Chet C Sherwood

George Washington University, Washington, Washington, D.C., United States

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Publications (117)530.74 Total impact

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    ABSTRACT: Humans are uniquely susceptible to age-related neurodegenerative pathologies, such as Alzheimer’s disease. This vulnerability is likely the result of evolutionary changes related to increased brain size and longevity compared to other primates. In humans, healthy aging is marked by varying degrees of neural deterioration and cognitive impairment. One region particularly affected by aging is the hippocampus, which exhibits a decrease in total volume and an increase in glial cell population and activation. Prior studies of great apes, including chimpanzees, did not find an age-associated decrease in hippocampus volume or a substantial neuronal loss in the CA1 subregion. These reports suggest the great ape brain may age differently than the normal human brain. The objective of the present analysis was to examine the effect of age on neuronal and glial densities in the hippocampus of chimpanzees, our closest living relatives. Using Nissl-stained sections and stereological methods, we quantified neuron and glial density in the CA1 and CA3 fields of the hippocampus in a sample of 16 chimpanzees (ages 12-58 years). Overall, CA3 possessed higher neuron and glial densities relative to CA1 (Mann-Whitney, p < 0.01). Variation in neuron densities was associated with age in both hippocampal subregions (CA1: p = 0.02, r2 = 0.32; CA3: p < 0.01, r2 = 0.49), while variation in glial densities was only correlated with age in the CA3 field (p = 0.030, r2 = 0.296). The ratio of glia to neurons in CA1 and CA3 was not altered with age in chimpanzees. Our preliminary results demonstrate a moderate, age-related decline of both neuron and glial densities for CA3 and neuron densities for CA1. Future analyses will reveal if this association remains with an increased sample size and is related to neurodegenerative pathologies in these individuals.
    Society for Neuroscience, Washington, D.C.; 11/2014
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    Proceedings of the National Academy of Sciences 11/2014; · 9.81 Impact Factor
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    ABSTRACT: Lipofuscin pigment accumulation is among the most prominent markers of cellular aging in postmitotic cells. The formation of lipofuscin is related to oxidative enzymatic activity and free radical-induced lipid peroxidation. In various mammals such as rat, dog, macaque as well as in cheirogaleid primates, most of the large neurons, such as cerebellar Purkinje cells and neocortical pyramidal cells, show heavy lipofuscin accumulation in adulthood. In contrast, a well-known yet poorly studied feature of the aging human brain is that although lipofuscin accumulation is most marked in large neurons of the cerebral cortex, the large neurons of the cerebellar cortex-the Purkinje cells-appear to remain free of lipofuscin accumulation. It is however, not known whether this characteristic of human Purkinje cells is shared with other primates or other mammals. This study reports results from histological observation of Purkinje cells in humans, non-human primates, and other mammals. Procedures include histochemistry, immunocytochemistry, and fluorescence microscopy. Abundant lipofuscin deposition was observed in Purkinje cells of all the species we examined except Homo sapiens (including Alzheimer's disease cases) and Pan troglodytes. In contrast, lipofuscin deposition was observed in neurons of the dentate nucleus. Our findings suggest that when compared with other primates, Purkinje cells in chimpanzees and humans might share a common aging pattern that involves mechanisms for neuroprotection. This observation is important when considering animal models of aging.
    Brain Structure and Function 11/2014; · 7.84 Impact Factor
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    ABSTRACT: Among primates, humans exhibit the most profound degree of age-related brain volumetric decline in particular regions, such as the hippocampus and the frontal lobe. Recent studies have shown that our closest living relatives, the chimpanzees, experience little to no volumetric decline in gray and white matter over the adult lifespan. However, these previous studies were limited with a small sample of chimpanzees of the most advanced ages. In the present study, we sought to further test for potential age-related decline in cortical organization in chimpanzees by expanding the sample size of aged chimpanzees. We used the BrainVisa software to measure total brain volume, gray and white matter volumes, gray matter thickness, and gyrification index in a cross-sectional sample of 219 captive chimpanzees (8–53 years old), with 38 subjects being 40 or more years of age. Mean depth and cortical fold opening of 11 major sulci of the chimpanzee brains were also measured. We found that chimpanzees showed increased gyrification with age and a cubic relationship between age and white matter volume. For the association between age and sulcus depth and width, the results were mostly non-significant with the exception of one negative correlation between age and the fronto-orbital sulcus. In short, results showed that chimpanzees exhibit few age-related changes in global cortical organization, sulcus folding and sulcus width. These findings support previous studies and the theory that the age-related changes in the human brain is due to an extended lifespan.
