Assessment of learning in rhesus monkeys on long-term calorie restriction
D. Ingram, J. Young, E. Hanson, M. Murray, G. Roth, M. Lane
National Institute on Aging,
5600 Nathan Shock Drive,
Baltimore, MD 21224
Calorie restriction (CR) is the only intervention consistently demonstrated to increase lifespan, reduce the incidence and onset of age-related chronic disease, and attenuate age-related decline in many physiological functions in laboratory rodents. Accumulating evidence from studies in rhesus monkeys suggests that CR can also retard many aspects of aging in species closely related to humans. A major question related to the effects of long-term CR in nonhuman primates is whether behavioral function will be impacted, either negatively or positively. We have begun studies to evaluate learning and memory in male and female rhesus monkeys involved in a long-term study of CR. Control monkeys have been provided a highly nutritious diet while monkeys on CR have had their intake of this diet reduced 30 percent from the level of comparable aged controls. Monkeys were introduced to the study at different stages in the lifespan, including juvenile, adult, and aged groups of monkeys. The length of CR within these groups has ranged from 8-15 years, which represents about 20-38 percent of the maximum lifespan of this species. Learning is being evaluated in a simple, two- object discrimination task as well as a two-object reversal task. The objects are presented on a tray attached to the home cage of the monkeys. To make a response, the monkey must reach out of the cage to displace an object on the tray and retrieve a raisin reward located under the object designated as the correct object. If the monkey displaced the wrong object, then it is not permitted to retrieve the reward. Performance was measured as the number of trials to criterion and showed a significant age effect for males (increased trails to criterion) but not for female monkeys in the control groups. CR had no significant effect on performance. In the reversal task, the monkey must choose the object that was incorrect previously. The number of trails to criterion also significantly increased with age among male and female controls. CR had no significant effect on performance among males but female CR monkeys had significantly better performance compared to controls. This study is continuing with about half the monkeys (52/106) in our study evaluated thus far and additional trails of object discrimination being added to the protocol.
Key words:
learning, memory, diet, brain, behavior
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