Brain organization of gorillas reflects species differences in ecology.

Gorillas include separate eastern (Gorilla beringei) and western (Gorilla gorilla) African species that diverged from each other approximately 2 million years ago. Although anatomical, genetic, behavioral, and socioecological differences have been noted among gorilla populations, little is known about variation in their brain structure. This study examines neuroanatomical variation between gorilla species using structural neuroimaging. Postmortem magnetic resonance images were obtained of brains from 18 captive western lowland gorillas (Gorilla gorilla gorilla), 15 wild mountain gorillas (Gorilla beringei beringei), and 3 Grauer's gorillas (Gorilla beringei graueri) (both wild and captive). Stereologic methods were used to measure volumes of brain structures, including left and right frontal lobe gray and white matter, temporal lobe gray and white matter, parietal and occipital lobes gray and white matter, insular gray matter, hippocampus, striatum, thalamus, each hemisphere and the vermis of the cerebellum, and the external and extreme capsules together with the claustrum. Among the species differences, the volumes of the hippocampus and cerebellum were significantly larger in G. gorilla than G. beringei. These anatomical differences may relate to divergent ecological adaptations of the two species. Specifically, G. gorilla engages in more arboreal locomotion and thus may rely more on cerebellar circuits. In addition, they tend to eat more fruit and have larger home ranges and consequently might depend more on spatial mapping functions of the hippocampus.

Clinical Impact and Generalizability of a Computer-Assisted Diagnostic Tool to Risk-Stratify Lung Nodules With CT.

OBJECTIVE: To evaluate whether an imaging classifier for radiology practice can improve lung nodule classification and follow-up. METHODS: A machine learning classifier was developed and trained using imaging data from the National Lung Screening Trial (NSLT) to produce a malignancy risk score (malignancy Similarity Index [mSI]) for individual lung nodules. In addition to NLST cohorts, external cohorts were developed from a tertiary referral lung cancer screening program data set and an external nonscreening data set of all nodules detected on CT. Performance of the mSI combined with Lung-RADS was compared with Lung-RADS alone and the Mayo and Brock risk calculators. RESULTS: We analyzed 963 subjects and 1,331 nodules across these cohorts. The mSI was comparable in accuracy (area under the curve = 0.89) to existing clinical risk models (area under the curve = 0.86-0.88) and independently predictive in the NLST cohort of 704 nodules. When compared with Lung-RADS, the mSI significantly increased sensitivity across all cohorts (25%-117%), with significant increases in specificity in the screening cohorts (17%-33%). When used in conjunction with Lung-RADS, use of mSI would result in earlier diagnoses and reduced follow-up across cohorts, including the potential for early diagnosis in 42% of malignant NLST nodules from prior-year CT scans. CONCLUSION: A computer-assisted diagnosis software improved risk classification from chest CTs of screening and incidentally detected lung nodules compared with Lung-RADS. mSI added predictive value independent of existing radiological and clinical variables. These results suggest the generalizability and potential clinical impact of a tool that is straightforward to implement in practice.

Long-term in vivo imaging of ß-amyloid plaque appearance and growth in a mouse model of cerebral ß-amyloidosis.

Extracellular deposition of the amyloid-ß peptide (Aß) in the brain parenchyma is a hallmark lesion of Alzheimer's disease (AD) and a predictive marker for the progression of preclinical to symptomatic AD. Here, we used multiphoton in vivo imaging to study Aß plaque formation in the brains of 3- to 4-month-old APPPS1 transgenic mice over a period of 6 months. A novel head fixation system provided robust and efficient long-term tracking of single plaques over time. Results revealed an estimated rate of 35 newly formed plaques per cubic millimeter of neocortical volume per week at 4-5 months of age. At later time points (i.e., in the presence of increasing cerebral ß-amyloidosis), the number of newly formed plaques decreased. On average, both newly formed and existing plaques grew at a similar growth rate of 0.3 µm (radius) per week. A solid knowledge of the dynamics of cerebral ß-amyloidosis in mouse models provides a powerful tool to monitor preclinical Aß targeting therapeutic strategies and eases the interpretation of diagnostic amyloid imaging in humans.

Neuron number and size in prefrontal cortex of children with autism.

