251
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Nicholson DA, Trana R, Katz Y, Kath WL, Spruston N, Geinisman Y. Distance-dependent differences in synapse number and AMPA receptor expression in hippocampal CA1 pyramidal neurons. Neuron 2006; 50:431-42. [PMID: 16675397 DOI: 10.1016/j.neuron.2006.03.022] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2005] [Revised: 02/22/2006] [Accepted: 03/16/2006] [Indexed: 11/29/2022]
Abstract
The ability of synapses throughout the dendritic tree to influence neuronal output is crucial for information processing in the brain. Synaptic potentials attenuate dramatically, however, as they propagate along dendrites toward the soma. To examine whether excitatory axospinous synapses on CA1 pyramidal neurons compensate for their distance from the soma to counteract such dendritic filtering, we evaluated axospinous synapse number and receptor expression in three progressively distal regions: proximal and distal stratum radiatum (SR), and stratum lacunosum-moleculare (SLM). We found that the proportion of perforated synapses increases as a function of distance from the soma and that their AMPAR, but not NMDAR, expression is highest in distal SR and lowest in SLM. Computational models of pyramidal neurons derived from these results suggest that they arise from the compartment-specific use of conductance scaling in SR and dendritic spikes in SLM to minimize the influence of distance on synaptic efficacy.
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Affiliation(s)
- Daniel A Nicholson
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 60611, USA
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252
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Hermel EES, Faccioni-Heuser MC, Marcuzzo S, Rasia-Filho AA, Achaval M. Ultrastructural features of neurons and synaptic contacts in the posterodorsal medial amygdala of adult male rats. J Anat 2006; 208:565-75. [PMID: 16637879 PMCID: PMC2100224 DOI: 10.1111/j.1469-7580.2006.00559.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/20/2005] [Indexed: 11/29/2022] Open
Abstract
The aim of the present study was to describe the ultrastructure of neurons (from eight animals) and to analyse the synaptic terminal distribution (from two animals) in the posterodorsal subnucleus of the medial amygdala (MePD) of adult male rats. Using transmission electron microscopy, it was possible to identify many spiny and aspiny dendrites, unmyelinated axonal bundles, single axonal processes, a few myelinated axons, blood vessels and glial processes in the neuropil. Axodendritic synapses were the most frequently observed (67.5%), appearing to be of either the inhibitory or the excitatory types. The presynaptic region contained round or flattened vesicles that occurred either singly or with dense-cored vesicles (DCVs). The dendrites often received many synapses on a single shaft, and axon terminals displayed synaptic contacts with one or more postsynaptic structures. Dendritic spines showed different morphologies and the synapses on them (23.1%) formed a single and apparently excitatory synaptic contact with round, electron-lucid vesicles alone or, less frequently, with DCVs. Inhibitory and excitatory axosomatic synapses (8.2%) and excitatory axoaxonic synapses (1.2%) were also identified. The present report provides new findings relevant to the study of the MePD cellular organization and could be combined with other morphological data in order to reveal the functional activity of this area in male rats.
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Affiliation(s)
- E E S Hermel
- Programa de Pós-Graduação em Neurociências, Universidade Federal do Rio Grande do Sul, Brazil
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253
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Depaz IM, Wilce PA. The novel cytoskeleton-associated protein Neuronal protein 22: Elevated expression in the developing rat brain. Brain Res 2006; 1081:59-64. [PMID: 16542643 DOI: 10.1016/j.brainres.2006.01.126] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Revised: 01/16/2006] [Accepted: 01/17/2006] [Indexed: 10/24/2022]
Abstract
Neuronal development and process targeting is mediated by proteins of the cytoskeleton. However, the signaling pathways underlying these mechanisms are complex and have not yet been fully elucidated. Neuronal protein 22 (NP22) has been identified as a cytoskeleton-associated protein. It colocalizes with microtubules and actin, the two major components of the cytoskeleton. It contains numerous signaling motifs and induces process formation in non-neuronal cells. Expression of rat NP22 (rNP22) rises incrementally at specific time points during brain development, with the greatest elevation occurring during synaptogenesis in the rat brain. Its neuronal localization is primarily at the plasma membrane of the soma in the embryonic brain and progresses into homogeneous expression in the postnatal rat brain. Data suggest that NP22 may play a role in mediating the molecular events governing development of the neuronal architecture. Furthermore, its sustained expression in postnatal brain implies a function in the maintenance of neuronal morphology.
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Affiliation(s)
- Iris M Depaz
- Alcohol Research Unit, Department of Biochemistry, School of Molecular and Microbial Sciences, Faculty of Biological and Medical Sciences, University of Queensland, St. Lucia Campus, Brisbane, Queensland, 4072, Australia.
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254
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Grossman AW, Elisseou NM, McKinney BC, Greenough WT. Hippocampal pyramidal cells in adult Fmr1 knockout mice exhibit an immature-appearing profile of dendritic spines. Brain Res 2006; 1084:158-64. [PMID: 16574084 DOI: 10.1016/j.brainres.2006.02.044] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2005] [Revised: 02/03/2006] [Accepted: 02/07/2006] [Indexed: 11/21/2022]
Abstract
Fragile X syndrome (FXS) is a common form of mental retardation caused by the absence of functional fragile X mental retardation protein (FMRP). FXS is associated with elevated density and length of dendritic spines, as well as an immature-appearing distribution profile of spine morphologies in the neocortex. Mice that lack FMRP (Fmr1 knockout mice) exhibit a similar phenotype in the neocortex, suggesting that FMRP is important for dendritic spine maturation and pruning. Examination of Golgi-stained pyramidal cells in hippocampal subfield CA1 of adult Fmr1 knockout mice reveals longer spines than controls and a morphology profile that, while essentially opposite of that described in the Fmr1 knockout neocortex, appears similarly immature. This finding strongly suggests that FMRP is required for the processes of spine maturation and pruning in multiple brain regions and that the specific pathology depends on the cellular context.
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Affiliation(s)
- Aaron W Grossman
- Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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255
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Pyter LM, Reader BF, Nelson RJ. Short photoperiods impair spatial learning and alter hippocampal dendritic morphology in adult male white-footed mice (Peromyscus leucopus). J Neurosci 2006; 25:4521-6. [PMID: 15872099 PMCID: PMC6725029 DOI: 10.1523/jneurosci.0795-05.2005] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although seasonal changes in brain morphology and function are well established in songbirds, seasonal plasticity of brain structure and function remain less well documented in mammals. Nontropical animals display many adaptations to reduce energy use to survive winter, including cessation of reproductive activities. Because of the high energetic costs of brain tissue, we hypothesized that male white-footed mice (Peromyscus leucopus) would reduce brain size in response to short days as well as regress their reproductive systems. Because short days may decrease hippocampal volume and impair spatial learning and memory in rodents and because of the potential for seasonal plasticity in the hippocampus, we hypothesized that photoperiod alters hippocampal morphology to affect spatial learning and memory. Mice housed in either long or short days for 10 weeks were examined for performance in a water maze; brains were then removed and weighed, and hippocampal volumes were determined. We also measured dendritic morphology and spine density in the CA1, CA3, and dentate gyrus. Short days decreased brain mass and hippocampal volume compared with long days. Short days also impaired long-term spatial learning and memory relative to long days but did not affect sensory discrimination or other types of memory. Short days decreased apical (stratum lacunosum-moleculare) CA1 spine density, as well as increased basilar (stratum oriens) CA3 spine density. Results from this study suggest that photoperiod alters brain size and morphology, as well as cognitive function. Understanding the mechanisms mediating these photoperiod-induced alterations may provide insight for treatment of seasonal cognitive and affective disorders.
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Affiliation(s)
- Leah M Pyter
- Department of Neuroscience and Institute of Behavioral Medicine Research, Ohio State University, Columbus, Ohio 43210, USA.
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256
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Meng J, Meng Y, Hanna A, Janus C, Jia Z. Abnormal long-lasting synaptic plasticity and cognition in mice lacking the mental retardation gene Pak3. J Neurosci 2006; 25:6641-50. [PMID: 16014725 PMCID: PMC6725420 DOI: 10.1523/jneurosci.0028-05.2005] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Mutations in the Pak3 gene lead to nonsyndromic mental retardation characterized by selective deficits in cognition. However, the underlying mechanisms are yet to be elucidated. We report here that the knock-out mice deficient in the expression of p21-activated kinase 3 (PAK3) exhibit significant abnormalities in synaptic plasticity, specifically hippocampal late-phase long-term potentiation, and deficiencies in learning and memory. A dramatic reduction in the active form of transcription factor cAMP-responsive element-binding protein in the knock-out mice implicates a novel signaling mechanism by which PAK3 and Rho signaling regulate synaptic function and cognition.
