Yoko Okaichi

Long-term dietary restriction causes negative effects on cognitive functions in rats.

Long-term dietary restriction is reported to increase life span and improve age-related cognitive deficits. The present study shows that the restriction increases the life span of rats but decreases their cognitive ability. Thirty-two rats were divided into restricted and ad lib feeding groups at 2.5 months of age. The restricted rats were kept at a weight of 280g. The restricted rats were poor in performing the Morris water maze task at 7-12 months. At 17-18 months, they were poor in performing the delayed matching-to-place task. At 24-27 months, the surviving 13 restricted and 5 ad lib rats performed the spatial discrimination task. The restricted rats were also poor in performing this task. Injection of glucose prior to the discrimination task improved their performance to the level of the ad lib rats. These results suggest that dietary restriction is beneficial for longevity but has negative effects on the performance of cognitive tasks, and that the cause of the negative effects may be a reduced availability of glucose in the food-restricted aged rats.

Arachidonic acid improves aged rats' spatial cognition

To examine the effects of arachidonic acid (AA) on age-related cognitive deficits, F-344 rats were administered with an AA-supplemented powder diet from 79 weeks of age (OA group). For comparison, we also used an age-matched control group of animals (OC group) that were fed with a non AA-supplemented powder diet. When the subjects reached 87 weeks old, they were trained for Morris water maze place and cue tasks. Escape latencies of the OA group on the place task were significantly shorter than those of the OC group in the latter half of training. The probe test showed that OA rats remembered the trained platform position significantly better than OC rats. In the cue task training, the OC group was significantly slower than the OA group at the beginning of training, but their performance soon matched with that of the OA group. Fatty acids in the hippocampi were measured after the behavioral testing. There was no difference in AA composition in hippocampal phospholipids between the OA and OC groups. However, regression analysis conducted on AA composition and place task performance showed a significant correlation between these two parameters. The present study suggests that AA administration to aged animals can alleviate age-related deficits in spatial cognition.

Open‐field Behaviors and Water‐maze Learning in the F Substrain of Ihara Epileptic Rats

Summary:  Purpose: Genetically epileptic model rats, Ihara epileptic rat (IER/F substrain), have neuropathologic abnormalities and develop generalized convulsive seizures when they reach the age of ∼5 months. Because the neuromorphologic abnormalities are centered in the hippocampus, we expected to observe spatial cognitive deficits. The present study aimed to evaluate emotionality and learning ability of the F substrain of IER.

Effects of fimbria-fornix lesions on avoidance tasks with temporal elements in rats

Sidman schedule active avoidance, passive avoidance, and multiple avoidance (continuous alternation of active and passive avoidance) tasks were given to fimbria-fornix (FF)-lesioned (n = 10) and control (n = 10) rats to assess the effects of fimbria-fornix lesions on unsignaled avoidance learning with temporal cognition requirement. Active avoidance required subjects to make running responses, and passive avoidance required them to stop running and remain immobile on a running wheel. The tasks could be achieved purely by temporal cues, and no spatial elements were involved. Animals in the FF group performed the active, passive, and multiple avoidance tasks as well as control animals, showing no deficits by lesions in either the number of running responses nor the number of shocks received, although animals in the FF group displayed a greater negative transfer in passive avoidance when they received the active training before the passive training. The results indicate that fimbria-fornix lesions do not impair avoidance tasks when the tasks do not require spatial information, even if temporal information and/or inhibition are necessary to perform the tasks.

Posttraining glucose in inhibitory avoidance facilitates memory consolidation in rats

The present research examines the effects of glucose on memory consolidation in rats over time. Several groups of rats were trained on inhibitory avoidance tasks and were then injected with 500 mg/kg of glucose or saline intraperitoneally under different footshock-drug injection intervals. Memory-facilitating effects were observed only at intervals of less than 30 min, suggesting that glucose affects the memory consolidation process. Our results with rats agree with the results of Kopf, Opezzo, and Baratti (1993), who worked with mice. The present research also showed that glucose does not have nonspecific effects on memory but does facilitate the memory of a shock experience.