Labeling of cerebral amyloid in vivo with a monoclonal antibody.

We assessed the ability of a murine monoclonal antibody to bind selectively to beta-amyloid in the brains of living nonhuman primates. To circumvent the blood-brain barrier, we injected unlabeled antibody 10D5 (murine whole IgG1 and/or Fab fragments) into the cerebrospinal fluid of the cisterna magna in three aged monkeys. A control animal was given an intracisternal injection of nonimmune mouse whole IgG plus Fab. Twenty-four hours later, the animals were perfused and prepared for immunohistochemical detection of bound murine immunoglobulin in brain. All three experimental animals showed selective binding of 10D5 to approximately 5-15% of amyloid deposits in cerebral cortex, primarily near the cortical surface. There was no labeling in the control animal. In vivo-labeled deposits were confirmed to be beta-amyloid by electron microscopy and by in vitro immunohistochemistry in adjacent sections. The animals tolerated the injection well, although some polymorphonuclear leukocytes infiltrated portions of the subarachnoid space and superficial neocortex. These results provide the first demonstration that it may be feasible to selectively direct a tagged monoclonal antibody to beta-amyloid in the brain for therapeutic or diagnostic purposes. With enhancement of labeling efficiency, the method also may be useful for studying the progression of beta-amyloidosis in experimental animals using emission tomography.

The effects of hormone replacement therapy on hypothalamic neuropeptide gene expression in a primate model of menopause.

Menopause is associated with increased neurokinin B (NKB) gene expression and decreased proopiomelanocortin (POMC) gene expression in the human hypothalamus. In the present study, young, ovariectomized cynomolgus monkeys were used in a model of menopause to examine the effects of hormone replacement therapy (HRT) on hypothalamic neuropeptide gene expression. A secondary goal was to determine whether HRT produces signs of estrogen toxicity in the primate hypothalamus by examining POMC neurons and microglial cells. In situ hybridization was performed using synthetic, radiolabeled, 48-base oligonucleotide probes. Alpha-napthyl butyrate esterase histochemistry was used to visualize microglial cells. Both estrogen and estrogen plus progesterone treatments produced a marked suppression of the number of infundibular neurons expressing NKB gene transcripts. In contrast, HRT had no effect on the POMC system of neurons or the number of microglial cells in the infundibular nucleus. These results provide strong support for the hypothesis that the increased NKB gene expression in the hypothalamus of postmenopausal women is secondary to estrogen withdrawal. Conversely, these data suggest that the dramatic decline in the numbers of neurons expressing POMC gene transcripts in older women is caused by factors other than ovarian failure. Finally, we found no evidence that HRT, in doses designed to mimic currently prescribed regimens, produces signs of estrogen toxicity in the primate infundibular nucleus.

Impairments in acquisition and reversals of two-choice discriminations by aged rhesus monkeys.

The ability to learn and perform reversals of two object, two patterns, and one spatial discrimination was examined in eight aged (28-34 years), and four adult (8-13 years) behaviorally naive monkeys. As a group, the aged monkeys demonstrated significant difficulties in learning and reversing some of the visual discrimination problems, but had no difficulty learning or reversing the spatial discrimination. Additional analyses revealed that an impairment in learning an object discrimination by the aged monkeys was characterized by a prolonged period of chance performance, and the impairments in performing visual discrimination reversals was related to difficulties in two distinct stages of reversal learning. Despite age-related differences, there was considerable variability in performance among the aged monkeys. These experiments provide the first evidence of significant impairments in learning and reversing visual discriminations by aged monkeys that have not had prior exposure to complex behavioral tasks.

Cognitive function and its neural mechanisms in nonhuman primate models of aging, Alzheimer disease, and menopause.

Nonhuman primates have been used as animal models in which to study cognitive changes associated with aging and age-related disease for decades. There are many advantages to using nonhuman primates for studies of aging including the capability to examine visual nonspatial cognitive processes and the ability to use operationally similar behavioral tasks to what is used with humans. Because some aspects of aging in humans do not develop naturally in nonhuman primates or do not follow the same course of natural development in monkeys, experimental models are necessary for some investigations. Research in our laboratory has identified similarities in the cognitive profiles of nonhuman primate models of aging, Alzheimer Disease, and menopause with their human counterparts. In addition, through the use of a variety of different techniques we have used these nonhuman primate models to begin to determine the neural substrates of age-related cognitive dysfunction noted with advanced age and age-related disease. In this paper, we review our observations made in nonhuman primate models of aging, Alzheimer Disease, and menopause and indicate areas for future research.

