Mesostriatal dopamine markers in aged Long-Evans rats with sensorimotor impairment

Changes in the mesostriatal dopamine system associated with normal aging 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 reaction time performance. Decreased levels of midbrain dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were observed in the aged rats as compared to young, but there was no evidence for age-related changes in the density of D1 or D2 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 rats exhibited higher density of D1 binding in rostrodorsal striatal patch areas, but lower overall levels of DA. In caudal striatum, aged RT-unimpaired rats exhibited lower DA and higher DOPAC levels.