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00061198-201306001-0001100061198_2013_22_s21_majewska_structure_miscellaneous-article< 41_0_3_2 >Journal of Glaucoma© 2013 by Lippincott Williams & Wilkins.Volume 22 Supplement 5 Suppl 1, Proceedings of the 18th Annual Optic Nerve Rescue and Restoration Think Tank: “Glaucoma and the Central Nervous System” September 16–17, 2011 New York, NY Sponsored by The Glaucoma Foundation (TGF)June/July 2013p S21–S23Imaging Visual Cortical Structure and Function In Vivo[Chapters]Majewska, Ania K. PhDDepartment of Neurobiology and Anatomy, Center for Visual Science University of Rochester, Rochester, NYDisclosure: The author declares no conflict of interest.AbstractThe recent advent of in vivo two-photon microscopy has allowed the repeat imaging of cortical structures at microscopic resolution within intact brains. Recent data obtained using this imaging technique shows that dendritic spines, the postsynaptic sites of the majority of excitatory synapses in the central nervous system (CNS), rapidly remodel in response to changes in the visual environment. We combined two-photon microscopy of dendritic segments with intrinsic signal imaging of visual cortical responses in the developing ferret visual cortex, and showed that when one eye was deprived during the developmental critical period for ocular dominance plasticity, both dendritic spines and visual responses to the deprived eye were rapidly altered. A brief period of recovery where the eye was re-opened resulted in a return to pre-deprivation levels for both responses and dendritic spine density, showing that structural and functional changes are linked even at very rapid timescales. Additionally, two-photon microscopy can assay other functional and structural aspects of visual cortical function which I will review. Lastly, I will compare this technique to other imaging modalities available for assessment of the visual cortex in vivo.Within the last decade, major advances have been made in imaging the nervous system with great resolution and minimal invasiveness. This has led to a leap in our understanding of changes in neuronal networks, single cells and subcellular compartments during behaviorally relevant manipulations such as sensation and learning. Macroscopic imaging modalities such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have allowed the read out of both structural and functional aspects of brain function non-invasively in humans and animal models, with the disadvantage of integration of signal over very large numbers of neurons and glia.1 Optical imaging, however, offers the ability to image over a large range of resolutions (Fig. 1) but requires more invasive procedures to deliver the light to the brain surface. Of great interest to in vivo brain imaging are two optical techniques. The first is intrinsic signal imaging, which relies on hemodynamic changes to track the function of neurons, but necessarily integrates over many neurons due to the nature of the hemodynamic signal.2 The other, two photon laser scanning microscopy (TPLSM), has been an important technique in the optical imaging arsenal due to its microscopic resolution and good depth penetration even in highly scattering organs such as the brain.3 TPLSM is a fluorescence-based technique and therefore, depending on the choice of fluorescent probe, can report on structural as well as functional aspects of cells with subcellular resolution. Thus TPLSM has provided unexpected insights in to the dynamics of neurons and glia in vivo.FIGURE 1. Spatial and temporal resolution of optical imaging compared to functional magnetic resonance imaging (fMRI) and positron emission tomography (PET).We have recently used TPLSM to show that the structure of visual cortical neurons is surprisingly plastic in response to manipulation of the visual environment during developmental periods. Dendritic spines are the postsynaptic structures of the overwhelming majority of excitatory synapses in the central nervous system.4 They have a peculiar “lollipop” shape whereby the spherical head of the spine is connected to the parent dendrite through a thin neck.5 Why excitatory synapses maintain these postsynaptic compartments is not yet well understood but the heterogeneity of dendritic spine morphology led Ramon y Cajal who first described these structures over 100 years ago to postulate that their shape related to learning.5 With the recent application of TPLSM to the intact brain it has been possible to examine the structural dynamics of dendritic spines in the same animals before and after manipulations of