Increase In Number Of Synapses Research Articles

Qifu-yin activates the Keap1/Nrf2/ARE signaling and ameliorates synaptic injury and oxidative stress in APP/PS1 mice

Ethnopharmacological relevanceThe traditional medicinal formulation, Qifu-yin (QFY), has been widely prescribed for Alzheimer's disease (AD) treatment in China, yet the comprehensive mechanisms through which QFY mitigates AD pathology remain to be fully delineated. Aim of the studyThis study aimed to explore the therapeutic implications of QFY on the synaptic injury and oxidative stress in the hippocampus of APPswe/PS1dE9 (APP/PS1) mice, with a concerted effort to elucidate the molecular mechanisms related to synaptic preservation and memory improvement. Materials and methodsThe components of QFY were identified by ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The neuroprotective effects of QFY was evaluated using six-month-old male APP/PS1 mice. Subsequent to a 15 days of QFY regimen, spatial memory was assessed utilizing the Morris water maze (MWM) test. Amyloid-beta (Aβ) aggregation was detected via immunostaining, while the quantification of Aβ1-40 and Aβ1-42 was achieved through enzyme-linked immunosorbent assay (ELISA). Transmission electron microscopy (TEM) was used to investigate the synaptic structure and mitochondrial morphology. Golgi staining was applied to examine dendritic spine density. Reactive oxygen species (ROS), 3-nitrotyrosine (3-NT) and 4-hydroxy-nonenal (4-HNE) assays were employed to assess oxidative stress. The expression profiles of Aβ metabolism-associated enzymes and the Keap1/Nrf2/ARE signaling pathway were determined by Western blot. ResultsA total of 20 principal compounds in QFY were identified. QFY mitigated memory deficits of APP/PS1 mice, including reducing escape latency and search distance and increasing the time and distance spent in the target quadrant. In addition, QFY increased platform crossings of APP/PS1 mice in the probe trial of MWM tests. TEM analysis showed that QFY increased synapse number in the CA1 region of APP/PS1 mice. Further studies indicated that QFY elevated the expression levels of Post synaptic density protein 95 (PSD95) and synaptophysin, and mitigated the loss of dendritic spine density in the hippocampus of APP/PS1 mice. QFY has been shown to ameliorated the structural abnormalities of mitochondria, including mitochondrial dissolution and degradation, up-regulate ATP synthesis and membrane potential in the hippocampus of APP/PS1 mice. Moreover, QFY activated the Keap1/Nrf2/ARE signaling pathway in the hippocampus of APP/PS1 mice, which might contribute to the neuroprotective effects of QFY. ConclusionQFY activates the Keap1/Nrf2/ARE signaling, and protects against synaptic and mitochondrial dysfunction in APP/PS1 mice, proposing a potential alternative therapeutic strategy for AD management.

Microanalytical Mass Spectrometry with Super-Resolution Microscopy Reveals a Proteome Transition During Development of the Brain's Circadian Pacemaker.

During brain development, neuronal proteomes are regulated in part by changes in spontaneous and sensory-driven activity in immature neural circuits. A longstanding model for studying activity-dependent circuit refinement is the developing mouse visual system where the formation of axonal projections from the eyes to the brain is influenced by spontaneous retinal activity prior to the onset of vision and by visual experience after eye-opening. The precise proteomic changes in retinorecipient targets that occur during this developmental transition are unknown. Here, we developed a microanalytical proteomics pipeline using capillary electrophoresis (CE) electrospray ionization (ESI) mass spectrometry (MS) in the discovery setting to quantify developmental changes in the chief circadian pacemaker, the suprachiasmatic nucleus (SCN), before and after the onset of photoreceptor-dependent visual function. Nesting CE-ESI with trapped ion mobility spectrometry time-of-flight (TOF) mass spectrometry (TimsTOF PRO) doubled the number of identified and quantified proteins compared to the TOF-only control on the same analytical platform. From 10 ng of peptide input, corresponding to <∼0.5% of the total local tissue proteome, technical triplicate analyses identified 1894 proteins and quantified 1066 proteins, including many with important canonical functions in axon guidance, synapse function, glial cell maturation, and extracellular matrix refinement. Label-free quantification revealed differential regulation for 166 proteins over development, with enrichment of axon guidance-associated proteins prior to eye-opening and synapse-associated protein enrichment after eye-opening. Super-resolution imaging of select proteins using STochastic Optical Reconstruction Microscopy (STORM) corroborated the MS results and showed that increased presynaptic protein abundance pre/post eye-opening in the SCN reflects a developmental increase in synapse number, but not presynaptic size or extrasynaptic protein expression. This work marks the first development and systematic application of TimsTOF PRO for CE-ESI-based microproteomics and the first integration of microanalytical CE-ESI TimsTOF PRO with volumetric super-resolution STORM imaging to expand the repertoire of technologies supporting analytical neuroscience.