CONTEXT: Autism often involves early brain overgrowth, including the prefrontal cortex (PFC). Although prefrontal abnormality has been theorized to underlie some autistic symptoms, the cellular defects that cause abnormal overgrowth remain unknown. OBJECTIVE: To investigate whether early brain overgrowth in children with autism involves excess neuron numbers in the PFC. DESIGN, SETTING, AND CASES: Postmortem prefrontal tissue from 7 autistic and 6 control male children aged 2 to 16 years was examined by expert anatomists who were blinded to diagnostic status. Number and size of neurons were quantified using stereological methods within the dorsolateral (DL-PFC) and mesial (M-PFC) subdivisions of the PFC. Cases were from the eastern and southeastern United States and died between 2000 and 2006. MAIN OUTCOME MEASURES: Mean neuron number and size in the DL-PFC and M-PFC were compared between autistic and control postmortem cases. Correlations of neuron number with deviation in brain weight from normative values for age were also performed. RESULTS: Children with autism had 67% more neurons in the PFC (mean, 1.94 billion; 95% CI, 1.57-2.31) compared with control children (1.16 billion; 95% CI, 0.90-1.42; P = .002), including 79% more in DL-PFC (1.57 billion; 95% CI, 1.20-1.94 in autism cases vs 0.88 billion; 95% CI, 0.66-1.10 in controls; P = .003) and 29% more in M-PFC (0.36 billion; 95% CI, 0.33-0.40 in autism cases vs 0.28 billion; 95% CI, 0.23-0.34 in controls; P = .009). Brain weight in the autistic cases differed from normative mean weight for age by a mean of 17.6% (95% CI, 10.2%-25.0%; P = .001), while brains in controls differed by a mean of 0.2% (95% CI, -8.7% to 9.1%; P = .96). Plots of counts by weight showed autistic children had both greater total prefrontal neuron counts and brain weight for age than control children. CONCLUSION: In this small preliminary study, brain overgrowth in males with autism involved an abnormal excess number of neurons in the PFC.

Independent effects of intra- and extracellular Abeta on learning-related gene expression.

Alzheimer's disease is characterized by numerous pathological abnormalities, including amyloid beta (Abeta) deposition in the brain parenchyma and vasculature. In addition, intracellular Abeta accumulation may affect neuronal viability and function. In this study, we evaluated the effects of different forms of Abeta on cognitive decline by analyzing the behavioral induction of the learning-related gene Arc/Arg3.1 in three different transgenic mouse models of cerebral amyloidosis (APPPS1, APPDutch, and APP23). Following a controlled spatial exploration paradigm, reductions in both the number of Arc-activated neurons and the levels of Arc mRNA were seen in the neocortices of depositing mice from all transgenic lines (deficits ranging from 14 to 26%), indicating an impairment in neuronal encoding and network activation. Young APPDutch and APP23 mice exhibited intracellular, granular Abeta staining that was most prominent in the large pyramidal cells of cortical layer V; these animals also had reductions in levels of Arc. In the dentate gyrus, striking reductions (up to 58% in aged APPPS1 mice) in the number of Arc-activated cells were found. Single-cell analyses revealed both the proximity to fibrillar amyloid in aged mice, and the transient presence of intracellular granular Abeta in young mice, as independent factors that contribute to reduced Arc levels. These results provide evidence that two independent Abeta pathologies converge in their impact on cognitive function in Alzheimer's disease.

Dynamics of the microglial/amyloid interaction indicate a role in plaque maintenance.

Microglial cells aggregate around amyloid plaques in Alzheimer's disease, but, despite their therapeutic potential, various aspects of their reactive kinetics and role in plaque pathogenesis remain hypothetical. Through use of in vivo imaging and quantitative morphological measures in transgenic mice, we demonstrate that local resident microglia rapidly react to plaque formation by extending processes and subsequently migrating toward plaques, in which individual transformed microglia somata remain spatially stable for weeks. The number of plaque-associated microglia increased at a rate of almost three per plaque per month, independent of plaque volume. Larger plaques were surrounded by larger microglia, and a subset of plaques changed in size over time, with an increase or decrease related to the volume of associated microglia. Far from adopting a more static role, plaque-associated microglia retained rapid process and membrane movement at the plaque/glia interface. Microglia internalized systemically injected amyloid-binding dye at a much higher rate in the vicinity of plaques. These results indicate a role for microglia in plaque maintenance and provide a model with multiple targets for therapeutic intervention.

Fornix lesions decouple the induction of hippocampal arc transcription from behavior but not plasticity.