the visual environment.6One of the first surprises was that dendritic spines, even in relatively adult animals, were not static but were constantly and rapidly changing their morphologies on a second to minute timescale.7 This spine motility was sensitive to vision as both binocular7 and monocular deprivation,8 as well as dark rearing,9 increased rapid spine dynamics. Surprisingly, dendritic spines could also be completely structurally dismantled and made de novo very rapidly in response to visual input.9Mice reared in the dark were imaged in the dark and then exposed to light for as little as two hours. The same dendrites were then re-identified and imaged after light exposure (Fig. 2). During the light exposure new protrusions grew at a rate 4 times that of control mice that were kept in complete darkness or in light throughout both imaging sessions. Interestingly, this time scale correlated well with functional imaging experiments using intrinsic signal imaging, which showed profound dampening of the cortical response to vision in dark reared mice compared with light reared controls, and a rapid gain the visually-driven cortical response after two hours of light exposure. This functional regulation of the cortical response to vision may be caused in part by the rapid establishment of new intracortical connections mediated by newly formed dendritic protrusions. This experiment is just one example of many recent studies that have implicated structural changes at dendritic spines as important contributors to functional plasticity.6,10FIGURE 2. Imaging neuronal structure and function in response to vision in vivo. A, Image showing an apical tuft of a layer 5 neuron genetically labeled with green fluorescent protein imaged in vivo in the visual cortex of a mouse using two photon laser scanning microscopy (TPLSM). Scale bar=100 μm. B, Higher magnification image of the boxed area in A, showing a dendrite studded with dendritic spines. Scale bar=5 μm. C, Image of the same dendrite imaged two hours apart. Left: Image from a dark reared mouse. Right: image taken two hours after the same mouse was exposed to light. Notice the growth of new protrusions (arrow). Scale bar=5 μm. D, Intrinsic signal amplitude images showing the visually driven response in visual cortex. LR=light reared; DR=dark reared; DR+2hrL=dark reared and exposed to light for two hours. Notice that dark rearing reduces the responsiveness of the cortex to vision (compared to LR) while very brief re-exposure to light significantly increases cortical responses. Color bar on right shows the scale of the dR/R response. Scale bar=1 mm.While neurons are traditionally studied as the mediators of plastic changes in the brain, glia are starting to be recognized for the important roles they play in nervous system function and disease.11 Astrocytes have established roles at synapses, where they contribute to synaptic transmission and plasticity. More recently, a role for microglia, the immune cells of the brain, in normal brain function has been uncovered.12–14 TPLSM studies have shown that these highly ramified cells dynamically sample the brain environment even in the absence of pathological changes15,16 and frequently interact with synaptic elements.12 Such dynamic interactions may lead to alterations in synaptic function, including remodeling of synaptic structure as well as phagocytosis and removal of synaptic elements, and are sensitive to sensory activity. Thus it appears that microglia may be important mediators of rapid synaptic changes in response to vision.How cortical changes influence the progression of glaucoma is currently being debated17 but rapid vision-mediated changes in cortical circuits could contribute to visual deficits in early glaucoma and limit recovery even if retinal ganglion cell function and connectivity to the brain could be re-established. TPLSM in combination with intrinsic signal imaging could be used to track changes in cortical visual function and structural and molecular level plasticity in dendrites, axons and glia in animal models of glaucoma. Such cortical changes could then be related to retinal deficits to decipher the interplay between retinal and cortical alterations. Recent improvements in endoscopic TPLSM could also allow the examination of similar changes in the lateral geniculate nucleus, the first synapse of retinal ganglion cell axons.18 Information obtained from such imaging studies would be invaluable for understanding cortical contribution to glaucoma.REFERENCES1. Raichle ME.Cognitive neuroscience. Bold insights.Nature.2001;412:128–130. [CrossRef] [Full