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Zaccard CR, Gippo I, Song A, Geula C, Penzes P. Dendritic spinule-mediated structural synaptic plasticity: Implications for development, aging, and psychiatric disease. Front Mol Neurosci 2023; 16:1059730. [PMID: 36741924 PMCID: PMC9895827 DOI: 10.3389/fnmol.2023.1059730] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2022] [Accepted: 01/04/2023] [Indexed: 01/22/2023] Open
Abstract
Dendritic spines are highly dynamic and changes in their density, size, and shape underlie structural synaptic plasticity in cognition and memory. Fine membranous protrusions of spines, termed dendritic spinules, can contact neighboring neurons or glial cells and are positively regulated by neuronal activity. Spinules are thinner than filopodia, variable in length, and often emerge from large mushroom spines. Due to their nanoscale, spinules have frequently been overlooked in diffraction-limited microscopy datasets. Until recently, our knowledge of spinules has been interpreted largely from single snapshots in time captured by electron microscopy. We summarize herein the current knowledge about the molecular mechanisms of spinule formation. Additionally, we discuss possible spinule functions in structural synaptic plasticity in the context of development, adulthood, aging, and psychiatric disorders. The literature collectively implicates spinules as a mode of structural synaptic plasticity and suggests the existence of morphologically and functionally distinct spinule subsets. A recent time-lapse, enhanced resolution imaging study demonstrated that the majority of spinules are small, short-lived, and dynamic, potentially exploring their environment or mediating retrograde signaling and membrane remodeling via trans-endocytosis. A subset of activity-enhanced, elongated, long-lived spinules is associated with complex PSDs, and preferentially contacts adjacent axonal boutons not presynaptic to the spine head. Hence, long-lived spinules can form secondary synapses with the potential to alter synaptic connectivity. Published studies further suggest that decreased spinules are associated with impaired synaptic plasticity and intellectual disability, while increased spinules are linked to hyperexcitability and neurodegenerative diseases. In summary, the literature indicates that spinules mediate structural synaptic plasticity and perturbations in spinules can contribute to synaptic dysfunction and psychiatric disease. Additional studies would be beneficial to further delineate the molecular mechanisms of spinule formation and determine the exact role of spinules in development, adulthood, aging, and psychiatric disorders.
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Affiliation(s)
- Colleen R. Zaccard
- Department of Neuroscience, Northwestern University Feinberg School of Medicine, Chicago, IL, United States
| | - Isabel Gippo
- Department of Neuroscience, Northwestern University Feinberg School of Medicine, Chicago, IL, United States
| | - Amy Song
- Department of Neuroscience, Northwestern University Feinberg School of Medicine, Chicago, IL, United States
| | - Changiz Geula
- Mesulam Center for Cognitive Neurology and Alzheimer's Disease, Northwestern University Feinberg School of Medicine, Chicago, IL, United States
| | - Peter Penzes
- Department of Neuroscience, Northwestern University Feinberg School of Medicine, Chicago, IL, United States,Department of Psychiatry and Behavioral Sciences, Northwestern University Feinberg School of Medicine, Chicago, IL, United States,*Correspondence: Peter Penzes,
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Country MW, Jonz MG. Goldfish and crucian carp are natural models of anoxia tolerance in the retina. Comp Biochem Physiol A Mol Integr Physiol 2022; 270:111244. [PMID: 35618216 DOI: 10.1016/j.cbpa.2022.111244] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 05/15/2022] [Accepted: 05/16/2022] [Indexed: 10/18/2022]
Abstract
Vertebrates need oxygen to survive. The central nervous system has an especially high energy demand, so brain and retinal neurons quickly die in anoxia. But fish of the genus Carassius are exceptionally anoxia-tolerant: the crucian carp (C. carassius) can survive months without oxygen in ice-covered ponds, and the common goldfish (C. auratus) can withstand hours of anoxia at room temperature. These fish previously offered insights into anoxia tolerance in the brain, heart, and liver. Here, we advance Carassius spp. as models to study anoxia tolerance in the retina. Electroretinogram and evoked potential recordings show that crucian carp reversibly downregulate their visual systems in anoxia, probably to save ATP. Notably, Carassius suppress their visual systems nearly twice as much as anoxia-tolerant turtles, Trachemys and Chrysemys spp., which are often promoted as the champions of anoxia tolerance. We summarize what is known about anoxia tolerance in the goldfish and crucian carp retinas, including cellular pathways which may protect retinal neurons from excitotoxic cell death. We compare the Carassius retina with two relevant models: natural anoxia tolerance in the turtle brain, and ischemic preconditioning in the rat retina. All three models include mitochondria as oxygen sensors: mitochondria depolarize due to mitochondrial ATP-dependent K+ channels, possibly to trigger neuroprotective second messenger cascades. The Carassius retina is an accessible and inexpensive model, with over 70 fruitful years of history in vision research. As a model for anoxia tolerance, it may provide new insights into diseases of the eye (like diabetes, macular degeneration, and eye stroke).
