following fenfluramine. However, the experiments do not provide evidence for any additive or synergistic action between camostate or STI and the anorectic serotonergic drug dl-fenfluramine on food intake.

Role of cholecystokinin type B receptors in ultrasound induced behavior in rats.

The cholecystokinin-tetrapeptide (CCK-4) can induce panic attacks in humans. The present study investigates the effects of CCK-4 and the CCK-B receptor antagonist L-365.260 on ultrasound induced defense behavior in the rat that may model the unconditioned aspects of panic behavior in man. CCK-4 (50 microg/kg) increased the defense response induced by ultrasound (95 dB) an effect prevented by pretreatment with L-365.260 (10 microg/kg). Compared with other antipanic/panicogenic drugs the effects of CCK-4 and L-365.260 were relatively small. In conclusion, drugs acting at the CCK-B receptor appear to have only a minor role in the modulation of an unconditioned aversive response.

Perinatal elevation of hypothalamic insulin, acquired malformation of hypothalamic galaninergic neurons, and syndrome x-like alterations in adulthood of neonatally overfed rats.

Overnutrition during critical developmental periods is suggested to be a risk factor for obesity and associated metabolic disorders in later life. Underlying mechanisms are unknown. Neuropeptides are essentially involved in the central nervous regulation of body weight. For instance, hypothalamic galanin (GAL) is a stimulator of food intake and body weight gain. To investigate long-term consequences of early postnatal overfeeding, the normal litter size of Wistar rats (n=10; controls) was reduced from day 3 to day 21 of life to only 3 pups per mother (small litters, SL; overnutrition). Throughout life, SL rats displayed hyperphagia (p<0.01), overweight (p<0.0001), hyperinsulinemia (p<0.01), impaired glucose tolerance (p<0.001), elevated triglycerides (p<0.001), and an increased systolic blood pressure (p<0.05). In adulthood, an increase of GAL-neurons in the arcuate hypothalamic nucleus (ARC) was found (p<0.001), positively correlated to body weight (p<0.001). A second experiment revealed hyperinsulinemia (p<0.001) and increased hypothalamic insulin levels (p<0.05) in SL rats during early postnatal life. Already on day 21 of life, i.e., at the end of the critical hypothalamic differentiation period, in SL rats the number of GAL-neurons was increased in the ARC (p<0.001), showing a positive correlation to body weight and insulin (p<0.05). In conclusion, neonatally acquired persisting malformation of hypothalamic galaninergic neurons, induced by early overfeeding and hyperinsulinism, might promote the development of overweight and syndrome X-like alterations during life.

Major biological actions of CCK--a critical evaluation of research findings.

Cholecystokinin (CCK) is one of the first discovered gastrointestinal hormones and one of the most abundant neuropeptides in the brain. Two types of CCK receptors have been identified: (1) CCK-A receptors are mainly located in the periphery, but are also found in some areas of the CNS; and (2) CCK-B receptors are widely distributed in the brain. Major biological actions of CCK are the reduction of food intake and the induction of anxiety-related behavior. Inhibition of feeding is mainly mediated by the A-type receptors, whereas anxiety-like behavior is induced by stimulating B-type receptors. This paper presents new findings on the effects of the biologically active CCK agonists, CCK-8S, CCK-4, and A71378. The results reviewed suggest that the hypophagic effects of CCK are strongly dependent on the experimental design, sex, and age of the rats. For example, food intake measured during the night or after food deprivation is reduced by CCK-8S in young adult and aged rats, whereas, under fixed feeding conditions, CCK-8S does not inhibit food intake in young adult rats. The sensitivity to the hypophagic CCK effect increases with age in male and female rats; however, female rats are less sensitive to the CCK action. Further, using a nongenetic and non-stressful model of obesity due to unspecific postnatal overfeeding, the satiating effect of moderate CCK-8S doses is weaker in obese than in normal rats. Again, the hypophagic effect is more pronounced in male than in female obese and normal rats. Considering that aversive reactions in rats are markedly influenced by strain and breeding-line variations, research results in this area are critically reviewed. It is shown that anxiety-like symptoms can only be induced by a selectively acting CCK-B agonist, whereas mixed CCK-A and -B agonists and selective CCK-A agonists fail to change behavior in anxiety tests. CCK-4 induces stable and reproducible anxiogenic-like behavior only in certain rat strains. Moreover, CCK-4 effects can be demonstrated in the conflict test, in the ultrasonic vocalization test in rat pups, on the elevated plus maze, and in the black and white box, but not in the social interaction test. CCK has also been reported to modulate memory processes. On the one hand, CCK-8S and CCK-4 enhanced habituation to the novelty of a hole board. On the other hand, repeated administration of CCK-8S did not improve maze performance in aged rats. The literature on the behavioral pharmacology of CCK is rife with inconsistency and contradiction. The major biological actions of CCK depend on the receptor selectivity of the CCK fragments used and on organismic and procedural variables. All these variables potentially influence behavioral responses in rats. Therefore, in CCK research more attention should be paid to the importance of these methodological factors.