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Affiliation(s)
- Jinsong Meng
- The Hospital for Sick Children, Toronto, Ontario, M5G 1X8, Canada
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257
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Gilbert ME, Sui L. Dose-dependent reductions in spatial learning and synaptic function in the dentate gyrus of adult rats following developmental thyroid hormone insufficiency. Brain Res 2006; 1069:10-22. [PMID: 16406011 DOI: 10.1016/j.brainres.2005.10.049] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2005] [Revised: 10/07/2005] [Accepted: 10/10/2005] [Indexed: 01/18/2023]
Abstract
Thyroid hormones are critical for the development and maturation of the central nervous system. Although somatic and neurological effects are well documented following severe thyroid hormone deprivation, much less is known of the functional consequences of moderate levels of hormone insufficiency. We have previously demonstrated that severe thyroid hormone reductions in the postnatal period are associated with impairments in synaptic transmission in the dentate gyrus. The present study was performed to examine the dose-response relationships of moderate levels of hormone disruption on synaptic function in the dentate gyrus in an in vivo preparation and to determine the effects on spatial learning. Pre- and postnatal thyroid hormone insufficiency was induced by administration of 3 or 10 ppm propylthiouracil (PTU) to pregnant and lactating dams via the drinking water from gestation day (GD) 6 until postnatal day (PN) 30. This regimen produced a 47% and 65% reduction in serum T4, in the dams of the low and high-dose groups, respectively. At the time of testing of adult offspring, hormone status had returned to control levels. In littermates, field potentials evoked in the dentate gyrus in response to stimulation of the perforant path were assessed under urethane anesthesia. The data reveal dose-dependent reductions in synaptic transmission and impairments in long-term potentiation (LTP) of the EPSP component of the compound field potential. In contrast, LTP of the population spike measure was paradoxically enhanced. Spatial learning in the Morris water maze was profoundly impaired in high-dose animals. Although the majority of subjects in the low-dose group eventually acquired the task, their acquisition rate lagged behind control values. Reversal learning was assessed in all animals reaching criterion performance and found to be impaired in PTU-exposed animals relative to controls. These data support previous findings in area CA1 in vitro, extend observations associated with dentate gyrus synaptic function to a lower dose range, and provide correlative evidence of behavioral disruption in a hippocampal-dependent learning task following developmental thyroid hormone insufficiency.
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Affiliation(s)
- M E Gilbert
- Neurotoxicology Division (MD-B105-05), National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
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258
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Diamond DM, Campbell AM, Park CR, Woodson JC, Conrad CD, Bachstetter AD, Mervis RF. Influence of predator stress on the consolidation versus retrieval of long-term spatial memory and hippocampal spinogenesis. Hippocampus 2006; 16:571-6. [PMID: 16741974 DOI: 10.1002/hipo.20188] [Citation(s) in RCA: 182] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We have studied the influence of predator stress (30 min of cat exposure) on long-term (24 h) spatial memory and the density of spines in basilar dendrites of CA1 neurons. Predator stress occurred either immediately before water maze training (Stress Pre-Training) or before the 24 h memory test (Stress Pre-Retrieval). The Control (nonstress) group exhibited excellent long-term spatial memory and a robust increase in the density of stubby, but not mushroom, shaped spines. The Stress Pre-Training group had impaired long-term memory and did not exhibit any changes in spine density. The Stress Pre-Retrieval group was also impaired in long-term memory performance, but this group exhibited an increase in the density of stubby, but not mushroom, shaped spines, which was indistinguishable from the control group. These findings indicate that: (1) A single day of water maze training under control conditions produced intact long-term memory and an increase in the density of stubby spines in CA1; (2) Stress before training interfered with the consolidation of information into long-term memory and suppressed the training-induced increase in spine density; and (3) Stress immediately before the 24 h memory test trial impaired the retrieval of the stored memory, but did not reverse the training-induced increase in CA1 spine density. Overall, this work provides evidence of structural plasticity in dendrites of CA1 neurons which may be involved in the consolidation process, and how spinogenesis and memory are modulated by stress.
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Affiliation(s)
- David M Diamond
- Medical Research Service, VA Hospital, Tampa, Florida 33612, USA.
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259
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Kozorovitskiy Y, Gross CG, Kopil C, Battaglia L, McBreen M, Stranahan AM, Gould E. Experience induces structural and biochemical changes in the adult primate brain. Proc Natl Acad Sci U S A 2005; 102:17478-82. [PMID: 16299105 PMCID: PMC1297690 DOI: 10.1073/pnas.0508817102] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Primates exhibit complex social and cognitive behavior in the wild. In the laboratory, however, the expression of their behavior is usually limited. A large body of literature shows that living in an enriched environment alters dendrites and synapses in the brains of adult rodents. To date, no studies have investigated the influence of living in a complex environment on brain structure in adult primates. We assessed dendritic architecture, dendritic spines, and synaptic proteins in adult marmosets housed in either a standard laboratory cage or in one of two differentially complex habitats. A month-long stay in either complex environment enhanced the length and complexity of the dendritic tree and increased dendritic spine density and synaptic protein levels in the hippocampus and prefrontal cortex. No differences were detected between the brains of marmosets living in the two differentially complex environments. Our results show that the structure of the adult primate brain remains highly sensitive even to modest levels of experiential complexity. For adult primates, living in standard laboratory housing may induce reversible dendritic spine and synapse decreases in brain regions important for cognition.
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260
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Komatsuzaki Y, Murakami G, Tsurugizawa T, Mukai H, Tanabe N, Mitsuhashi K, Kawata M, Kimoto T, Ooishi Y, Kawato S. Rapid spinogenesis of pyramidal neurons induced by activation of glucocorticoid receptors in adult male rat hippocampus. Biochem Biophys Res Commun 2005; 335:1002-7. [PMID: 16111661 DOI: 10.1016/j.bbrc.2005.07.173] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2005] [Accepted: 07/20/2005] [Indexed: 11/18/2022]
Abstract
Modulation of hippocampal synaptic plasticity by glucocorticoids has been attracting much attention, due to its importance in stress responses. Dendritic spines are essential for memory storage processes. Here, we investigated the effect of dexamethasone (DEX), a specific agonist of glucocorticoid receptor (GR), on density and morphology of dendritic spines in adult male rat hippocampus by imaging of Lucifer Yellow-injected spines in slices. The application of 100 nM DEX (stressful high concentration) induced rapid modulation of the density and morphology of dendritic spines in CA1 pyramidal neurons within 1h. The total spine density increased from 0.88 spines/microm (control) to 1.36 spines/microm (DEX-treated). DEX significantly increased the density of thin and mushroom type spines, however only a slight increase was observed for stubby and filopodium type spines. Because the presence of 10 microM cycloheximide, an inhibitor of protein synthesis, did not suppress the DEX effect, these responses are probably non-genomic. Western immunoblot analysis demonstrated the localization of classical type GR in Triton-insoluble synaptosomal fractions (enriched in postsynaptic membranes) from hippocampal slices, suggesting a possible action site of DEX at spines.
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Affiliation(s)
- Yoshimasa Komatsuzaki
- School of Science and Technology, Meiji University, 1-1-1 Higasimita, Tama, Kawasaki, Kanagawa 214, Japan
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261
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Abstract
The formation of synapses in the vertebrate central nervous system is a complex process that occurs over a protracted period of development. Recent work has begun to unravel the mysteries of synaptogenesis, demonstrating the existence of multiple molecules that influence not only when and where synapses form but also synaptic specificity and stability. Some of these molecules act at a distance, steering axons to their correct receptive fields and promoting neuronal differentiation and maturation, whereas others act at the time of contact, providing positional information about the appropriateness of targets and/or inductive signals that trigger the cascade of events leading to synapse formation. In addition, correlated synaptic activity provides critical information about the appropriateness of synaptic connections, thereby influencing synapse stability and elimination. Although synapse formation and elimination are hallmarks of early development, these processes are also fundamental to learning, memory, and cognition in the mature brain.
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Affiliation(s)
- Clarissa L Waites
- Department of Psychiatry and Behavioral Science, Nancy Pritzker Laboratory, Stanford University, Palo Alto, CA 94304-5485, USA.
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262
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Newey SE, Velamoor V, Govek EE, Van Aelst L. Rho GTPases, dendritic structure, and mental retardation. ACTA ACUST UNITED AC 2005; 64:58-74. [PMID: 15884002 DOI: 10.1002/neu.20153] [Citation(s) in RCA: 276] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A consistent feature of neurons in patients with mental retardation is abnormal dendritic structure and/or alterations in dendritic spine morphology. Deficits in the regulation of the dendritic cytoskeleton affect both the structure and function of dendrites and synapses and are believed to underlie mental retardation in some instances. In support of this, there is good evidence that alterations in signaling pathways involving the Rho family of small GTPases, key regulators of the actin and microtubule cytoskeletons, contribute to both syndromic and nonsyndromic mental retardation disorders. Because the Rho GTPases have been shown to play increasingly well-defined roles in determining dendrite and dendritic spine development and morphology, Rho signaling has been suggested to be important for normal cognition. The purpose of this review is to summarize recent data on the Rho GTPases pertaining to dendrite and dendritic spine morphogenesis, as well as to highlight their involvement in mental retardation resulting from a variety of genetic mutations within regulators and effectors of these molecules.