    NeuroImage 11/2014; 101:59–67. · 6.13 Impact Factor
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    ABSTRACT: 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. Am J Phys Anthropol, 2014. © 2014 Wiley Periodicals, Inc.
    American Journal of Physical Anthropology 10/2014; · 2.51 Impact Factor
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    ABSTRACT: The high energetic costs of human brain development have been hypothesized to explain distinctive human traits, including exceptionally slow and protracted preadult growth. Although widely assumed to constrain life-history evolution, the metabolic requirements of the growing human brain are unknown. We combined previously collected PET and MRI data to calculate the human brain's glucose use from birth to adulthood, which we compare with body growth rate. We evaluate the strength of brain-body metabolic trade-offs using the ratios of brain glucose uptake to the body's resting metabolic rate (RMR) and daily energy requirements (DER) expressed in glucose-gram equivalents (glucosermr% and glucoseder%). We find that glucosermr% and glucoseder% do not peak at birth (52.5% and 59.8% of RMR, or 35.4% and 38.7% of DER, for males and females, respectively), when relative brain size is largest, but rather in childhood (66.3% and 65.0% of RMR and 43.3% and 43.8% of DER). Body-weight growth (dw/dt) and both glucosermr% and glucoseder% are strongly, inversely related: soon after birth, increases in brain glucose demand are accompanied by proportionate decreases in dw/dt. Ages of peak brain glucose demand and lowest dw/dt co-occur and subsequent developmental declines in brain metabolism are matched by proportionate increases in dw/dt until puberty. The finding that human brain glucose demands peak during childhood, and evidence that brain metabolism and body growth rate covary inversely across development, support the hypothesis that the high costs of human brain development require compensatory slowing of body growth rate.
    Proceedings of the National Academy of Sciences 08/2014; · 9.81 Impact Factor
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    ABSTRACT: The central sulcus (CS) divides the pre- and postcentral gyri along the dorsal-ventral plane of which all motor and sensory functions are topographically organized. The motor-hand area of the precentral gyrus or KNOB has been described as the anatomical substrate of the hand in humans. Given the importance of the hand in primate evolution, here we examine the evolution of the motor-hand area by comparing the relative size and pattern of cortical folding of the CS surface area from magnetic resonance images in 131 primates, including Old World monkeys, apes and humans. We found that humans and great apes have a well-formed motor-hand area that can be seen in the variation in depth of the CS along the dorsal-ventral plane. We further found that great apes have relatively large CS surface areas compared to Old World monkeys. However, relative to great apes, humans have a small motor-hand area in terms of both adjusted and absolute surface areas. © 2014 S. Karger AG, Basel.
    Brain Behavior and Evolution 08/2014; · 2.89 Impact Factor
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    ABSTRACT: The present study documents the morphology of neurons in several regions of the neocortex from the bottlenose dolphin (Tursiops truncatus), the North Atlantic minke whale (Balaenoptera acutorostrata), and the humpback whale (Megaptera novaeangliae). Golgi-stained neurons (n = 210) were analyzed in the frontal and temporal neocortex as well as in the primary visual and primary motor areas. Qualitatively, all three species exhibited a diversity of neuronal morphologies, with spiny neurons including typical pyramidal types, similar to those observed in primates and rodents, as well as other spiny neuron types that had more variable morphology and/or orientation. Five neuron types, with a vertical apical dendrite, approximated the general pyramidal neuron morphology (i.e., typical pyramidal, extraverted, magnopyramidal, multiapical, and bitufted neurons), with a predominance of typical and extraverted pyramidal neurons. In what may represent a cetacean morphological apomorphy, both typical pyramidal and magnopyramidal neurons frequently exhibited a tri-tufted variant. In the humpback whale, there were also large, star-like neurons with no discernable apical dendrite. Aspiny bipolar and multipolar interneurons were morphologically consistent with those reported previously in other mammals. Quantitative analyses showed that neuronal size and dendritic extent increased in association with body size and brain mass (bottlenose dolphin < minke whale < humpback whale). The present data thus suggest that certain spiny neuron morphologies may be apomorphies in the neocortex of cetaceans as compared to other mammals and that neuronal dendritic extent covaries with brain and body size.