Reproducibility of repeated measures of cholinergic terminal density using.

UNLABELLED: [18F](+)-4-fluorobenzyltrozamicol (FBT), which selectively binds to the vesicular acetylcholine transporter in the presynaptic cholinergic neuron, has previously been shown to be a useful ligand for the study of cholinergic terminal density in the basal ganglia with PET. The goal of this study was to assess the test-retest variability of [18F]FBT and PET measurements under baseline conditions in the basal ganglia. METHODS: After approval from the Animal Care and Use Committee, 6 rhesus monkeys underwent a series of 2 [18F]FBT PET scans (time between scans, 32-301 d) under isoflurane anesthesia. Each scan was initiated on the bolus injection of the radiotracer and consisted of 26 frames acquired during 180 min. Arterial blood samples were collected over the course of each scan to determine the metabolite-corrected arterial input function. Tissue time-activity curves were obtained from the scan data by drawing regions of interest over the basal ganglia and cerebellum. The distribution volume ratio for the basal ganglia was then determined for each scan by taking the ratio of the basal ganglia (specific binding) to cerebellum (nonspecific binding) distribution volume. Distribution volumes were derived using the Logan graphic analysis technique as well as a standard 3-compartment model. Additionally, the radioactivity concentration ratio was calculated as the ratio of the average [18F]FBT concentration in the basal ganglia to that in the cerebellum during the last half of the study (85-170 min). The constant K1, determined using the standard 3-compartment model, was used as an index of blood flow changes between studies. RESULTS: For all subjects, the test-retest variability was less than 15% for the distribution volume ratio and 12% for the radioactivity concentration ratio. Good agreement was found between the distribution volume ratio calculated using the graphic technique and the standard 3-compartment model. Using K1 as an index, the variability in blood flow seen in both the basal ganglia and the cerebellum was significantly reduced in their ratio. CONCLUSION: These results show the reproducibility of [18F]FBT and PET measurements in the basal ganglia.

Effects of ovariectomy on the neuroendocrine axes regulating reproduction and energy balance in young cynomolgus macaques.

Degeneration of the ovary in middle-aged women results in castrate levels of ovarian steroids and increased gonadotropin secretion from the anterior pituitary gland. Ageing in women is also accompanied by significant changes in energy homeostasis. We have observed alterations in hypothalamic morphology and gene expression in older women, including hypertrophy and increased gene expression of neurokinin B (NKB) neurones, elevated levels of gonadotropin releasing-hormone (GnRH) mRNA and decreased numbers of neurones expressing pro-opiomelanocortin (POMC) mRNA. To determine if loss of ovarian steroids could produce comparable changes in gene expression in young primates, we measured the effects of ovariectomy on NKB, GnRH and POMC gene expression in young cynomolgus monkeys. We also measured serum leptin and body weight to examine the consequences of ovariectomy on energy balance. NKB neurones in the infundibular nucleus of ovariectomized monkeys were larger, more numerous and displayed increased levels of NKB mRNA compared to those of intact controls. Moreover, ovariectomy increased the number of neurones expressing GnRH gene transcripts and elevated serum luteinizing hormone. By contrast, several parameters related to energy balance, including POMC gene expression, serum leptin and body weights, were unchanged by ovariectomy. Thus, the rise in NKB and GnRH gene expression in older women was simulated by ovariectomy in monkeys, but the changes in POMC gene expression and energy balance were not. This study provides strong support for the hypothesis that ovarian failure contributes to the increased NKB and GnRH gene expression observed in postmenopausal women.

The effects of long-term ovariectomy and estrogen replacement therapy on learning and memory in monkeys (Macaca fascicularis).

This study determined the effects of estrogen loss and replacement therapy on learning and memory function in monkeys (Macaca fascicularis). The ability to learn, remember, and perform reversals of object discriminations and the accuracy on a spatial delayed response task were found to be comparable in young adult surgically menopausal monkeys receiving estrogen or placebo treatment for 5 or 16 months. Learning and memory abilities were comparable with baseline values following 2, 12, or 24 months of ovariectomy in monkeys. Pre- and postoperative injections of scopolamine in a subset of monkeys revealed only subtle increases in sensitivity on the delayed response task following ovariectomy. These observations in surgically menopausal monkeys have some parallels with those made in surgically menopausal women and suggest that, in the absence of other confounding factors, certain aspects of learning and memory may not be influenced by estrogen in primates.