Text] [Medline Link] [Context Link]2. Lieke EE, Frostig RD, Arieli A, et al..Optical imaging of cortical activity: real-time imaging using extrinsic dye-signals and high resolution imaging based on slow intrinsic-signals.Annu Rev Physiol.1989;51:543–559. [Context Link]3. Denk W, Svoboda K.Photon upmanship: why multiphoton imaging is more than a gimmick.Neuron.1997;18:351–357. [CrossRef] [Medline Link] [Context Link]4. Gray EG.Electron microscopy of synaptic contacts on dendrite spines of the cerebral cortex.Nature.1959;183:1592–1593. [CrossRef] [Medline Link] [Context Link]5. Ramón Y, Cajal S.La textura del sistema nerviosa del hombre y los vertebrados.1904.Madrid:Moya. [Context Link]6. Rittenhouse CD, Majewska AK.Synaptic mechanisms of activity-dependent remodeling in visual cortex.J Exp Neurosci.2009;2:23–41. [Context Link]7. Majewska A, Sur M.Motility of dendritic spines in visual cortex in vivo: Changes during the critical period and effects of visual deprivation.PNAS.2003;100:16024–16029. [Context Link]8. Oray S, Majewska A, Sur M.Dendritic spine dynamics are regulated by monocular deprivation and extracellular matrix degradation.Neuron.2004;44:1021–1030. [CrossRef] [Medline Link] [Context Link]9. Tropea D, Majewska AK, Garcia R, et al..Structural dynamics of synapses in vivo correlate with functional changes during experience-dependent plasticity in visual cortex.J Neurosci.2010;30:11086–11095. [Context Link]10. Yu X, Zuo Y.Spine plasticity in the motor cortex.Curr Opin Neurobiol.2011;21:169–174. [CrossRef] [Medline Link] [Context Link]11. Barres BA.The mystery and magic of glia: a perspective on their roles in health and disease.Neuron.2008;60:430–440. [CrossRef] [Medline Link] [Context Link]12. Tremblay ME, Lowery RL, Majewska AK.Microglial interactions with synapses are modulated by visual experience.PLoS Biol.2010;8:1000527. [Context Link]13. Wake H, Moorhouse AJ, Jinno S, et al..Resting microglia directly monitor the functional state of synapses in vivo and determine the fate of ischemic terminals.J Neurosci.2009;29:3974–3980. [Context Link]14. Paolicelli RC, Bolasco G, Pagani F, et al..Synaptic pruning by microglia is necessary for normal brain development.Science.2011;333:1456–1458. [Context Link]15. Davalos D, Grutzendler J, Yang G, et al..ATP mediates rapid microglial response to local brain injury in vivo.Nat Neurosci.2005;8:752–758. [Context Link]16. Nimmerjahn A, Kirchhoff F, Helmchen F.Resting microglial cells are highly dynamic surveillants of brain parenchyma in vivo.Science.2005;308:1314–1318. [CrossRef] [Full Text] [Medline Link] [Context Link]17. Gupta N, Yucel YH.What changes can we expect in the brain of glaucoma patients?Surv Ophthalmol.2007;52:122–126. [Context Link]18. Ghosh KK, Burns LD, Cocker ED, et al..Miniaturized integration of a fluorescence microscope.Nat Methods.2011;8:871–878. [Context Link]ovid.com:/bib/ovftdb/00061198-201306001-0001100006056_2001_412_128_raichle_neuroscience_|00061198-201306001-00011#xpointer(id(R1-11))|11065213||ovftdb|SL00006056200141212811065213P20[CrossRef]10.1038%2F35084300ovid.com:/bib/ovftdb/00061198-201306001-0001100006056_2001_412_128_raichle_neuroscience_|00061198-201306001-00011#xpointer(id(R1-11))|11065404||ovftdb|SL00006056200141212811065404P20[Full Text]00006056-200107120-00029ovid.com:/bib/ovftdb/00061198-201306001-0001100006056_2001_412_128_raichle_neuroscience_|00061198-201306001-00011#xpointer(id(R1-11))|11065405||ovftdb|SL00006056200141212811065405P20[Medline Link]11449247ovid.com:/bib/ovftdb/00061198-201306001-0001100002117_1997_18_351_denk_multiphoton_|00061198-201306001-00011#xpointer(id(R3-11))|11065213||ovftdb|SL0000211719971835111065213P22[CrossRef]10.1016%2FS0896-6273%2800%2981237-4ovid.com:/bib/ovftdb/00061198-201306001-0001100002117_1997_18_351_denk_multiphoton_|00061198-201306001-00011#xpointer(id(R3-11))|11065405||ovftdb|SL0000211719971835111065405P22[Medline Link]9115730ovid.com:/bib/ovftdb/00061198-201306001-0001100006056_1959_183_1592_gray_microscopy_|00061198-201306001-00011#xpointer(id(R4-11))|11065213||ovftdb|SL000060561959183159211065213P23[CrossRef]10.1038%2F1831592a0ovid.com:/bib/ovftdb/00061198-201306001-0001100006056_1959_183_1592_gray_microscopy_|00061198-201306001-00011#xpointer(id(R4-11))|11065405||ovftdb|SL000060561959183159211065405P23[Medline Link]13666826ovid.com:/bib/ovftdb/00061198-201306001-0001100002117_2004_44_1021_oray_extracellular_|00061198-201306001-00011#xpointer(id(R8-11))|11065213||ovftdb|SL00002117200444102111065213P27[CrossRef]10.1016%2Fj.neuron.2004.12.001ovid.com:/bib/ovftdb/00061198-201306001-0001100002117_2004_44_1021_oray_extracellular_|00061198-201306001-00011#xpointer(id(R8-11))|11065405||ovftdb|SL00002117200444102111065405P27[Medline