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

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.

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.

Behavioral effects of the cyclic cholecystokinin peptide analogue JMV-320

The in vivo effects of JMV-320 (a highly selective CCKB receptor ligand) and of CCK-4 on exploratory activity and memory in rats were compared. JMV-320 and CCK-4 did not modulate exploratory activity in an open field test but decreased it in an elevated plus-maze. CCK-4 (50 micrograms/kg) impaired passive avoidance response 3 h after training and JMV-320 (1 and 10 micrograms/kg) decreased active avoidance response 24 h after training. The behavioral effects of JMV-320 resemble the effects of CCK-4 and suggest that in vivo JMV-320 acts as a CCKB receptor agonist.

Effects of cholecystokinin octapeptide and BC 264, a potent and selective CCK-B agonist on aspartate and glutamate release from rat hippocampal slices

In rat hippocampal slices, BC 264 (0.1-1 microM), a highly potent and selective CCK-B agonist, was found to increase basal release of endogenous glutamate and aspartate but not that of GABA. The natural peptide cholecystokinin octapeptide (CCK8) at 1 microM, induced the same effect. The selective CCK-B receptor antagonist, L-365,260, completely reversed these responses, confirming that they are related to CCK-B receptor activation. In the absence of extracellular Ca2+, the increase in excitatory amino acid release was completely abolished. In contrast to the basal release, the potassium evoked release of aspartate and glutamate was not modified by BC 264.

Cholecystokinin receptors and memory: a radial maze study

CCK receptor agonists and antagonists have repeatedly been demonstrated to improve and impair, respectively, learning and memory functions. However, all studies to date have exploited avoidance paradigms. In the present study, the effect of some CCK receptor agonists and antagonists on the ability to learn an appetitively motivated task and to influence spatial working memory was investigated. In the first experiment, drugs were given immediately after each training session in the radial maze and the animals were tested, drug-free, during a 2-week period. After the initial treatments with caerulein, an unselective CCK receptor agonist (100 ng/kg SC), the animals were slightly less successful to obtain food pellets during the sessions on the first 2 days; whereas proglumide, an unselective CCK receptor antagonist (1 mg/kg SC) was without any effect. However, on the following days, all the three groups of rats (saline, caerulein, and proglumide) performed in a similar way. In the second experiment, drugs were given before each test session to well-trained animals. Scopolamine (0.15 and 0.3 mg/kg IP), the reference amnestic drug, produced dose-dependent impairment of working memory in the radial maze test. Proglumide (1 and 10 mg/kg SC) and devazepide, (a selective CCK-A receptor antagonist; 0.01 and 1 mg/kg SC), as well as caerulein (0.01, 0.1 and 1 microgram/kg SC) and CCK-4 (a selective CCK-B receptor agonist; 25 and 50 micrograms/kg SC) had no reliable effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of anti-CCK-8 antiserum on acquisition and retrieval by mice in an appetitive task

Endogenous cholecystokinin (CCK) was blocked in the posterior cingulate cortex of BALB/c mice using a local injection of anti-CCK-8 antiserum, and memory effects were tested using Go-No Go visual discrimination conditioning. Injection of 0.4 microliter of anti-CCK-8 antiserum diluted to 1:10, 10-15 min before each session, produced substantial learning impairment on the discrimination task. But when injections were stopped, animals began to learn the task normally, showing that the anti-CCK antiserum effect was reversible. When the antiserum was administered at the same dose before a single test session 14 days after the end of the initial training, the retrieval process was also disturbed. These results show that cingulate cholecystokinin is essential for memory processes and suggest that cholecystokinin octapeptide may be a neuromodulator of the thalamo-cingulate pathway of Papez's circuit, which is involved in memory processes.

Effect of caerulein on decreased latency of passive avoidance response in rats treated with NMDA receptor antagonists

The effect of subcutaneous injection of caerulein on memory impairment induced by intracerebroventricular administration of NMDA receptor antagonists was examined in the passive avoidance response of the rat. When rats were treated with AP5, AP7, CPP or MK-801, the retention latencies decreased markedly. However, in rats that received caerulein immediately after the training trials, the latency increased to some extent. Pretreatment with caerulein and subsequent injection of the competitive NMDA receptor antagonists AP5, AP7 and CPP caused a more apparent increase in the latency. The noncompetitive NMDA receptor antagonist MK-801 was not affected by pretreatment with caerulein. The difference might be, at least in part, due to the sites of action of these NMDA receptor antagonists.