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Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Canada. https://twitter.com/biologycountry
| | - Michael G Jonz
- Department of Biology, University of Ottawa, Canada; Brain and Mind Research Institute, University of Ottawa, Canada.
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Country MW, Haase K, Blank K, Canez CR, Roberts JA, Campbell BFN, Smith JC, Pelling AE, Jonz MG. Seasonal changes in membrane structure and excitability in retinal neurons of goldfish (Carassius auratus) under constant environmental conditions. J Exp Biol 2022; 225:275230. [PMID: 35485205 DOI: 10.1242/jeb.244238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 04/25/2022] [Indexed: 11/20/2022]
Abstract
Seasonal modifications in the structure of cellular membranes occur as an adaptive measure to withstand exposure to prolonged environmental change. Little is known about whether such changes may occur independently of external cues, such as photoperiod or temperature, or how they may impact the central nervous system. We compared membrane properties of neurons isolated from the retina of goldfish (Carassius auratus), an organism well-adapted to extreme environmental change, during the summer and winter months. Goldfish were maintained in a facility under constant environmental conditions throughout the year. Analysis of whole-retina phospholipid composition using mass spectrometry-based lipidomics revealed a two-fold increase in phosphatidylethanolamine species during the winter, suggesting an increase in cell membrane fluidity. Atomic force microscopy was used to produce localized, nanoscale-force deformation of neuronal membranes. Measurement of Young's modulus indicated increased membrane-cortical stiffness (or decreased elasticity) in neurons isolated during the winter. Voltage-clamp electrophysiology was used to assess physiological changes in neurons between seasons. Winter neurons displayed a hyperpolarized reversal potential (Vrev) and a significantly lower input resistance (Rin) compared to summer neurons. This was indicative of a decrease in membrane excitability during the winter. Subsequent measurement of intracellular Ca2+ activity using Fura-2 microspectrofluorometry confirmed a reduction in action potential activity, including duration and action potential profile, in neurons isolated during the winter. These studies demonstrate chemical and biophysical changes that occur in retinal neurons of goldfish throughout the year without exposure to seasonal cues, and suggest a novel mechanism of seasonal regulation of retinal activity.
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Affiliation(s)
| | | | - Katrin Blank
- Department of Chemistry, Carleton University, Canada
| | | | | | | | | | | | - Michael G Jonz
- Department of Biology, University of Ottawa, Canada.,Brain and Mind Research Institute, University of Ottawa, Canada
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Li Q, Zhu H, Fan M, Sun J, Reinach PS, Wang Y, Qu J, Zhou X, Zhao F. Form-deprivation myopia downregulates calcium levels in retinal horizontal cells in mice. Exp Eye Res 2022; 218:109018. [PMID: 35240197 DOI: 10.1016/j.exer.2022.109018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2021] [Revised: 02/14/2022] [Accepted: 02/25/2022] [Indexed: 11/25/2022]
Abstract
The process of eye axis lengthening in myopic eyes is regulated by multiple mechanisms in the retina, and horizontal cells (HCs) are an essential interneuron in the visual regulatory system. Wherein intracellular Ca2+ plays an important role in the events involved in the regulatory role of HCs in the retinal neural network. It is unknown if intracellular Ca2+ regulation in HCs mediates changes in the retinal neural network during myopia progression. We describe here a novel calcium fluorescence indicator system that monitors HCs' intracellular Ca2+ levels during form-deprivation myopia (FDM) in mice. AAV injection of GCaMP6s, as a protein calcium sensor, into a Gja10-Cre mouse monitored the changes in Ca2+signaling in HC that accompany FDM progression in mice. An alternative Gja10-Cre/Ai96-GCaMP6s mouse model was created by cross mating Gja10-Cre with Ai96 mice. Immunofluorescence imaging and live imaging of the retinal cells verified the identity of these animal models. Changes in retinal horizontal cellular Ca2+ levels were resolved during FDM development. The numbers of GCaMP6s and the proportion of HCs were tracked based on profiling changes in GCaMP6s+calbindin+/calbindin+ coimmunostaining patterns. They significantly decreased more after either two days (P < 0.01) or two weeks (P < 0.001) in form deprived eyes than in the untreated fellow eyes. These decreases in their proportion reached significance only in the retinal central region rather than also in the retinal periphery. A novel approach employing a GCaMP6s mouse model was developed that may ultimately clarify if HCs mediate Ca2+ signals that contribute to controlling FDM progression in mice. The results indicate so far that FDM progression is associated with declines in HC Ca2+ signaling activity.