The immediate-early gene (IEG) Arc is transcribed after behavioral and physiological treatments that induce synaptic plasticity and is implicated in memory consolidation. The relative contributions of neuronal activity and learning-related plasticity to the behavioral induction of Arc remain to be defined. To differentiate the contributions of each, we assessed the induction of Arc transcription in rats with fornix lesions that impair hippocampal learning yet leave cortical connectivity and neuronal firing essentially intact. Arc expression was assessed after exploration of novel environments and performance of a novel water maze task during which normal rats learned the spatial location of an escape platform. During the same task, rats with fornix lesions learned to approach a visible platform but did not learn its spatial location. Rats with fornix lesions had normal baseline levels of hippocampal Arc mRNA, but unlike normal rats, expression was not increased in response to water maze training. The integrity of signaling pathways controlling Arc expression was demonstrated by stimulation of the medial perforant path, which induced normal synaptic potentiation and Arc in rats with fornix lesions. Together, the results demonstrate that Arc induction can be decoupled from behavior and is more likely to indicate the engagement of synaptic plasticity mechanisms than synaptic or neuronal activity per se. The results further imply that fornix lesions may impair memory in part by decoupling neuronal activity from signaling pathways required for long-lasting hippocampal synaptic plasticity.

Reactive plasticity in the dentate gyrus following bilateral entorhinal cortex lesions in cynomolgus monkeys.

Hippocampal structural plasticity induced by entorhinal cortex (EC) lesions has been studied extensively in the rat, but little comparable research has been conducted in primates. In the current study we assessed the long-term effects of bilateral aspiration lesions of the EC on multiple markers of circuit organization in the hippocampal dentate gyrus of young adult monkeys (Macaca fascicularis). Alternate histological sections were processed for the visualization of somatostatin and vesicular acetylcholine transporter (VAChT) immunoreactivity and acetylcholinesterase histochemistry (AChE). The markers revealed the distinct laminar organization of dentate gyrus circuitry for stereology-based morphometric quantification. Consistent with findings in rats, the volume of the somatostatin-immunopositive outer molecular layer (OML), innervated by projections from the EC, was decreased by 42% relative to control values. The inner molecular layer (IML) displayed a corresponding volumetric expansion in response to denervation of the OML as measured by AChE staining, but not when visualized for quantification by VAChT immunoreactivity. Nonetheless, stereological estimation revealed a 36% increase in the total length of VAChT-positive cholinergic fibers in the IML after EC damage, along with no change in the OML. Together, these findings suggest that despite substantial species differences in the organization of hippocampal circuitry, the capacity for reactive plasticity following EC damage, previously documented in rats, is at least partly conserved in the primate dentate gyrus.

Abnormal Capillary Vasodynamics Contribute to Ictal Neurodegeneration in Epilepsy.

Seizure-driven brain damage in epilepsy accumulates over time, especially in the hippocampus, which can lead to sclerosis, cognitive decline, and death. Excitotoxicity is the prevalent model to explain ictal neurodegeneration. Current labeling technologies cannot distinguish between excitotoxicity and hypoxia, however, because they share common molecular mechanisms. This leaves open the possibility that undetected ischemic hypoxia, due to ictal blood flow restriction, could contribute to neurodegeneration previously ascribed to excitotoxicity. We tested this possibility with Confocal Laser Endomicroscopy (CLE) and novel stereological analyses in several models of epileptic mice. We found a higher number and magnitude of NG2+ mural-cell mediated capillary constrictions in the hippocampus of epileptic mice than in that of normal mice, in addition to spatial coupling between capillary constrictions and oxidative stressed neurons and neurodegeneration. These results reveal a role for hypoxia driven by capillary blood flow restriction in ictal neurodegeneration.

Cholinergic changes in the APP23 transgenic mouse model of cerebral amyloidosis.

Alzheimer's Disease (AD) is a neurodegenerative disorder that is characterized by extracellular deposits of amyloid-beta peptide (Abeta) and a severe depletion of the cholinergic system, although the relationship between these two events is poorly understood. In the neocortex, there is a loss of cholinergic fibers and receptors and a decrease of both choline acetyltransferase (ChAT) and acetylcholinesterase enzyme activities. The nucleus basalis of Meynert (NBM), which provides the major cholinergic input to the neocortex, undergoes profound neuron loss in AD. In the present study, we have examined the cholinergic alterations in amyloid precursor protein transgenic mice (APP23), a mouse model of cerebral beta-amyloidosis. In aged APP23 mice, our results reveal modest decreases in cortical cholinergic enzyme activity compared with age-matched wild-type mice. Total cholinergic fiber length was more severely affected, with 29 and 35% decreases in the neocortex of aged APP23 mice compared with age-matched wild-type mice and young transgenic mice, respectively. However, there was no loss of cholinergic basal forebrain neurons in these aged APP23 mice, suggesting that the cortical cholinergic deficit in APP23 mice is locally induced by the deposition of amyloid and is not caused by a loss of cholinergic basal forebrain neurons. To study the impact of cholinergic basal forebrain degeneration on cortical amyloid deposition, we performed unilateral NBM lesions in adult APP23 mice. Three to 8 months after lesioning, a 38% reduction in ChAT activity and significant cholinergic fiber loss were observed in the ipsilateral frontal cortex. There was a 19% decrease in Abeta levels of the ipsilateral compared with contralateral frontal cortex with no change in the ratio of Abeta40 to Abeta42. We conclude that the severe cholinergic deficit in AD is caused by both the loss of cholinergic basal forebrain neurons and locally by cerebral amyloidosis in the neocortex. Moreover, our results suggest that disruption of the basal cholinergic forebrain system does not promote cerebral amyloidosis in APP23 transgenic mice.