Spatial orienting of attention in adult and aged rhesus monkeys.

Aging produces changes in a variety of neural systems that result in a distinct neuropsychological profile of cognitive deficits. To determine the extent of functional decline in cognition with aging, the authors assessed attentional ability in adult (10-15 years old) and aged (28-33 years old) rhesus monkeys (Macaca mulatta) in 3 experiments, using a paradigm adapted from M. I. Posner, J. A. Walker, F. J. Friedrich, and R. D. Rafal (1984), in which a peripheral cue indicates the probable location of a target. Orienting of attention was not disrupted in aged monkeys. Response times of aged monkeys were comparable with adult monkeys' both in the attention task and in a simple reaction time task. These results suggest that the neural systems that subserve spatial orienting of attention remain intact in aged nonhuman primates.

Visual learning suppressed by cooling the temporal pole.

Three monkeys were trained to remember colored photographs of objects over delays of 0, 15, 30, and 45 s. Then two pairs of cooling devices were implanted bilaterally over the anterior 9 mm of the temporal lobe. The devices consisted of 3 X 10 mm loops of stainless steel tubing into which cooled methanol could be pumped. One pair (anterior pair) covered the medial part of the temporal tip (area TG), starting at the rhinal sulcus and extending 3 mm laterally. The second pair (posterior pair) was placed 3 mm lateral to the anterior pair, covering the rest of TG and the anterior extreme of the inferotemporal gyri, anterior TE. Cooling either pair of probes produced a deficit at all delays, but the deficit was greater at the longest delays. There was no difference between cooling the anterior pair and cooling the posterior pair except that cooling the anterior pair greatly increased the disruption of recall that is produced by an interfering stimulus. When all four probes were cooled, which suppressed the function of the entire temporal tip, performance dropped to chance at all delays. While under this condition, the animals could not learn new visual discriminations but could perform previously learned visual discriminations. These results are consistent with the suggestion that the temporal pole is the store for the brief anterograde memory that is available to the medial temporal amnesics.

Visual learning and retention examined with reversible cold lesions of the anterior temporal lobe.

Learning and retention of visual discriminations and delayed match-to-sample (DMS) performance were examined in monkeys while cooling the anterior temporal lobe. Four cryodes were bilaterally implanted on the dura overlying the anterior temporal cortex, an anterior pair covered the temporal pole (TP) and a posterior pair covered the anterior inferior temporal cortex (AIT). The visual discriminations were examined under 4 different test combinations of cooling and not cooling the anterior temporal lobe. Learning deficits were produced by cooling either TP or AIT. Once learned, there was no difficulty recalling discriminations under cooling or control conditions for either TP or AIT. There was a deficit during cooling in the recall of discriminations that had been learned prior to cooling TP or AIT. The animals were then trained and tested on a DMS task at a 0-s and 10-s delay. They performed at chance when either TP or AIT was cooled in the 0-s delay. Only TP was cooled at the 10-s delay and it also resulted in chance performance. The cold lesions demonstrated that the anterior temporal cortex, i.e. TP and AIT, has an important role in the processes of learning and, to a lesser extent, retention of visual information. The results also support previous findings regarding the participation of this area in DMS performance. The findings were discussed in relation to the amnesic syndrome.

Cognitive functions of the basal forebrain cholinergic system in monkeys: memory or attention?

The cholinergic hypothesis of memory dysfunction originally proposed that dysfunction of cholinergic neurons in the basal forebrain cholinergic system (BFCS) may be responsible for the memory deficits associated with aging and Alzheimer's disease (AD). This hypothesis directed focus on the BFCS in experimental animal models of AD. In contrast to numerous studies in rodents, fewer investigations have been conducted in monkeys with BFCS lesions. The medical septal nucleus/nucleus of the diagonal band of Broca (MS/NDBB) and the nucleus basalis of Meynert (NBM) may be involved in different cognitive functions in monkeys. Although few investigations have specifically addressed the issue of cognitive functions of the MS/NDBB in monkeys, there is some indication that these regions may be important for memory. In contrast, lesions of the NBM do not consistently disrupt mnemonic functions in monkeys. Recent electrophysiological and lesion studies of monkeys indicate that the NBM may play a more important role in attention functions, impairments of which are an early and significant feature of patients with AD.