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Affiliation(s)
- Qihang Li
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - He Zhu
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Miaomiao Fan
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Jing Sun
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Peter S Reinach
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Yuhan Wang
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China
| | - Jia Qu
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China; Research Unit of Myopia Basic Research and Clinical Prevention and Control, Chinese Academy of Medical Sciences (2019RU025), Wenzhou, Zhejiang, China; Oujiang Laboratory, Zhejiang Lab for Regenerative Medicine, Vision and Brain Health, Wenzhou, Zhejiang, China
| | - Xiangtian Zhou
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China; Research Unit of Myopia Basic Research and Clinical Prevention and Control, Chinese Academy of Medical Sciences (2019RU025), Wenzhou, Zhejiang, China; Oujiang Laboratory, Zhejiang Lab for Regenerative Medicine, Vision and Brain Health, Wenzhou, Zhejiang, China.
| | - Fuxin Zhao
- School of Optometry and Ophthalmology and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, China; State Key Laboratory of Optometry, Ophthalmology and Vision Science, Wenzhou, Zhejiang, China.
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Country MW, Jonz MG. Mitochondrial KATP channels stabilize intracellular Ca2+ during hypoxia in retinal horizontal cells of goldfish (Carassius auratus). J Exp Biol 2021; 224:271844. [PMID: 34402511 DOI: 10.1242/jeb.242634] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Accepted: 08/11/2021] [Indexed: 01/20/2023]
Abstract
Neurons of the retina require oxygen to survive. In hypoxia, neuronal ATP production is impaired, ATP-dependent ion pumping is reduced, transmembrane ion gradients are dysregulated, and intracellular Ca2+ concentration ([Ca2+]i) increases enough to trigger excitotoxic cell death. Central neurons of the common goldfish (Carassius auratus) are hypoxia tolerant, but little is known about how goldfish retinas withstand hypoxia. To study the cellular mechanisms of hypoxia tolerance, we isolated retinal interneurons (horizontal cells; HCs), and measured [Ca2+]i with Fura-2. Goldfish HCs maintained [Ca2+]i throughout 1 h of hypoxia, whereas [Ca2+]i increased irreversibly in HCs of the hypoxia-sensitive rainbow trout (Oncorhynchus mykiss) with just 20 min of hypoxia. Our results suggest mitochondrial ATP-dependent K+ channels (mKATP) are necessary to stabilize [Ca2+]i throughout hypoxia. In goldfish HCs, [Ca2+]i increased when mKATP channels were blocked with glibenclamide or 5-hydroxydecanoic acid, whereas the mKATP channel agonist diazoxide prevented [Ca2+]i from increasing in hypoxia in trout HCs. We found that hypoxia protects against increases in [Ca2+]i in goldfish HCs via mKATP channels. Glycolytic inhibition with 2-deoxyglucose increased [Ca2+]i, which was rescued by hypoxia in a mKATP channel-dependent manner. We found no evidence of plasmalemmal KATP channels in patch-clamp experiments. Instead, we confirmed the involvement of KATP in mitochondria with TMRE imaging, as hypoxia rapidly (<5 min) depolarized mitochondria in a mKATP channel-sensitive manner. We conclude that mKATP channels initiate a neuroprotective pathway in goldfish HCs to maintain [Ca2+]i and avoid excitotoxicity in hypoxia. This model provides novel insight into the cellular mechanisms of hypoxia tolerance in the retina.