Altered excitatory and inhibitory neocortical circuitry leads to increased convulsive severity after pentylenetetrazol injection in an animal model of schizencephaly, but not of microgyria.

ObjectiveMalformations of the polymicrogyria spectrum can be mimicked in rodents through neonatal transcranial focal cortical freeze lesions. The animals presenting the malformations present both altered synaptic events and epileptiform activity in the vicinity of the microgyrus, but the comprehension of their contribution to increased predisposition or severity of seizures require further studies.MethodsIn order to investigate these issues, we induced both microgyria and schizencephaly in 57 mice and evaluated: their convulsive susceptibility and severity after pentyleneterazol (PTZ) treatment, the quantification of their symmetric and asymmetric synapses, the morphology of their dendritic arbors, and the content of modulators of synaptogenesis, such as SPARC, gephyrin and GAP‐43 within the adjacent visual cortex.ResultsOur results have shown that only schizencephalic animals present increased convulsive severity. Nevertheless, both microgyric and schizencephalic cortices present increased synapse number and dendritic complexity of layer IV and layer V‐located neurons. Specifically, the microgyric cortex presented reduced inhibitory synapses, while the schizencephalic cortex presented increased excitatory synapses. This altered synapse number is correlated with decreased content of both the anti‐synaptogenic factor SPARC and the inhibitory postsynaptic organizer gephyrin in both malformed groups. Besides, GAP‐43 content and dendritic spines number are enhanced exclusively in schizencephalic cortices.SignificanceIn conclusion, our study supports the hypothesis that the sum of synaptic alterations drives to convulsive aggravation in animals with schizencephaly, but not microgyria after PTZ treatment. These findings reveal that different malformations of cortical development should trigger epilepsy via different mechanisms, requiring further studies for development of specific therapeutic interventions.

Imaging the fetal nonhuman primate brain with SV2A positron emission tomography (PET).

Exploring synaptic density changes during brain growth is crucial to understanding brain development. Previous studies in nonhuman primates report a rapid increase in synapse number between the late gestational period and the early neonatal period, such that synaptic density approaches adult levels by birth. Prenatal synaptic development may have an enduring impact on postnatal brain development, but precisely how synaptic density changes in utero are unknown because current methods to quantify synaptic density are invasive and require post-mortem brain tissue. We used synaptic vesicle glycoprotein 2A (SV2A) positron emission tomography (PET) radioligands [11C]UCB-J and [18F]Syn-VesT-1 to conduct the first assessment of synaptic density in the developing fetal brain in gravid rhesus monkeys. Eight pregnant monkeys were scanned twice during the third trimester at two imaging sites. Fetal post-mortem samples were collected near term in a subset of subjects to quantify SV2A density by Western blot. Image-derived fetal brain SV2A measures increased during the third trimester. SV2A concentrations were greater in subcortical regions than in cortical regions at both gestational ages. Near term, SV2A density was higher in primary motor and visual areas than respective associative regions. Post-mortem quantification of SV2A density was significantly correlated with regional SV2A PET measures. While further study is needed to determine the exact relationship of SV2A and synaptic density, the imaging paradigm developed in the current study allows for the effective in vivo study of SV2A development in the fetal brain.

Activity-dependent regulation of mitochondrial motility in developing cortical dendrites.

