Dendritic Spines

Sigma-1 receptors (Sig-1Rs) are endoplasmic reticulum (ER)-resident proteins known to be involved in learning and memory. Dendritic spines in hippocampal neurons play important roles in neuroplasticity and learning and memory. This study tested the hypothesis that Sig-1Rs might regulate denritic spine formation in hippocampal neurons and examined potential mechanisms therein. In rat hippocampal primary neurons, the knockdown of Sig-1Rs by siRNAs causes a deficit in the formation of dendritic spines that is unrelated to ER Ca 2+ signaling or apoptosis, but correlates with the mitochondrial permeability transition and cytochrome c release, followed by caspase-3 activation, Tiam1 cleavage, and a reduction in Rac1·GTP. Sig-1R-knockdown neurons contain higher levels of free radicals when compared to control neurons. The activation of superoxide dismutase or the application of the hydroxyl-free radical scavenger N-acetyl cysteine (NAC) to the Sig-1R-knockdown neurons rescues dendritic spi...

The adult brain is not as hard-wired as traditionally thought. By modifying their small- or large-scale morphology, neurons can make new synaptic connections or break existing ones (structural plasticity). Structural changes accompany memory formation and learning, and are induced by neurogenesis, neurodegeneration and brain injury such as stroke. Exploring the role of structural plasticity in the brain can be greatly assisted by mathematical and computational models, as they enable us to bridge the gap between system-level dynamics and lower level cellular and molecular processes. However, most traditional neural network models have fixed neuronal morphologies and a static connectivity pattern, with plasticity merely arising from changes in the strength of existing synapses (synaptic plasticity). In The Rewiring Brain, the editors bring together, for the first time, contemporary modeling studies that investigate the implications of structural plasticity for brain function and pathology. Starting with an experimental background on structural plasticity in the adult brain, the book covers computational studies on homeostatic structural plasticity, the impact of structural plasticity on cognition and cortical connectivity, the interaction between synaptic and structural plasticity, neurogenesis-related structural plasticity, and structural plasticity in neurological disorders. Structural plasticity adds a whole new dimension to brain plasticity, and The Rewiring Brain shows how computational approaches may help to gain a better understanding of the full adaptive potential of the adult brain. The book is written for both computational and experimental neuroscientists. Key features: • Reviews the current state of knowledge of structural plasticity in the adult brain. • Gives a comprehensive overview of computational studies on structural plasticity. • Provides insights into the potential driving forces of structural plasticity and the functional implications of structural plasticity for learning and memory. • Serves as inspiration for developing novel treatment strategies for stimulating functional repair after brain damage. For a preview and to order the book, go to: https://www.elsevier.com/books/the-rewiring-brain/van-ooyen/978-0-12-803784-3

Emerging researches point to a relevant role of postsynaptic density (PSD) proteins, such as PSD-95, Homer, Shank, and DISC-1, in the pathophysiology of schizophrenia and autism spectrum disorders. The PSD is a thickness, detectable at electronic microscopy, localized at the postsynaptic membrane of glutamatergic synapses, and made by scaffolding proteins, receptors, and effector proteins; it is considered a structural and functional crossroad where multiple neurotransmitter systems converge, including the dopaminergic, serotonergic, and glutamatergic ones, which are all implicated in the pathophysiology of psychosis. Decreased PSD-95 protein levels have been reported in postmortem brains of schizophrenia patients. Variants of Homer1, a key PSD protein for glutamate signaling, have been associated with schizophrenia symptoms severity and therapeutic response. Mutations in Shank gene have been recognized in autism spectrum disorder patients, as well as reported to be associated to behaviors reminiscent of schizophrenia symptoms when expressed in genetically engineered mice. Here, we provide a critical appraisal of PSD proteins role in the pathophysiology of schizophrenia and autism spectrum disorders. Then, we discuss how antipsychotics may affect PSD proteins in brain regions relevant to psychosis pathophysiology, possibly by controlling synaptic plasticity and dendritic spine rearrangements through the modulation of glutamate-related targets. We finally provide a framework that may explain how PSD proteins might be useful candidates to develop new therapeutic approaches for schizophrenia and related disorders in which there is a need for new biological treatments, especially against some symptom domains, such as negative symptoms, that are poorly affected by current antipsychotics.

The ability of neurons to modulate synaptic strength underpins synaptic plasticity, learning and memory, and adaptation to sensory experience. Despite the importance of synaptic adaptation in directing, reinforcing, and revising the behavioral response to environmental influences, the cellular and molecular mechanisms underlying synaptic adaptation are far from clear. Brain-derived neurotrophic factor (BDNF) is a prime initiator of structural and functional synaptic adaptation. However, the signaling cascade activated by BDNF to initiate these adaptive changes has not been elucidated. We have previously shown that BDNF activates mitogen-and stress-activated kinase 1 (MSK1), which regulates gene transcription via the phosphorylation of both CREB and histone H3. Using mice with a kinase-dead knock-in mutation of MSK1, we now show that MSK1 is necessary for the upregulation of synaptic strength in response to environmental enrichment in vivo. Furthermore, neurons from MSK1 kinase-dead mice failed to show scaling of synaptic transmission in response to activity deprivation in vitro, a deficit that could be rescued by reintroduction of wild-type MSK1. We also show that MSK1 forms part of a BDNF-and MAPK-dependent signaling cascade required for homeostatic synaptic scaling, which likely resides in the ability of MSK1 to regulate cell surface GluA1 expression via the induction of Arc/Arg3.1. These results demonstrate that MSK1 is an integral part of a signaling pathway that underlies the adaptive response to synaptic and environmental experience. MSK1 may thus act as a key homeostat in the activity-and experience-dependent regulation of synaptic strength.