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263
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Spires TL, Meyer-Luehmann M, Stern EA, McLean PJ, Skoch J, Nguyen PT, Bacskai BJ, Hyman BT. Dendritic spine abnormalities in amyloid precursor protein transgenic mice demonstrated by gene transfer and intravital multiphoton microscopy. J Neurosci 2005; 25:7278-87. [PMID: 16079410 PMCID: PMC1820616 DOI: 10.1523/jneurosci.1879-05.2005] [Citation(s) in RCA: 412] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2005] [Revised: 06/13/2005] [Accepted: 07/01/2005] [Indexed: 12/16/2022] Open
Abstract
Accumulation of amyloid-beta (Abeta) into senile plaques in Alzheimer's disease (AD) is a hallmark neuropathological feature of the disorder, which likely contributes to alterations in neuronal structure and function. Recent work has revealed changes in neurite architecture associated with plaques and functional changes in cortical signaling in amyloid precursor protein (APP) expressing mouse models of AD. Here we developed a method using gene transfer techniques to introduce green fluorescent protein (GFP) into neurons, allowing the investigation of neuronal processes in the vicinity of plaques. Multiphoton imaging of GFP-labeled neurons in living Tg2576 APP mice revealed disrupted neurite trajectories and reductions in dendritic spine density compared with age-matched control mice. A profound deficit in spine density (approximately 50%) extends approximately 20 mum from plaque edges. Importantly, a robust decrement (approximately 25%) also occurs on dendrites not associated with plaques, suggesting widespread loss of postsynaptic apparatus. Plaques and dendrites remained stable over the course of weeks of imaging. Postmortem analysis of axonal immunostaining and colocalization of synaptophysin and postsynaptic density 95 protein staining around plaques indicate a parallel loss of presynaptic and postsynaptic partners. These results show considerable changes in dendrites and dendritic spines in APP transgenic mice, demonstrating a dramatic synaptotoxic effect of dense-cored plaques. Decreased spine density will likely contribute to altered neural system function and behavioral impairments observed in Tg2576 mice.
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Affiliation(s)
- Tara L Spires
- Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts 02129, USA
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264
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Popov VI, Deev AA, Klimenko OA, Kraev LV, Kuz'minykh SB, Medvedev NI, Patrushev IV, Popov RV, Rogachevskii VV, Khutsiyan SS, Stewart MG, Fesenko EE. Three-dimensional reconstruction of synapses and dendritic spines in the rat and ground squirrel hippocampus: new structural-functional paradigms for synaptic function. ACTA ACUST UNITED AC 2005; 35:333-41. [PMID: 15929558 DOI: 10.1007/s11055-005-0030-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Published data are reviewed along with our own data on synaptic plasticity and rearrangements of synaptic organelles in the central nervous system. Contemporary laser scanning and confocal microscopy techniques are discussed, along with the use of serial ultrathin sections for in vivo and in vitro studies of dendritic spines, including those addressing relationships between morphological changes and the efficiency of synaptic transmission, especially in conditions of the long-term potentiation model. Different categories of dendritic spines and postsynaptic densities are analyzed, as are the roles of filopodia in originating spines. The role of serial ultrathin sections for unbiased quantitative stereological analysis and three-dimensional reconstruction is assessed. The authors' data on the formation of more than two synapses on single mushroom spines on neurons in hippocampal field CA1 are discussed. Analysis of these data provides evidence for new paradigms in both the organization and functioning of synapses.
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Affiliation(s)
- V I Popov
- Institute of Cell Biophysics, Russian Academy of Sciences.
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265
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Petrak LJ, Harris KM, Kirov SA. Synaptogenesis on mature hippocampal dendrites occurs via filopodia and immature spines during blocked synaptic transmission. J Comp Neurol 2005; 484:183-90. [PMID: 15736233 DOI: 10.1002/cne.20468] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
During development, dendritic spines emerge as stubby protrusions from single synapses on dendritic shafts or from retracting filopodia, many of which have more than one synapse. These structures are rarely encountered in the mature brain. Recently, confocal and two-photon microscopy have revealed a proliferation of new filopodia-like protrusions in mature hippocampal slices, especially when synaptic transmission was blocked. It was not known whether these protrusions have synapses nor whether they are accompanied by the other immature spine forms. Here, reconstruction from serial section electron microscopy (ssEM) was used to answer these questions. Acute hippocampal slices from mature male rats, ages 56 and 63 days, were maintained in vitro in control medium or in a nominally calcium-free medium with high magnesium, glutamate receptor antagonists, and sodium and calcium channel blockers. At the end of each 8-hour experiment, all slices were fixed, coded, and processed for ssEM. In agreement with light microscopy, there were more filopodia along dendrites in slices with blocked synaptic transmission. These filopodia were identified by their pointy tips and either the absence of synapses or presence of multiple synapses along them. There was also a proliferation of stubby spines. Filopodia along mature dendrites were typically shorter than developmental filopodia, with outgrowth likely being constrained by reduced extracellular space and compact neuropil, providing numerous candidate presynaptic partners in the vicinity of the mature dendrites. These findings suggest that synaptogenesis and spine formation are readily initiated under conditions of reduced activity in the mature brain.
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Affiliation(s)
- Lara J Petrak
- Department of Biology, Boston University, Boston, Massachusetts 02215, USA
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266
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Sá SI, Madeira MD. Estrogen modulates the sexually dimorphic synaptic connectivity of the ventromedial nucleus. J Comp Neurol 2005; 484:68-79. [PMID: 15717306 DOI: 10.1002/cne.20451] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Neurons in the ventrolateral division of the hypothalamic ventromedial nucleus (VMNvl) display a remarkable estrogen-dependent functional and structural plasticity, which is likely to be mediated, in part at least, by neuronal afferents. The present study was designed to determine whether the number of synapses per neuron and the size of individual synapses in the VMNvl vary across the estrus cycle and, also, whether they differ between the sexes. To accomplish this, the VMNvl of adult female rats at proestrus or diestrus day 1 and of age-matched male rats was analyzed using electron microscopy. We found that a single VMNvl neuron receives around 7,000 synapses during diestrus and approximately 10,000 during proestrus. This estrus cycle-related variation is accounted for by increases in the number of all types of synapses. In males, the number of synapses received by each VMNvl neuron is similar to that of diestrus rats (approximately 7,500). However, in males the number of axodendritic and axospinous synapses is smaller than in proestrus rats, whereas the number of axosomatic synapses is higher than in diestrus rats. In addition, we found that the size of the postsynaptic densities of axospinous and axosomatic synapses is consistently larger in males than in females. Our results show that the synaptic organization of the VMNvl is sexually dimorphic, with females having more dendritic synapses and males more somatic synapses. They also show that the synaptic plasticity induced by estrogen in the VMNvl is characterized by changes in the number, but not the size, of the synapses.
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Affiliation(s)
- Susana I Sá
- Department of Anatomy, Porto Medical School, 4200-319 Porto, Portugal
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267
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Golan HM, Lev V, Hallak M, Sorokin Y, Huleihel M. Specific neurodevelopmental damage in mice offspring following maternal inflammation during pregnancy. Neuropharmacology 2005; 48:903-17. [PMID: 15829260 DOI: 10.1016/j.neuropharm.2004.12.023] [Citation(s) in RCA: 182] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2004] [Revised: 11/02/2004] [Accepted: 12/10/2004] [Indexed: 10/25/2022]
Abstract
Intrauterine inflammation is a major risk for offspring neurodevelopmental brain damage and may result in cognitive limitations and poor cognitive and perceptual outcomes. Pro-inflammatory cytokines, stimulated during inflammatory response, have a pleotrophic effect on neurons and glia cells. They act in a dose-dependent manner, activate cell-death pathways and also act as trophic factors. In the present study, we have examined in mice the effect of short, systemic maternal inflammation on fetal brain development. Maternal inflammation, induced by lipopolysaccharide (LPS) at gestation day 17, did not affect morphogenic parameters and reflex development during the first month of life. However, maternal inflammation specifically increased the number of pyramidal and granular cells in the hippocampus, as well as the shrinkage of pyramidal cells, but not of the granular cells. No additional major morphological differences were observed in the cerebral cortex or cerebellum. In accordance with the morphological effects, maternal inflammation specifically impaired distinct forms of learning and memory, but not motor function or exploration in the adult offspring. The specific deficiency observed, following maternal inflammation, may suggest particular sensitivity of the hippocampus and other associated brain regions to inflammatory factors during late embryonic development.
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Affiliation(s)
- H M Golan
- Department of Developmental Molecular Genetics and Zlotowski Center for Neuroscience, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
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268
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Abstract
A recent flurry of time-lapse imaging studies of live neurons have tried to address the century-old question: what morphological changes in dendritic spines can be related to long-term memory? Changes that have been proposed to relate to memory include the formation of new spines, the enlargement of spine heads and the pruning of spines. These observations also relate to a more general question of how stable dendritic spines are. The objective of this review is to critically assess the new data and to propose much needed criteria that relate spines to memory, thereby allowing progress in understanding the morphological basis of memory.
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Affiliation(s)
- Menahem Segal
- Department of Neurobiology, The Weizmann Institute, Rehovot, 76100 Israel.
