Radial maze performance in young and aged mice: neurochemical correlates

Young (8 month) and aged (27-28 month) male C57BL/6J mice were trained in a spatial discrimination task requiring working memory. The mice were tested during three trials daily in an eight-arm radial maze for 36 test days. Correct choices were reinforced with isotonic saline. In contrast to past reports, young mice learned the task. Old mice also learned the task, and no significant age-related differences in performance were observed. Following maze training, the mice were killed, the brains removed, and the specific activities of choline acetyltransferase (E.C.2.3.1.6., ChAT) and L-glutamic acid decarboxylase (E.C.4.1.1.15., GAD) were assayed in the hippocampus, and in frontal, sensorimotor, and cingulate areas of the cerebral cortex. The activities of these neurotransmitter synthetic enzymes did not differ significantly between young and old mice. Correct responding in the radial maze was positively correlated to ChAT activity in the cingulate cortex and negatively correlated to ChAT activity in the sensorimotor cortex. There was a similar pattern of correlation between performance and regional GAD activity, although none of the correlations involving GAD reached statistical significance.