Link]15603744ovid.com:/bib/ovftdb/00061198-201306001-0001100008367_2011_21_169_yu_plasticity_|00061198-201306001-00011#xpointer(id(R10-11))|11065213||ovftdb|SL0000836720112116911065213P29[CrossRef]10.1016%2Fj.conb.2010.07.010ovid.com:/bib/ovftdb/00061198-201306001-0001100008367_2011_21_169_yu_plasticity_|00061198-201306001-00011#xpointer(id(R10-11))|11065405||ovftdb|SL0000836720112116911065405P29[Medline Link]20728341ovid.com:/bib/ovftdb/00061198-201306001-0001100002117_2008_60_430_barres_perspective_|00061198-201306001-00011#xpointer(id(R11-11))|11065213||ovftdb|SL0000211720086043011065213P30[CrossRef]10.1016%2Fj.neuron.2008.10.013ovid.com:/bib/ovftdb/00061198-201306001-0001100002117_2008_60_430_barres_perspective_|00061198-201306001-00011#xpointer(id(R11-11))|11065405||ovftdb|SL0000211720086043011065405P30[Medline Link]ovid.com:/bib/ovftdb/00061198-201306001-0001100007529_2005_308_1314_nimmerjahn_surveillants_|00061198-201306001-00011#xpointer(id(R16-11))|11065213||ovftdb|00007529-200505270-00020SL000075292005308131411065213P35[CrossRef]10.1126%2Fscience.1110647ovid.com:/bib/ovftdb/00061198-201306001-0001100007529_2005_308_1314_nimmerjahn_surveillants_|00061198-201306001-00011#xpointer(id(R16-11))|11065404||ovftdb|00007529-200505270-00020SL000075292005308131411065404P35[Full Text]00007529-200505270-00020ovid.com:/bib/ovftdb/00061198-201306001-0001100007529_2005_308_1314_nimmerjahn_surveillants_|00061198-201306001-00011#xpointer(id(R16-11))|11065405||ovftdb|00007529-200505270-00020SL000075292005308131411065405P35[Medline Link]15831717Imaging Visual Cortical Structure and Function In VivoMajewska, Ania K. PhDChapters22
00061198-201306001-0001100061198_2013_22_s21_majewska_structure_miscellaneous-article< 41_0_3_2 >Journal of Glaucoma© 2013 by Lippincott Williams & Wilkins.Volume 22 Supplement 5 Suppl 1, Proceedings of the 18th Annual Optic Nerve Rescue and Restoration Think Tank: “Glaucoma and the Central Nervous System” September 16–17, 2011 New York, NY Sponsored by The Glaucoma Foundation (TGF)June/July 2013p S21–S23Imaging Visual Cortical Structure and Function In Vivo[Chapters]Majewska, Ania K. PhDDepartment of Neurobiology and Anatomy, Center for Visual Science University of Rochester, Rochester, NYDisclosure: The author declares no conflict of interest.AbstractThe recent advent of in vivo two-photon microscopy has allowed the repeat imaging of cortical structures at microscopic resolution within intact brains. Recent data obtained using this imaging technique shows that dendritic spines, the postsynaptic sites of the majority of excitatory synapses in the central nervous system (CNS), rapidly remodel in response to changes in the visual environment. We combined two-photon microscopy of dendritic segments with intrinsic signal imaging of visual cortical responses in the developing ferret visual cortex, and showed that when one eye was deprived during the developmental critical period for ocular dominance plasticity, both dendritic spines and visual responses to the deprived eye were rapidly altered. A brief period of recovery where the eye was re-opened resulted in a return to pre-deprivation levels for both responses and dendritic spine density, showing that structural and functional changes are linked even at very rapid timescales. Additionally, two-photon microscopy can assay other functional and structural aspects of visual cortical function which I will review. Lastly, I will compare this technique to other imaging modalities available for assessment of the visual cortex in vivo.Within the last decade, major advances have been made in imaging the nervous system with great resolution and minimal invasiveness. This has led to a leap in our understanding of changes in neuronal networks, single cells and subcellular compartments during behaviorally relevant manipulations such as sensation and learning. Macroscopic imaging modalities such as positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have allowed the read out of both structural and functional aspects of brain function non-invasively in humans and animal models, with the disadvantage of integration of signal over very large numbers of neurons and glia.1 Optical imaging, however, offers the ability to image over a large range of resolutions (Fig. 1) but requires more invasive procedures to deliver the light to the brain surface. Of great interest to in vivo brain imaging are two optical techniques. The first is intrinsic signal imaging, which relies on hemodynamic changes to track