Developing neurons form synapses at a high rate. Synaptic transmission is very energy-demanding and likely requires ATP production by mitochondria nearby. Mitochondria might be targeted to active synapses in young dendrites, but whether such motility regulation mechanisms exist is unclear. We investigated the relationship between mitochondrial motility and neuronal activity in the primary visual cortex of young mice in vivo and in slice cultures. During the first 2 postnatal weeks, mitochondrial motility decreases while the frequency of neuronal activity increases. Global calcium transients do not affect mitochondrial motility. However, individual synaptic transmission events precede local mitochondrial arrest. Pharmacological stimulation of synaptic vesicle release, but not focal glutamate application alone, stops mitochondria, suggesting that an unidentified factor co-released with glutamate is required for mitochondrial arrest. A computational model of synaptic transmission-mediated mitochondrial arrest shows that the developmental increase in synapse number and transmission frequency can contribute substantially to the age-dependent decrease of mitochondrial motility.

Uncovering microglial pathways driving sex-specific neurobiological effects in stress and depression

Women suffer from major depressive disorder (MDD) more often than men and report greater MDD symptom severity. Mounting evidence suggests that sex differences in MDD may be driven, in part, by sex-specific neurobiological mechanisms. Chronic stress is a significant risk factor in MDD, and preclinical rodent models show differential patterns of stress-induced neural remodeling and cognitive-behavioral dysfunction in males and females. For instance, chronic stress leads to synapse loss in the medial prefrontal cortex in male rodents yet has either no effect on- or increases-synapse number in females. Recent reports have implicated microglia, the immune cells of the brain, in MDD, and findings demonstrate sex-specific microglial signatures in both preclinical stress models and MDD patients. Given that microglia can remodel neural architecture, modulate synaptic transmission, and affect subsequent changes in behavior, it is plausible that microglial pathways contribute to differential stress effects on neuroplasticity and function in males and females. As such, this review examines the evidence for sex-specific microglia-neuron interactions in preclinical stress models and in patients with MDD. Discoveries highlighted herein demonstrate divergent microglial contributions in males and females and suggest that future studies investigating stress-linked disorders should be guided by sex-dependent neurobiological and behavioral findings. Examining these pathways represents a clear avenue toward both a richer understanding of brain, behavior, and immunity, and innovative psychoneuroimmunology-based applications in personalized medicine.

Ultrastructural investigation of synaptic alterations in the rat hippocampus after irradiation and hyperthermia

ABSTRACT This study aimed to investigate ultrastructural synaptic alterations in rat hippocampus after in utero exposure to irradiation (IR) and postnatal exposure to hyperthermia (HT). There were four groups in each of the time points (3rd and 6th months). IR group: Pregnant rats were exposed to radiation on the 17th gestational day. HT group: Hyperthermia was applied to the rat pups on the 10th day after their birth. IR+HT group: Both IR and HT were applied at the same time periods. Control group: No IR or HT was applied. Rat pups were sacrificed after 3 and 6 months. Thin sections from the dentate gyrus (DG) and the CA3 of hippocampus were evaluated for synapse numbers by electron microscopy. Synapses were counted, and statistical analysis was performed. Abnormalities in myelin sheath, mossy terminals and neuropil were observed in the CA3 and DG of all groups. The synapses in the CA3 region were significantly increased in the IR-3rd month, IR-6th month, and IR+HT-3rd month groups vs control group. Synapses were significantly increased in the DG of HT-3rd month group. A trend for an increase in synapse numbers was seen in the CA3 and DG. Increased number of synapses in the rat hippocampus may be due to mossy fiber sprouting, possibly caused by in utero irradiation and/or postnatal hyperthermia.

Sonic hedgehog signaling in astrocytes mediates cell type-specific synaptic organization.

Astrocytes have emerged as integral partners with neurons in regulating synapse formation and function, but the mechanisms that mediate these interactions are not well understood. Here, we show that Sonic hedgehog (Shh) signaling in mature astrocytes is required for establishing structural organization and remodeling of cortical synapses in a cell type-specific manner. In the postnatal cortex, Shh signaling is active in a subpopulation of mature astrocytes localized primarily in deep cortical layers. Selective disruption of Shh signaling in astrocytes produces a dramatic increase in synapse number specifically on layer V apical dendrites that emerges during adolescence and persists into adulthood. Dynamic turnover of dendritic spines is impaired in mutant mice and is accompanied by an increase in neuronal excitability and a reduction of the glial-specific, inward-rectifying K+ channel Kir4.1. These data identify a critical role for Shh signaling in astrocyte-mediated modulation of neuronal activity required for sculpting synapses.

Sestrin modulator NV-5138 produces rapid antidepressant effects via direct mTORC1 activation.