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269
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Hoogland TM, Saggau P. Facilitation of L-type Ca2+ channels in dendritic spines by activation of beta2 adrenergic receptors. J Neurosci 2005; 24:8416-27. [PMID: 15456814 PMCID: PMC6729902 DOI: 10.1523/jneurosci.1677-04.2004] [Citation(s) in RCA: 90] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
We studied the contribution of L-type Ca2+ channels to action potential-evoked Ca2+ influx in dendritic spines of CA1 pyramidal neurons and the modulation of these channels by the beta2 adrenergic receptor. Backpropagating action potentials (bAPs) (three at 50 Hz) were evoked by brief somatic current injections, and Ca2+ transients were recorded in proximal basal dendrites and associated spines. The R- and T-type Ca2+ channel blocker NiCl2 (100 microm) significantly reduced Ca2+ transients in both spines and their parent dendrites (approximately 50%), suggesting that these channels are the major source of bAP-evoked Ca2+ influx in these structures. The L-type Ca2+ channel blockers nimodipine and nifedipine (both 10 microm) reduced spine Ca2+ transients by approximately 10%, whereas the L-type Ca2+ channel activators FPL 64176 (2,5-dimethyl-4-[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylic acid methylester) and Bay K 8644 ((+/-)-1,4-dihydro-2,6-dimethyl-5-nitro-4-[2-(trifluoromethyl)-phenyl]-3-pyridine carboxylic acid methyl ester) (both 10 microm) significantly enhanced the spine Ca2+ transients by 40-50%. Activation of beta2 adrenergic receptors with salbutamol (40 microm) or formoterol (5 microm) resulted in significant enhancements of the spine (40-50%) but not dendritic Ca2+ transients. This increase was prevented when L-type Ca2+ channels were blocked with nimodipine (10 microm) or when cAMP-dependent protein kinase A (PKA) was inhibited with KT5720 (3 microm), Rp-cAMPS (Rp-adenosine cyclic 3',5'-phosphorothioate) (100 microm), or PKI (100 microm). The above data suggest that L-type Ca2+ channels are functionally present in dendritic spines of CA1 pyramidal neurons, contribute to spine Ca2+ influx, and can be modulated by the beta2 adrenergic receptor through PKA in a highly compartmentalized manner.
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Affiliation(s)
- Tycho M Hoogland
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, USA
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270
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Ethell IM, Pasquale EB. Molecular mechanisms of dendritic spine development and remodeling. Prog Neurobiol 2005; 75:161-205. [PMID: 15882774 DOI: 10.1016/j.pneurobio.2005.02.003] [Citation(s) in RCA: 264] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2004] [Revised: 01/28/2005] [Accepted: 02/22/2005] [Indexed: 12/19/2022]
Abstract
Dendritic spines are small protrusions that cover the surface of dendrites and bear the postsynaptic component of excitatory synapses. Having an enlarged head connected to the dendrite by a narrow neck, dendritic spines provide a postsynaptic biochemical compartment that separates the synaptic space from the dendritic shaft and allows each spine to function as a partially independent unit. Spines develop around the time of synaptogenesis and are dynamic structures that continue to undergo remodeling over time. Changes in spine morphology and density influence the properties of neural circuits. Our knowledge of the structure and function of dendritic spines has progressed significantly since their discovery over a century ago, but many uncertainties still remain. For example, several different models have been put forth outlining the sequence of events that lead to the genesis of a spine. Although spines are small and apparently simple organelles with a cytoskeleton mainly composed of actin filaments, regulation of their morphology and physiology appears to be quite sophisticated. A multitude of molecules have been implicated in dendritic spine development and remodeling, suggesting that intricate networks of interconnected signaling pathways converge to regulate actin dynamics in spines. This complexity is not surprising, given the likely importance of dendritic spines in higher brain functions. In this review, we discuss the molecules that are currently known to mediate the exquisite sensitivity of spines to perturbations in their environment and we outline how these molecules interface with each other to mediate cascades of signals flowing from the spine surface to the actin cytoskeleton.
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Affiliation(s)
- Iryna M Ethell
- Division of Biomedical Sciences, University of California Riverside, Riverside, CA 92521, USA
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271
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Gray NW, Kruchten AE, Chen J, McNiven MA. A dynamin-3 spliced variant modulates the actin/cortactin-dependent morphogenesis of dendritic spines. J Cell Sci 2005; 118:1279-90. [PMID: 15741233 DOI: 10.1242/jcs.01711] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Immature dendrites extend many actin-rich filopodial structures that can be replaced by synapse-containing dendritic spines as the neuron matures. The large GTPase dynamin-3 (Dyn3) is a component of the postsynapse in hippocampal neurons but its function is undefined. Here, we demonstrate that a specific Dyn3 variant (Dyn3baa) promotes the formation of immature dendritic filopodia in cultured neurons. This effect is dependent upon Dyn3 GTPase activity and a direct interaction with the F-actin-binding protein cortactin. Consistent with these findings, Dyn3baa binds to cortactin with a 200% higher affinity than Dyn3aaa, a near identical isoform that does not induce dendritic filopodia when expressed in cultured neurons. Finally, levels of Dyn3baa-encoding mRNA are tightly regulated during neuronal maturation and are markedly upregulated during synaptogenesis. Together, these findings provide the first evidence that an enhanced interaction between a specific Dyn3 splice variant and cortactin modulate actin-membrane dynamics in developing neurons to regulate the morphogenesis of dendritic spines.
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Affiliation(s)
- Noah W Gray
- Molecular Neuroscience Program and Graduate School, Mayo Clinic, Rochester, MN 55905, USA
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272
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Granados-Rojas L, Aguilar A, Díaz-Cintra S. The mossy fiber system of the hippocampal formation is decreased by chronic and postnatal but not by prenatal protein malnutrition in rats. Nutr Neurosci 2005; 7:301-8. [PMID: 15682926 DOI: 10.1080/10284150400017306] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
We tested in 70-day-old Sprague-Dawley rats, whether malnutrition imposed during different periods of hippocampal development produced deleterious effects on the total reference volume of the mossy fiber system. Animals were treated under four nutritional conditions: (a) well nourished; (b) prenatal protein malnourished; (c) chronic protein malnourished and (d) postnatal protein malnourished. Timm's stained material was used in coronal hippocampal sections (40 microm) to estimate--using the Principle of Cavalieri--the total reference volume of the mossy fiber system in each experimental group. Our results show that chronic and postnatal protein malnourished, but not prenatal malnourished rats, decrease the mossy fiber system and the total reference volume of the mossy fiber system are selectively vulnerable to the type of dietary restriction. Thus, chronic and posnatal protein malnutrition produce deleterious effects, but only rats under prenatal protein malnutrition were able to reorganize synapses in this plexus. These findings raise the possibility that chronic malnutrition, as a long-term stressful factor, might be an important paradigm to test structural hippocampal changes that produce physiological and pathophysiological effects, or the possibility to recover its function for nutritional rehabilitation.
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Affiliation(s)
- Leticia Granados-Rojas
- Departamento de Neurobiología del Desarrollo y Neurofisiologia, Instituto de Neurobiologia, Universidad Nacional Autónoma de México, Campus UNAM-UAQ Juriquilla, Querétaro, Qro 76001, Mexico
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273
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Savtchenko LP. Influence of the Geometry of an Axo-Dendritic Synapse and Its Position on the Dendrite on the Current Recorded from the Neuronal Soma. NEUROPHYSIOLOGY+ 2005. [DOI: 10.1007/s11062-005-0049-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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274
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Knafo S, Ariav G, Barkai E, Libersat F. Olfactory learning-induced increase in spine density along the apical dendrites of CA1 hippocampal neurons. Hippocampus 2005; 14:819-25. [PMID: 15382252 DOI: 10.1002/hipo.10219] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We have previously shown that rule learning of an olfactory discrimination task is accompanied by increased spine density along the apical dendrites of piriform cortex pyramidal neurons. The purpose of the present study was to examine whether such olfactory learning task, in which the hippocampus is actively involved, induces morphological modifications in CA1 pyramidal neurons as well. Rats were trained to discriminate positive cues in pairs of odors for a water reward. Morphological modifications were studied in Golgi-impregnated neurons with light microscopy, 1 and 3 days after training completion. Spine densities were measured on the proximal region of apical dendrites and on basal dendrites after rule learning. Three days after training completion, the mean spine density on apical dendrites in neurons from trained rats was significantly higher by 20.5% than in neurons from pseudo-trained and naive animals, which did not differ from each other. By contrast, there was no significant difference in spine density of basal dendrites among the three groups. As length and diameter of spiny dendritic segments did not change after learning, the learning-related increase in spine density in neurons from trained rats may reflect a net increase in the number of excitatory synapses in the hippocampus following olfactory rule learning.
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Affiliation(s)
- Shira Knafo
- Faculty of Health Sciences and Zlotowski Center for Neuroscience, Ben-Gurion University, Beersheva, Israel
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275
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Halpain S, Spencer K, Graber S. Dynamics and pathology of dendritic spines. PROGRESS IN BRAIN RESEARCH 2005; 147:29-37. [PMID: 15581695 DOI: 10.1016/s0079-6123(04)47003-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Dendritic spines are key players in information processing in the brain. Changes in spine shape and wholesale spine turnover provide mechanisms for modifying existing synaptic connections and altering neuronal connectivity. Although neuronal cell death in acute and chronic neurodegenerative diseases is clearly an important factor in decline of cognitive or motor function, loss of dendritic spines, in the absence of cell death, may also contribute to impaired brain function in these diseases, as well as in psychiatric disorders and aging. Because spines can function in neuroprotection in vitro, advances toward a molecular understanding of spine maintenance might one day aid in the design of therapies to minimize neurological damage following excitotoxic injury. In addition, progress in defining the biochemical basis of spine development and stabilization may yield insights into mental retardation and psychiatric disorders.
