CCK-8S increases the firing frequency of CCK-positive neurons and facilitates excitatory synaptic transmission in primary rat hippocampal neurons

The potential role of the cholecystokinin system in declarative memory

As one of the most abundant neuropeptides in the central nervous system, cholecystokinin (CCK) has been suggested to be associated with higher brain functions, including learning and memory. In this review, we examined the potential role of the CCK system in declarative memory. First, we summarized behavioral studies that provide evidence for an important role of CCK in two forms of declarative memory-fear memory and spatial memory. Subsequently, we examined the electrophysiological studies that support the diverse roles of CCK-2 receptor activation in neocortical and hippocampal synaptic plasticity, and discussed the potential mechanisms that may be involved. Last but not least, we discussed whether the reported CCK-mediated synaptic plasticity can explain the strong influence of the CCK signaling system in neocortex and hippocampus dependent declarative memory. The available research supports the role of CCK-mediated synaptic plasticity in neocortex dependent declarative memory acquisition, but further study on the association between CCK-mediated synaptic plasticity and neocortex dependent declarative memory consolidation and retrieval is necessary. Although a direct link between CCK-mediated synaptic plasticity and hippocampus dependent declarative memory is missing, noticeable evidence from morphological, behavioral, and electrophysiological studies encourages further investigation regarding the potential role of CCK-dependent synaptic plasticity in hippocampus dependent declarative memory.

The effects of CCK-8S on spatial memory and long-term potentiation at CA1 during induction of stress in rats

Objectives

Cholecystokinin (CCK) has been proposed as a mediator in stress. However, it is still not fully documented what are its effects. We aimed to evaluate the effects of systemic administration of CCK exactly before induction of stress on spatial memory and synaptic plasticity at CA1 in rats.

Materials and Methods

Male Wistar rats were divided into 4 groups: the control, the control-CCK, the stress and the stress-CCK. Restraint stress was induced 6 hr per day, for 24 days. Cholecystokinin sulfated octapeptide (CCK-8S) was injected (1.6 µg/kg, IP) before each session of stress induction. Spatial memory was evaluated by Morris water maze test. Long-term potentiation (LTP) in Schaffer collateral-CA1 synapses was assessed (by 100 Hz tetanization) in order to investigate synaptic plasticity.

Results

Stress impaired spatial memory significantly (P<0.01). CCK in the control rats improved memory (P<0.05), and prevented the impairments in the stress group. With respect to the control group, both fEPSP amplitude and slope were significantly (P<0.05) decreased in the stress group. However, there were no differences between responses of the control-CCK and Stress-CCK groups compared to the control group.

Conclusion

The present results suggest that high levels of CCK-8S during induction of stress can modulate the destructive effects of stress on hippocampal synaptic plasticity and memory. Therefore, the mediatory effects of CCK in stress are likely as compensatory responses.

Effects of repeated treatment with cholecystokinin sulfated octapeptide on passive avoidance memory under chronic restraint stress in male rats

Background:

Cholecystokinin (CCK), a peptide hormone found in the gut is the most abundant peptide neurotransmitter in the brain as well, and its effects on learning, memory, and anxiety have been shown. However, it is not clear whether this substance acts as a mediator for anxiety and stress induction or inhibits them. Hence, the purpose of this study was to evaluate the effects of CCK on memory function under stress conditions.

Materials and Methods:

Male Wistar rats were divided into four groups: The control, the control-CCK, the stress, and stress-CCK. To induce stress, the rats were placed within adjustable restraint chambers for 6 h daily, for 24 days. CCK-8S (cholecystokinin sulfated octapeptide was injected before induction of stress (1.6 μg/kg, intraperitoneal) for 24 days. Passive avoidance learning test was used for evaluation of learning and memory. Rats received foot electrical shock before stress induction and CCK injection and step through latencies were evaluated 1-day after the last session of stress and treatments.

Results:

Stress impaired memory significantly (P < 0.05). Although CCK per se decreased memory (P < 0.05), it prevented the memory impairments in the stress group as there was no significant difference between the control and stress-CCK groups.

Conclusion:

Stress has a profound effect on cognition and CCK probably acts as a mediator for its action. Our results showed that a high concentration of CCK during stress may be helpful in alleviating the effects of stress on the brain.