Effects of estradiol and aging on fine manual performance in female rhesus monkeys

Effects of long term diabetogenic high fat diet on bone in ovariectomized female rats

A diabetogenic high fat diet (HFD) can be used to induce insulin resistance and obesity in animal models; however, its effects on bone are unknown. We investigated the effects of long term HFD on bone in ovariectomized (OVX) female rats. We used 12-week-old female rats divided randomly into four groups: sham operation (sham), sham operation with HFD (SHFD), OVX and OVX with HFD (OVX + HFD). Ovaries were removed in the OVX and OVX + HFD groups and the SHFD and OVX + HFD groups were fed a HFD for 28 weeks. Serum estrogen, testosterone, lipid, adiponectin, leptin, tartrate-resistant acid phosphatase (TRAP) and N-mid fragment of osteocalcin (N-MID-OT) levels were measured. Structure, apoptosis and specific transcription factors in bone were evaluated using pathologic, densitometric and immunohistochemical analysis. Body weight, serum leptin, TRAP and testosterone levels were increased, while serum N-MID-OT, estrogen and adiponectin levels were decreased in the SHFD, OVX and OVX + HFD groups. Expression of BCL2-associated X protein, caspase-3, matrix metalloproteinase-9 and calcitonin was increased, while bone mineral density (BMD) and content (BMC) in femurs and lumbar spine, and expression of B cell lymphoma 2, type 1 collagen and osteocalcin were decreased in the bones of the SHFD, OVX and OVX + HFD groups. All indices were greatest in the OVX + HFD group and HFD produced a detrimental effect on bone in both normal and OVX rats, which may be due to increased apoptosis in bone and increased leptin and decreased adiponectin levels in serum. The effects of HFD and OVX may be synergistic.

Oral curcumin supplementation improves fine motor function in the middle-aged rhesus monkey

Aged individuals experience decreased fine motor function of the hand and digits, which could result, in part, from the chronic, systemic state of inflammation that occurs with aging. Recent research for treating age-related inflammation has focused on the effects of nutraceuticals that have anti-inflammatory properties. One particular dietary polyphenol, curcumin, the principal curcuminoid of the spice turmeric, has been shown to have significant anti-inflammatory effects and there is mounting evidence that curcumin may serve to reduce systemic inflammation. Therefore, it could be useful for alleviating age-related impairments in fine motor function. To test this hypothesis we assessed the efficacy of a dietary intervention with a commercially available optimized curcumin to ameliorate or delay the effects of aging on fine motor function of the hand of rhesus monkeys. We administered oral daily doses of curcumin or a control vehicle to 11 monkeys over a 14- to 18-month period in which they completed two rounds of fine motor function testing. The monkeys receiving curcumin were significantly faster at retrieving a food reward by round 2 of testing than monkeys receiving a control vehicle. Further, the monkeys receiving curcumin demonstrated a greater degree of improvement in performance on our fine motor task by round 2 of testing than monkeys receiving a control vehicle. These findings reveal that fine motor function of the hand and digits is improved in middle-aged monkeys receiving chronic daily administration of curcumin.

Handedness influences intermanual transfer in chimpanzees (Pan troglodytes) but not rhesus monkeys (Macaca mulatta)

Intermanual transfer refers to an effect, whereby training one hand to perform a motor task improves performance in the opposite untrained hand. We tested the hypothesis that handedness facilitates intermanual transfer in two nonhuman primate species: rhesus monkeys (N = 13) and chimpanzees (N = 52). Subjects were grouped into one of four conditions: (1) left-handers trained with the left (dominant) hand; (2) left-handers trained with the right (nondominant) hand; (3) right-handers trained with the left (nondominant) hand; and (4) right-handers trained with the right (dominant) hand. Intermanual transfer was measured using a task where subjects removed a Life Savers(®) candy (monkeys) or a washer (chimpanzees) from metal shapes. Transfer was measured with latency by comparing the average time taken to solve the task in the first session with the trained hand compared to the first session with the untrained hand. Hypotheses and predictions were derived from three models of transfer: access: benefit training with nondominant hand; proficiency: benefit training with dominant hand; and cross-activation: benefit irrespective of trained hand. Intermanual transfer (i.e., shorter latency in untrained hand) occurred regardless of whether monkeys trained with the dominant hand or nondominant hand, supporting the cross-activation model. However, transfer was only observed in chimpanzees that trained with the dominant hand. When handedness groups were examined separately, the transfer effect was only significant for right-handed chimpanzees, partially supporting the proficiency model. Findings may be related to neurophysiological differences in motor control as well as differences in handedness patterning between rhesus monkeys and chimpanzees.