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Affiliation(s)
- Shelley Halpain
- The Scripps Research Institute, Department of Cell Biology and Institute for Childhood and Neglected Diseases, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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276
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Alonso M, Medina JH, Pozzo-Miller L. ERK1/2 activation is necessary for BDNF to increase dendritic spine density in hippocampal CA1 pyramidal neurons. Learn Mem 2004; 11:172-8. [PMID: 15054132 PMCID: PMC379687 DOI: 10.1101/lm.67804] [Citation(s) in RCA: 310] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Brain-derived neurotrophic factor (BDNF) is a potent modulator of synaptic transmission and plasticity in the CNS, acting both pre- and postsynaptically. We demonstrated recently that BDNF/TrkB signaling increases dendritic spine density in hippocampal CA1 pyramidal neurons. Here, we tested whether activation of the prominent ERK (MAPK) signaling pathway was responsible for BDNF's effects on spine growth. Slice cultures were transfected with enhanced yellow fluorescent protein (eYFP) by particle-mediated gene transfer, and CA1 pyramidal neurons were imaged by laser-scanning confocal microscopy. We confirmed that BDNF (24 h) increases spine density in apical dendrites of CA1 neurons. The MEK (ERK kinase) inhibitors PD98059 and U0126 completely prevented the increase in spine density induced by BDNF, without having an effect on spine density by themselves. In contrast to its actions on cortical pyramidal neurons, BDNF had minor and rather localized effects on dendritic complexity in hippocampal pyramidal neurons, increasing the total length, but not the branching of apical dendrites within CA1 stratum radiatum, without affecting basal dendrites in stratum oriens. Our results support the hypothesis that the ERK-signaling pathway not only mediates long-term synaptic plasticity and hippocampal-dependent learning, but it is also involved in the structural remodeling of excitatory spine synapses triggered by neurotrophins.
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Affiliation(s)
- Mariana Alonso
- Instituto de Biología Celular y Neurociencias, Facultad de Medicina, Universidad de Buenos Aires, 112I Buenos Aires, Argentina
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277
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Golan H, Kashtuzki I, Hallak M, Sorokin Y, Huleihel M. Maternal hypoxia during pregnancy induces fetal neurodevelopmental brain damage: Partial protection by magnesium sulfate. J Neurosci Res 2004; 78:430-41. [PMID: 15389830 DOI: 10.1002/jnr.20269] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Fetal low brain oxygenation may be an outcome of maternal complications during pregnancy and is associated with increased risk of cerebral palsy and periventricular leukomalacia in newborns. One treatment used for prevention of fetal brain damage is maternal treatment with MgSO(4). Although this treatment is indicated to reduce the risk of cerebral palsy in newborns, its use remains controversial. We have shown previously that pretreatment with MgSO(4) in a mouse model of maternal hypoxia prevented a delay in the development of motor reflexes induced by hypoxia. We demonstrate here that pretreatment with MgSO(4) reduces hypoxia-induced motor disabilities in adult offspring. This effect is associated with histologic protection of the Purkinje cells in the cerebellum and stabilization of brain-derived neurotrophic factor (BDNF) levels in the cerebellum. MgSO(4) did not prevent the reduction in cerebral cortex cell density and cell size induced by maternal hypoxia, however, nor did it interfere with the modulation of BDNF and nerve growth factor (NGF) expression in the cerebral cortex. MgSO(4) pretreatment also prevented the impairment of short-term memory (30 min, P < 0.05) but not long-term memory (7 days). Nevertheless, maternal pretreatment with MgSO(4) reduced CA1 cell layer width and induced alterations in both NGF and BDNF in the hippocampus. These results support the prophylactic effect of MgSO(4) against motor disabilities; however, they may also indicate possible harmful effects on the cerebral cortex and hippocampus.
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Affiliation(s)
- H Golan
- Department of Developmental Molecular Genetics, Faculty of Health Sciences, Ben-Gurion University of the Negev, Beer-Sheva, Israel.
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278
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Chklovskii DB. Synaptic connectivity and neuronal morphology: two sides of the same coin. Neuron 2004; 43:609-17. [PMID: 15339643 DOI: 10.1016/j.neuron.2004.08.012] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2003] [Revised: 07/13/2004] [Accepted: 08/04/2004] [Indexed: 10/25/2022]
Abstract
Neurons often possess elaborate axonal and dendritic arbors. Why do these arbors exist and what determines their form and dimensions? To answer these questions, I consider the wiring up of a large highly interconnected neuronal network, such as the cortical column. Implementation of such a network in the allotted volume requires all the salient features of neuronal morphology: the existence of branching dendrites and axons and the presence of dendritic spines. Therefore, the requirement of high interconnectivity is, in itself, sufficient to account for the existence of these features. Moreover, the actual lengths of axons and dendrites are close to the smallest possible length for a given interconnectivity, arguing that high interconnectivity is essential for cortical function.
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279
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Wang H, Pickel VM. Activity-regulated cytoskeleton-associated protein Arc is targeted to dendrites and coexpressed with mu-opioid receptors in postnatal rat caudate-putamen nucleus. J Neurosci Res 2004; 77:323-33. [PMID: 15248288 DOI: 10.1002/jnr.20173] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Dendritic expression of the activity-regulated cytoskeleton-associated protein (Arc) is dramatically enhanced by increased synaptic activity in adult brain. We used immunocytochemical electron microscopy to determine whether the subcellular localization of Arc in developing dendrites corresponds to the peak period of synaptogenesis in the postnatal rat caudate-putamen nucleus (CPN). The distribution was compared with that of mu-opioid receptors (MORs), whose localization in dendritic spines closely parallels excitatory synapse formation during postnatal development (Wang et al. [2003] Neuroscience 118:695-708). Sections were processed for immunocytochemical detection of antisera against Arc or MORs at the beginning (postnatal day 15; P15) and the end (P30) of the peak period of synaptogenesis in rat CPN. At P15, immunolabeling for Arc showed a punctate distribution in the cytoplasm of dendritic shafts, some of which was associated with polyribosomes. In some spiny dendrites, Arc immunoreactivity was more intensely localized in putative spines than in their parental dendrites, whereas, in other spiny dendrites, Arc labeling was restricted in the shafts. Many dendritic shafts and spines also showed immunoreactivity for MORs, although dually labeled spines were less numerous than the shafts. At P30, the proportion of singly and dually labeled spines significantly increased from 2.0% to 7.5% and from 9.5% to 21%, respectively. Arc labeling in spines was more detectable beneath the postsynaptic density or at extrasynaptic sites on the plasma membrane. Our results suggest a correlation between Arc expression in dendritic spines during postnatal development and the onset of synaptogenesis in opioid-responsive neurons in the rat CPN.
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Affiliation(s)
- Hong Wang
- Department of Neurology and Neuroscience, Joan and Sanford I Weill Medical College of Cornell University, New York, New York 10021, USA.
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280
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Rácz B, Blanpied TA, Ehlers MD, Weinberg RJ. Lateral organization of endocytic machinery in dendritic spines. Nat Neurosci 2004; 7:917-8. [PMID: 15322548 DOI: 10.1038/nn1303] [Citation(s) in RCA: 158] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2004] [Accepted: 07/29/2004] [Indexed: 02/05/2023]
Abstract
Postsynaptic membrane trafficking plays an important role in synaptic plasticity, but the organization of trafficking machinery within dendritic spines is poorly understood. We use immunocytochemical analysis of rat hippocampal neurons to show that proteins mediating endocytosis are systematically arrayed within dendritic spines, tangential to the synapse. Thus, previously unrecognized lateral domains of the spine organize endocytic protein machinery at sites removed from the postsynaptic density.
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Affiliation(s)
- Bence Rácz
- Department of Cell & Developmental Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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281
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Mizrahi A, Crowley JC, Shtoyerman E, Katz LC. High-resolution in vivo imaging of hippocampal dendrites and spines. J Neurosci 2004; 24:3147-51. [PMID: 15056694 PMCID: PMC6730023 DOI: 10.1523/jneurosci.5218-03.2004] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Structural changes in hippocampal dendrites and dendritic spines are thought to be a consequence of a wide range of experience- and activity-dependent manipulations. We explored the dynamics of hippocampal dendritic spines in vivo by developing a surgical preparation of the adult mouse brain that enabled two-photon imaging of fluorescently labeled CA1 pyramidal neurons. Dendritic trees and spines were repeatedly visualized over many hours in exquisite detail. We tested spine stability under both control conditions and during prolonged epileptic seizures. Remarkably, spines remained structurally stable after 30 min of experimental induction of epileptic seizures. Spines began to disappear only several hours after induction of epileptic activity. We thus demonstrate that this technique provides a methodology for direct in vivo optical studies of the intact mammalian hippocampus.
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Affiliation(s)
- Adi Mizrahi
- Howard Hughes Medical Institute and Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA.