Preclinical studies demonstrate that rapid acting antidepressants, including ketamine require stimulation of mTORC1 signaling. This pathway is regulated by neuronal activity, endocrine and metabolic signals, notably the amino acid leucine, which activates mTORC1 signaling via binding to the upstream regulator sestrin. Here, we examined the antidepressant actions of NV-5138, a novel highly selective small molecule modulator of sestrin that penetrates the blood brain barrier. The results demonstrate that a single dose of NV-5138 produced rapid and long-lasting antidepressant effects, and rapidly reversed anhedonia caused by chronic stress exposure. The antidepressant actions of NV-5138 required BDNF release as the behavioral responses are blocked by infusion of a BDNF neutralizing antibody into the medial prefrontal cortex (mPFC) or in mice with a knock-in of a BDNF polymorphism that blocks activity dependent BDNF release. NV-5138 administration also rapidly increased synapse number and function in the mPFC, and reversed the synaptic deficits caused by chronic stress. Together, the results demonstrate that NV-5138 produced rapid synaptic and antidepressant behavioral responses via activation of the mTORC1 pathway and BDNF signaling, indicating that pharmacological modulation of sestrin is a novel approach for development of rapid acting antidepressants.

Psychedelics Promote Structural and Functional Neural Plasticity

SUMMARYAtrophy of neurons in the prefrontal cortex (PFC) plays a key role in the pathophysiology of depression and related disorders. The ability to promote both structural and functional plasticity in the PFC has been hypothesized to underlie the fast-acting antidepressant properties of the dissociative anesthetic ketamine. Here, we report that, like ketamine, serotonergic psychedelics are capable of robustly increasing neuritogenesis and/or spinogenesis both in vitro and in vivo. These changes in neuronal structure are accompanied by increased synapse number and function, as measured by fluorescence microscopy and electrophysiology. The structural changes induced by psychedelics appear to result from stimulation of the TrkB, mTOR, and 5-HT2A signaling pathways and could possibly explain the clinical effectiveness of these compounds. Our results underscore the therapeutic potential of psychedelics and, importantly, identify several lead scaffolds for medicinal chemistry efforts focused on developing plasticity-promoting compounds as safe, effective, and fast-acting treatments for depression and related disorders.

APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer’s Disease Phenotypes in Human iPSC-Derived Brain Cell Types

The apolipoprotein E4 (APOE4) variant is the single greatest genetic risk factor for sporadic Alzheimer's disease (sAD). However, the cell-type-specific functions of APOE4 in relation to AD pathology remain understudied. Here, we utilize CRISPR/Cas9 and induced pluripotent stem cells (iPSCs) to examine APOE4 effects on human brain cell types. Transcriptional profiling identified hundreds of differentially expressed genes in each cell type, with the most affected involving synaptic function (neurons), lipid metabolism (astrocytes), and immune response (microglia-like cells). APOE4 neurons exhibited increased synapse number and elevated Aβ42 secretion relative to isogenic APOE3 cells while APOE4 astrocytes displayed impaired Aβ uptake and cholesterol accumulation. Notably, APOE4 microglia-like cells exhibited altered morphologies, which correlated with reduced Aβ phagocytosis. Consistently, converting APOE4 to APOE3 in brain cell types from sAD iPSCs was sufficient to attenuate multiple AD-related pathologies. Our study establishes a reference for human cell-type-specific changes associated with the APOE4 variant. VIDEO ABSTRACT.

Orb2 as modulator of Brat and their role at the neuromuscular junction

How synapses are built and dismantled is a central question in neurobiology. A wide range of proteins and processes from gene transcription to protein degradation are involved. Orb2 regulates mRNA translation depending on its monomeric or oligomeric state to modulate nervous system development and memory. Orb2 is expressed in Drosophila larval brain and neuromuscular junction (NMJ), Orb2 knockdown causes a reduction of synapse number and defects in neuronal morphology. Brain tumor (Brat) is an Orb2 target; it is expressed in larval brain related with cell growth and proliferation. Brat downregulation induces an increase in synapse number and abnormal growth of buttons and branches in neurons. In absence of Orb2, Brat is overexpressed suggesting that Orb2 is negatively regulating Brat mRNA translation. Orb2 or Brat control the expression of specific genes related to neuronal function. Orb2 is required for Liprin and Synaptobrevin transcription meanwhile Brat is required for Synaptobrevin and Synaptotagmin transcription. We present here evidences of a novel genetic mechanism to regulate synapse fine tuning during development and propose an equilibrium between Orb2 conformational state and nervous system formation.