Short-term testosterone manipulations do not affect cognition or motor function but differentially modulate emotions in young and older male rhesus monkeys

Human aging is characterized by declines in cognition and fine motor function as well as improved emotional regulation. In men, declining levels of testosterone (T) with age have been implicated in the development of these age-related changes. However, studies examining the effects of T replacement on cognition, emotion and fine motor function in older men have not provided consistent results. Rhesus monkeys (Macaca mulatta) are excellent models for human cognitive aging and may provide novel insights on this issue. We tested 10 aged intact male rhesus monkeys (mean age=19, range 15-25) on a battery of cognitive, motor and emotional tasks at baseline and under low or high T experimental conditions. Their performance was compared to that of 6 young males previously tested in the same paradigm (Lacreuse et al., 2009; Lacreuse et al., 2010). Following a 4-week baseline testing period, monkeys were treated with a gonadotropin releasing hormone agonist (Depot Lupron, 200 μg/kg) to suppress endogenous T and were tested on the task battery under a 4-week high T condition (injection of Lupron+T enanthate, 20 mg/kg, n=8) or 4-week low T condition (injection of Lupron+oil vehicle, n=8) before crossing over to the opposite treatment. The cognitive tasks consisted of the Delayed Non-Matching-to-Sample (DNMS), the Delayed Response (DR), and the Delayed Recognition Span Test (spatial-DRST). The emotional tasks included an object Approach-Avoidance task and a task in which monkeys were played videos of unfamiliar conspecifics in different emotional context (Social Playbacks). The fine motor task was the Lifesaver task that required monkeys to remove a Lifesaver candy from rods of different complexity. T manipulations did not significantly affect visual recognition memory, working memory, reference memory or fine motor function at any age. In the Approach-Avoidance task, older monkeys, but not younger monkeys, spent more time in proximity of novel objects in the high T condition relative to the low T condition. In both age groups, high T increased watching time of threatening social stimuli in the Social Playbacks. These results suggest that T affects some aspects of emotional processing but has no effect on fine motor function or cognition in young or older male macaques. It is possible that the duration of T treatment was not long enough to affect cognition or fine motor function or that T levels were too high to improve these outcomes. An alternative explanation for the discrepancies of our findings with some of the cognitive and emotional effects of T reported in rodents and humans may be the use of a chemical castration, which reduced circulating gonadotropins in addition to T. Further studies will investigate whether the luteinizing hormone LH mediates the effects of T on brain function in male primates.

Assessment of motor function of the hand in aged rhesus monkeys

In the elderly, intact motor functions of the upper extremity are critical for the completion of activities of daily living. Many studies have provided insight into age-related changes in motor function. However, the precise nature and extent of motor impairments of the upper extremity remains unclear. In the current study we have modified two tasks to assess hand/digit function in both young and aged rhesus monkeys. We tested monkeys from 9 to 26 years of age on these tasks to determine the level of fine motor performance across the adult age range. Compared to young monkeys (9-12 years of age), aged monkeys (15-26 years of age) were mildly impaired on fine motor control of the digits. These findings are consistent with previous studies that have found age-related impairment in fine motor function. However, the magnitude and extent of impairment in the current study does differ from previous findings and is likely due to methodological differences in the degree of task complexity.

Estrogen, testosterone, and sequential movement in men

Behavioral and physiological data suggest that the striatal dopaminergic system is important in the production and execution of sequential movements. Striatal function is also modulated by sex hormones, and previous studies show that estradiol is related to sequential movement in women. The authors examined whether sex hormones are involved in the production of sequential movement in healthy older and younger men. Testosterone was modified for a 6-week period such that levels in older men matched those of younger men, the conversion of testosterone to estradiol was blocked, the production of testosterone was blocked, or the men received no treatment (placebo). Sequential movement was measured before and after hormone treatment. Older men were slower and more accurate than younger men on the sequential movement task pre- and posttreatment. Hormone manipulation had no effect on movement speed. Hormone levels were not correlated with sequential movement performance in either older or younger men, suggesting that sex hormones do not modulate sequential movement in men, and hormone replacement may not restore a loss of sequential movement ability in elderly men or men with Parkinson's disease.