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282
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Blanpied TA, Ehlers MD. Microanatomy of dendritic spines: emerging principles of synaptic pathology in psychiatric and neurological disease. Biol Psychiatry 2004; 55:1121-7. [PMID: 15184030 DOI: 10.1016/j.biopsych.2003.10.006] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2003] [Revised: 10/03/2003] [Accepted: 10/08/2003] [Indexed: 11/26/2022]
Abstract
Psychiatric and neurologic disorders ranging from mental retardation to addiction are accompanied by structural and functional alterations of synaptic connections in the brain. Such alterations include abnormal density and morphology of dendritic spines, synapse loss, and aberrant synaptic signaling and plasticity. Recent work is revealing an unexpectedly complex biochemical and subcellular organization of dendritic spines. In this review, we highlight the molecular interplay between functional domains of the spine, including the postsynaptic density, the actin cytoskeleton, and membrane trafficking domains. This research points to an emerging level of analysis--a microanatomical understanding of synaptic physiology--that will be critical for discerning how synapses operate in normal physiologic states and for identifying and reversing microscopic changes in psychiatric and neurologic disease.
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Affiliation(s)
- Thomas A Blanpied
- Department of Neurobiology, Duke University Medical Center, Durham, North Carolina 27710, USA
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283
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Amateau SK, McCarthy MM. Induction of PGE2 by estradiol mediates developmental masculinization of sex behavior. Nat Neurosci 2004; 7:643-50. [PMID: 15156148 DOI: 10.1038/nn1254] [Citation(s) in RCA: 225] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2004] [Accepted: 04/23/2004] [Indexed: 11/08/2022]
Abstract
Adult male sexual behavior in mammals requires the neuronal organizing effects of gonadal steroids during a sensitive perinatal period. During development, estradiol differentiates the rat preoptic area (POA), an essential brain region in the male copulatory circuit. Here we report that increases in prostaglandin-E(2) (PGE(2)), resulting from changes in cyclooxygenase-2 (COX-2) regulation induced by perinatal exposure to estradiol, are necessary and sufficient to organize the crucial neural substrate that mediates male sexual behavior. Briefly preventing prostaglandin synthesis in newborn males with the COX inhibitor indomethacin permanently downregulates markers of dendritic spines in the POA and severely impairs male sexual behavior. Developmental exposure to the COX inhibitor aspirin results in mild impairment of sexual behavior. Conversely, administration of PGE(2) to newborn females masculinizes the POA and leads to male sex behavior in adults, thereby highlighting the pathway of steroid-independent brain masculinization. Our findings show that PGE(2) functions as a downstream effector of estradiol to permanently masculinize the brain.
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Affiliation(s)
- Stuart K Amateau
- Program in Neuroscience and Department of Physiology, University of Maryland at Baltimore School of Medicine, Baltimore, Maryland 21201, USA
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284
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Abstract
For more than a century dendritic spines have been a source of fascination and speculation. The long-held belief that these anatomical structures are involved in learning and memory are addressed. Specifically, two lines of evidence that support this claim are reviewed. In the first, we review evidence that experimental manipulations that affect dendritic spine number in the hippocampus also affect learning processes of various sorts. In the second, we review evidence that learning itself affects the presence of dendritic spines in the hippocampus. Based on these observations, we propose that the presence of spines enhances synaptic efficacy and thereby the excitability of the network involved in the learning process. With this scheme, learning is not dependent on changes in spine density but rather changes in the presence of dendritic spines provide anatomical support for the processing of novel information used in memory formation.
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Affiliation(s)
- Benedetta Leuner
- Department of Psychology, Center for Collaborative Neuroscience, Rutgers University, Piscataway, NJ 08854
| | - Tracey J. Shors
- Department of Psychology, Center for Collaborative Neuroscience, Rutgers University, Piscataway, NJ 08854
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285
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Li C, Brake WG, Romeo RD, Dunlop JC, Gordon M, Buzescu R, Magarinos AM, Allen PB, Greengard P, Luine V, McEwen BS. Estrogen alters hippocampal dendritic spine shape and enhances synaptic protein immunoreactivity and spatial memory in female mice. Proc Natl Acad Sci U S A 2004; 101:2185-90. [PMID: 14766964 PMCID: PMC357073 DOI: 10.1073/pnas.0307313101] [Citation(s) in RCA: 283] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Estrogen (E) treatment induces axospinous synapses in rat hippocampus in vivo and in cultured hippocampal neurons in vitro. To better explore the molecular mechanisms underlying this phenomenon, we have established a mouse model for E action in the hippocampus by using Golgi impregnation to examine hippocampal dendritic spine morphology, radioimmunocytochemistry (RICC) and silver-enhanced immunocytochemistry to examine expression levels of synaptic protein markers, and hippocampal-dependent object-placement memory as a behavioral readout for the actions of E. In ovariectomized mice of several strains and F(1) hybrids, the total dendritic spine density on neurons in the CA1 region was not enhanced by E treatment, a finding that differs from that in the female rat. E treatment of ovariectomized C57BL/6J mice, however, caused an increase in the number of spines with mushroom shapes. By RICC and silver-enhanced immunocytochemistry, we found that the immunoreactivity of postsynaptic markers (PSD95 and spinophilin) and a presynaptic marker (syntaxin) were enhanced by E treatment throughout all fields of the dorsal hippocampus. In the object-placement tests, E treatment enhanced performance of object placement, a spatial episodic memory task. Taken together, the morphology and RICC results suggest a previously uncharacterized role of E in synaptic structural plasticity that may be interpreted as a facilitation of the spine-maturation process and may be associated with enhancement of hippocampal-dependent memory.
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Affiliation(s)
- Chenjian Li
- Department of Neurology and Neuroscience, Weill Medical College of Cornell University, New York, NY 10021, USA.
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286
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Dhanrajan TM, Lynch MA, Kelly A, Popov VI, Rusakov DA, Stewart MG. Expression of long-term potentiation in aged rats involves perforated synapses but dendritic spine branching results from high-frequency stimulation alone. Hippocampus 2004; 14:255-64. [PMID: 15098730 PMCID: PMC3369534 DOI: 10.1002/hipo.10172] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Evidence for morphological substrates of long-term changes in synaptic efficacy is controversial, partly because it is difficult to employ an unambiguous control. We have used a high-frequency stimulation protocol in vivo to induce long-term potentiation (LTP) in the hippocampal dentate gyrus of aged (22-month-old) rats and have found a clear distinction between animals that sustain LTP and those that fail to sustain it. The "failure group" was used as a specific/"like-with-like" control for morphological changes associated with the expression of LTP per se. Quantitative optical and electron microscopy was used to analyze large populations of dendritic spines and excitatory perforant path synapses; LTP was found to be associated with an increase in numbers of segmented (perforated) postsynaptic densities in spine synapses. In contrast, an increase in the number of branched spines appears to result from high-frequency stimulation alone. These data shed light on the current controversy about the expression mechanism of LTP.
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Affiliation(s)
| | | | - Aine Kelly
- Department of Physiology, Trinity College, Dublin, Ireland
| | - Victor I. Popov
- Department of Biological Sciences, The Open University, Milton Keynes, United Kingdom
- Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Russia
| | - Dmitri A. Rusakov
- Department of Biological Sciences, The Open University, Milton Keynes, United Kingdom
- Institute of Neurology, University College London, London, United Kingdom
| | - Michael G. Stewart
- Department of Biological Sciences, The Open University, Milton Keynes, United Kingdom
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287
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Affiliation(s)
- Raphael Lamprecht
- Center for Neural Science, New York University, 4 Washington Place, New York, New York 10003, USA
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288
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Chih CP, Roberts EL. Energy substrates for neurons during neural activity: a critical review of the astrocyte-neuron lactate shuttle hypothesis. J Cereb Blood Flow Metab 2003; 23:1263-81. [PMID: 14600433 DOI: 10.1097/01.wcb.0000081369.51727.6f] [Citation(s) in RCA: 231] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Glucose had long been thought to fuel oxidative metabolism in active neurons until the recently proposed astrocyte-neuron lactate shuttle hypothesis (ANLSH) challenged this view. According to the ANLSH, activity-induced uptake of glucose takes place predominantly in astrocytes, which metabolize glucose anaerobically. Lactate produced from anaerobic glycolysis in astrocytes is then released from astrocytes and provides the primary metabolic fuel for neurons. The conventional hypothesis asserts that glucose is the primary substrate for both neurons and astrocytes during neural activity and that lactate produced during activity is removed mainly after neural activity. The conventional hypothesis does not assign any particular fraction of glucose metabolism to the aerobic or anaerobic pathways. In this review, the authors discuss the theoretical background and critically review the experimental evidence regarding these two hypotheses. The authors conclude that the experimental evidence for the ANLSH is weak, and that existing evidence and theoretical considerations support the conventional hypothesis.
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Affiliation(s)
- Ching-Ping Chih
- Geriatric Research, Education, and Clinical Center, and Research Office, Miami VA Medical Center, Miami, Florida, USA
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289
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Affiliation(s)
- Luc Pellerin
- Institut de Physiologie, Université de Lausanne, Switzerland.
