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Sherwood CC, Miller SB, Karl M, Stimpson CD, Phillips KA, Jacobs B, Hof PR, Raghanti MA, Smaers JB. Invariant Synapse Density and Neuronal Connectivity Scaling in Primate Neocortical Evolution. Cereb Cortex 2020; 30:5604-5615. [PMID: 32488266 DOI: 10.1093/cercor/bhaa149] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 03/31/2020] [Accepted: 05/07/2020] [Indexed: 12/20/2022] Open
Abstract
Synapses are involved in the communication of information from one neuron to another. However, a systematic analysis of synapse density in the neocortex from a diversity of species is lacking, limiting what can be understood about the evolution of this fundamental aspect of brain structure. To address this, we quantified synapse density in supragranular layers II-III and infragranular layers V-VI from primary visual cortex and inferior temporal cortex in a sample of 25 species of primates, including humans. We found that synapse densities were relatively constant across these levels of the cortical visual processing hierarchy and did not significantly differ with brain mass, varying by only 1.9-fold across species. We also found that neuron densities decreased in relation to brain enlargement. Consequently, these data show that the number of synapses per neuron significantly rises as a function of brain expansion in these neocortical areas of primates. Humans displayed the highest number of synapses per neuron, but these values were generally within expectations based on brain size. The metabolic and biophysical constraints that regulate uniformity of synapse density, therefore, likely underlie a key principle of neuronal connectivity scaling in primate neocortical evolution.
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Affiliation(s)
- Chet C Sherwood
- Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052, USA
| | - Sarah B Miller
- Department of Psychological and Brain Sciences, Dartmouth College, Hanover, NH 03755, USA
| | - Molly Karl
- Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052, USA
| | - Cheryl D Stimpson
- Department of Anthropology, Center for the Advanced Study of Human Paleobiology, The George Washington University, Washington, DC 20052, USA
| | | | - Bob Jacobs
- Department of Psychology, Laboratory of Quantitative Neuromorphology, Colorado College, Colorado Springs, CO 80946, USA
| | - Patrick R Hof
- Nash Family Department of Neuroscience, Friedman Brain Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
| | - Mary Ann Raghanti
- Department of Anthropology, School of Biomedical Sciences, Brain Health Research Institute, Kent State University, Kent, OH 44242, USA
| | - Jeroen B Smaers
- Department of Anthropology, Stony Brook University, Stony Brook, NY 11794, USA.,Division of Anthropology, American Museum of Natural History, New York, NY 10024, USA
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Ross JD, Cullen DK, Harris JP, LaPlaca MC, DeWeerth SP. A three-dimensional image processing program for accurate, rapid, and semi-automated segmentation of neuronal somata with dense neurite outgrowth. Front Neuroanat 2015; 9:87. [PMID: 26257609 PMCID: PMC4507056 DOI: 10.3389/fnana.2015.00087] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 06/18/2015] [Indexed: 12/02/2022] Open
Abstract
Three-dimensional (3-D) image analysis techniques provide a powerful means to rapidly and accurately assess complex morphological and functional interactions between neural cells. Current software-based identification methods of neural cells generally fall into two applications: (1) segmentation of cell nuclei in high-density constructs or (2) tracing of cell neurites in single cell investigations. We have developed novel methodologies to permit the systematic identification of populations of neuronal somata possessing rich morphological detail and dense neurite arborization throughout thick tissue or 3-D in vitro constructs. The image analysis incorporates several novel automated features for the discrimination of neurites and somata by initially classifying features in 2-D and merging these classifications into 3-D objects; the 3-D reconstructions automatically identify and adjust for over and under segmentation errors. Additionally, the platform provides for software-assisted error corrections to further minimize error. These features attain very accurate cell boundary identifications to handle a wide range of morphological complexities. We validated these tools using confocal z-stacks from thick 3-D neural constructs where neuronal somata had varying degrees of neurite arborization and complexity, achieving an accuracy of ≥95%. We demonstrated the robustness of these algorithms in a more complex arena through the automated segmentation of neural cells in ex vivo brain slices. These novel methods surpass previous techniques by improving the robustness and accuracy by: (1) the ability to process neurites and somata, (2) bidirectional segmentation correction, and (3) validation via software-assisted user input. This 3-D image analysis platform provides valuable tools for the unbiased analysis of neural tissue or tissue surrogates within a 3-D context, appropriate for the study of multi-dimensional cell-cell and cell-extracellular matrix interactions.