Pharmacological evaluation of a modified open-field test sensitive to anxiolytic drugs.

In a recent study it has been shown that benzodiazepine receptor agonists attenuate novelty-induced suppression of feeding and increase the percentage of animals feeding in the open field. Food-deprived rats were placed in one corner of the open field containing food in the center. The number of rats beginning to eat in the first 5 min was recorded. In the present study this test was validated pharmacologically using known "anxiolytic" or "nonanxiolytic" drugs. The following substances (effective doses, given IP) increased the number of rats feeding within 5 min in the center of the open field: meprobamate (30.0-300 mg/kg), 8-OH-DPAT (10 and 30 microg/kg), ipsapirone (1.0 and 2.0 mg/kg), ritanserin (0.125-0.5 mg/kg), tropisetron (0.1-10.0 microg/kg), ondansetron (0.3-3.0 microg/kg), lisuride (0.28-0.55 mg/kg), morphine (0.3 and 1.0 mg/kg), propranolol (0.3 and 1.0 mg/kg), clozapine (1.0 mg/kg). Drugs without "anxiolytic" effects in other animal models or in humans, including amphetamine, apomorphine, haloperidol, sulpiride, and mCPP did not increase the incidence of food intake in this test. Ethanol and hexobarbital, in nonsedative doses, had no effect in this paradigm. Drugs and doses effective in the modified open-field test caused no increase in food intake in an independent food consumption test using food-deprived rats staying in the familiar cages. The results suggest that the modified open-field test can detect "anxiolytic" drug properties and is valid for the assessment of "anxiolytic" effects from different classes of drugs.

Effect of L364.718 during suckling on the sensitivity to the hypophagic effect of cholecystokinin in adult rats.

1. In the present study it was investigated whether drugs acting at the cholecystokinin (CCK)-A receptor given to rat pups may result in long-lasting changes in body weight or regulation of food intake controlled by CCK. 2. From day 3 to day 10 of life, male and female Wistar rat pups were treated with the CCK-A receptor antagonist L-364.718 and the CCK-A + B agonist CCK-8S. 3. In adult rats, treated with L364.718 during suckling, the sensitivity to the acute hypophagic action of CCK-8S was weaker or abolished compared to adults treated with saline during suckling. In adult rats given CCK-8S during suckling acute treatment with CCK-8S reduced food intake to the same extent as in the group treated with saline postnatally. 4. These data show that early postnatal treatment with the CCK-A receptor antagonist L364.718 has an impact on the hypophagic response to CCK-8S in later life.

Obesity induced by unspecific early postnatal overfeeding in male and female rats: hypophagic effect of CCK-8S.

The response to cholecystokinin (CCK) as a satiety peptide in obesity or anorexia has been tested mainly in extreme models of food intake control. In the present study, the effect of CCK-8S on food intake was investigated in a nongenetic and less-stressful model of obesity due to unspecific early postnatal overfeeding in male and female rats. Reducing the normal litter size of ten to three newborn rats on day 3 of life led to an enhanced food intake resulting in an increased body weight until adulthood. Freely fed male and female, normal and obese rats were given 10 micrograms/kg CCK-8S i.p. on day 41 and 40 micrograms/kg CCK-8S on day 91 of life and food intake was measured for 24 h. Compared with treatment with saline (i.p.) 1 day before the test, the lower dose of 10 micrograms/kg CCK-8S reduced food intake for 2 h in normal, but not in obese rats. Conversely, the higher dose of 40 micrograms/kg CCK-8S reduced food intake in both normal and obese rats for 2 h, but this effect was more evident in the obese rats. Moreover, the satiating effect of CCK-8S was more pronounced and longer lasting in male than in female rats. In summary, the data suggest that the response to CCK-8S differs in normal and obese rats and depends on sex.

Comparison of the satiating effect of the CCKA receptor agonist A71378 with CCK-8S.

The satiating effect of the selective cholecystokininA (CCKA) receptor agonist A71378 and the mixed A and B receptor agonist CCK-8S were compared in 24-h food-deprived rats. After systemic application of 1.6, 8.0, and 40 micrograms/kg A71378 or CCK-8S, respectively, food intake was measured for 24 h. During the first hour A71378 and CCK-8S decreased food intake similarly. Two and 4 h after treatment, the satiating effect of A71378 continued. In contrast, 2 h after administration of CCK-8S a slight effect was observed at the highest dose (40 micrograms/kg), which totally disappeared after 4 h. In summary, the effect of A71378 on food intake is longer lasting compared to CCK-8S.

Effects of cholecystokinin octapeptide (CCK-8) on food intake in adult and aged rats under different feeding conditions.

