Impaired learning and memory in OLETF rats without cholecystokinin (CCK)-A receptor.

Cholecystokinin (CCK) is one of the most abundant neurotransmitter peptides in the brain. As OLETF rats lack CCK-A receptor because of a genetic abnormality, we examined whether learning and memory were impaired in these animals using an elevated eight-arm radial maze. After the completion of a radial maze study, the animals were sacrificed for histological examination of the brain. In some animals, long-term potentiation (LTP) in the hippocampus was measured. In the radial maze, the level of activity (seconds/entry) and the time remaining in the arms were significantly longer in OLETF rats. The number of errors was also significantly higher, and that of the correct choices was significantly lower in OLETF rats compared to the controls (LETO rats). The LTP of the population spike was significantly lower in the OLETF than in the LETO rats. No histological abnormalities were observed. From these observations, we concluded that learning and memory functions were impaired in the OLETF rats.