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Glutamatergic Dysfunction and Synaptic Ultrastructural Alterations in Schizophrenia and Autism Spectrum Disorder: Evidence from Human and Rodent Studies. Int J Mol Sci 2020; 22:ijms22010059. [PMID: 33374598 PMCID: PMC7793137 DOI: 10.3390/ijms22010059] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2020] [Revised: 12/15/2020] [Accepted: 12/22/2020] [Indexed: 12/12/2022] Open
Abstract
The correlation between dysfunction in the glutamatergic system and neuropsychiatric disorders, including schizophrenia and autism spectrum disorder, is undisputed. Both disorders are associated with molecular and ultrastructural alterations that affect synaptic plasticity and thus the molecular and physiological basis of learning and memory. Altered synaptic plasticity, accompanied by changes in protein synthesis and trafficking of postsynaptic proteins, as well as structural modifications of excitatory synapses, are critically involved in the postnatal development of the mammalian nervous system. In this review, we summarize glutamatergic alterations and ultrastructural changes in synapses in schizophrenia and autism spectrum disorder of genetic or drug-related origin, and briefly comment on the possible reversibility of these neuropsychiatric disorders in the light of findings in regular synaptic physiology.
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Santuy A, Rodriguez JR, DeFelipe J, Merchan-Perez A. Volume electron microscopy of the distribution of synapses in the neuropil of the juvenile rat somatosensory cortex. Brain Struct Funct 2017; 223:77-90. [PMID: 28721455 PMCID: PMC5772167 DOI: 10.1007/s00429-017-1470-7] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 07/04/2017] [Indexed: 11/29/2022]
Abstract
Knowing the proportions of asymmetric (excitatory) and symmetric (inhibitory) synapses in the neuropil is critical for understanding the design of cortical circuits. We used focused ion beam milling and scanning electron microscopy (FIB/SEM) to obtain stacks of serial sections from the six layers of the juvenile rat (postnatal day 14) somatosensory cortex (hindlimb representation). We segmented in three-dimensions 6184 synaptic junctions and determined whether they were established on dendritic spines or dendritic shafts. Of all these synapses, 87–94% were asymmetric and 6–13% were symmetric. Asymmetric synapses were preferentially located on dendritic spines in all layers (80–91%) while symmetric synapses were mainly located on dendritic shafts (62–86%). Furthermore, we found that less than 6% of the dendritic spines establish more than one synapse. The vast majority of axospinous synapses were established on the spine head. Synapses on the spine neck were scarce, although they were more common when the dendritic spine established multiple synapses. This study provides a new large quantitative dataset that may contribute not only to the knowledge of the ultrastructure of the cortex, but also towards defining the connectivity patterns through all cortical layers.
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Affiliation(s)
- A Santuy
- Laboratorio Cajal de Circuitos Corticales, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid, Pozuelo de Alarcón, 28223, Madrid, Spain.,CIBERNED, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, Madrid, Spain
| | - J R Rodriguez
- Laboratorio Cajal de Circuitos Corticales, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid, Pozuelo de Alarcón, 28223, Madrid, Spain.,Instituto Cajal, Consejo Superior de Investigaciones Científicas, 28002, Madrid, Spain.,CIBERNED, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, Madrid, Spain
| | - J DeFelipe
- Laboratorio Cajal de Circuitos Corticales, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid, Pozuelo de Alarcón, 28223, Madrid, Spain.,Instituto Cajal, Consejo Superior de Investigaciones Científicas, 28002, Madrid, Spain.,CIBERNED, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, Madrid, Spain
| | - A Merchan-Perez
- Laboratorio Cajal de Circuitos Corticales, Centro de Tecnología Biomédica, Universidad Politécnica de Madrid, Pozuelo de Alarcón, 28223, Madrid, Spain. .,CIBERNED, Centro de Investigación Biomédica en Red de Enfermedades Neurodegenerativas, Madrid, Spain. .,Departamento de Arquitectura y Tecnología de sistemas Informáticos, Universidad Politécnica de Madrid, Boadilla del Monte, 28660, Madrid, Spain.
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Onufriev MV, Semenova TP, Volkova EP, Sergun’kina MA, Yakovlev AA, Zakharova NM, Gulyaeva NV. Seasonal changes in actin and Cdk5 expression in different brain regions of the Yakut ground squirrel (Spermophilus undulatus). NEUROCHEM J+ 2016. [DOI: 10.1134/s1819712416020070] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Popov VI, Stewart MG. Complexity of contacts between synaptic boutons and dendritic spines in adult rat hippocampus: Three-dimensional reconstructions from serial ultrathin sections in vivo. Synapse 2009; 63:369-77. [DOI: 10.1002/syn.20613] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Nikonenko I, Boda B, Steen S, Knott G, Welker E, Muller D. PSD-95 promotes synaptogenesis and multiinnervated spine formation through nitric oxide signaling. ACTA ACUST UNITED AC 2009; 183:1115-27. [PMID: 19075115 PMCID: PMC2600742 DOI: 10.1083/jcb.200805132] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Postsynaptic density 95 (PSD-95) is an important regulator of synaptic structure and plasticity. However, its contribution to synapse formation and organization remains unclear. Using a combined electron microscopic, genetic, and pharmacological approach, we uncover a new mechanism through which PSD-95 regulates synaptogenesis. We find that PSD-95 overexpression affected spine morphology but also promoted the formation of multiinnervated spines (MISs) contacted by up to seven presynaptic terminals. The formation of multiple contacts was specifically prevented by deletion of the PDZ(2) domain of PSD-95, which interacts with nitric oxide (NO) synthase (NOS). Similarly, PSD-95 overexpression combined with small interfering RNA-mediated down-regulation or the pharmacological blockade of NOS prevented axon differentiation into varicosities and multisynapse formation. Conversely, treatment of hippocampal slices with an NO donor or cyclic guanosine monophosphate analogue induced MISs. NOS blockade also reduced spine and synapse density in developing hippocampal cultures. These results indicate that the postsynaptic site, through an NOS-PSD-95 interaction and NO signaling, promotes synapse formation with nearby axons.