The performance of visual tasks while segments of the inferotemporal cortex are suppressed by cold.

Cold was used to suppress the function of subdivisions of the inferotemporal cortex. Three cryodes were placed bilaterally, one over the lower bank of the superior temporal sulcus (sts), one over the middle temporal gyrus (mtg) and one over the inferior temporal gyrus (itg). The animals were tested with delayed match-to-sample (DMS) and simultaneous visual discriminations. The DMS required the animal to recall a projected image of an object over delays of 0, 15, 30 and 45 s. The 3 cryodes were cooled separately during the performance of the DMS and only itg cooling produced a deficit. This was compared to the effects of ablative bilateral lesions; damage to itg but not mtg disrupted performance of DMS. The greatest deficit was in an animal with a small lesion in the ventral pole and anterior extreme of itg. Cooling individual cryodes was without effect on a discrimination between horizontal and vertical stripes, but produced a significant deficit from each of the 3 placements on a discrimination between monkey faces. Chance performance on all visual discriminations resulted from cooling all cryodes. Unilateral cooling of all cryodes produced significant effects on the face discrimination, but there was no significant difference between the two sides in the severity of the deficit.

17alpha-Dihydroequilenin increases hippocampal dendritic spine density of ovariectomized rats.

The effects of estradiol and 17alpha-dihydroequilenin on the apical dendrite spine density of pyramidal cells of the CA1 region of rat hippocampus were compared. 17alpha-Dihydroequilenin was as effective as estradiol in increasing spine densities relative to controls. 17alpha-Dihydroequilenin is not uterotrophic like estradiol but does have beneficial effects on the cardiovascular system, suggesting that it may be an effective single-agent hormone replacement therapy to treat menopausal symptoms and reduce chronic disease risk in menopausal women.

Comparative cognition and assessment of cognitive processes in animals.

Comparative cognition is an approach that seeks to describe cognitive processes in general computational terms so that the appropriate behavioral testing procedures can be established for any animal, including humans. Some examples of this approach are discussed in the context of memory and attention, emphasizing the ways in which historically disparate research traditions can be integrated together to provide new approaches for behavioral testing in animals. This comparative approach helps to integrate animal models using different species, and to develop tasks that have more direct connection to the assessment of cognitive processes in people.

Ensuring the success of women faculty at AMCs: lessons learned from the National Centers of Excellence in Women's Health.

Since the early 1970s, the numbers of women entering medical school and, subsequently, academic medicine have increased substantially. However, women faculty have not advanced at the expected rate to senior academic ranks or positions of leadership. In 1996, to counter this trend, the U.S. Department of Health and Human Services (DHHS) Office on Women's Health included women's leadership as a required component of the nationally funded Centers of Excellence in Women's Health to identify effective strategies and initiate model programs to advance women faculty in academic medicine. The authors describe the experience of Centers at seven U.S. medical schools in initiating and sustaining leadership programs for women. The processes used for program formation, the current programmatic content, and program evaluation approaches are explained. Areas of success (e.g., obtaining support from the institution's leaders) and difficulties faced in maintaining an established program (such as institutional fiscal constraints and the diminishing time available to women to participate in mentoring and leadership activities) are reviewed. Strategies to overcome these and other difficulties (e.g., prioritize and tightly focus the program with the help of an advisory group) are proposed. The authors conclude by reviewing issues that programs for women in academic medicine will increasingly need to focus on (e.g., development of new kinds of skills; issues of recruitment and retention of faculty; and increasing faculty diversity).

Basal forebrain cholinergic system: a functional analysis.

