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Motor Slowing and Parkinsonian Signs in Aging Rhesus Monkeys Mirror Human Aging

^a Departments of Anatomy and Neurobiology, College of Medicine, University of Kentucky, Lexington
^b Departments of Neurology, College of Medicine, University of Kentucky, Lexington
^c Magnetic Resonance Imaging and Spectroscopy Center, College of Medicine, University of Kentucky, Lexington
^d Departments of Pharmacology and Psychiatry, Neuroscience Training Program, and Rocky Mountain Center for Sensor Technology, University of Colorado Health Sciences Center, Denver

Don Gash, Anatomy and Neurobiology, University of Kentucky Medical Center, 800 Rose Street, MN224, Lexington, KY 40536-0298 E-mail: dongash{at}pop.uky.edu.

Decision Editor: Jay Roberts, PhD

Motor slowing is a universal feature of human aging, and parkinsonian signs are commonly expressed in human senescence. In the present study, age-associated declines in motor functions in 31 female rhesus monkeys were quantified by activity monitors and an automated test panel, and the incidence of parkinsonian signs was scored using a movement dysfunction assessment scale. Activity levels in middle-aged monkeys (12–17 years old) were less than half that of young animals (5–8 years old) and were further depressed in aged monkeys (21–27 years old). Movement dysfunction scores increased significantly with increasing age. Two or more parkinsonian signs were exhibited by 20% of the middle-aged monkeys and 36% of the aged monkeys. Slowing performance times on fine-motor hand tasks correlated significantly with increasing age. Motor learning was seen in all age groups, but improved faster in the young monkeys. The data suggest that aging rhesus monkeys provide an appropriate model to analyze the biological processes leading to motor slowing and the expression of parkinsonian signs in human senescence.