the function of neurons, but necessarily integrates over many neurons due to the nature of the hemodynamic signal.2 The other, two photon laser scanning microscopy (TPLSM), has been an important technique in the optical imaging arsenal due to its microscopic resolution and good depth penetration even in highly scattering organs such as the brain.3 TPLSM is a fluorescence-based technique and therefore, depending on the choice of fluorescent probe, can report on structural as well as functional aspects of cells with subcellular resolution. Thus TPLSM has provided unexpected insights in to the dynamics of neurons and glia in vivo.FIGURE 1. Spatial and temporal resolution of optical imaging compared to functional magnetic resonance imaging (fMRI) and positron emission tomography (PET).We have recently used TPLSM to show that the structure of visual cortical neurons is surprisingly plastic in response to manipulation of the visual environment during developmental periods. Dendritic spines are the postsynaptic structures of the overwhelming majority of excitatory synapses in the central nervous system.4 They have a peculiar “lollipop” shape whereby the spherical head of the spine is connected to the parent dendrite through a thin neck.5 Why excitatory synapses maintain these postsynaptic compartments is not yet well understood but the heterogeneity of dendritic spine morphology led Ramon y Cajal who first described these structures over 100 years ago to postulate that their shape related to learning.5 With the recent application of TPLSM to the intact brain it has been possible to examine the structural dynamics of dendritic spines in the same animals before and after manipulations of the visual environment.6One of the first surprises was that dendritic spines, even in relatively adult animals, were not static but were constantly and rapidly changing their morphologies on a second to minute timescale.7 This spine motility was sensitive to vision as both binocular7 and monocular deprivation,8 as well as dark rearing,9 increased rapid spine dynamics. Surprisingly, dendritic spines could also be completely structurally dismantled and made de novo very rapidly in response to visual input.9Mice reared in the dark were imaged in the dark and then exposed to light for as little as two hours. The same dendrites were then re-identified and imaged after light exposure (Fig. 2). During the light exposure new protrusions grew at a rate 4 times that of control mice that were kept in complete darkness or in light throughout both imaging sessions. Interestingly, this time scale correlated well with functional imaging experiments using intrinsic signal imaging, which showed profound dampening of the cortical response to vision in dark reared mice compared with light reared controls, and a rapid gain the visually-driven cortical response after two hours of light exposure. This functional regulation of the cortical response to vision may be caused in part by the rapid establishment of new intracortical connections mediated by newly formed dendritic protrusions. This experiment is just one example of many recent studies that have implicated structural changes at dendritic spines as important contributors to functional plasticity.6,10FIGURE 2. Imaging neuronal structure and function in response to vision in vivo. A, Image showing an apical tuft of a layer 5 neuron genetically labeled with green fluorescent protein imaged in vivo in the visual cortex of a mouse using two photon laser scanning microscopy (TPLSM). Scale bar=100 μm. B, Higher magnification image of the boxed area in A, showing a dendrite studded with dendritic spines. Scale bar=5 μm. C, Image of the same dendrite imaged two hours apart. Left: Image from a dark reared mouse. Right: image taken two hours after the same mouse was exposed to light. Notice the growth of new protrusions (arrow). Scale bar=5 μm. D, Intrinsic signal amplitude images showing the visually driven response in visual cortex. LR=light reared; DR=dark reared; DR+2hrL=dark reared and exposed to light for two hours. Notice that dark rearing reduces the responsiveness of the cortex to vision (compared to LR) while very brief re-exposure to light significantly increases cortical responses. Color bar on right shows the scale of the dR/R response. Scale bar=1 mm.While neurons are traditionally studied as the mediators of plastic changes in the brain, glia are starting to be recognized for the important roles they play in nervous system function and disease.11 Astrocytes have established roles at synapses, where they contribute to synaptic transmission and