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Dickins EM, Salinas PC. Wnts in action: from synapse formation to synaptic maintenance. Front Cell Neurosci 2013; 7:162. [PMID: 24223536 PMCID: PMC3819050 DOI: 10.3389/fncel.2013.00162] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 08/04/2013] [Indexed: 11/13/2022] Open
Abstract
A proper balance between synapse assembly and disassembly is crucial for the formation of functional neuronal circuits and synaptic plasticity in the adult brain. During development, synaptogenesis generates a vast excess of synapses, which are subsequently eliminated. Importantly, aberrant synaptic disassembly during development underpins many neurological disorders. Wnt secreted proteins are robust synaptogenic factors that regulate synapse assembly and function in the developing and mature brain. Recent studies show that Wnt blockade with the antagonist Dickkopf-1 (Dkk1) induces the rapid disassembly of synapses in mature neurons. Importantly, Dkk1 mediates synaptic loss induced by Amyloid-ß, a key pathogenic molecule in Alzheimer's disease (AD). These findings provide new insights into the potential contribution of dysfunctional Wnt signaling to synaptic loss observed in neurodegenerative diseases. In this review, we discuss the role of Wnt signaling in vertebrate synaptic assembly, function and maintenance, and consider how dysfunction of Wnt signaling could contribute to synaptic disassembly in neurodegenerative diseases such as AD.
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Affiliation(s)
- Ellen M Dickins
- Department of Cell and Developmental Biology, University College London London, UK
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Yang G, Pan F, Parkhurst CN, Grutzendler J, Gan WB. Thinned-skull cranial window technique for long-term imaging of the cortex in live mice. Nat Protoc 2010; 5:201-8. [PMID: 20134419 DOI: 10.1038/nprot.2009.222] [Citation(s) in RCA: 306] [Impact Index Per Article: 21.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Imaging neurons, glia and vasculature in the living brain has become an important experimental tool for understanding how the brain works. Here we describe in detail a protocol for imaging cortical structures at high optical resolution through a thinned-skull cranial window in live mice using two-photon laser scanning microscopy (TPLSM). Surgery can be performed within 30-45 min and images can be acquired immediately thereafter. The procedure can be repeated multiple times allowing longitudinal imaging of the cortex over intervals ranging from days to years. Imaging through a thinned-skull cranial window avoids exposure of the meninges and the cortex, thus providing a minimally invasive approach for studying structural and functional changes of cells under normal and pathological conditions in the living brain.
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Affiliation(s)
- Guang Yang
- Molecular Neurobiology Program, Department of Physiology and Neuroscience, Skirball Institute, New York University School of Medicine, New York, New York, USA
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Abstract
Dendritic spines are the postsynaptic components of most excitatory synapses in the mammalian brain. Spines accumulate rapidly during early postnatal development and undergo a substantial loss as animals mature into adulthood. In past decades, studies have revealed that the number and size of dendritic spines are regulated by a variety of gene products and environmental factors, underscoring the dynamic nature of spines and their importance to brain plasticity. Recently, in vivo time-lapse imaging of dendritic spines in the cerebral cortex suggests that, although spines are highly plastic during development, they are remarkably stable in adulthood, and most of them last throughout life. Therefore, dendritic spines may provide a structural basis for lifelong information storage, in addition to their well-established role in brain plasticity. Because dendritic spines are the key elements for information acquisition and retention, understanding how spines are formed and maintained, particularly in the intact brain, will likely provide fundamental insights into how the brain possesses the extraordinary capacity to learn and to remember.
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Affiliation(s)
- D Harshad Bhatt
- Molecular Neurobiology Program, The Helen and Martin Kimmel Center for Biology and Medicine at Skirball Institute of Biomolecular Medicine, New York University School of Medicine, New York, NY 10016, USA
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Holtmaat A, Svoboda K. Experience-dependent structural synaptic plasticity in the mammalian brain. Nat Rev Neurosci 2009; 10:647-58. [PMID: 19693029 DOI: 10.1038/nrn2699] [Citation(s) in RCA: 1254] [Impact Index Per Article: 83.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Synaptic plasticity in adult neural circuits may involve the strengthening or weakening of existing synapses as well as structural plasticity, including synapse formation and elimination. Indeed, long-term in vivo imaging studies are beginning to reveal the structural dynamics of neocortical neurons in the normal and injured adult brain. Although the overall cell-specific morphology of axons and dendrites, as well as of a subpopulation of small synaptic structures, are remarkably stable, there is increasing evidence that experience-dependent plasticity of specific circuits in the somatosensory and visual cortex involves cell type-specific structural plasticity: some boutons and dendritic spines appear and disappear, accompanied by synapse formation and elimination, respectively. This Review focuses on recent evidence for such structural forms of synaptic plasticity in the mammalian cortex and outlines open questions.
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Affiliation(s)
- Anthony Holtmaat
- Department of Basic Neurosciences, Medical Faculty, University of Geneva, Switzerland.
