REDUCTION IN THE NUMBER OF NADPH-DIAPHORASE-POSITIVE CELLS IN THE CEREBRAL-CORTEX AND STRIATUM IN AGED RATS

Nitric oxide (NO) plays an important role as a diffusible messenger in learning and memory. To determine whether changes in NO production in the brain may be involved in aging-associated brain dysfunction, we m easured the performance of aged rats in a radial arm maze task, and ca rried out histochemical examination of the changes in NADPH diaphorase (NADPH-d)-containing neurons in the brains of aged rats. The performa nce of aged rats (30 months old) in a radial arm maze task was signifi cantly impaired compared to the performance of young rats (3 months ol d). The number of neurons containing NADPH-d reactivity in the cerebra l cortex and striatum of aged rats was significantly reduced, by appro ximately 50 and 30%, respectively, compared to that in young rats. NO synthase activity in discrete brain regions of aged rats, i.e., in the cerebral cortex, striatum and hippocampus was not different from that in young rats, although the activity in the cerebellum of aged rats w as significantly lower than that in young rats. These results suggest that the reduction in the number of NADPH-d-positive cells in the brai ns of aged rats may be involved in aging-associated learning impairmen t in rats.