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Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Ottawa, ON, CanadaK1N 6N5
| | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, ON, CanadaK1N 6N5.,Brain and Mind Research Institute, University of Ottawa, Ottawa, ON, CanadaK1H 8M5
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Zaccard CR, Shapiro L, Martin-de-Saavedra MD, Pratt C, Myczek K, Song A, Forrest MP, Penzes P. Rapid 3D Enhanced Resolution Microscopy Reveals Diversity in Dendritic Spinule Dynamics, Regulation, and Function. Neuron 2020; 107:522-537.e6. [PMID: 32464088 DOI: 10.1016/j.neuron.2020.04.025] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2018] [Revised: 12/19/2019] [Accepted: 04/27/2020] [Indexed: 12/31/2022]
Abstract
Dendritic spinules are thin protrusions, formed by neuronal spines, not adequately resolved by diffraction-limited light microscopy, which has limited our understanding of their behavior. Here we performed rapid structured illumination microscopy and enhanced resolution confocal microscopy to study spatiotemporal spinule dynamics in cortical pyramidal neurons. Spinules recurred at the same locations on mushroom spine heads. Most were short-lived, dynamic, exploratory, and originated near simple PSDs, whereas a subset was long-lived, elongated, and associated with complex PSDs. These subtypes were differentially regulated by Ca2+ transients. Furthermore, the postsynaptic Rac1-GEF kalirin-7 regulated spinule formation, elongation, and recurrence. Long-lived spinules often contained PSD fragments, contacted distal presynaptic terminals, and formed secondary synapses. NMDAR activation increased spinule number, length, and contact with distal presynaptic elements. Spinule subsets, dynamics, and recurrence were validated in cortical neurons of acute brain slices. Thus, we identified unique properties, regulatory mechanisms, and functions of spinule subtypes, supporting roles in neuronal connectivity.
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Affiliation(s)
- Colleen R Zaccard
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA
| | - Lauren Shapiro
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA
| | | | - Christopher Pratt
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA
| | - Kristoffer Myczek
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA
| | - Amy Song
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA
| | - Marc P Forrest
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA
| | - Peter Penzes
- Department of Physiology, Northwestern University, Chicago, IL 60611, USA; Department of Psychiatry and Behavioral Sciences, Northwestern University, Chicago, IL 60611, USA.
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Country MW, Campbell BFN, Jonz MG. Spontaneous action potentials in retinal horizontal cells of goldfish ( Carassius auratus) are dependent upon L-type Ca 2+ channels and ryanodine receptors. J Neurophysiol 2019; 122:2284-2293. [PMID: 31596629 DOI: 10.1152/jn.00240.2019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Horizontal cells (HCs) are interneurons of the outer retina that undergo graded changes in membrane potential during the light response and provide feedback to photoreceptors. We characterized spontaneous Ca2+-based action potentials (APs) in isolated goldfish (Carassius auratus) HCs with electrophysiological and intracellular imaging techniques. Transient changes in intracellular Ca2+ concentration ([Ca2+]i) were observed with fura-2 and were abolished by removal of extracellular Ca2+ or by inhibition of Ca2+ channels by 50 µM Cd2+ or 100 µM nifedipine. Inhibition of Ca2+ release from stores with 20 µM ryanodine or 50 µM dantrolene abolished Ca2+ transients and increased baseline [Ca2+]i. This increased baseline was prevented by blocking L-type Ca2+ channels with nifedipine, suggesting that Ca2+-induced Ca2+ release from stores may be needed to inactivate membrane Ca2+ channels. Caffeine (3 mM) increased the frequency of Ca2+ transients, and the store-operated channel antagonist 2-aminoethyldiphenylborinate (100 μM) counteracted this effect. APs were detected with voltage-sensitive dye imaging (FluoVolt) and current-clamp electrophysiology. In current-clamp recordings, regenerative APs were abolished by removal of extracellular Ca2+ or in the presence of 5 mM Co2+ or 100 µM nifedipine, and APs were amplified with 15 mM Ba2+. Collectively, our data suggest that during APs Ca2+ enters through L-type Ca2+ channels and that Ca2+ stores (gated by ryanodine receptors) contribute to the rise in [Ca2+]i. This work may lead to further understanding of the possible role APs have in vision, such as transitioning from light to darkness or modulating feedback from HCs to photoreceptors.NEW & NOTEWORTHY Horizontal cells (HCs) are interneurons of the outer retina that provide inhibitory feedback onto photoreceptors. HCs respond to light via graded changes in membrane potential. We characterized spontaneous action potentials in HCs from goldfish and linked action potential generation to a rise in intracellular Ca2+ via plasma membrane channels and ryanodine receptors. Action potentials may play a role in vision, such as transitioning from light to darkness, or in modulating feedback from HCs to photoreceptors.
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Affiliation(s)
- Michael W Country
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | | | - Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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