Cholecystokinin octapeptide prevents extinction of active avoidance behavior in the rat

Early social learning triggers neurogenomic expression changes in a swordtail fish

Mate choice can play a pivotal role in the nature and extent of reproductive isolation between species. Mating preferences are often dependent on an individual's social experience with adult phenotypes throughout development. We show that olfactory preference in a swordtail fish (Xiphophorus malinche) is affected by previous experience with adult olfactory signals. We compare transcriptome-wide gene expression levels of pooled sensory and brain tissues between three treatment groups that differ by social experience: females with no adult exposure, females exposed to conspecifics and females exposed to heterospecifics. We identify potential functionally relevant genes and biological pathways differentially expressed not only between control and exposure groups, but also between groups exposed to conspecifics and heterospecifics. Based on our results, we speculate that vomeronasal receptor type 2 paralogs may detect species-specific pheromone components and thus play an important role in reproductive isolation between species.

CCK in anxiety and cognitive processes

Extensive studies were carried out on the involvement of the CCKergic system in anxiety-, panic- and stress-related behaviour. The stimulation of CCK-A or CCK-B receptors is implicated in the physical and psychological responses of CCK to stress. Furthermore, several selective CCK-B agonists produce anxiogenic-like effects, while CCK-B antagonists induce anxiolytic-like responses in several models of anxiety. However, BC264 a highly selective CCK-B agonist, does not produce anxiogenic-like effects but increases attention and/or memory. These effects are dependent on the dopaminergic systems. Together with biochemical data, this led to the hypothesis of the existence of two CCK-B binding sites, CCK-B1 and CCK-B2, which could correspond to different activation states of a single molecular entity. Investigations into CCK-B1 and CCK-B2 systems might be of critical interest, since only one site, CCK-B1, appears to be responsible for the effects of anxiety. Furthermore, the improvement of attention and/or memory processes by CCK, through CCK-B2 receptors, could offer a new perspective in the treatment of attention and/or memory disorders.

Systemic administration of CCK-8S, but not CCK-4, enhances dopamine turnover in the posterior nucleus accumbens: a microdialysis study in freely moving rats

The present study was carried out to examine the effects of peripheral administration of sulfatedcholecystokinin octapeptide (CCK-8S) on dopamine (DA) turnover in the posterior nucleus accumbens (PNAc) and the caudate-putamen (CP) in awake rats. Microdialysis was used to quantify the extracellular concentrations of DA and its two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). Intraperitoneal injections of CCK-8S (0.3 mg/kg b.wt.) caused a significant increase in DOPAC and HVA concentrations in the PNAc, but did not affect the DA level. Such increases in the metabolite contents were not found in the CP. Similar injections of vehicle (1% NaHCO3 solution, 1 ml/kg b.wt.) did not have an effect in either brain region. In an attempt to determine the type of receptor involved in the CCK-8S-induced changes, CCK tetrapeptide (CCK-4, 0.3 mg/kg b.wt.) known to have high affinity for CCKB subtype or vehicle (10% DMSO-saline, 1 ml/kg b.wt.) was administered intraperitoneally. Neither CCK-4 nor vehicle caused significant changes in any of extracellular DA, DOPAC and HVA contents in the PNAc. These results suggest that peripherally administered CCK-8S has stimulatory effects on the dopaminergic system in the PNAc, and raise the possibility that the effect appears to be mediated via CCKA receptors.

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.

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.

Systemic administration of a cholecystokinin analogue, ceruletide, protects against ischemia-induced neurodegeneration in gerbils

The neuroprotective action of a cholecystokinin octapeptide analogue, ceruletide, was evaluated in models of cerebral ischemia using Mongolian gerbils. Ceruletide significantly suppressed the hyperactivity and amnesia induced by ischemia when injected s.c. 30 min before 5-min occlusion of the bilateral common carotid arteries at room temperature or immediately after their reperfusion. Ceruletide also reduced behavioral changes in ischemic gerbils whose body temperature was maintained at 37 degrees C during the 3-min occlusion. In these groups, delayed neuronal cell death in the hippocampal CA1 area following ischemia was markedly attenuated by s.c. administration of ceruletide. On the other hand, ceruletide could not inhibit the behavioral changes or the neurodegeneration induced in the hippocampal CA1 area by 5-min occlusion at 37 degrees C. These findings indicate that peripheral injection of ceruletide produces a neuroprotective action against moderate cerebral ischemia, which is the first evidence suggesting the efficacy of ceruletide in neurodegenerative diseases.

Pretreatment with caerulein protects against memory impairment induced by protein kinase C inhibitors in the rat

The effect of subcutaneously injected caerulein (CER) on memory impairment induced by protein kinase C (PKC) inhibitors, H-7 and melittin, was examined in rats. Intracerebroventricular injection of PKC inhibitors caused marked memory impairment in one-trial passive avoidance response and Morris water tank tasks. However, when rats were pretreated with CER at a subcutaneous dose of 1 microgram/kg 3 hours before the training trials, the reduced latency of the passive avoidance response was significantly increased, and in the Morris water pool tasks the memory deficit induced by PKC inhibitors completely disappeared. These results indicate that CER can offer protection against the effect of PKC inhibitors at least from the viewpoint of the 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.

Long-term diazepam treatment produces changes in cholecystokinin receptor binding in rat brain

This study examined the effect of chronic diazepam administration on central benzodiazepine and CCK-8 receptor binding in rat brain. After a two-week treatment with diazepam (5 mg/kg per day) tolerance developed towards the sedative but not towards the anxiolytic action of this drug as determined using elevated plus-maze and open field tests. The % entries the rats made onto open arms and % time the rats spent in open arms were markedly decreased 24 h after the last dose of diazepam, probably indicating withdrawal anxiety. There were no changes in [3H]flunitrazepam binding either 30 min or 24 h after the last diazepam dose. However, 30 min after the last diazepam administration the apparent number of sulphated [3H]CCK-8 binding sites was significantly increased in the primary olfactory cortex. Acute diazepam treatment (5 mg/kg) had no influence on [3H]flunitrazepam or sulphated [3H]CCK-8 binding in any brain region studied. Cessation of chronic diazepam treatment was followed after 24 h by an increase in the number of CCK-8 receptors in frontal cortex and hippocampus as compared to the vehicle group. These results demonstrate that certain alterations in CCK-8 receptor characteristics may be important in the anti-anxiety effect, tolerance, and withdrawal reaction reaction after benzodiazepine administration.

Memory effect of caerulein and its analogs in active and passive avoidance responses in the rat

The memory effects of caerulein (CER) and its analogs ([des-Gln2]-CER and [Leu5,Nle8]-CER) were compared with that of cholecystokinin octapeptide (CCK-8) using active and passive avoidance responses in rats. In the active avoidance test, single subcutaneous (SC) injection of CER and its analogs immediately after the learning trials at doses of 10 and 100 ng/kg prevented extinction of learned task for 10 days, and at a dose of 1000 ng/kg for at least 15 days, but the effect of CCK-8 was somewhat weaker. In the saline control group, the number of responses decreased after 5 days. In the passive avoidance response, electroconvulsive shock (ECS)-induced amnesia was partially prevented by CCK-8 at doses of 100 and 1000 ng/kg SC, while CER and its analogs at doses of more than 100 ng/kg totally prevented the ECS-induced amnesia. Intraperitoneal administration of scopolamine caused complete amnesia which was also partially prevented by CCK-8, while CER could totally prevent the amnesia following SC injection of 2 micrograms/kg. These results indicate that CER and its analogs are more effective than CCK-8 for preventing experimental amnesia.