Iron accumulation in the striatum predicts aging-related decline in motor function in rhesus monkeys

Iron in chronic brain disorders: imaging and neurotherapeutic implications

Iron is important for brain oxygen transport, electron transfer, neurotransmitter synthesis, and myelin production. Though iron deposition has been observed in the brain with normal aging, increased iron has also been shown in many chronic neurological disorders including Alzheimer's disease, Parkinson's disease, and multiple sclerosis. In vitro studies have demonstrated that excessive iron can lead to free radical production, which can promote neurotoxicity. However, the link between observed iron deposition and pathological processes underlying various diseases of the brain is not well understood. It is not known whether excessive in vivo iron directly contributes to tissue damage or is solely an epiphenomenon. In this article, we focus on the imaging of brain iron and the underlying physiology and metabolism relating to iron deposition. We conclude with a discussion of the potential implications of iron-related toxicity to neurotherapeutic development.

Motor memory preservation in aged monkeys mirrors that of aged humans on a similar task

We studied long-term motor memory preservation in rhesus monkeys tested on a task similar to that employed in humans. First, motor speed and rate of motor decline was measured in 23 animals ranging from 4 to 26 years old. The task for the animals consisted of removing a food reward from a curved rod within the inner chamber of an automated panel. Young animals performed twice as fast as the aged animals. Second, young (n=6) and aged (n=10) animals were re-tested 1 year later on the same task with no intervening practice. We anticipated a decline in motor speed of 144 ms/year, instead the average performance time recorded during the repeat session improved significantly by 17% in the aged animals. This finding mirrors that of a longitudinal study conducted in humans using a similar test panel and supports that, while initial performance times of a novel motor task decline with age, motor memory traces are preserved over an extended time interval, even without continued practice. The data also support that the rhesus monkey could be used as a model to study the mechanisms by which long-term retention of motor memory occurs in aging.

Nonhuman Primate Models of Parkinson's Disease

Nonhuman primate (NHP) models of Parkinson's disease (PD) play an essential role in the understanding of PD pathophysiology and the assessment of PD therapies. NHP research enabled the identification of environmental risk factors for the development of PD. Electrophysiological studies in NHP models of PD identified the neural circuit responsible for PD motor symptoms, and this knowledge led to the development of subthalamic surgical ablation and deep brain stimulation. Similar to human PD patients, parkinsonian monkeys are responsive to dopamine replacement therapies and present complications associated with their long-term use, a similarity that facilitated the assessment of new symptomatic treatments, such as dopaminergic agonists. New generations of compounds and novel therapies that use directed intracerebral delivery of drugs, cells, and viral vectors benefit from preclinical evaluation in NHP models of PD. There are several NHP models of PD, each with characteristics that make it suitable for the study of different aspects of the disease or potential new therapies. Investigators who use the models and peer scientists who evaluate their use need information about the strengths and limitations of the different PD models and their methods of evaluation. This article provides a critical review of available PD monkey models, their utilization, and how they compare to emerging views of PD as a multietiologic, multisystemic disease. The various models are particularly useful for representing different aspects of PD at selected time points. This conceptualization provides clues for the development of new NHP models and facilitates the clinical translation of findings. As ever, successful application of any model depends on matching the model to the scientific question to be answered. Adequate experimental designs, with multiple outcome measures of clinical relevance and an appropriate number of animals, are essential to minimize the limitations of models and increase their predictive clinical validity.

Relationships among cognitive function, fine motor speed and age in the rhesus monkey

Declines in fine motor skills and cognitive function are well known features of human aging. Yet, the relationship between age-related impairments in motor and cognitive function remains unclear. Rhesus monkeys, like humans, show marked decline in cognitive and fine motor function with age and are excellent models to investigate potential interactions between age-related declines in cognitive and motor functioning. We investigated the relationships among cognition, motor function and age in 30 male and female rhesus monkeys, 5-28 years of age, tested on a battery of cognitive tasks [acquisition of the delayed non-matching-to-sample (DNMS), DNMS-120s, DNMS-600s, acquisition of delayed recognition span test (DRST), spatial-DRST and object-DRST] and a fine motor task (Lifesaver test). Global cognitive ability, as assessed by the cognitive performance index (CPI), was impaired with age in both sexes, while age-related motor slowing was found only in males. After age was controlled for, half the variance in CPI was predicted by motor speed, with better cognitive ability associated with slower motor skills. Analyses at the level of each cognitive task revealed that motor speed and age predicted the rate of acquisition of the DNMS. This relationship was robust in males and absent in females. Motor speed was not a significant predictor of any other cognitive variable. We conclude that the relationship between cognition and motor function (1) may be limited to non-spatial tasks; (2) exists independently of age; (3) may reflect different contributions of the fronto-striatal system; (4) may be particularly evident in males.