Presynaptic LRP4 promotes synapse number and function of excitatory CNS neurons.

Precise coordination of synaptic connections ensures proper information flow within circuits. The activity of presynaptic organizing molecules signaling to downstream pathways is essential for such coordination, though such entities remain incompletely known. We show that LRP4, a conserved transmembrane protein known for its postsynaptic roles, functions presynaptically as an organizing molecule. In the Drosophila brain, LRP4 localizes to the nerve terminals at or near active zones. Loss of presynaptic LRP4 reduces excitatory (not inhibitory) synapse number, impairs active zone architecture, and abolishes olfactory attraction - the latter of which can be suppressed by reducing presynaptic GABAB receptors. LRP4 overexpression increases synapse number in excitatory and inhibitory neurons, suggesting an instructive role and a common downstream synapse addition pathway. Mechanistically, LRP4 functions via the conserved kinase SRPK79D to ensure normal synapse number and behavior. This highlights a presynaptic function for LRP4, enabling deeper understanding of how synapse organization is coordinated.

Protein Kinase Cϵ (PKCϵ) Promotes Synaptogenesis through Membrane Accumulation of the Postsynaptic Density Protein PSD-95

Protein kinase Cϵ (PKCϵ) promotes synaptic maturation and synaptogenesis via activation of synaptic growth factors such as BDNF, NGF, and IGF. However, many of the detailed mechanisms by which PKCϵ induces synaptogenesis are not fully understood. Accumulation of PSD-95 to the postsynaptic density (PSD) is known to lead to synaptic maturation and strengthening of excitatory synapses. Here we investigated the relationship between PKCϵ and PSD-95. We show that the PKCϵ activators dicyclopropanated linoleic acid methyl ester and bryostatin 1 induce phosphorylation of PSD-95 at the serine 295 residue, increase the levels of PSD-95, and enhance its membrane localization. Elimination of the serine 295 residue in PSD-95 abolished PKCϵ-induced membrane accumulation. Knockdown of either PKCϵ or JNK1 prevented PKCϵ activator-mediated membrane accumulation of PSD-95. PKCϵ directly phosphorylated PSD-95 and JNK1 in vitro Inhibiting PKCϵ, JNK, or calcium/calmodulin-dependent kinase II activity prevented the effects of PKCϵ activators on PSD-95 phosphorylation. Increase in membrane accumulation of PKCϵ and phosphorylated PSD-95 (p-PSD-95(S295)) coincided with an increased number of synapses and increased amplitudes of excitatory post-synaptic potentials (EPSPs) in adult rat hippocampal slices. Knockdown of PKCϵ also reduced the synthesis of PSD-95 and the presynaptic protein synaptophysin by 30 and 44%, respectively. Prolonged activation of PKCϵ increased synapse number by 2-fold, increased presynaptic vesicle density, and greatly increased PSD-95 clustering. These results indicate that PKCϵ promotes synaptogenesis by activating PSD-95 phosphorylation directly through JNK1 and calcium/calmodulin-dependent kinase II and also by inducing expression of PSD-95 and synaptophysin.

Mitogen-Activated Protein Kinase Phosphatase-2 Deletion Impairs Synaptic Plasticity and Hippocampal-Dependent Memory.

Mitogen-activated protein kinases (MAPKs) regulate brain function and their dysfunction is implicated in a number of brain disorders, including Alzheimer's disease. Thus, there is great interest in understanding the signaling systems that control MAPK function. One family of proteins that contribute to this process, the mitogen-activated protein kinase phosphatases (MKPs), directly inactivate MAPKs through dephosphorylation. Recent studies have identified novel functions of MKPs in development, the immune system, and cancer. However, a significant gap in our knowledge remains in relation to their role in brain functioning. Here, using transgenic mice where the Dusp4 gene encoding MKP-2 has been knocked out (MKP-2(-/-) mice), we show that long-term potentiation is impaired in MKP-2(-/-) mice compared with MKP-2(+/+) controls whereas neuronal excitability, evoked synaptic transmission, and paired-pulse facilitation remain unaltered. Furthermore, spontaneous EPSC (sEPSC) frequency was increased in acute slices and primary hippocampal cultures prepared from MKP-2(-/-) mice with no effect on EPSC amplitude observed. An increase in synapse number was evident in primary hippocampal cultures, which may account for the increase in sEPSC frequency. In addition, no change in ERK activity was detected in both brain tissue and primary hippocampal cultures, suggesting that the effects of MKP-2 deletion were MAPK independent. Consistent with these alterations in hippocampal function, MKP-2(-/-) mice show deficits in spatial reference and working memory when investigated using the Morris water maze. These data show that MKP-2 plays a role in regulating hippocampal function and that this effect may be independent of MAPK signaling.