    Brain Structure and Function 08/2014; · 7.84 Impact Factor
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    ABSTRACT: The dorsal cochlear nucleus (DCN) is a brainstem structure that receives input from the auditory nerve. Many studies in a diversity of species have shown that the DCN has a laminar organization and identifiable neuron types with predictable synaptic relations to each other. In contrast, studies on the human DCN have found a less distinct laminar organization and fewer cell types, although there has been disagreement among studies in how to characterize laminar organization and which of the cell types identified in other animals are also present in humans. We have reexamined DCN organization in the human using immunohistochemistry to analyze the expression of several proteins that have been useful in delineating the neurochemical organization of other brainstem structures in humans: nonphosphorylated neurofilament protein (NPNFP), nitric oxide synthase (nNOS), and three calcium-binding proteins. The results for humans suggest a laminar organization with only two layers, and the presence of large projection neurons that are enriched in NPNFP. We did not observe evidence in humans of the inhibitory interneurons that have been described in the cat and rodent DCN. To compare humans and other animals directly we used immunohistochemistry to examine the DCN in the macaque monkey, the cat, and three rodents. We found similarities between macaque monkey and human in the expression of NPNFP and nNOS, and unexpected differences among species in the patterns of expression of the calcium-binding proteins. Anat Rec, 2014. © 2014 Wiley Periodicals, Inc.
    The Anatomical Record Advances in Integrative Anatomy and Evolutionary Biology 08/2014; 297(10). · 1.34 Impact Factor
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    ABSTRACT: Although the basic morphological characteristics of neurons in the cerebellar cortex have been documented in several species, virtually nothing is known about the quantitative morphological characteristics of these neurons across different taxa. To that end, the present study investigated cerebellar neuronal morphology among eight different, large-brained mammalian species comprising a broad phylogenetic range: afrotherians (African elephant, Florida manatee), carnivores (Siberian tiger, clouded leopard), cetartiodactyls (humpback whale, giraffe) and primates (human, common chimpanzee). Specifically, several neuron types (e.g., stellate, basket, Lugaro, Golgi, and granule neurons; N = 317) of the cerebellar cortex were stained with a modified rapid Golgi technique and quantified on a computer-assisted microscopy system. There was a 64-fold variation in brain mass across species in our sample (from clouded leopard to the elephant) and a 103-fold variation in cerebellar volume. Most dendritic measures tended to increase with cerebellar volume. The cerebellar cortex in these species exhibited the trilaminate pattern common to all mammals. Morphologically, neuron types in the cerebellar cortex were generally consistent with those described in primates (Fox et al., 1967) and rodents (Palay and Chan-Palay, 1974), although there was substantial quantitative variation across species. In particular, Lugaro neurons in the elephant appeared to be disproportionately larger than those in other species. To explore potential quantitative differences in dendritic measures across species, MARSplines analyses were used to evaluate whether species could be differentiated from each other based on dendritic characteristics alone. Results of these analyses indicated that there were significant differences among all species in dendritic measures.