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290
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Meng Y, Zhang Y, Tregoubov V, Falls DL, Jia Z. Regulation of spine morphology and synaptic function by LIMK and the actin cytoskeleton. Rev Neurosci 2003; 14:233-40. [PMID: 14513866 DOI: 10.1515/revneuro.2003.14.3.233] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Filamentous actin (F-actin) is highly enriched in the dendritic spine, a specialized postsynaptic structure on which the great majority of the excitatory synapses are formed in the mammalian central nervous system (CNS). The protein kinases of the Lim-kinase (LIMK) family are potent regulators of actin dynamics in many cell types and they are abundantly expressed in the CNS, including the hippocampus. Using a combination of genetic manipulations and electrophysiological recordings in mice, we have demonstrated that LIMK-1 signaling is important in vivo in the regulation of the actin cytoskeleton, spine morphology, and synaptic function, including hippocampal long-term potentiation (LTP), a prominent form of long lasting synaptic plasticity thought to be critical to memory formation. Our results provide strong genetic evidence that LIMK and its substrate ADF/cofilin are involved in spine morphology and synaptic properties and are consistent with the notion that the Rho family small GTPases and the actin cytoskeleton are critical to spine structure and synaptic regulation.
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Affiliation(s)
- Yanghong Meng
- Program in Brain and Behavior, The Hospital For Sick Children, Toronto, Ontario, Canada
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291
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Tyler WJ, Pozzo-Miller L. Miniature synaptic transmission and BDNF modulate dendritic spine growth and form in rat CA1 neurones. J Physiol 2003; 553:497-509. [PMID: 14500767 PMCID: PMC2343578 DOI: 10.1113/jphysiol.2003.052639] [Citation(s) in RCA: 212] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The refinement and plasticity of neuronal connections require synaptic activity and neurotrophin signalling; their specific contributions and interplay are, however, poorly understood. We show here that brain-derived neurotrophic factor (BDNF) increased spine density in apical dendrites of CA1 pyramidal neurones in organotypic slice cultures prepared from postnatal rat hippocampal slices. This effect was observed also in the absence of action potentials, and even when miniature synaptic transmission was inhibited with botulinum neurotoxin C (BoNT/C). There were, however, marked differences in the morphology of individual spines induced by BDNF across these different levels of spontaneous ongoing synaptic activity. During both normal synaptic transmission, and when action potentials were blocked with TTX, BDNF increased the proportion of stubby, type-I spines. However, when SNARE-dependent vesicular release was inhibited with BoNT/C, BDNF increased the proportion of thin, type-III spines. Our results indicate that BDNF increases spine density irrespective of the levels of synaptic transmission. In addition, miniature synaptic transmission provides sufficient activity for the functional translation of BDNF-triggered spinogenesis into clearly defined morphological spine types, favouring those spines potentially responsible for coordinated Ca2+ transients thought to mediate synaptic plasticity. We propose that BDNF/TrkB signalling represents a mechanism of expression of both morphological and physiological homeostatic plasticity in the hippocampus, leading to a more efficient synaptic information transfer across widespread levels of synaptic activity.
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Affiliation(s)
- William J Tyler
- Department of Neurobiology and Psychology, Civitan International Research Center, University of Alabama at Birmingham, Birmingham, AL 35294-0021, USA
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292
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Abstract
Mammalian retinal degenerations initiated by gene defects in rods, cones or the retinal pigmented epithelium (RPE) often trigger loss of the sensory retina, effectively leaving the neural retina deafferented. The neural retina responds to this challenge by remodeling, first by subtle changes in neuronal structure and later by large-scale reorganization. Retinal degenerations in the mammalian retina generally progress through three phases. Phase 1 initiates with expression of a primary insult, followed by phase 2 photoreceptor death that ablates the sensory retina via initial photoreceptor stress, phenotype deconstruction, irreversible stress and cell death, including bystander effects or loss of trophic support. The loss of cones heralds phase 3: a protracted period of global remodeling of the remnant neural retina. Remodeling resembles the responses of many CNS assemblies to deafferentation or trauma, and includes neuronal cell death, neuronal and glial migration, elaboration of new neurites and synapses, rewiring of retinal circuits, glial hypertrophy and the evolution of a fibrotic glial seal that isolates the remnant neural retina from the surviving RPE and choroid. In early phase 2, stressed photoreceptors sprout anomalous neurites that often reach the inner plexiform and ganglion cell layers. As death of rods and cones progresses, bipolar and horizontal cells are deafferented and retract most of their dendrites. Horizontal cells develop anomalous axonal processes and dendritic stalks that enter the inner plexiform layer. Dendrite truncation in rod bipolar cells is accompanied by revision of their macromolecular phenotype, including the loss of functioning mGluR6 transduction. After ablation of the sensory retina, Müller cells increase intermediate filament synthesis, forming a dense fibrotic layer in the remnant subretinal space. This layer invests the remnant retina and seals it from access via the choroidal route. Evidence of bipolar cell death begins in phase 1 or 2 in some animal models, but depletion of all neuronal classes is evident in phase 3. As remodeling progresses over months and years, more neurons are lost and patches of the ganglion cell layer can become depleted. Some survivor neurons of all classes elaborate new neurites, many of which form fascicles that travel hundreds of microns through the retina, often beneath the distal glial seal. These and other processes form new synaptic microneuromas in the remnant inner nuclear layer as well as cryptic connections throughout the retina. Remodeling activity peaks at mid-phase 3, where neuronal somas actively migrate on glial surfaces. Some amacrine and bipolar cells move into the former ganglion cell layer while other amacrine cells are everted through the inner nuclear layer to the glial seal. Remodeled retinas engage in anomalous self-signaling via rewired circuits that might not support vision even if they could be driven anew by cellular or bionic agents. We propose that survivor neurons actively seek excitation as sources of homeostatic Ca(2+) fluxes. In late phase 3, neuron loss continues and the retina becomes increasingly glial in composition. Retinal remodeling is not plasticity, but represents the invocation of mechanisms resembling developmental and CNS plasticities. Together, neuronal remodeling and the formation of the glial seal may abrogate many cellular and bionic rescue strategies. However, survivor neurons appear to be stable, healthy, active cells and given the evidence of their reactivity to deafferentation, it may be possible to influence their emergent rewiring and migration habits.
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Affiliation(s)
- Robert E Marc
- John A. Moran Eye Center, Department of Ophthalmology, University of Utah School of Medicine, 50 N Medical Center, Salt Lake City, UT 84132, USA
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293
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Wang H, Cuzon VC, Pickel VM. Postnatal development of mu-opioid receptors in the rat caudate-putamen nucleus parallels asymmetric synapse formation. Neuroscience 2003; 118:695-708. [PMID: 12710977 DOI: 10.1016/s0306-4522(02)00926-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The mu-opioid receptor (MOR) in the caudate-putamen nucleus (CPN) appears early during prenatal development, and shows a patch-like distribution throughout the postnatal period and adulthood. In the adult rat CPN, neurons in patch compartments receive glutamatergic excitatory input mainly from the cortex through synapses onto spines, many of which express MORs. Thus, MOR expression in spines may be related to corticostriatal synaptogenesis. We used electron microscopic immunocytochemistry to determine potential age-dependent changes in the distribution pattern of MOR during postnatal synaptogenesis in the rat CPN. Immunogold-silver labeling revealed that the dendritic plasmalemmal density of MOR at postnatal day (P) 0 was significantly lower than, but after P10 was similar to, that of adult. In contrast, such age-dependent changes were not observed in axon terminals. Stereological analysis of immunoperoxidase labeling for MOR showed a good correlation in the developmental numerical densities of synapses with MOR-labeled spines and those of total asymmetric axospinous synapses, linear correlation coefficient r=0.99. Synapses with MOR-labeled dendrites, however, had a low correlation with axodendritic synapses (r=0.61), and synapses with MOR-labeled terminals showed no correlation with axospinous and axodendritic synapses (r=0.19). These results provide ultrastructural evidence that the targeting of MOR on the plasma membrane of dendrites and spines parallels the peak period of synaptogenesis during the third postnatal week in the rat CPN. Thus, the postnatal spatiotemporal expression pattern of MOR appears to match the functional maturation of corticostriatal glutamate transmission.
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Affiliation(s)
- H Wang
- Division of Neurobiology, Department of Neurology and Neuroscience, Joan and Sanford I. Weill Medical College of Cornell University, 411 East 69th Street, New York, NY 10021, USA.
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294
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De Simoni A, Griesinger CB, Edwards FA. Development of rat CA1 neurones in acute versus organotypic slices: role of experience in synaptic morphology and activity. J Physiol 2003; 550:135-47. [PMID: 12879864 PMCID: PMC2343027 DOI: 10.1113/jphysiol.2003.039099] [Citation(s) in RCA: 221] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2003] [Accepted: 04/15/2003] [Indexed: 11/08/2022] Open
Abstract
Despite their wide use, the physiological relevance of organotypic slices remains controversial. Such cultures are prepared at 5 days postnatal. Although some local circuitry remains intact, they develop subsequently in isolation from the animal and hence without plasticity due to experience. Development of synaptic connectivity and morphology might be expected to proceed differently under these conditions than in a behaving animal. To address these questions, patch-clamp techniques and confocal microscopy were used in the CA1 region of the rat hippocampus to compare acute slices from the third postnatal week with various stages of organotypic slices. Acute slices prepared at postnatal days (P) 14, 17 and 21 were found to be developmentally equivalent to organotypic slices cultured for 1, 2 and 3 weeks, respectively, in terms of development of synaptic transmission and dendritic morphology. The frequency of inhibitory and excitatory miniature synaptic currents increased in parallel. Development of dendritic length and primary branching as well as spine density and proportions of different spine types were also similar in both preparations,at these corresponding stages. The most notable difference between organotypic and acute slices was a four- to five-fold increase in the absolute frequency of glutamatergic (but not GABAergic)miniature postsynaptic currents in organotypic slices. This was probably related to an increase in complexity of higher order dendritic branching in organotypic slices, as measured by fractal analysis, resulting in an increased total synapse number. Both increased excitatory miniature synaptic current frequency and dendritic complexity were already established during the first week in culture. The level of complexity then stayed constant in both preparations over subsequent stages, with synaptic frequency increasing in parallel. Thus, although connectivity was greater in organotypic slices, once this was established, development continued in both preparations at are markably similar rate. We conclude that, for the parameters studied, changes seem to be preprogrammed by 5 days and their subsequent development is largely independent of environment.