This chapter has been organized empirically, focusing on the types of approaches that have been taken to understand BFCS function. This approach reflects the state of our knowledge about the behavioral and psychological functions of the BFCS. Considerable information has been gathered in the very short time that the BFCS has been the object of intense investigation. The results from the neurotoxic lesions and from the HACU studies provide some points of consistency and some puzzling differences. Both approaches to the study of basal forebrain function suggest that the MSA is involved in tasks that require spatial working memory; MSA lesions impaired choice accuracy, and HACU in the HIP was increased after performance. The pattern of results in simpler tasks is more difficult to interpret. In a left-right reference memory discrimination in a T-maze, MSA lesions did not impair acquisition or performance, whereas HACU in the HIP was activated during performance. This pattern of results suggests that although the MSA is engaged during this type of task, its activity is not necessary for normal performance. These, and other comparisons indicate the need for a systematic analysis of task demand (Olton, 1989b). Parametric manipulations of different task demands in a systematic fashion can indicate the extent to which the BFCS is involved in the function associated with each parametric manipulation. Ultimately, of course, the organization of this material should focus on particular psychological functions, rather than the techniques and procedures used to gather the information. Achieving this goal is going to require careful attention to the design of behavioral experiments so that definitive conclusions can be made about the extent to which the BFCS is involved in a given psychological function. A systematic application of task analysis can achieve this goal (Olton, 1986, 1989a, 1989b). For example, BFCS lesions in rats impair choice accuracy in spatial working memory tasks, and performance in these tasks engages the HACU system, at least in the HIP. If the spatial functions of this task involve the BFCS, then a nonspatial version of the task should produce a different pattern of results. If the spatial nature of the task is unimportant for BFCS function, then a nonspatial version of the task should produce the same results. By systematically changing one characteristic of the task at a time, the contribution of each component can be assessed.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential effects on visual and spatial recognition memory of a novel hormone therapy regimen of estrogen alone or combined with progesterone in older surgically menopausal monkeys.

Building upon our initial studies in young adult surgically menopausal monkeys, this study examined the effects of a novel schedule of administration of estradiol therapy alone, or in combination with progesterone, on visual and spatial recognition memory in older monkeys. Monkeys were preoperatively trained on a delayed matching-to-sample task and a delayed response task. At the time of ovariectomy, monkeys began their hormonal treatments and were cognitively assessed at 2, 12 and 24 weeks following treatment initiation. A schedule of hormone administration was used that closely modeled the normal fluctuations of hormones during the course of a normal primate menstrual cycle. Monkeys receiving placebo had lower levels of accuracy than monkeys receiving estrogen therapies on the delayed matching-to-sample task that were not apparent until 12 weeks following initiation of therapy and were no longer detected at the 24-week assessment. There was no effect of hormone therapy on accuracy in the delayed response task at any of the postoperative assessments. In both tasks, monkeys treated with estrogen plus progesterone had longer choice response latencies, especially on trials in which they made errors; however these effects did not influence accuracy measures in these animals. Our findings indicate that visual recognition ability may be more sensitive than spatial recognition memory to this novel hormone therapy regimen, that treatment with estradiol plus progesterone was equivalent to that of estradiol alone, and that neither therapy had significant negative impact on memory profiles.

Functional and neurobiological similarities of aging in monkeys and humans.

Aging in humans may be accompanied by alterations in several functional abilities. However, there is a great deal of individual variability in the functions that may be altered with age within and across aged people. One potential source of age-related behavioral variation may lie in a differential vulnerability of neurobiological systems to the aging process in particular individuals. Aged monkeys demonstrate behavioral and brain alterations that have many parallels with those observed in aged humans and are valuable animal models in which to investigate the interrelationships between age, behavior and neurobiological measures. This review outlines the similarities of functional and neurobiological aging in monkeys and humans, notes the variability that exists in both behavioral and neural systems in aging, and identifies some of the areas of aging that are in need of further investigation.

Cholinergic immunoreactive fibers in monkey anterior temporal cortex.

Cholinergic processes in anterior temporal cortex of rhesus monkeys were identified using immunocytochemical techniques for ChAT. Labeled fibers were present throughout the temporal pole and anterior aspects of the superior temporal, middle temporal, and inferior temporal gyri. ChAT-immunoreactive fibers were most dense in layer I to superficial layer III throughout anterior temporal cortex. In temporal pole, agranular and dysgranular regions had a greater density of labeled fibers in superficial layers as compared to granular regions. In addition to the superficial concentration of cholinergic fibers in lateral temporal regions, numerous labeled fibers were also present in deep cortical layers in the inferior temporal gyrus of lateral temporal cortex, with lesser concentrations of immunoreactive fibers present in these layers in superior and middle temporal gyri. These patterns of cholinergic innervation may reflect the degree of cholinergic modulation of functions in anterior temporal cortex.