Neocortical synaptic bouton number is maintained despite robust amyloid deposition in APP23 transgenic mice.

Major pathological findings in Alzheimer's disease (AD) brain include the deposition of amyloid-beta and synapse loss. Synaptic loss has been shown to correlate with the cognitive decline in AD patients, but the relationship between cerebral amyloidosis and synapse loss is complicated by the presence of neurofibrillary tangles and other lesions in AD brain. With the use of the APP23 transgenic mouse model that overexpresses human amyloid precursor protein (APP) with the Swedish double mutation, we investigated whether the development of cortical amyloid deposition was accompanied by synaptic bouton loss. With stereological methods, we show that despite robust age-related cortical amyloid deposition with associated synaptic degeneration, the total number of cortical synaptophysin-positive presynaptic terminals is not changed in 24-month-old animals compared with 3-, 8-, and 15-month-old APP23 mice. Wild-type mice also do not show an age-related loss of presynaptic boutons in the neocortex and are not significantly different from APP23 mice. Synaptophysin Western blotting revealed no significant difference between APP23 mice and wild-type controls at 3 and 25 months of age. Our results suggest that cerebral amyloidosis is not sufficient to account for the global synapse loss in AD. Alternatively, a putative trophic effect of APP may prevent, compensate, or delay a loss of synapses in this mouse model.

Reduction of ß-amyloid and γ-secretase by calorie restriction in female Tg2576 mice.

Research indicates that female risk of developing Alzheimer's disease (AD) is greater than that of males. Moderate reduction of calorie intake, known as calorie restriction (CR), reduces pathology in AD mouse models and is a potentially translatable prevention measure for individuals at-risk for AD, as well as an important tool for understanding how the brain endogenously attenuates age-related pathology. Whether sex influences the response to CR remains unknown. In this study, we assessed the effect of CR on beta-amyloid peptide (Aß) pathology and hippocampal CA1 neuron specific gene expression in the Tg2576 mouse model of cerebral amyloidosis. Relative to ad libitum (AL) feeding, CR feeding significantly reduced hippocampal Aß burden in 15-month-old female, but not age-matched male, Tg2576 mice. Sustained CR also significantly reduced expression of presenilin enhancer 2 (Psenen) and presenilin 1, components of the γ-secretase complex, in Tg2576 females. These results indicate that long-term CR significantly reduces age-dependent female Tg2576 Aß pathology, which is likely to involve CR-mediated reductions in γ-secretase-dependent amyloid precursor protein (APP) metabolism.

Reduction in hippocampal cholinergic innervation is unrelated to recognition memory impairment in aged rhesus monkeys.

Alterations in the basal forebrain cholinergic system have been widely studied in brain aging and Alzheimer's disease, but the magnitude of decline and relationship to cognitive impairment are still a matter of debate. The rhesus monkey (Macaca mulatta) provides a compelling model to study age-related memory decline, as the pattern of impairment closely parallels that observed in humans. Here, we used antibodies against the vesicular acetylcholine transporter and a new stereological technique to estimate total cholinergic fiber length in hippocampal subregions of behaviorally characterized young and aged rhesus monkeys. The analysis revealed an age-related decline in the length of cholinergic fibers of 22%, which was similar across the hippocampal subregions studied (dentate gyrus granule cell and molecular layers, CA2/3-hilus, and CA1), and across the rostral-caudal extent of the hippocampus. This effect, however, was unrelated to performance on the delayed nonmatching-to-sample task, a test of recognition memory sensitive to hippocampal system dysfunction and cognitive aging in monkeys. These findings indicate that a decline in cholinergic input fails to account for the influence of normal aging on memory supported by the primate hippocampal region.

Age and gender effects on microglia and astrocyte numbers in brains of mice.