Long-lasting memories are formed when the stimulus is temporally distributed (spacing effect). However, the synaptic mechanisms underlying this robust phenomenon and the precise time course of the synaptic modifications that occur during learning remain unclear. Here we examined the adaptation of horizontal optokinetic response in mice that underwent 1 h of massed and spaced training at varying intervals. Despite similar acquisition by all training protocols, 1 h of spacing produced the highest memory retention at 24 h, which lasted for 1 mo. The distinct kinetics of memory are strongly correlated with the reduction of floccular parallel fiber-Purkinje cell synapses but not with AMPA receptor (AMPAR) number and synapse size. After the spaced training, we observed 25%, 23%, and 12% reduction in AMPAR density, synapse size, and synapse number, respectively. Four hours after the spaced training, half of the synapses and Purkinje cell spines had been eliminated, whereas AMPAR density and synapse size were recovered in remaining synapses. Surprisingly, massed training also produced long-term memory and halving of synapses; however, this occurred slowly over days, and the memory lasted for only 1 wk. This distinct kinetics of structural plasticity may serve as a basis for unique temporal profiles in the formation and decay of memory with or without intervals. cerebellar motor learning | AMPA receptor reduction | synapse shrinkage and elimination D uring learning, memories are formed in a specific population of neuronal circuits and are consolidated for persistence (1, 2). These memory processes are supported by discrete subcellular events such as reversible modifications in the efficacy of synaptic transmission (3-5) or persistent structural modifications in the size and number of synaptic connections (6-8). However, how these synaptic modifications relate to the dynamics of formation and decay of memories in behaving animals remains elusive. Memory formation and its persistence are also sensitive to the temporal features of stimulus presentation, as observed in the well-known "spacing effect." Training trials that include resting intervals between them (spaced training) produce stronger and longer-lasting memories than do the same number of trials with no intervals (massed training) (9). The spacing effect has been observed in a variety of explicit and implicit memory tasks (10-13), and the molecular mechanisms supporting this phenomenon have been reported (14-18). Various intracellular signaling molecules such as CREB , mitogen-activated protein (MAP) kinase (20, 21), and PKA (22, 23) underlie the spacing effect and are implicated in the remodeling of neuronal structures (23). In vitro studies showed that spaced stimuli induced the protrusion of new filopodia (20) and the recruitment of new synapses (24) in hippocampal neurons. However, despite the existence of numerous behavioral and molecular studies, no conjoint study has elucidated the synaptic correlates that underpin the expression of the spacing effect during learning. Here we studied the temporal evolution and decay of memory and its correlation with synaptic modifications during learning with distinct temporal patterns of training.

Friedrich Miescher Institute Maulbeerstrasse 66 functional features of the postsynaptic component, es-CH-4058 Basel pecially of dendritic spines, play an important role in Switzerland determining the influence of specific afferents impinging 2 UPR2356 on the same dendritic arbor. Presently, this form of orga-CNRS nization is well established for brain areas with a laminar F-67084 Strasbourg structure, like the hippocampus, the neocortex, and the France cerebellum (Chicurel and Harris, 1992; Harris and Kater, 3 Biozentrum 1994; Yuste and Bonhoeffer, 2004), but it is unclear University of Basel whether the same basic principle operates in nuclear Klingelbergstrasse 70 structures such as the amygdala. It is thus a crucial CH-4056 Basel question of whether, and if so how, structural parti-Switzerland tioning of afferents to postsynaptic sites on dendrites occurs or, if this is not the case, then what principles of afferent specificity apply in these cases. Summary Projection neurons in the lateral nucleus of the amygdala (LA) exhibit dendritic arbors largely lacking spatial Functional compartmentalization of dendrites is thought polarization (Paré et al., 1995; Faber et al., 2001) and to underlie afferent-specific integration of neural acreceive converging excitatory inputs from the thalamus tivity in laminar brain structures. Here we show that and from the cortex (Carlsen and Heimer, 1988; Farb in the lateral nucleus of the amygdala (LA), an area and LeDoux, 1997, 1999; Smith et al., 2000). Activitylacking apparent laminar organization, thalamic and dependent Hebbian plasticity at cortical and/or thalamic cortical afferents converge on the same dendrites, afferents to LA projection neurons is generally thought contacting neighboring but morphologically and functo underlie, at least in part, classical Pavlovian fear contionally distinct spine types. Large spines contacted ditioning (LeDoux, 2000; Maren, 2001; Tsvetkov et al., by thalamic afferents exhibited larger Ca 2؉ transients 2002). In other brain areas, Hebbian long-term potentiaduring action potential backpropagation than did small tion (LTP) or long-term depression (LTD) can be induced spines contacted by cortical afferents. Accordingly, depending on the relative timing of presynaptic input induction of Hebbian plasticity, dependent on postsynand postsynaptic backpropagating action potentials aptic spikes, was restricted to thalamic afferents. This (BPAPs) (Markram et al., 1997; Magee and Johnston, synapse-specific effect involved activation of R-type 1997; Debanne et al., 1998; Bi and Poo, 1998, 2001). voltage-dependent Ca 2؉ channels preferentially lo-This so-called spike timing-dependent plasticity (STDP) cated at thalamic inputs. These results indicate that requires postsynaptic Ca 2ϩ elevation (Mainen, 1999; afferent-specific mechanisms of postsynaptic, asso-Sjö strö m and Nelson, 2002). Several sources of Ca 2ϩ , ciative Hebbian plasticity in LA projection neurons desuch as N-methyl-D-aspartate (NMDA) receptors and pend on local, spine-specific morphological and movoltage-dependent Ca 2ϩ channels (VDCCs), have been lecular properties, rather than global differences implicated in the induction of STDP (Magee, 1999; between dendritic compartments. Mainen, 1999; Sabatini and Svoboda, 2000; Yasuda et al., 2003). BPAPs are particularly effective in activating Introduction VDCCs in the dendritic arbor of hippocampal and cortical pyramidal cells (Sabatini and Svoboda, 2000; Magee, Neuronal network function relies on precise and input-1999). specific changes in synaptic strength. Induction of asso-To investigate afferent specific plasticity at identified ciative, Hebbian synaptic plasticity at excitatory synthalamic and cortical synapses on dendrites of LA proapses onto principal (projection) neurons is classically jection neurons, we have used a combination of twomediated by postsynaptic Ca 2ϩ -dependent mechanisms photon confocal imaging and whole-cell recording tech-(Bliss and Collingridge, 1994; Bi and Poo, 2001). Input niques. We find that the morphologies of spines located specificity of postsynaptic Ca 2ϩ signaling, and hence on the same dendritic branches are specifically matched Hebbian plasticity, is thought to require compartmentalto different presynaptic inputs. This morphological diization of local synaptic Ca 2ϩ transients in dendritic versity is correlated with distinct spine Ca 2ϩ dynamics spines (Harris and Kater, 1994; Yuste et al., 2000; Nimand different mechanisms of Hebbian plasticity: BPAPs chinsky et al., 2002).

