Complex maze performance in young and aged rats: Response to glucose treatment and relationship to blood insulin and glucose

Abstract

In aged rats and humans, impaired glucose regulation has been correlated with poor memory performance, and glucose treatment can result in improved performance. We tested this glucose hypothesis with rats in a 14-unit T-maze that has provided robust evidence of age-related performance decline. Aged (24–25 month) and young (6–7 month) male F-344 rats were pretrained for one-way active avoidance before receiving complex maze training (4 daily trials over 5 days) with the contingency of moving through each of 5 segments to avoid footshock. Ten min before daily training, aged rats received either saline or glucose in doses of 10, 100, or 500 mg/kg IP, while young rats received saline. Significant ( ps<0.05) age-related increases in errors, runtime, and shock duration were observed. Glucose treatment had no significant effect on the number of maze errors committed; however, performance variables such as runtime and shock duration appeared to be reduced in rats receiving glucose. About 4–6 weeks later, a sample of these rats was fasted overnight, injected IP with glucose (150 mg/kg), and bled at various postinjection intervals to obtain estimates of blood glucose and insulin levels. Significant correlations ( ps<0.05) were observed between maze errors and baseline glucose levels, r(21)=−.62, and peak glucose response, r(19)=.49. However, within the aged group, significant correlations ( ps<0.01) with maze errors emerged only for baseline glucose, r(13)=−.69, and peak insulin response, r(13)=−.65. Thus, regulation of insulin, but not glucose, appeared related to learning abilities among aged rats. In a second experiment, young (6 month) F-344 rats were given 500 mg/kg glucose IP immediately after the third trial in the 14-unit T-maze. This glucose treatment had no significant effects on maze performance when the rats were retested 24-h later.