MESOSTRIATAL DOPAMINE MARKERS IN AGED LONG-EVANS RATS WITH SENSORIMOTOR IMPAIRMENT

Changes in the mesostriatal dopamine system associated with normal agi ng are observed in both human and laboratory animals, but the specific behavioral consequences of these nonpathological changes are largely unexplored. The present study (a) assessed the effects of normal aging on markers for the mesostriatal dopamine system, and (b) examined the relationship of age-related changes in this system to decline in reac tion time performance. Decreased levels of midbrain dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were observed in the aged rats as c ompared to young, but there was no evidence for age-related changes in the density of D-1 or D-2 receptor binding or the density of dopamine uptake sites. Some differences were observed when the aged rats were grouped according to reaction time performance. Aged RT-unimpaired rat s exhibited higher density of D-1 binding in rostrodorsal striatal pat ch areas, but lower overall levels of DA. In caudal striatum, aged RT- unimpaired rats exhibited lower DA and higher DOPAC levels.