No effect of different estrogen receptor ligands on cognition in adult female monkeys

Many studies in women and animal models suggest that estrogens affect cognitive function. Yet, the mechanisms by which estrogens may impact cognition remain unclear. The goal of the present study was to assess the effects of different estrogen receptor (ER) ligands on cognitive function in adult ovariectomized female rhesus monkeys. The monkeys were tested for 6 weeks on a battery of memory and attentional tasks administered on a touchscreen: the object, face, and spatial versions of the Delayed Recognition Span Test (DRST) and a Visual Search task. Following a 2-week baseline period with oil vehicle treatment, monkeys were randomly assigned to one of 3 treatment groups: estradiol benzoate (EB), selective ERbeta agonist (diarylpropionitrile DPN) or selective ER modulator tamoxifen (TAM). In each treatment group, monkeys received oil vehicle for 2 weeks and the drug for 2 weeks, in a cross-over design. After a 4-week washout, a subset of monkeys was re-tested on the battery when treated with a selective ERalpha agonist (propyl-pyrazole-triol, PPT) or oil vehicle. Overall, drug treatments had no or negligible effects on cognitive performance. These results support the contention that exogenous estrogens and selective estrogen receptor modulators (SERMS) do not significantly affect cognition in young adult female macaques. Additional studies are needed to determine whether the cognitive effects of estrogens in monkeys of more advanced age are mediated by ERbeta, ERalpha or complex interactions between the two receptors.

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.

Calorie restriction in nonhuman primates: assessing effects on brain and behavioral aging

Dietary caloric restriction (CR) is the only intervention repeatedly demonstrated to retard the onset and incidence of age-related diseases, maintain function, and extend both lifespan and health span in mammals, including brain and behavioral function. In 70 years of study, such beneficial effects have been demonstrated in rodents and lower animals. Recent results emerging from ongoing studies of CR in humans and nonhuman primates suggest that many of the same anti-disease and anti-aging benefits observed in rodent studies may be applicable to long-lived species. Results of studies in rhesus monkeys indicate that CR animals (30% less than controls) are healthier than fully-fed counterparts based on reduced incidence of various diseases, exhibit significantly better indices of predisposition to disease and may be aging at a slower rate based on analysis of selected indices of aging. The current review discusses approaches taken in studies of rhesus monkeys to analyze age-related changes in brain and behavioral function and the impact of CR on these changes. Approaches include analyses of gross and fine locomotor performance as well as brain imaging. In a related study it was observed that short-term CR (6 months) in adult rhesus monkeys can provide protection against a neurotoxic insult. Increasing interest in the CR paradigm will expand its role in demonstrating how nutrition can modulate the rate of aging and the mechanisms responsible for this modulation.

Hand use by tufted capuchins (Cebus apella) to extract a small food item from a tube: digit movements, hand preference, and performance

The aim of this study was to analyze the manual patterns used by tufted capuchin monkeys (Cebus apella) to retrieve a small food item from a narrow tube, with special attention focused on the independent use of single fingers, fine digit movements, hand preference, and intermanual differences in the time it took the monkeys to obtain the food. The capuchins (n = 20) mainly used their forefinger to extract the food from the tube. The simultaneous use of the index and middle fingers occurred less frequently, and the use of the forefinger in combination with other digits occurred rarely. The capuchins demonstrated a capacity to move single digits independently when the fingers were locating the food inside the tube, and displayed a high mobility of the distal phalanx joints. However, they possessed only a limited capacity to coordinate single fingers in space, and displayed only a slight degree of manual preshaping when they approached the tube. A hand-preference analysis failed to reveal any significant lateral bias for the group, since both adults (> or = 5 years) and immature individuals (<5 years) of both sexes used either hand with the same frequency. Conversely, a latency analysis showed a significant interaction between the subject's age and performance difference between hands: in adults, but not in immature individuals, the left hand was faster than the right hand in retrieving food.

Effects of aging and hormonal status on bimanual motor coordination in the rhesus monkey

Studies of age-related changes in motor function in nonhuman primates have been based exclusively on unimanual motor tasks. In this study, we examined whether aging affects bimanual motor coordination in the monkey model. In addition, we compared performance of ovariectomized and intact females on the task, to examine whether estrogen deficiency impairs motor function. The task required 29 rhesus monkeys (6-26 years old) to extract a maximum of 15 raisins from a testing hole-board. While the task could most efficiently be performed with two hands, other motor strategies were possible. The number of raisins extracted per minute was measured in each of eight sessions, the first and last of which were videotaped for analysis of motor patterns. The number of raisins retrieved per minute declined significantly with age. All monkeys improved with practice, but aged monkeys improved more slowly than young ones. The proportion of bimanual actions tended to increase between the first and the last sessions but was not significantly different between young and aged monkeys. Hormonal status did not affect performance. Finally, performance on the bimanual task was significantly correlated with performance on a previously administered unimanual motor test emphasizing speed, suggesting that age-related motor slowing may explain deficits in both tasks.

Age Influences the Expression of GAP-43 in the Rat Hippocampus following Seizure

BACKGROUND

Normal aging is associated with impairments in learning and memory and motor function. One viable hypothesis is that these changes reflect an age-related decrease in brain plasticity.

OBJECTIVE

The aim of the present study was to identify age-related changes in the time course of expression of the axonal growth associated protein 43 (GAP-43) in a rat model of brain plasticity.