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295
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Jones SP, Rahimi O, O'Boyle MP, Diaz DL, Claiborne BJ. Maturation of granule cell dendrites after mossy fiber arrival in hippocampal field CA3. Hippocampus 2003; 13:413-27. [PMID: 12722981 DOI: 10.1002/hipo.10121] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Most granule neurons in the rat dentate gyrus are born over the course of the first 2 postnatal weeks. The resulting heterogeneity has made it difficult to define the relationship between dendritic and axonal maturation and to delineate a time course for the morphological development of the oldest granule neurons. By depositing crystals of the fluorescent label Dil in hippocampal field CA3, we retrogradely labeled granule neurons in fixed tissue slices from rats aged 2-9 days. The results showed that all labeled granule cells, regardless of the age of the animal, exhibited apical dendrites. On day 2, every labeled neuron had rudimentary apical dendrites, and a few dendrites on each cell displayed immature features such as growth cones, varicosities, and filopodia. Some cells displayed basal dendrites. By day 4, the most mature granule neurons had longer and more numerous apical branches, as well as various immature features. Most had basal dendrites. On days 5 and 6, the immature features and the basal dendrites had begun to regress on the oldest cells, and varying numbers of spines were present. On day 7, the first few adult-like neurons were seen: immature features and basal dendrites had disappeared, all dendrites reached the top of the molecular layer, and the entire dendritic tree was covered with spines. These data show that dendritic outgrowth occurs before, or concurrent with, axon arrival in the CA3 target region, and that adult-like granule neurons are present by the end of the first week.
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Affiliation(s)
- Shawn P Jones
- Department of Biology, University of Texas at San Antonio, San Antonio, Texas 78249, USA
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296
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Olivera S, Rodriguez-Ithurralde D, Henley JM. Acetylcholinesterase promotes neurite elongation, synapse formation, and surface expression of AMPA receptors in hippocampal neurones. Mol Cell Neurosci 2003; 23:96-106. [PMID: 12799140 PMCID: PMC3314531 DOI: 10.1016/s1044-7431(03)00021-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Here we show that chronic application of low concentrations (0.01-0.05 U/ml) or a single application of 1-5 U/ml acetylcholinesterase (AChE) promotes the extension of neuronal processes, synapse formation, and alpha-amino-3-hydroxy-5-methylisoxazolepropionate receptor (AMPAR) surface expression in both embryonic and postnatal hippocampal cultures. The total number of AMPARs was unchanged but the proportion of receptors that were surface-expressed, predominantly at synapses, was approximately doubled following AChE treatment. Blockade of the peripheral anionic site of endogenous AChE in the cultures dramatically reduced neurite outgrowth but did not alter the appearance of synaptic markers SV2a and PSD95. These results indicate that AChE is necessary for normal dendrite and axon formation in hippocampal neurones and suggest that it may also play a role in excitatory synapse development, plasticity, and remodelling.
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Affiliation(s)
- Silvia Olivera
- MRC Centre for Synaptic Plasticity, Anatomy Department, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
- Molecular Neuroscience Unit, Instituto de Investigaciones Biológicas Clemente Estable, Av. Italia 3318, 11600 Montevideo, Uruguay
| | - Daniel Rodriguez-Ithurralde
- Molecular Neuroscience Unit, Instituto de Investigaciones Biológicas Clemente Estable, Av. Italia 3318, 11600 Montevideo, Uruguay
| | - Jeremy M. Henley
- MRC Centre for Synaptic Plasticity, Anatomy Department, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
- Corresponding author. Fax: +0117-929-1686 (J.M. Henley)
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297
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Penzes P, Beeser A, Chernoff J, Schiller MR, Eipper BA, Mains RE, Huganir RL. Rapid induction of dendritic spine morphogenesis by trans-synaptic ephrinB-EphB receptor activation of the Rho-GEF kalirin. Neuron 2003; 37:263-74. [PMID: 12546821 DOI: 10.1016/s0896-6273(02)01168-6] [Citation(s) in RCA: 349] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The morphogenesis of dendritic spines, the major sites of excitatory synaptic transmission in the brain, is important in synaptic development and plasticity. We have identified an ephrinB-EphB receptor trans-synaptic signaling pathway which regulates the morphogenesis and maturation of dendritic spines in hippocampal neurons. Activation of the EphB receptor induces translocation of the Rho-GEF kalirin to synapses and activation of Rac1 and its effector PAK. Overexpression of dominant-negative EphB receptor, catalytically inactive kalirin, or dominant-negative Rac1, or inhibition of PAK eliminates ephrin-induced spine development. This novel signal transduction pathway may be critical for the regulation of the actin cytoskeleton controlling spine morphogenesis during development and plasticity.
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Affiliation(s)
- Peter Penzes
- Department of Neuroscience, The Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA
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298
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Grossman AW, Churchill JD, Bates KE, Kleim JA, Greenough WT. A brain adaptation view of plasticity: is synaptic plasticity an overly limited concept? PROGRESS IN BRAIN RESEARCH 2002; 138:91-108. [PMID: 12432765 DOI: 10.1016/s0079-6123(02)38073-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A view that is emerging is that the brain has multiple forms of plasticity that must be governed, at least in part, by independent mechanisms. This view is illustrated by: (1) the apparent separate governance of some non-neural changes by activity, in contrast to synaptic changes driven by learning; (2) the apparent independence of different kinds of synaptic changes that occur in response to the learning aspects of training; (3) the occurrence of separate patterns of synaptic plasticity in the same system in response to different task demands; and (4) apparent dissociations between behaviorally induced synaptogenesis and LTP. The historical focus of research and theory in areas ranging from learning and memory to experiential modulation of brain development has been heavily upon synaptic plasticity since shortly after the discovery of the synapse. Based upon available data, it could be argued that: (1) synaptic, and even neuronal, plasticity is but a small fraction of the range of changes that occur in response to experience; and (2) we are just beginning to understand the importance of these other forms of brain plasticity. Appreciation of this aspect of the brain's adaptive process may allow us to better understand the capacity of the brain to tailor a particular set of changes to the demands of the specific experiences that generated them.
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Affiliation(s)
- Aaron W Grossman
- Beckman Institute, Neuroscience Program, Medical Scholars Program, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
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299
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Abstract
The mechanisms establishing and maintaining dendritic spines in the mammalian CNS remain primarily unknown. We report a novel mechanism of neuronal spine plasticity in the developing preoptic area in which estradiol induces prostaglandin-E2 (PGE2) synthesis that in turn increases the density of spine-like processes. Estradiol requires PGE2 synthesis, in vivo and in vitro, and upregulates the dendritic spine protein spinophilin, an effect attenuated by antagonism of the AMPA-kainate receptor. This signaling pathway may involve cross talk between neighboring neurons and astrocytes and appears specific to the preoptic area in that hippocampal neurons responded with an increase in spinophilin to estradiol but not PGE2. Regionally specific mechanisms of estradiol-mediated synaptic plasticity allow for epigenetic control of complex sex-typic behaviors.
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300
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Blanpied TA, Scott DB, Ehlers MD. Dynamics and regulation of clathrin coats at specialized endocytic zones of dendrites and spines. Neuron 2002; 36:435-49. [PMID: 12408846 DOI: 10.1016/s0896-6273(02)00979-0] [Citation(s) in RCA: 293] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Endocytosis is a fundamental mechanism by which neurons control intercellular signaling, nutrient uptake, and synaptic transmission. This process is carried out by the assembly of clathrin coats and the budding of clathrin-coated vesicles from the neuronal plasma membrane. Here, we demonstrate that in young neurons, clathrin assembly and disassembly occur rapidly, locally, and repeatedly at "hot spots" throughout dendrites and at the tips of dendritic filopodia. In contrast, clathrin coats in mature dendrites reside in stable, long-lasting zones at sites of endocytosis, where clathrin undergoes continuous exchange with local cytosolic pools. In dendritic spines, endocytic zones lie lateral to the postsynaptic density (PSD) where they develop and persist independent of synaptic activity, akin to the PSD itself. These results reveal the presence of a novel specialization dedicated to endocytosis near the postsynaptic membrane.
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Affiliation(s)
- Thomas A Blanpied
- Department of Neurobiology, Duke University Medical Center, Durham, NC 27710, USA
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