The morphological changes that occur during normal brain aging are not well understood. This study used modern stereology to assess the effects of age and gender on total numbers of astrocytes and microglia in the hippocampal formation in C57Bl/6NNIA (B6) mice. Astrocytes and microglia were visualized using immunocytochemistry for glial fibrillary acidic protein (GFAP) and complement receptor 3 (Mac-1), respectively, and numbers of each cell type in dentate gyrus (DG) and CA1 regions were estimated using the optical fractionator method. The results reveal significantly greater ( approximately 20%) numbers of microglia and astrocytes in aged females compared to young female B6 mice. We also report that on average female B6 mice have 25-40% more astrocytes and microglia in DG and CA1 regions than age-matched male C57Bl/6J mice. Since astrocytes and microglia are thought to be targets of gonadal hormones, the effects of sex hormones and reproductive aging may be responsible for these findings.

Repeatable target localization for long-term in vivo imaging of mice with 2-photon microscopy.

Repetitive in vivo imaging in mice has become an indispensable tool for studying dynamic changes in structure and function of the brain. We describe a head fixation system, which allows rapid re-localization of previously imaged regions of interest (ROIs) within the brain. Such ROIs can be automatically relocated and imaged over weeks to months with negligible rotational change and only minor translational errors. Previously stored imaging positions can be fully automated re-localized within a few seconds. This automated rapid and accurate relocation simplifies image acquisition and post-processing in longitudinal imaging experiments. Moreover, as the laser is only used for data acquisition and not for finding previously imaged ROIs, the risk of laser induced tissue damage and photobleaching is greatly reduced. Thus, here described head fixation device appears well suited for in vivo repetitive long-term imaging in rodent brain.

Early onset amyloid lesions lead to severe neuritic abnormalities and local, but not global neuron loss in APPPS1 transgenic mice.

APPPS1 transgenic mice develop amyloid-ß 42 (Aß42)-driven early-onset cerebral ß-amyloidosis. Stereological analysis of neocortical neuron number in groups of 2-, 10-, and 17-month-old APPPS1 mice did not reveal any changes compared with wild-type control animals despite massive amyloid-ß (Aß) load and disrupted cytoarchitecture. However, in subregions with high neuron density such as the granule cell layer of the dentate gyrus, modest but significant neuron loss was found, reminiscent of findings in previously published mouse models with late onset cerebral ß-amyloidosis and predominant amyloid-ß 40 (Aß40) expression.

Age-related spatial learning impairment is unrelated to spinophilin immunoreactive spine number and protein levels in rat hippocampus.

Age-related impairments in hippocampus-dependent learning and memory tasks are not associated with a loss of hippocampal neurons, but may be related to alterations in synaptic integrity. Here we used stereological techniques to estimate spine number in hippocampal subfields using immunostaining for the spine-associated protein, spinophilin, as a marker. Quantification of the immunoreactive profiles was performed using the optical disector/fractionator technique. Aging was associated with a modest increase in spine number in the molecular layer of the dentate gyrus and CA1 stratum lacunosum-moleculare. By comparison, spinophilin protein levels in the hippocampus, measured by Western blot analysis, failed to differ as a function of age. Neither the morphological nor the protein level data were correlated with spatial learning ability across individual aged rats. The results extend current evidence on synaptic integrity in the aged brain, indicating that a substantial loss of dendritic spines and spinophilin protein in the hippocampus are unlikely to contribute to age-related impairment in spatial learning.

Abeta42-driven cerebral amyloidosis in transgenic mice reveals early and robust pathology.

We have generated a novel transgenic mouse model on a C57BL/6J genetic background that coexpresses KM670/671NL mutated amyloid precursor protein and L166P mutated presenilin 1 under the control of a neuron-specific Thy1 promoter element (APPPS1 mice). Cerebral amyloidosis starts at 6-8 weeks and the ratio of human amyloid (A)beta42 to Abeta40 is 1.5 and 5 in pre-depositing and amyloid-depositing mice, respectively. Consistent with this ratio, extensive congophilic parenchymal amyloid but minimal amyloid angiopathy is observed. Amyloid-associated pathologies include dystrophic synaptic boutons, hyperphosphorylated tau-positive neuritic structures and robust gliosis, with neocortical microglia number increasing threefold from 1 to 8 months of age. Global neocortical neuron loss is not apparent up to 8 months of age, but local neuron loss in the dentate gyrus is observed. Because of the early onset of amyloid lesions, the defined genetic background of the model and the facile breeding characteristics, APPPS1 mice are well suited for studying therapeutic strategies and the pathomechanism of amyloidosis by cross-breeding to other genetically engineered mouse models.