    Frontiers in Neuroanatomy 07/2014; 8:24. · 4.18 Impact Factor
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    ABSTRACT: The present quantitative study extends our investigation of cetartiodactyls by exploring the neuronal morphology in the giraffe (Giraffa camelopardalis) neocortex. Here, we investigate giraffe primary visual and motor cortices from perfusion-fixed brains of three subadults stained with a modified rapid Golgi technique. Neurons (n = 244) were quantified on a computer-assisted microscopy system. Qualitatively, the giraffe neocortex contained an array of complex spiny neurons that included both "typical" pyramidal neuron morphology and "atypical" spiny neurons in terms of morphology and/or orientation. In general, the neocortex exhibited a vertical columnar organization of apical dendrites. Although there was no significant quantitative difference in dendritic complexity for pyramidal neurons between primary visual (n = 78) and motor cortices (n = 65), there was a significant difference in dendritic spine density (motor cortex > visual cortex). The morphology of aspiny neurons in giraffes appeared to be similar to that of other eutherian mammals. For cross-species comparison of neuron morphology, giraffe pyramidal neurons were compared to those quantified with the same methodology in African elephants and some cetaceans (e.g., bottlenose dolphin, minke whale, humpback whale). Across species, the giraffe (and cetaceans) exhibited less widely bifurcating apical dendrites compared to elephants. Quantitative dendritic measures revealed that the elephant and humpback whale had more extensive dendrites than giraffes, whereas the minke whale and bottlenose dolphin had less extensive dendritic arbors. Spine measures were highest in the giraffe, perhaps due to the high quality, perfusion fixation. The neuronal morphology in giraffe neocortex is thus generally consistent with what is known about other cetartiodactyls.
    Brain Structure and Function 07/2014; · 7.84 Impact Factor
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    ABSTRACT: Different brain components can evolve in a coordinated manner or they can show divergent evolutionary trajectories according to a mosaic pattern of variation. Understanding the relationship between these brain evolutionary patterns, which are not mutually exclusive, can be informed by the examination of intraspecific variation. Our study evaluates patterns of brain anatomical covariation in chimpanzees and humans to infer their influence on brain evolution in the hominin clade. We show that chimpanzee and human brains have a modular structure that may have facilitated mosaic evolution from their last common ancestor. Spatially adjacent regions covary with one another to the strongest degree and separated regions are more independent from each other, which might be related to a predominance of local association connectivity. Despite the undoubted importance of developmental and functional factors in determining brain morphology, we find that these constraints are subordinate to the primary effect of local spatial interactions.
    Nature Communications 07/2014; 5:4469. · 10.74 Impact Factor
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    ABSTRACT: The claustrum is a subcortical nucleus present in all placental mammals. Many anatomical studies have shown that its inputs are predominantly from the cerebral cortex and its outputs are back to the cortex. This connectivity thus suggests that the claustrum serves to amplify or facilitate information processing in the cerebral cortex. The size and the complexity of the cerebral cortex varies dramatically across species. Some species have lissencephalic brains, with few cortical areas, while others have a greatly expanded cortex and many cortical areas. This evolutionary diversity in the cerebral cortex raises several questions about the claustrum. Does its volume expand in coordination with the expansion of cortex and does it acquire new functions related to the new cortical functions? Here we survey the organization of the claustrum in animals with large brains, including great apes and cetaceans. Our data suggest that the claustrum is not always a continuous structure. In monkeys and gorillas there are a few isolated islands of cells near the main body of the nucleus. In cetaceans, however, there are many isolated cell islands. These data suggest constraints on the possible function of the claustrum. Some authors propose that the claustrum has a more global role in perception or consciousness that requires intraclaustral integration of information. These theories postulate mechanisms like gap junctions between claustral cells or a "syncytium" to mediate intraclaustral processing. The presence of discontinuities in the structure of the claustrum, present but minimal in some primates, but dramatically clear in cetaceans, argues against the proposed mechanisms of intraclaustral processing of information. The best interpretation of function, then, is that each functional subdivision of the claustrum simply contributes to the function of its cortical partner.
    Frontiers in Systems Neuroscience 07/2014; 8:117.