The extracellular protein Reelin regulates radial neuronal migration in the embryonic brain, promotes dendrite outgrowth in the developing postnatal forebrain, and strengthens synaptic transmission in the adult brain. Heterozygous reeler mice expressing reduced levels of Reelin are grossly normal but exhibit behavioral and physiological abnormalities. We previously demonstrated that dendritic spine density is reduced in the developing hippocampus of these mice. In this study, we investigated the consequence of Reelin deficiency on synapse formation in adult heterozygous reeler mice using imaging and biochemical approaches. Using a reeler colony that expresses yellow fluorescent protein in selected neurons, we analyzed spine density in hippocampal area CA1 by confocal microscopy and found modest abnormalities in heterozygous reeler mice. However, biochemical analysis of synaptic composition revealed specific postsynaptic defects in scaffolding proteins, neurotransmitter receptors, and signaling proteins. Using whole brain homogenates and purified pre-and postsynaptic fractions, we found that the defects were localized to the postsynaptic compartment of heterozygous reeler synapses. Decreased levels of postsynaptic density-95 (PSD-95), the N-methyl D-aspartate (NMDA) receptor subunits NR2A and NR2B, and the phosphatase PTEN were found specifically in the postsynaptic density fraction obtained from these mice. Furthermore, we found that PSD-95, NR2A, and PTEN interact with each other at the synapse. Finally, we show that levels of NR2A are reduced in conditional Pten knock out mice, demonstrating that the PTEN phosphatase regulates NMDA receptor expression at the synapse in vivo. These studies may provide insights into the etiology of cognitive disorders associated with deficien-cies in Reelin signaling and PTEN dysfunction.

α2 adrenoceptors have been shown to regulate the development of dendrites in mammalian cortical neurones. In this study we have investigated how agonists of α2 adrenoceptors affect length and density of dendritic spines in cultured cortical neurones from C57/B6 mice. A twenty-four hour incubation of 14 day old cultured neurones with UK 14304, an α2-adrenoceptor agonist, resulted in a significant increase in the average length and density of dendritic spines. Furthermore, incubation of neurones with the selective α2A agonist guanfacine resulted in 1.2-fold increase in spine length and 1.8-fold increase in spine density. These effects were blocked by RX 821002 and BRL 44408, α2- and α2A-adrenoceptor antagonists, respectively. The observed changes in the density and length of dendritic spines were correlated with increased expression of spinophilin, a key cytoskeletal protein in the formation and maintenance of dendritic spines, and a decrease in the phosphorylation of spinophilin on serine residues. The latter finding points to a possible mechanism by which adrenoceptors may regulate spinophilin function in dendritic spine development and structure in cortical neurones in vitro.

The stabilization of new spines in the barrel cortex is enhanced after whisker trimming, but its relationship to experience-dependent plasticity is unclear. Here we show that in wild type mice whisker potentiation and spine stabilization is most pronounced for layer 5 neurons at the border between spared and deprived barrel columns. In homozygote αCaMKII-T286A mice, which lack experience-dependent potentiation of responses to spared whiskers, there is no increase in new spine stabilization at the border between barrel columns after whisker trimming. Our data provide a causal link between new spine synapses and plasticity of adult cortical circuits and suggest that αCaMKII autophosphorylation plays a role in the stabilization but not formation of new spines.

Female reproductive behaviour in quadruped animals includes a mating posture called lordosis. A brain region criticial for female reproductive behaviour is the hypothalamic ventromedial nucleus (VMH), which has transynaptic connections to lordosis-producing muscles (1). For example, the primate VMH displays increased spike rates during the lordosis response, a direct measure of increased neurotransmission (2). The rodent VMH also displays increased rates of firing in response to the vaginocervical stimulation that would normally accompany mating (3). In addition, the reptile ventromedial hypothalamus increases its uptake of 2-deoxyglucose during female sexual behaviour, suggesting increased neuronal metabolic activity (4). Finally, the rodent ventrolateral VMH (vlVMH) manufac-tures immediate-early gene (IEG) products, such as Fos, after mating activity (5-7), which reflects increased second messenger production and genomic activation (8). Thus, VMH activity during mating can be detected at the electrophysiological, biochemical and molecular levels, and occurs in a wide range of vertebrates.

