GLUCOSE-ENHANCED PERFORMANCE BY AGED RATS ON A TEST OF CONDITIONAL DISCRIMINATION-LEARNING

Groups of normal old rats and young adult rats were administered a tes t of conditional discrimination learning (CDL) with variable intervals between stimulus presentation and response selection. Previous work w ith this task showed that CDL acquisition depends on frontal-lobe invo lvement, whereas the ability to recall conditional stimuli at relative ly long intervals requires an intact hippocampus. Old rats were slower to learn the CDL habit and their impairment increased with the length of the stimulus-response interval. Peripheral injections of glucose ( 100 mg/kg) improved performance of old rats at delays of 5 and 15 sec, but had no effect in the 0-sec delay condition. Young rats did not re spond to glucose treatment. The enhancing effects of glucose in the ol d group were found to correlate positively with measures of glucose me tabolism. The results provide evidence that glucose-induced attenuatio n of cognitive loss in old rats is especially pronounced for specific memory function under hippocampal control.