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    ABSTRACT: Metabolite concentrations reflect the physiological states of tissues and cells. However, the role of metabolic changes in species evolution is currently unknown. Here, we present a study of metabolome evolution conducted in three brain regions and two non-neural tissues from humans, chimpanzees, macaque monkeys, and mice based on over 10,000 hydrophilic compounds. While chimpanzee, macaque, and mouse metabolomes diverge following the genetic distances among species, we detect remarkable acceleration of metabolome evolution in human prefrontal cortex and skeletal muscle affecting neural and energy metabolism pathways. These metabolic changes could not be attributed to environmental conditions and were confirmed against the expression of their corresponding enzymes. We further conducted muscle strength tests in humans, chimpanzees, and macaques. The results suggest that, while humans are characterized by superior cognition, their muscular performance might be markedly inferior to that of chimpanzees and macaque monkeys.
    PLoS Biology 05/2014; 12(5):e1001871. · 11.77 Impact Factor
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    ABSTRACT: With the evolution of a relatively large brain size in haplorhine primates (i.e. tarsiers, monkeys, apes, and humans), there have been associated changes in the molecular machinery that delivers energy to the neocortex. Here we investigated variation in lactate dehydrogenase (LDH) expression and isoenzyme composition of the neocortex and striatum in primates using quantitative Western blotting and isoenzyme analysis of total homogenates and synaptosomal fractions. Analysis of isoform expression revealed that LDH in synaptosomal fractions from both forebrain regions shifted towards a predominance of the heart-type, aerobic isoform LDH-B among haplorhines as compared to strepsirrhines (i.e. lorises and lemurs), while in the total homogenate of the neocortex and striatum there was no significant difference in LDH isoenzyme composition between the primate suborders. The largest increase occurred in synapse-associated LDH-B expression in the neocortex, with an especially remarkable elevation in the ratio of LDH-B/LDH-A in humans. The phylogenetic variation in the ratio of LDH-B/LDH-A was correlated with species-typical brain mass but not the encephalization quotient. A significant LDH-B increase in the subneuronal fraction from haplorhine neocortex and striatum suggests a relatively higher rate of aerobic glycolysis that is linked to synaptosomal mitochondrial metabolism. Our results indicate that there is a differential composition of LDH isoenzymes and metabolism in synaptic terminals that evolved in primates to meet increased energy requirements in association with brain enlargement. © 2014 S. Karger AG, Basel.
    Brain Behavior and Evolution 03/2014; · 2.89 Impact Factor
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    ABSTRACT: Efforts to understand nervous system structure and function have received new impetus from the federal Brain Research through Advancing Innovative Neurotechnologies (BRAIN) Initiative. Comparative analyses can contribute to this effort by leading to the discovery of general principles of neural circuit design, information processing, and gene-structure-function relationships that are not apparent from studies on single species. We here propose to extend the comparative approach to nervous system ‘maps’ comprising molecular, anatomical, and physiological data. This research will identify which neural features are likely to generalize across species, and which are unlikely to be broadly conserved. It will also suggest causal relationships between genes, development, adult anatomy, physiology, and, ultimately, behavior. These causal hypotheses can then be tested experimentally. Finally, insights from comparative research can inspire and guide technological development. To promote this research agenda, we recommend that teams of investigators coalesce around specific research questions and select a set of ‘reference species’ to anchor their comparative analyses. These reference species should be chosen not just for practical advantages, but also with regard for their phylogenetic position, behavioral repertoire, well-annotated genome, or other strategic reasons. We envision that the nervous systems of these reference species will be mapped in more detail than those of other species. The collected data may range from the molecular to the behavioral, depending on the research question. To integrate across levels of analysis and across species, standards for data collection, annotation, archiving, and distribution must be developed and respected. To that end, it will help to form networks or consortia of researchers and centers for science, technology, and education that focus on organized data collection, distribution, and training. These activities could be supported, at least in part, through existing mechanisms at NSF, NIH, and other agencies. It will also be important to develop new integrated software and database systems for cross-species data analyses. Multidisciplinary efforts to develop such analytical tools should be supported financially. Finally, training opportunities should be created to stimulate multidisciplinary, integrative research into brain structure, function, and evolution. J. Comp. Neurol., 2014. © 2014 Wiley Periodicals, Inc.