Recent studies show that dendritic spines are dynamic structures. Their rapid creation, destruction and shapechanging are essential for short-and long-term plasticity at excitatory synapses on pyramidal neurons in the cerebral cortex. The onset of long-term potentiation, spine-volume growth and an increase in receptor trafficking are coincident, enabling a 'functional readout' of spine structure that links the age, size, strength and lifetime of a synapse. Spine dynamics are also implicated in long-term memory and cognition: intrinsic fluctuations in volume can explain synapse maintenance over long periods, and rapid, activity-triggered plasticity can relate directly to cognitive processes. Thus, spine dynamics are cellular phenomena with important implications for cognition and memory. Furthermore, impaired spine dynamics can cause psychiatric and neurodevelopmental disorders.

A major effort in neuroscience is directed towards understanding the roles of Ca2+ signalling in the induction of synaptic plasticity. Here, we summarize the evidence concerning Ca2+ signalling, paying particular attention to CA1 excitatory synapses, and its relationship to the induction of long-term potentiation and long-term depression. We discuss the ways in which synaptic activation can elevate Ca2+ postsynaptically and how dendritic spines may act as a Ca2+ compartment which can both isolate and integrate Ca2+ signals.

An enriched environment consists of a combination of enhanced social relations, physical exercise and interactions with non-social stimuli that leads to behavioral and neuronal modifications. In the present study, we analyzed the behavioral effects of environmental complexity on different facets of spatial function, and we assessed dendritic arborisation and spine density in a cortical area mainly involved in the spatial learning, as the parietal cortex. Wistar rat pups (21 days old) were housed in enriched conditions (10 animals in a large cage with toys and a running wheel), or standard condition (two animals in a standard cage, without objects). At the age of 3 months, both groups were tested in the radial maze task and Morris water maze (MWM). Morphological analyses on layer-III pyramidal neurons of parietal cortex were performed in selected animals belonging to both experimental groups. In the radial maze task, enriched animals exhibited high performance levels, by exploiting procedural competencies and working memory abilities. Furthermore, when the requirements of the context changed, they promptly reorganized their strategies by shifting from prevalently using spatial procedures to applying mnesic competencies. In the Morris water maze, enriched animals more quickly acquired tuned navigational strategies. Environmental enrichment provoked increased dendritic arborisation as well as increased density of dendritic spines in layer-III parietal pyramidal neurons.

Modulation of local protein synthesis in neuronal dendrites plays a key role in the production of long-term, activity-dependent changes in synapse structure and functional efficacy. Such long-term changes also require regulation of actin dynamics in dendritic spines. Recent evidence couples local protein synthesis to regulation of actin dynamics in long-term synaptic plasticity. Translation of the dendritically localized mRNA, Arc, is required for consolidation of LTP and stabilization of nascent polymerized actin. BDNF signaling activates Arc-dependent LTP consolidation and is required for actin polymerization and stable expansion of dendritic spines during LTP. Regulation of actin pools within dendritic spines modulates spine size and enlargement, organization of the postsynaptic density, receptor trafficking, and localization of the translational machinery.

NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) and depression (LTD) are forms of synaptic plasticity underlying learning and memory that are expressed through increases and decreases, respectively, in dendritic spine size and AMPA receptor (AMPAR) phosphorylation and postsynaptic localization. The A-kinase anchoring protein (AKAP) 79/150 signaling scaffold regulates AMPAR phosphorylation, channel activity, and endosomal trafficking associated with LTP and LTD. AKAP79/150 is targeted to dendritic spine plasma membranes by an N-terminal polybasic domain that binds phosphoinositide lipids, F-actin, and cadherin cell adhesion molecules. However, we do not understand how regulation of AKAP targeting controls AMPAR endosomal trafficking. Here we report that palmitoylation of the AKAP N-terminal polybasic domain targets it to postsynaptic lipid rafts and dendritic recycling endosomes. AKAP palmitoylation was regulated by seizure activity in vivo and LTP/LTD plasticity-inducing stimuli in cultured rat hippocampal neurons. With chemical LTP induction, we observed AKAP79 dendritic spine recruitment that required palmityolation and Rab11-regulated endosome recycling coincident with spine enlargement and AMPAR surface delivery. Importantly, a palmitoylationdeficient AKAP79 mutant impaired regulation of spine size, endosome recycling, AMPAR trafficking, and synaptic potentiation. These findings emphasize the emerging importance of palmitoylation in controlling synaptic function and reveal novel roles for the AKAP79/150 signaling complex in dendritic endosomes.

Dendritic spines are the primary site of excitatory input on most principal neurons. Long-lasting changes in synaptic activity are accompanied by alterations in spine shape, size and number. The responsiveness of thin spines to increases and decreases in synaptic activity has led to the suggestion that they are 'learning spines', whereas the stability of mushroom spines suggests that they are 'memory spines'. Synaptic enhancement leads to an enlargement of thin spines into mushroom spines and the mobilization of subcellular resources to potentiated synapses. Thin spines also concentrate biochemical signals such as Ca 2+ , providing the synaptic specificity required for learning. Determining the mechanisms that regulate spine morphology is essential for understanding the cellular changes that underlie learning and memory.