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Abstract
Information processing in the nervous system relies on properly localized and organized synaptic structures at the correct locations. The formation of synapses is a long and intricate process involving multiple interrelated steps. Decades of research have identified a large number of molecular components of the presynaptic compartment. In addition to neurotransmitter-containing synaptic vesicles, presynaptic terminals are defined by cytoskeletal and membrane specializations that allow highly regulated exo- and endocytosis of synaptic vesicles and that maintain precise registration with postsynaptic targets. Functional studies at multiple levels have revealed complex interactions between the transport of vesicular intermediates, the presynaptic cytoskeleton, growth cone navigation, and synaptic targets. With the advent of finer anatomical, physiological, and molecular tools, great insights have been gained toward the mechanistic dissection of functionally redundant processes controlling the specificity and dynamics of synapses. This review highlights the recent findings pertaining to the cellular and molecular regulation of presynaptic differentiation.
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Affiliation(s)
- Yishi Jin
- Division of Biological Sciences, Section of Neurobiology, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093, USA.
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Bearer EL. Overview of image analysis, image importing, and image processing using freeware. ACTA ACUST UNITED AC 2008; Chapter 14:Unit 14.15. [PMID: 18265322 DOI: 10.1002/0471142727.mb1415s63] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Quantitative image analysis turns microscopic data that might otherwise be merely descriptive into reliable mechanistic information. This unit provides an overview of the types of analysis that have been useful in the past, as well as descriptions of emerging applications. In addition, two protocols are included for importing data and for the first steps of data manipulation in the more common analytical applications of the freeware, NIH Image and ImageJ, as well as commercially available imaging software, Adobe Photoshop.
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Affiliation(s)
- E L Bearer
- Brown University, Providence, Rhode Island, USA
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Xu HT, Pan F, Yang G, Gan WB. Choice of cranial window type for in vivo imaging affects dendritic spine turnover in the cortex. Nat Neurosci 2007; 10:549-51. [PMID: 17417634 DOI: 10.1038/nn1883] [Citation(s) in RCA: 302] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2006] [Accepted: 02/27/2007] [Indexed: 11/08/2022]
Abstract
Determining the degree of synapse formation and elimination is essential for understanding the structural basis of brain plasticity and pathology. We show that in vivo imaging of dendritic spine dynamics through an open-skull glass window, but not a thinned-skull window, is associated with high spine turnover and substantial glial activation during the first month after surgery. These findings help to explain existing discrepancies in the degree of dendritic spine plasticity observed in the mature cortex.
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Affiliation(s)
- Hua-Tai Xu
- Molecular Neurobiology Program, Skirball Institute, Department of Physiology and Neuroscience, New York University School of Medicine, 540 First Avenue, New York, New York 10016, USA
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Abstract
Two-photon microscopy (TPM) has become an increasingly important tool for imaging the structure and function of brain cells in living animals. TPM imaging studies of neuronal structures over intervals ranging from seconds to years have begun to provide important insights into the structural plasticity of synapses and the modulating effects of experience in the intact brain. TPM has also started to reveal how neuronal connections are altered in animal models of neurodegeneration, acute brain injury, and cerebrovascular disease. Here, we review some of these studies with special emphasis on the degree of structural dynamism of postsynaptic dendritic spines in the adult mouse brain as well as synaptic pathology in mouse models of Alzheimer's disease and cerebral ischemia. We also discuss technical considerations that are critical for the acquisition and interpretation of data from TPM in vivo.
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Affiliation(s)
- Jaime Grutzendler
- />Northwestern University, 303 East Chicago Avenue, Ward Building 10-132, 60611 Chicago, IL
| | - Wen-Biao Gan
- />Skirball Institute of Biomolecular Medicine, Department of Physiology and Neuroscience, New York University School of Medicine, 540 First Avenue, 10016 New York, NY
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Garner CC, Waites CL, Ziv NE. Synapse development: still looking for the forest, still lost in the trees. Cell Tissue Res 2006; 326:249-62. [PMID: 16909256 DOI: 10.1007/s00441-006-0278-1] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2006] [Accepted: 06/08/2006] [Indexed: 01/23/2023]
Abstract
Synapse development in the vertebrate central nervous system is a highly orchestrated process occurring not only during early stages of brain development, but also (to a lesser extent) in the mature nervous system. During development, the formation of synapses is intimately linked to the differentiation of neuronal cells, the extension of their axons and dendrites, and the course wiring of the nervous system. Subsequently, the stabilization, elimination, and strengthening of synaptic contacts is coupled to the refinement of axonal and dendritic arbors, to the establishment of functionally meaningful connections, and probably also to the day-to-day acquisition, storage, and retrieval of memories, higher order thought processes, and behavioral patterns.
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Affiliation(s)
- Craig C Garner
- Department of Psychiatry and Behavioral Science, Nancy Pritzer Laboratory, Stanford University, Palo Alto, CA 94304-5485, USA.
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Abstract
Recently, there has been increasing interest in the use of in vivo imaging approaches in the study of the way that synaptic circuits become established and the degree to which they stabilize in mature brains. We review progress since the first efforts, two decades ago, at in vivo synaptic imaging and highlight the more recent advances in molecular biology, optics and neurobiological imaging that have fueled a mini-renaissance in this line of inquiry. Many of the technical problems that limited early efforts still remain, but the rapid pace of molecular and optical innovation might soon transform this specialized field into one that is more 'mainstream'.
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Affiliation(s)
- Narayanan Kasthuri
- Washington University School of Medicine, 660 S. Euclid, St Louis, MO 63110, USA
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