METHODS

We examined by Northern blotting, in situ hybridization, and immunohistochemistry the effects of age on the time course of the expression GAP-43 following pentylenetetrazole-induced seizure in the hippocampus of 3-, 18-, and 28-month-old rats.

RESULTS

In this model of brain plasticity, young rats displayed a decrease in GAP-43 mRNA levels in CA1, CA3, and polymorphic regions, lasting from 10 h to 3 days after seizure. This was followed by recovery, with peak expression between days 10 and 20. The baseline levels of GAP-43 mRNA decreased with age, especially in the CA3 region. Despite lower baseline levels, middle-aged rats showed the same pattern of upregulation of GAP-43 mRNA expression as the young animals. Old rats showed only minimal upregulation, however, and this occurred only in the polymorphic layer. The level GAP-43 protein itself was higher in old control rats than in the other two control groups, a condition that was transiently reversed by seizure activity.

CONCLUSIONS

Middle-aged rats are still capable of a sustained, though diminished, response to seizure activity, while old rats lose this ability. Disruption of the temporal and anatomical coordination of expression of GAP-43 may contribute to the general decline in brain plasticity with age.

Sex differences in age-related motor slowing in the rhesus monkey: behavioral and neuroimaging data

The nigrostriatal system is critical for fine motor function and its deterioration during aging is thought to underlie the decline in fine manual ability of old persons. Because estrogen has a neuroprotective effect on this system, one might expect women's motor function to be less vulnerable to the detrimental effects of aging than that of men. We examined this hypothesis in the rhesus monkey, which has been established as an excellent model of human age-related motor impairment. We tested 28 young and old rhesus monkeys of both sexes in a task involving the retrieval of a Life Saver candy from rods of different complexity to determine whether fine motor ability (1) is sexually dimorphic, (2) declines with age and (3) declines differently in males and females. In addition, we measured the whole brain volume, the volumes of the caudate, putamen, hippocampal formation and the area of the corpus callosum in a subset of the monkeys (n=15) for which magnetic resonance images of the brain were available. All monkeys performed similarly in the test with the simplest rod. In the test with complex rods; however, age-related slowing of motor function was evident in males, but not in females. Age-related decreases in the normalized caudate and putamen volumes were similar in males and in females. In addition, motor speed was not significantly correlated to any of the neuroanatomical measures under study. Further studies will be necessary to uncover the neurohormonal bases of the differential age-related motor decline between males and females.

Further evidence of a right hand advantage in motor skill by chimpanzees (Pan troglodytes)

Asymmetries in motor skill when grasping small food items was evaluated in a sample of captive chimpanzees. In two experiments, error rates in grasping food were assessed when controlling for individual differences in grip morphology. In both experiments, chimpanzees were found to make more errors with the left compared to the right hand. Male chimpanzees were also found to make more errors compared to females. These results are discussed in the context of a presumed disassociation between hand preference and performance as indicators of cerebral dominance in motor functions.

Temporal Dynamics of Degenerative and Regenerative Events Associated with Cerebral Ischemia in Aged Rats

BACKGROUND AND PURPOSE

The age-related decline in plasticity of the brain may be one factor underlying the poor functional recovery after stroke. In the present work we tested the hypothesis that the attenuation of neural plasticity could be the result of an age-related REDUCTION in the upregulation of factors promoting brain plasticity (microtubule-associated protein 1B [MAP1B], beta-amyloid precursor protein [betaAPP]), and an age-related INCREASE in glial reactivity and the accumulation of Abeta, a proteolytic cleavage product of betaAPP with neurotoxic properties.

METHODS

Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague-Dawley rats. The functional outcome was assessed in neurobehavioral tests 3, 7, 14 and 28 days after surgery. At the indicated time points, brains were removed and immunostained for glial cells. Abeta, as well as the markers of brain plasticity, betaAPP and MAP1B.

RESULTS

Histologically, in young rats there was a gradual activation of both microglia and astrocytes that peaked by days 14-28 with the formation of a glial scar. In contrast, aged rats showed an accelerated astrocytic and microglial reaction that peaked in the first week after stroke. The expression patterns of a growth-associated phenotype of betaAPP as well as with MAP1B accumulation in varicosities along axons in cortical areas affected by stroke peaked between days 14 and 28 in young animals. In aged rats their expression was both delayed (28 days) and reduced. In addition the carboxy terminal fragment of betaAPP steadily accumulated over time and reached a maximum by day 14 in aged rats as compared to 28 days in young rats.

CONCLUSIONS

These results suggest that a temporally anomalous gliotic reaction to cerebral ischemia in aged rats in conjunction with a late and limited upregulation of neuronal plasticity proteins as well as a diminished neurogenesis potential lead to the prevalence of scar tissue that impedes functional recovery from stroke.