Dendritic spines are small mushroom-like protrusions arising from neurons where most excitatory synapses reside. Their peculiar shape suggests that spines can serve as an autonomous postsynaptic compartment that isolates chemical and electrical signaling. How neuronal activity modifies the morphology of the spine and how these modifications affect synaptic transmission and plasticity are intriguing issues. Indeed, the induction of long-term potentiation (LTP) or depression (LTD) is associated with the enlargement or shrinkage of the spine, respectively. This structural plasticity is mainly controlled by actin filaments, the principal cytoskeletal component of the spine. Here we review the pioneering microscopic studies examining the structural plasticity of spines and propose how changes in actin treadmilling might regulate spine morphology.

The NMDA-type glutamate receptor (NMDAR) is essential for synaptogenesis, synaptic plasticity, and higher cognitive function. Emerging evidence indicates that NMDAR Ca 2ϩ permeability is under the control of cAMP/protein kinase A (PKA) signaling. Whereas the functional impact of PKA on NMDAR-dependent Ca 2ϩ signaling is well established, the molecular target remains unknown. Here we identify serine residue 1166 (Ser1166) in the carboxy-terminal tail of the NMDAR subunit GluN2B to be a direct molecular and functional target of PKA phosphorylation critical to NMDAR-dependent Ca 2ϩ permeation and Ca 2ϩ signaling in spines. Activation of ␤-adrenergic and D 1 /D 5 -dopamine receptors induces Ser1166 phosphorylation. Loss of this single phosphorylation site abolishes PKA-dependent potentiation of NMDAR Ca 2ϩ permeation, synaptic currents, and Ca 2ϩ rises in dendritic spines. We further show that adverse experience in the form of forced swim, but not exposure to fox urine, elicits striking phosphorylation of Ser1166 in vivo, indicating differential impact of different forms of stress. Our data identify a novel molecular and functional target of PKA essential to NMDAR-mediated Ca 2ϩ signaling at synapses and regulated by the emotional response to stress.

Neonatal maternal separation (MS) in rats has widely been used as a neurodevelopmental model to mimic mood-related disorders. MS produces a wide array of behavioral deficits that persist throughout adulthood. In this study we investigate the effect of MS and substitute maternal handling (human handling) on the dendritic morphology of neurons in the prefrontal cortex (PFC), the CA1 ventral hippocampus, and the nucleus accumbens (NAcc), brain regions in male rats that have been associated with affective disorders at pre-pubertal (postnatal day 35 (PND35)) and post-pubertal (PND60) ages. The morphological characteristics of dendrites were studied by using the Golgi-Cox staining method. MS induced decreases in total dendritic length and dendritic spine density in the neurons of the PFC, the CA1 ventral hippocampus, and the NAcc at a post-pubertal age. Conversely, human handling produced an increase in dendritic spine density in the pyramidal neurons of the PFC and the hippocampus at a prepubertal age, and a decrease in the dendritic length of the NAcc neurons at a post-pubertal age. These results suggest that the maternal care condition affects the dendritic morphology of neurons in the PFC, the CA1 ventral hippocampus, and the NAcc at different ages. These anatomical modifications may be relevant to altered behaviors observed in maternally separated animals. ß

The majority of excitatory synapses in the mammalian brain form on filopodia and spines, actin-rich membrane protrusions present on neuronal dendrites. The biochemical events that induce filopodia and remodel these structures into dendritic spines remain poorly understood. Here, we show that the neuronal actin-and protein phosphatase-1-binding protein,

The postsynaptic density (PSD) is a postsynaptic membrane specialization at excitatory synapses. The PSD is made of macromolecular multiprotein complexes, which contain a variety of synaptic proteins including membrane, scaffolding, and signaling proteins. By coaggregating with postsynaptic cell adhesion molecules, PSD proteins promote the formation and maturation of excitatory synapses. PSD proteins organize signaling pathways to coordinate structural and functional changes in synapses, and they regulate trafficking and recycling of glutamate receptors, which determines synaptic strength and plasticity. Synaptic activity dynamically regulates the assembly of the PSD through mechanisms including protein phosphorylation, palmitoylation, and protein degradation. PSD proteins associate with diverse motor proteins, suggesting that they function as adaptors linking motors to their specific cargoes.

Numerous reports indicate that learning and memory of conditioned responses are accompanied by genesis of dendritic spines in the hippocampus, although there is a conspicuous lack of information regarding spine modifications after behavioral extinction. There is ample evidence that treatments that typically produce amnesia become innocuous when animals are submitted to a procedure of enhanced training. We now report that extinction of inhibitory avoidance (IA), trained with relatively low foot-shock intensities, induces pruning of dendritic spines along the length of the apical dendrites of hippocampal CA1 neurons. When animals are trained with a relatively high foot-shock there is a high resistance to extinction, and pruning in the proximal and medial segments of the apical dendrite are seen, while spine count in the distal dendrite remains normal. These results indicate that pruning is involved in behavioral extinction, while maintenance of spines is a probable mechanism that medi...

Stress affects the hippocampus, a brain region crucial for memory. In rodents, acute stress may reduce density of dendritic spines, the location of postsynaptic elements of excitatory synapses, and impair long-term potentiation and memory. Steroid stress hormones and neurotransmitters have been implicated in the underlying mechanisms, but the role of corticotropin-releasing hormone (CRH), a hypothalamic hormone also released during stress within hippocampus, has not been elucidated. In addition, the causal relationship of spine loss and memory defects after acute stress is unclear. We used transgenic mice that expressed YFP in hippocampal neurons and found that a 5-h stress resulted in profound loss of learning and memory. This deficit was associated with selective disruption of long-term potentiation and of dendritic spine integrity in commissural/associational pathways of hippocampal area CA3. The degree of memory deficit in individual mice correlated significantly with the reduced density of area CA3 apical dendritic spines in the same mice. Moreover, administration of the CRH receptor type 1 (CRFR 1 )blocker NBI 30775 directly into the brain prevented the stress-induced spine loss and restored the stress-impaired cognitive functions. We conclude that acute, hours-long stress impairs learning and memory via mechanisms that disrupt the integrity of hippocampal dendritic spines. In addition, establishing the contribution of hippocampal CRH-CRFR 1 signaling to these processes highlights the complexity of the orchestrated mechanisms by which stress impacts hippocampal structure and function.