    The Journal of Comparative Neurology 02/2014; · 3.51 Impact Factor
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    ABSTRACT: Increased relative brain size characterizes the evolution of primates, suggesting that enhanced cognition plays an important part in the behavioral adaptations of this mammalian order. In addition to changes in brain anatomy, cognition can also be regulated by molecular changes that alter synaptic function, but little is known about modifications of synapses in primate brain evolution. The aim of the current study was to investigate the expression patterns and evolution of 20 synaptic genes from the prefrontal cortex of 12 primate species. The genes investigated included glutamate receptors, scaffolding proteins, synaptic vesicle components, as well as factors involved in synaptic vesicle release and structural components of the nervous system. Our analyses revealed that there have been significant changes during primate brain evolution in the components of the glutamatergic signaling pathway in terms of gene expression, protein expression, and promoter sequence changes. These results could entail functional modifications in the regulation of specific genes related to processes underlying learning and memory.
    Cerebral Cortex 01/2014; · 8.31 Impact Factor
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    ABSTRACT: Neuropeptide Y (NPY) plays a role in a variety of basic physiological functions and has also been implicated in regulating cognition, including learning and memory. A decrease in neocortical NPY has been reported for Alzheimer's disease, schizophrenia, bipolar disorder, and depression, potentially contributing to associated cognitive deficits. The goal of the present analysis was to examine variation in neocortical NPY-immunoreactive axon and varicosity density among haplorhine primates (monkeys, apes, and humans). Stereologic methods were used to measure the ratios of NPY-expressing axon length density to total neuron density (ALv/Nv) and NPY-immunoreactive varicosity density to neuron density (Vv/Nv), as well as the mean varicosity spacing in neocortical areas 10, 24, 44, and 22 (Tpt) of humans, African great apes, New World monkeys, and Old World monkeys. Humans and great apes showed increased cortical NPY innervation relative to monkey species for ALv/Nv and Vv/Nv. Furthermore, humans and great apes displayed a conserved pattern of varicosity spacing across cortical areas and layers, with no differences between cortical layers or among cortical areas. These phylogenetic differences may be related to shared life history variables and may reflect specific cognitive abilities.
    Frontiers in Human Neuroscience 01/2014; 8:101. · 2.90 Impact Factor

Publication Stats

2k Citations
530.74 Total Impact Points


  • 2006–2014
    • George Washington University
      • • Department of Anthropology
      • • Center for the Advanced Study of Hominid Paleobiology
      Washington, Washington, D.C., United States
  • 2013
    • University of Coimbra
      • Departamento de Ciências da Vida
      Coimbra, Distrito de Coimbra, Portugal
  • 2012–2013
    • University of California, San Diego
      • Department of Anthropology
      San Diego, CA, United States
    • University at Buffalo, The State University of New York
      • Department of Physiology and Biophysics
      Buffalo, NY, United States
    • University of the Witwatersrand
      • School of Anatomical Science
      Johannesburg, Gauteng, South Africa
    • Wisconsin National Primate Research Center
      Madison, Wisconsin, United States
  • 2008–2013
    • Wayne State University
      • Center for Molecular Medicine and Genetics
      Detroit, MI, United States
  • 2011–2012
    • Trinity University
      • Department of Psychology
      San Antonio, TX, United States
    • University College London
      • Department of Anthropology
      London, ENG, United Kingdom
    • Dartmouth College
      • Department of Anthropology
      Hanover, NH, United States
  • 2004–2012
    • Kent State University
      • • Department of Biological Sciences
      • • Department of Anthropology
      Kent, OH, United States
  • 2003–2011
    • Mount Sinai School of Medicine
      • Department of Neuroscience
      Manhattan, NY, United States
  • 2010
    • Colorado College
      Colorado Springs, Colorado, United States
    • Agnes Scott College
      • Department of Psychology
      Decatur, Illinois, United States
  • 2007–2008
    • Hiram College
      Georgia, United States
  • 2005
    • Emory University
      • Department of Neuroscience and Behavioral Biology
      Atlanta, GA, United States
  • 2003–2004
    • Columbia University
      • Department of Anthropology
      New York City, New York, United States