plasticity. More recently, a role for microglia, the immune cells of the brain, in normal brain function has been uncovered.12–14 TPLSM studies have shown that these highly ramified cells dynamically sample the brain environment even in the absence of pathological changes15,16 and frequently interact with synaptic elements.12 Such dynamic interactions may lead to alterations in synaptic function, including remodeling of synaptic structure as well as phagocytosis and removal of synaptic elements, and are sensitive to sensory activity. Thus it appears that microglia may be important mediators of rapid synaptic changes in response to vision.How cortical changes influence the progression of glaucoma is currently being debated17 but rapid vision-mediated changes in cortical circuits could contribute to visual deficits in early glaucoma and limit recovery even if retinal ganglion cell function and connectivity to the brain could be re-established. TPLSM in combination with intrinsic signal imaging could be used to track changes in cortical visual function and structural and molecular level plasticity in dendrites, axons and glia in animal models of glaucoma. Such cortical changes could then be related to retinal deficits to decipher the interplay between retinal and cortical alterations. Recent improvements in endoscopic TPLSM could also allow the examination of similar changes in the lateral geniculate nucleus, the first synapse of retinal ganglion cell axons.18 Information obtained from such imaging studies would be invaluable for understanding cortical contribution to glaucoma.REFERENCES1. Raichle ME.Cognitive neuroscience. Bold insights.Nature.2001;412:128–130. [CrossRef] [Full Text] [Medline Link] [Context Link]2. Lieke EE, Frostig RD, Arieli A, et al..Optical imaging of cortical activity: real-time imaging using extrinsic dye-signals and high resolution imaging based on slow intrinsic-signals.Annu Rev Physiol.1989;51:543–559. [Context Link]3. Denk W, Svoboda K.Photon upmanship: why multiphoton imaging is more than a gimmick.Neuron.1997;18:351–357. [CrossRef] [Medline Link] [Context Link]4. Gray EG.Electron microscopy of synaptic contacts on dendrite spines of the cerebral cortex.Nature.1959;183:1592–1593. [CrossRef] [Medline Link] [Context Link]5. Ramón Y, Cajal S.La textura del sistema nerviosa del hombre y los vertebrados.1904.Madrid:Moya. [Context Link]6. Rittenhouse CD, Majewska AK.Synaptic mechanisms of activity-dependent remodeling in visual cortex.J Exp Neurosci.2009;2:23–41. [Context Link]7. Majewska A, Sur M.Motility of dendritic spines in visual cortex in vivo: Changes during the critical period and effects of visual deprivation.PNAS.2003;100:16024–16029. [Context Link]8. Oray S, Majewska A, Sur M.Dendritic spine dynamics are regulated by monocular deprivation and extracellular matrix degradation.Neuron.2004;44:1021–1030. [CrossRef] [Medline Link] [Context Link]9. Tropea D, Majewska AK, Garcia R, et al..Structural dynamics of synapses in vivo correlate with functional changes during experience-dependent plasticity in visual cortex.J Neurosci.2010;30:11086–11095. [Context Link]10. Yu X, Zuo Y.Spine plasticity in the motor cortex.Curr Opin Neurobiol.2011;21:169–174. [CrossRef] [Medline Link] [Context Link]11. Barres BA.The mystery and magic of glia: a perspective on their roles in health and disease.Neuron.2008;60:430–440. [CrossRef] [Medline Link] [Context Link]12. Tremblay ME, Lowery RL, Majewska AK.Microglial interactions with synapses are modulated by visual experience.PLoS Biol.2010;8:1000527. [Context Link]13. Wake H, Moorhouse AJ, Jinno S, et al..Resting microglia directly monitor the functional state of synapses in vivo and determine the fate of ischemic terminals.J Neurosci.2009;29:3974–3980. [Context Link]14. Paolicelli RC, Bolasco G, Pagani F, et al..Synaptic pruning by microglia is necessary for normal brain development.Science.2011;333:1456–1458. [Context Link]15. Davalos D, Grutzendler J, Yang G, et al..ATP mediates rapid microglial response to local brain injury in vivo.Nat Neurosci.2005;8:752–758. [Context Link]16. Nimmerjahn A, Kirchhoff F, Helmchen F.Resting microglial cells are highly dynamic surveillants of brain parenchyma in vivo.Science.2005;308:1314–1318. [CrossRef] [Full Text] [Medline Link] [Context Link]17. Gupta N, Yucel YH.What changes can we expect in the brain of glaucoma patients?Surv Ophthalmol.2007;52:122–126. [Context Link]18. Ghosh KK, Burns LD, Cocker ED, et al..Miniaturized integration of a fluorescence microscope.Nat Methods.2011;8:871–878. [Context Link] Imaging Visual Cortical Structure and Function In Vivo