The effects of CCK on food intake were investigated under fixed feeding conditions in comparison to a test meal taken after 16 h of food deprivation. The experiments were performed on young adult rats (8 weeks old) as well on aged rats (23 months old). Intraperitoneal CCK-8 (8 and 40 micrograms/kg) significantly reduced the size of a test meal following 16-h food deprivation. This effect was independent of the age of the rats. However, under fixed feeding conditions neither of the doses used in this study reduced food intake in the young adult rats, whereas the highest dose of 40 micrograms/kg did so in the aged rats. These results suggest that the hypophagic effect of exogenous CCK-8 depends on experimental conditions, food intake being reduced after a period of food deprivation but not under a fixed feeding regimen in adult animals. Furthermore, the data suggest that age is a factor contributing to the complex behavioral actions of CCK, because only old animals were more susceptible to an anorectic action of CCK under the fixed feeding schedule. An explanation may lie in an interaction of other known behavioral effects of CCK (e.g., anxiogenic, mnemonic action) with its effects under the different feeding schedules.

Application of 'nose-poke habituation' validation with post-trial diazepam- and cholecystokinin-induced hypo- and hypermnesia.

The present study describes the use of nose-poke habituation as a memory task and demonstrates that it is sensitive to hypo- and hypermnestic pharmacological treatments administered post-trial. Habituation of nose-poke behavior of rats was defined as a reduction in number of nose-pokes compared to baseline. It was measured using a board with 16 holes, to which animals were exposed on 2 consecutive days (baseline and test) for 10 min, respectively. After the first exposure, rats were injected intraperitoneally (i.p.) immediately or with a delay of 2.5 h with doses of diazepam (0.9-4.5 mg/kg) known to be hypomnestic, or cholecystokinin (CCK-8S; 0.2-25 micrograms/kg), which was reported to have memory facilitating effects. An enhancement of habituation in comparison with vehicle controls was interpreted in terms of a hypermnestic effect of the treatment. Conversely, hypomnestic action of the drug treatment was inferred from a reduced habituation. The results show that when diazepam was injected immediately post-trial, the normal reduction in number of nose-pokes during test was prevented, indicative of a failure to habituate presumably due to an amnesia for the baseline/training trial. In contrast, enhanced habituation (facilitation of memory) was induced when CCK-8S was injected immediately post-trial, as reflected by a decrease in number of nose-pokes during test compared to control animals. The effects were not due to enduring proactive effects of the compounds on performance during test, since post-trial injections of diazepam or CCK-8S with a delay of 2.5 h did not have the effects that immediate post-trial injection had.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation-dependent effect of antiepileptic drugs in amygdala kindled rats on both seizure score and duration of afterdischarges.

The ED50 for abolition of generalized seizures and reduction of afterdischarges to 20% of the control duration was determined in kindled rats for phenobarbital, carbamazepine, phenytoin, valproic acid, clonazepam, and diazepam, both at a stimulation intensity of 200 microA and at 10 microA above the threshold for generalized seizures (threshold stimulation). Phenobarbital, carbamazepine, and valproic acid acted in a stimulus-dependent manner, i.e. the ED50 was higher at 200 microA than at threshold stimulation. Phenytoin had the same ED50 irrespective of the stimulus intensity. Generalized seizures and afterdischarges were suppressed by the same doses of the drugs mentioned. The benzodiazepines, clonazepam and diazepam, had a differential effect: they suppressed generalized seizures at low doses, whereas afterdischarges were only suppressed incompletely at relatively high doses. The ED50 of both benzodiazepines was independent of stimulus intensity. In order to avoid erroneous conclusions a standardization of kindling parameters, especially stimulation intensity, is proposed when drug effects are to be compared.

Evidence for mnemotropic action of cholecystokinin fragments Boc-CCK-4 and CCK-8S.

Memory-modulating and reinforcing effects of the cholecystokinin (CCK) fragments, CCK-8S and Boc-CCK-4, after systemic application in rats were investigated. Habituation to the novelty of environmental stimuli was used to test for mnemonic effects using two different tasks (rearing behavior in an open field; head-dips in a hole-board). Immediate posttrial administration of CCK-8S and Boc-CCK-4 resulted in a reduction of rearing and head-dip behavior during testing, indicative of enhanced habituation and, thus, facilitation of memory. In contrast, administration of CCK-8S and Boc-CCK-4 with a delay of 2.5 or 5 h after training or pretrial injection of CCK-8S did not enhance habituation. No evidence for reinforcing or aversive properties of CCK-8S and Boc-CCK-4 was observed in a conditioned place preference task. In summary, the results indicate memory-enhancing effects of peripherally, posttrial-administered CCK-8S and Boc-CCK-4.

Effect of psychotropic agents on a model of absence epilepsy in rats.

The effect of different groups of psychotropic agents on the spontaneous absence-like paroxysms in the ECoG of rats was studied in order to evaluate the specificity of the model for antiabsence drugs. Morphine-like analgesics increased the number of paroxysms, whereas this was depressed or the discharges were completely abolished by the following drugs: d-amphetamine, tricyclic antidepressants, centrally acting anticholinergics and L-DOPA, NMDA antagonists and memantine. Since the latter drugs have been reported to be effective in petit mal epilepsy, or the NMDA antagonists and memantine, have a potential anticonvulsant effect, the results are in favour of the usefulness of the model for antiabsence drugs.