AMPA receptors (AMPARs) are tetrameric ion channels assembled from GluA1-GluA4 subunits that mediate the majority of fast excitatory synaptic transmission in the brain. In the hippocampus, most synaptic AMPARs are composed of GluA1/2 or GluA2/3 with the GluA2 subunit preventing Ca 2+ influx. However, a small number of Ca 2+ -permeable GluA1 homomeric receptors reside in extrasynaptic locations where they can be rapidly recruited to synapses during synaptic plasticity. Phosphorylation of GluA1 S845 by the cAMP-dependent protein kinase (PKA) primes extrasynaptic receptors for synaptic insertion in response to NMDA receptor (NMDAR) Ca 2+ signaling during long-term potentiation (LTP), while phosphatases dephosphorylate S845 and remove synaptic and extrasynaptic GluA1 during long-term depression (LTD). PKA and the Ca 2+activated phosphatase calcineurin (CaN) are targeted to GluA1 through binding to A-kinase anchoring protein (AKAP) 150 in a complex with PSD-95, but we do not understand how the opposing activities of these enzymes are balanced to control plasticity. Here, we generated AKAP150ΔPIX knock-in mice to selectively disrupt CaN anchoring in vivo. We found that AKAP150ΔPIX mice lack LTD but express enhanced LTP at CA1 synapses. Accordingly, basal GluA1 S845 phosphorylation is elevated in AKAP150ΔPIX hippocampus, and LTD-induced dephosphorylation and removal of GluA1, AKAP150, and PSD-95 from synapses is impaired. In addition, basal synaptic activity of GluA2-lacking AMPARs is increased in AKAP150ΔPIX mice and pharmacologic antagonism of these receptors restores normal LTD and inhibits the enhanced LTP. Thus, AKAP150-anchored CaN opposes PKA phosphorylation of GluA1 to restrict synaptic incorporation of Ca 2+ -permeable AMPARs both basally and during LTP and LTD.

Background: Synaptic defects represent a major mechanism underlying altered brain functions of patients suffering Alzheimer's disease (AD) . An increasing body of work indicates that the oligomeric forms of β-amyloid (Aβ) molecules exert profound inhibition on synaptic functions and can cause a significant loss of neurotransmitter receptors from the postsynaptic surface, but the underlying mechanisms remain poorly understood. In this study, we investigated a potential contribution of mitochondria to Aβ inhibition of AMPA receptor (AMPAR) trafficking. Results: We found that a brief exposure of hippocampal neurons to Aβ oligomers not only led to marked removal of AMPARs from postsynaptic surface but also impaired rapid AMPAR insertion during chemically-induced synaptic potentiation. We also found that Aβ oligomers exerted acute impairment of fast mitochondrial transport, as well as mitochondrial translocation into dendritic spines in response to repetitive membrane depolarization. Quantitative analyses at the single spine level showed a positive correlation between spine-mitochondria association and the surface accumulation of AMPARs. In particular, we found that spines associated with mitochondria tended to be more resistant to Aβ inhibition on AMPAR trafficking. Finally, we showed that inhibition of GSK3β alleviated Aβ impairment of mitochondrial transport, and effectively abolished Aβ-induced AMPAR loss and inhibition of AMPAR insertion at spines during cLTP.

Neonatal basolateral amygdala (nBLA) lesions in rats have been widely used as a neurodevelopmental model that mimics schizophrenia-like behaviors. Recently, we reported that nBLA lesions result in significant decreases in the dendritic spine number of layer 3 prefrontal cortex (PFC) pyramidal cells and medium spiny neurons of the nucleus accumbens (NAcc), which all changes after puberty. At present, we aimed to evaluate the effect of this lesion in pyramidal neurons of CA1 of the ventral hippocampus (VH) and layer 5 of the PFC. In order to assess the effects of nBLA lesions on the dendritic morphology of the PFC and VH neurons, we carried out nBLA lesions in rats on postnatal day (PD) 7, and then we studied the dendritic morphology of these two limbic subregions at prepubertal (PD35) and postpubertal (PD60) ages. Dendritic characteristics were measured by Golgi-Cox procedure followed by Sholl analysis. We also evaluated the effects of nBLA lesions on the prepulse inhibition (PPI) and acoustic startle responses. The nBLA lesion induced a significant increase in dendritic length of layer 5 pyramidal neurons of the PFC at both ages, with a decrease in the dendritic spines density after puberty. The spine density of CA1 VH pyramidal neurons showed significant decreases at both ages. PPI was decreased in adulthood in the animals with an nBLA lesion. These results show that an nBLA lesion alters the dendritic morphology at the level of the PFC and VH in distinct ways before puberty, suggesting a disconnection between these limbic structures at an early age, and increasing our understanding of the implications of the VH in early amygdala dysfunction in schizophrenia. Synapse 66:373-382, 2012. V V C 2011 Wiley Periodicals, Inc. R.A.V.-R. and O.S. contributed equally to this work. in Wiley Online Library (wileyonlinelibrary. com).