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Affiliation(s)
- James D Ross
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory Atlanta, GA, USA ; School of Electrical and Computer Engineering, Georgia Institute of Technology Atlanta, GA, USA
| | - D Kacy Cullen
- Department of Neurosurgery, University of Pennsylvania Philadelphia, PA, USA ; Philadelphia Veterans Affairs Medical Center Philadelphia, PA, USA
| | - James P Harris
- Department of Neurosurgery, University of Pennsylvania Philadelphia, PA, USA ; Philadelphia Veterans Affairs Medical Center Philadelphia, PA, USA
| | - Michelle C LaPlaca
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory Atlanta, GA, USA
| | - Stephen P DeWeerth
- Coulter Department of Biomedical Engineering, Georgia Institute of Technology/Emory Atlanta, GA, USA ; School of Electrical and Computer Engineering, Georgia Institute of Technology Atlanta, GA, USA
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O’Kusky J, Ye P. Neurodevelopmental effects of insulin-like growth factor signaling. Front Neuroendocrinol 2012; 33:230-51. [PMID: 22710100 PMCID: PMC3677055 DOI: 10.1016/j.yfrne.2012.06.002] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 05/09/2012] [Accepted: 06/07/2012] [Indexed: 11/28/2022]
Abstract
Insulin-like growth factor (IGF) signaling greatly impacts the development and growth of the central nervous system (CNS). IGF-I and IGF-II, two ligands of the IGF system, exert a wide variety of actions both during development and in adulthood, promoting the survival and proliferation of neural cells. The IGFs also influence the growth and maturation of neural cells, augmenting dendritic growth and spine formation, axon outgrowth, synaptogenesis, and myelination. Specific IGF actions, however, likely depend on cell type, developmental stage, and local microenvironmental milieu within the brain. Emerging research also indicates that alterations in IGF signaling likely contribute to the pathogenesis of some neurological disorders. This review summarizes experimental studies and shed light on the critical roles of IGF signaling, as well as its mechanisms, during CNS development.
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Affiliation(s)
- John O’Kusky
- Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, British Columbia, Canada V5Z 1M9
| | - Ping Ye
- Department of Pediatrics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, United States
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Cullen DK, Gilroy ME, Irons HR, Laplaca MC. Synapse-to-neuron ratio is inversely related to neuronal density in mature neuronal cultures. Brain Res 2010; 1359:44-55. [PMID: 20800585 DOI: 10.1016/j.brainres.2010.08.058] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2008] [Revised: 08/16/2010] [Accepted: 08/19/2010] [Indexed: 12/23/2022]
Abstract
Synapse formation is a fundamental process in neurons that occurs throughout development, maturity, and aging. Although these stages contain disparate and fluctuating numbers of mature neurons, tactics employed by neuronal networks to modulate synapse number as a function of neuronal density are not well understood. The goal of this study was to utilize an in vitro model to assess the influence of cell density and neuronal maturity on synapse number and distribution. Specifically, cerebral cortical neurons were plated in planar culture at densities ranging from 10 to 5000 neurons/mm², and synapse number and distribution were evaluated via immunocytochemistry over 21 days in vitro (DIV). High-resolution confocal microscopy revealed an elaborate three-dimensional distribution of neurites and synapses across the heights of high-density neuronal networks by 21 DIV, which were up to 18 μm thick, demonstrating the complex degree of spatial interactions even in planar high-density cultures. At 7 DIV, the mean number of synapses per neuron was less than 5, and this did not vary as a function of neuronal density. However, by 21 DIV, the number of synapses per neuron had jumped 30- to 80-fold, and the synapse-to-neuron ratio was greatest at lower neuronal densities (< 500 neurons/mm²; mean approximately 400 synapses/neuron) compared to mid and higher neuronal densities (500-4500 neurons/mm²; mean of approximately 150 synapses/neuron) (p<0.05). These results suggest a relationship between neuronal density and synapse number that may have implications in the neurobiology of developing neuronal networks as well as processes of cell death and regeneration.
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Affiliation(s)
- D Kacy Cullen
- Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA 19104, USA.
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Casanova MF. Neuropathological and genetic findings in autism: the significance of a putative minicolumnopathy. Neuroscientist 2006; 12:435-41. [PMID: 16957005 DOI: 10.1177/1073858406290375] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Autism is a condition manifested as abnormalities of relatedness, communication, range of interests, and repetitive behaviors. Despite alarming prevalence estimates and exhortations to research, little is known regarding its pathophysiology. Recent reports of a putative minicolumnopathy explain changes in brain size, gray/white matter ratios, and interareal connectivity. This article summarizes possible links between minicolumns and other topics-cortical modularity, age of onset, gliosis, and genetics-relevant to the pathophysiology of autism.
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Affiliation(s)
- Manuel F Casanova
- Department of Psychiatry and Behavioral Sciences University of Louisville, 500 South Preston Street, Louisville, KY, USA.
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Buxhoeveden DP, Hasselrot U, Buxhoeveden NE, Booze RM, Mactutus CF. Microanatomy in 21 day rat brains exposed prenatally to cocaine. Int J Dev Neurosci 2006; 24:335-41. [PMID: 16814973 DOI: 10.1016/j.ijdevneu.2006.04.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2006] [Revised: 04/06/2006] [Accepted: 04/06/2006] [Indexed: 11/15/2022] Open
Abstract
We examined cell minicolumns, apical dendrite bundles, and inhibitory interneurons, in prefrontal and somatosensory cortex of 21-day-old rat brains exposed to cocaine during fetal development. Cell columns and apical dendrite bundles were found to be narrower, or closer together, in all three areas following in utero cocaine exposure. The inter-rater reliability among different observers was R(2)=0.89. The number of cells stained for glutamic acid decarboxylase (GAD) was not significantly different in the prenatal cocaine exposed group compared to saline controls. The present data suggests that recreational doses of cocaine administered intravenously in early pregnancy, have the capacity to modify the maturation of the ontogenetic cell column.
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Affiliation(s)
- Daniel P Buxhoeveden
- Department of Anthropology, University of South Carolina, Columbia, SC 29803, USA.
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