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Affiliation(s)
- Irina Nikonenko
- Department of Fundamental Neuroscience, Geneva Neuroscience Center, University of Geneva School of Medicine, CH-1211 Geneva, Switzerland
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Popov VI, Medvedev NI, Patrushev IV, Ignat'ev DA, Morenkov ED, Stewart MG. Reversible reduction in dendritic spines in CA1 of rat and ground squirrel subjected to hypothermia-normothermia in vivo: A three-dimensional electron microscope study. Neuroscience 2007; 149:549-60. [PMID: 17919827 DOI: 10.1016/j.neuroscience.2007.07.059] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2007] [Revised: 07/07/2007] [Accepted: 07/18/2007] [Indexed: 10/22/2022]
Abstract
A study was made at electron microscope level of changes in the three-dimensional (3-D) morphology of dendritic spines and postsynaptic densities (PSDs) in CA1 of the hippocampus in ground squirrels, taken either at low temperature during hibernation (brain temperature 2-4 degrees C), or after warming and recovery to the normothermic state (34 degrees C). In addition, the morphology of PSDs and spines was measured in a non-hibernating mammal, rat, subjected to cooling at 2 degrees C at which time core rectal temperature was 15 degrees C, and then after warming to normothermic conditions. Significant differences were found in the proportion of thin and stubby spines, and shaft synapses in CA1 for rats and ground squirrels for normothermia compared with cooling or hibernation. Hypothermia induced a decrease in the proportion of thin spines, and an increase in stubby and shaft spines, but no change in the proportion of mushroom spines. The changes in redistribution of these three categories of spines in ground squirrel are more prominent than in rat. There were no significant differences in synapse density determined for ground squirrels or rats at normal compared with low temperature. Measurement of spine and PSD volume (for mushroom and thin spines) also showed no significant differences between the two functional states in either rats or ground squirrels, nor were there any differences in distances between neighboring synapses. Spinules on dendritic shafts were notable qualitatively during hibernation, but absent in normothermia. These data show that hypothermia results in morphological changes which are essentially similar in both a hibernating and a non-hibernating animal.
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Affiliation(s)
- V I Popov
- The Open University, Department of Biological Sciences, Faculty of Sciences, Walton Hall, Milton Keynes MK7 6AA, UK
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Ruediger J, Van der Zee EA, Strijkstra AM, Aschoff A, Daan S, Hut RA. Dynamics in the ultrastructure of asymmetric axospinous synapses in the frontal cortex of hibernating European ground squirrels (Spermophilus citellus). Synapse 2007; 61:343-52. [PMID: 17318885 DOI: 10.1002/syn.20380] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Recent theories on the function of arousals from torpor in hibernating mammals focus on the repair of the central nervous system from damage accumulating during prolonged hypothermia. In this framework, we investigated the synaptic ultrastructure in Layer 2 of the frontal cortex from hibernating European ground squirrels (Spermophilus citellus) sacrificed at four different phases in the torpor-arousal cycle. Using electron microscopy, we quantified synapse number and morphometric data on asymmetric axospinous synapses. Length, width, and surface area of postsynaptic densities (PSDs), and the synaptic apposition length of the analyzed synapse were measured. Five groups of animals were compared during entrance into torpor (Torpor Early, TE, n = 6), late torpor (Torpor Late, TL, n = 5), beginning of euthermic arousal episodes (Arousal Early, AE, n = 5), late in the euthermic arousal episode (Arousal Late, AL, n = 5), and during continuous euthermy in spring (EU, n = 6). The results showed that during torpor and at the beginning of arousals the PSD length and synaptic apposition length are significantly increased compared to synapses during late arousal and in spring conditions. In contrast, the width and surface area of the PSDs are decreased in torpor. At the beginning of an arousal the width of the PSD increases and gains maximum value in late arousals (AL), returning to spring (EU) values. No differences were found in total number of synapses during the torpor-arousal cycle. The results indicate reversible changes in ultrastructure of (asymmetric axospinous) synapses in the frontal cortex, which may be critical for the maintenance of cortical neuronal networks and for protection against potential deleterious effects of prolonged hypothermic phases of hibernation.
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Affiliation(s)
- J Ruediger
- Institute of Anatomy, Friedrich-Schiller-University, Jena, Germany
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