Dendritic spines of pyramidal cells are the main postsynaptic targets of cortical excitatory synapses and as such, they are fundamental both in neuronal plasticity and for the integration of excitatory inputs to pyramidal neurons. There is significant variation in the number and density of dendritic spines among pyramidal cells located in different cortical areas and species, especially in primates. This variation is believed to contribute to functional differences reported among cortical areas. In this study, we analyzed the density of dendritic spines in the motor, somatosensory and visuo-temporal regions of the mouse cerebral cortex. Over 17,000 individual spines on the basal dendrites of layer III pyramidal neurons were drawn and their morphologies compared among these cortical regions. In contrast to previous observations in primates, there was no significant difference in the density of spines along the dendrites of neurons in the mouse. However, systematic differences in spine dimensions (spine head size and spine neck length) were detected, whereby the largest spines were found in the motor region, followed by those in the somatosensory region and those in visuo-temporal region.

Glutamatergic axons in the mammalian forebrain terminate predominantly onto dendritic spines. Long-term changes in the efficacy of these excitatory synapses are tightly coupled to changes in spine morphology. The reorganization of the actin cytoskeleton underlying this spine "morphing" involves numerous proteins that provide the machinery needed for adaptive cytoskeletal remodeling. Here, we review recent literature addressing the chemical architecture of the spine, focusing mainly on actin-binding proteins (ABPs). Accumulating evidence suggests that ABPs are organized into functionally distinct microdomains within the spine cytoplasm. This functional compartmentalization provides a structural basis for regulation of the spinoskeleton, offering a novel window into mechanisms underlying synaptic plasticity.

The experience of peer play during the juvenile phase in rats is known to be important for the development of adult social competence. Adult social competence is also compromised by damage to the orbitofrontal cortex (OFC), an area known to be involved in social behavior. We therefore hypothesized that the functioning of the OFC in social behavior is facilitated through the experience of peer play during the juvenile period. Further, because the OFC and medial prefrontal cortex (mPFC) are known to be reciprocally responsive to a variety of manipulations, we suspected that the functioning of the mPFC is also responsive to the experience of peer play during development. Female Long-Evans rats were raised in conditions that varied with respect to the experience of peer play, and Golgi techniques were used to examine the neuronal morphology of the OFC and mPFC. The results indicated that the neurons of the OFC responded to the number of peers present, not whether those peers engaged in play or not, whereas the neurons of the mPFC responded specifically to the experience of play.

Protein localization in dendritic spines is the focus of intense investigations within neuroscience. Applications of super-resolution microscopy to dissect nanoscale protein distributions, as shown in this work with dual-color STED, generate spatial correlation coefficients having quite small values. This means that colocalization analysis to some extent looses part of its correlative impact. In this study we thus introduced nearest neighbor analysis to quantify the spatial relations between two important proteins in neurons, the dopamine D1 receptor and Na 1 ,K 1 -ATPase. The analysis gave new information on how dense the D1 receptor and Na 1 ,K 1 -ATPase constituting nanoclusters are located both with respect to the homogenous (self to same) and the heterogeneous (same to other) topology. The STED dissected nanoscale topologies provide evidence for both a joint as well as a separated confinement of the D1 receptor and the Na 1 ,K 1 -ATPase in the postsynaptic areas of dendritic spines. This confined topology may have implications for generation of local sodium gradients and for structural and functional interactions modulating slow synaptic transmission processes. Microsc. Res. Tech. 00:000-000,

Psychiatric and neurodevelopmental disorders may arise from anomalies in long-range neuronal connectivity downstream of pathologies in dendritic spines. However, the mechanisms that may link spine pathology to circuit abnormalities relevant to atypical behavior remain unknown. Using a mouse model to conditionally disrupt a critical regulator of the dendritic spine cytoskeleton, the actin-related protein 2/3 complex (Arp2/3), we report here a molecular mechanism that unexpectedly reveals the inter-relationship of progressive spine pruning, elevated frontal cortical excitation of pyramidal neurons and striatal hyperdopaminergia in a cortical-to-midbrain circuit abnormality. The main symptomatic manifestations of this circuit abnormality are psychomotor agitation and stereotypical behaviors, which are relieved by antipsychotics. Moreover, this antipsychotic-responsive locomotion can be mimicked in wild-type mice by optogenetic activation of this circuit. Collectively these results reve...

The presubiculum (PrS) plays critical roles in spatial information processing and memory consolidation and has also been implicated in temporal lobe epileptogenesis. Despite its involvement in these processes, a basic structure-function analysis of PrS cells remains far from complete. To this end, we performed whole-cell recording and biocytin labeling of PrS neurons in layer (L)II and LIII to examine their electrophysiological and morphological properties. We characterized the cell types based on electrophysiological criteria, correlated their gross morphology, and classified them into distinct categories using unsupervised hierarchical cluster analysis. We identified seven distinct cell types: regularspiking (RS), irregular-spiking (IR), initially bursting (IB), stuttering (Stu), single-spiking (SS), fast-adapting (FA), and late-spiking (LS) cells, of which RS and IB cells were common to LII and LIII, LS cells were specific to LIII, and the remaining types were identified exclusively in LII. Recorded neurons were either pyramidal or nonpyramidal and, except for Stu cells, displayed spine-rich dendrites. The RS, IB, and IR cells appeared to be projection neurons based on extension of their axons into LIII of the medial entorhinal area (MEA) and/or angular bundle. We conclude that LII and LIII of PrS are distinct in their neuronal populations and together constitute a more diverse population of neurons than previously suggested. PrS neurons serve as major drivers of circuits in superficial (LII-III) entorhinal cortex (ERC) and couple neighboring structures through robust afferentation, thereby substantiating the PrS's critical role in the parahippocampal region. J. Comp. Neurol. 521: 3116-3132, 2013.

Transmembrane AMPA receptor regulatory proteins (TARPs) play pivotal roles in AMP A receptor trafficking and gating. Here we examined cellular and subcellular distribution of TARP γ-8 in the mouse brain. Immunoblot and immunofluorescence revealed the highest concentration of γ-8 in the hippocampus. Immunogold electron microscopy demonstrated dense distribution of γ-8 on the synaptic and extrasynaptic surface of hippocampal neurons with very low intracellular labeling. Of the neuronal surface, γ-8 was distributed at the highest level on asymmetrical synapses of pyramidal cells and interneurons, whereas their asymmetrical synapses selectively lacked immunogold labeling. Then, the role of γ-8 in AMPA receptor expression was pursued in the hippocampus using mutant mice defective in the γ-8

Hormone exposure, including testosterone and its metabolite estradiol, induces a myriad of effects during a critical period of brain development that are necessary for brain sexual differentiation. Nuclear volume, neuronal morphology and astrocyte complexity are examples of the wide range of effects by which testosterone and estradiol can induce permanent changes in the function of neurons for the purpose of reproduction in adulthood. This review will examine the multitude of mechanisms by which steroid hormones induce these permanent changes in brain structure and function. Elucidating how steroids alter brain development sheds light on how individual variation in neuronal phenotype is established during a critical period.

Post-mortem cortices from patients diagnosed with Alzheimer's disease (AD) exhibit reduced levels of drebrin, an F-actin binding protein of dendritic spines and shafts. We used a mouse model of familial AD (FAD) to determine whether the density of cortical spines engaged in asymmetric (presumably excitatory) synapses and containing drebrin A is reduced and if so, whether this occurs prior to the emergence of h amyloid deposits, when only soluble h amyloid (Ah) is present. Quantitative electron microscopic immunocytochemistry revealed that by 6 months, the proportion of postsynaptic spines with drebrin A within somatosensory cortex layer I was smaller for the FAD model mice, when compared to the corresponding region of WT mice (P < 0.0005). However, the areal density of postsynaptic spines containing drebrin A was relatively constant from 3 to 18 months and beyond for both genotypes, suggesting that drebrin A confers stability to postsynaptic spines. Further measurements confirmed that the reduced proportion of drebrin A-containing spines in brains of FAD mice at 6 months is due to the greater size and areal density of spine profiles lacking drebrin A. Thus, soluble Ah could affect spines lacking drebrin A more strongly than spines containing drebrin A. At 6 months and older, a larger fraction of spinous drebrin A in 2xKI mice was located near the synaptic membrane, as compared to those of WT mice. This pattern may reflect an altered trafficking of synaptic molecules within spines, a factor adding to the decline of synaptic function and plasticity.

Hippocampal dendritic spine and synapse numbers in female rats vary across the estrous cycle and following experimental manipulation of hormone levels in adulthood. Based on behavioral studies demonstrating that learning patterns are altered following puberty, we hypothesized that dendritic spine number in rat hippocampal CA1 region would change postpubertally. Female Sprague–Dawley rats were divided into prepubertal (postnatal day (P) 22),

This study examines the extent to which simultaneous olfactory discrimination learning increases spine density on hippocampal CA1 pyramidal neurons in C57BL/6J (C57) and DBA/2J (DBA) inbred mice, characterized by spontaneous differences in hippocampal plasticity and hippocampus-related learning. The behavioral data first showed a clear-cut difference in performance between the two strains. C57 mice learned to identify the positively reinforced olfactory cue whereas DBA did not. Both strains, however, similarly acquired the procedural aspects of the task. The morphological analysis performed 24 h posttraining revealed that spine density was significantly increased along apical, oblique, and basal dendrites in trained C57 mice compared to trained DBA mice, and to pseudotrained as well as to control cage mice of both strains. These findings confirm the ability of C57 mice to solve hippocampal-dependent tasks and provide the first evidence that simultaneous olfactory discrimination learning elicits spine growth in the mouse hippocampus. In addition, the finding that DBA mice failed to discriminate between the two olfactory cues but were as efficient as C57 mice in learning the procedural aspects of the task outlines that the structural changes observed in the latter strain were independent from any procedural learning component. V V C 2006 Wiley-Liss, Inc.

Stress increases associative learning and the density of dendritic spines in the hippocampus of male rats. In contrast, exposure to the same stressor impairs associative learning and reduces spine density in females. These effects in females are most evident when they are in the proestrus phase of the estrous cycle. An injection of testosterone at the time of birth masculinizes the female brain. In adulthood, masculinized females respond like males do to stress, i.e. they learn better. Here, we hypothesized that stress would increase spine densities on pyramidal neurons in area CA1 of the hippocampus of masculinized females, because stress enhances learning ability in both males and masculinized females. To test this, we used Golgi impregnation to stain tissue from masculinized and cycling females that were exposed to an acute stressor and sacrificed 1 day later. There was a significant interaction between stressor exposure and testosterone treatment at birth (p < 0.001). In general, cycling females that were stressed tended to possess fewer spines on apical and basal dendrites in the CA1 area of the hippocampus, whereas the masculinized females possessed significantly more spines after the stressor. These findings underscore the plastic nature of dendritic spines. They suggest that their response to stress in adulthood is organized by the presence of testosterone during very early development. Such a process may represent a mechanism for altering learning abilities after an acute traumatic experience.