Ghrelin stimulates synaptic formation in cultured cortical networks in a dose-dependent manner

Ghrelin was initially related to appetite stimulation and growth hormone secretion. However, it also has a neuroprotective effect in neurodegenerative diseases and regulates cognitive function. The cellular basis of these processes is related to synaptic efficacy and plasticity. Previous studies indicated that ghrelin has an excitatory effect on neuronal activity, and stimulates synaptic plasticity in vivo. Plasticity in the adult brain occurs in many different ways, including changes in synapse morphology and number. Therefore, we used in vitro neuronal cultures to investigate how ghrelin affects synaptogenesis. We used dissociated cortical cultures of newborn rats, chronically treated with different doses of ghrelin (0.5, 1, 1.5 and 2μM). After one-, two-, three- or four weeks cultures were immunostained for the presynaptic marker synaptophysin. In parallel, additional groups of non-treated cultures were immunostained for detection of ghrelin receptor (GHSR1). During development, GHSR1was increasingly expressed in all type of neurons, as well as the synaptophysin. Synaptic density depended on ghrelin concentration, and was much higher than in controls in all age groups. In conclusion, ghrelin leads to earlier network formation in dissociated cortical networks and an increase in number of synapses. The effect is probably mediated by GHSR1. These findings suggest that ghrelin may provide a novel therapeutic strategy for the treatment of disorders related to synaptic impairment.

The novel synaptogenic protein Farp1 links postsynaptic cytoskeletal dynamics and transsynaptic organization

Synaptic adhesion organizes synapses, yet the signaling pathways that drive and integrate synapse development remain incompletely understood. We screened for regulators of these processes by proteomically analyzing synaptic membranes lacking the synaptogenic adhesion molecule SynCAM 1. This identified FERM, Rho/ArhGEF, and Pleckstrin domain protein 1 (Farp1) as strongly reduced in SynCAM 1 knockout mice. Farp1 regulates dendritic filopodial dynamics in immature neurons, indicating roles in synapse formation. Later in development, Farp1 is postsynaptic and its 4.1 protein/ezrin/radixin/moesin (FERM) domain binds SynCAM 1, assembling a synaptic complex. Farp1 increases synapse number and modulates spine morphology, and SynCAM 1 requires Farp1 for promoting spines. In turn, SynCAM 1 loss reduces the ability of Farp1 to elevate spine density. Mechanistically, Farp1 activates the GTPase Rac1 in spines downstream of SynCAM 1 clustering, and promotes F-actin assembly. Farp1 furthermore triggers a retrograde signal regulating active zone composition via SynCAM 1. These results reveal a postsynaptic signaling pathway that engages transsynaptic interactions to coordinate synapse development.

Presynaptic PI3K activity triggers the formation of glutamate receptors at neuromuscular terminals of Drosophila

Synapse transmission depends on the precise structural and functional assembly between pre- and postsynaptic elements. This tightly regulated interaction has been thoroughly characterised in vivo in the Drosophila glutamatergic larval neuromuscular junction (NMJ) synapse, a suitable model to explore synapse formation, dynamics and plasticity. Previous findings have demonstrated that presynaptic upregulation of phosphoinositide 3-kinase (PI3K) increases synapse number, generating new functional contacts and eliciting changes in behaviour. Here, we show that genetically driven overexpression of PI3K in the presynaptic element also leads to a correlated increase in the levels of glutamate receptor (GluRII) subunits and the number of postsynaptic densities (PSDs), without altering GluRII formation and assembly dynamics. In addition to GluRIIs, presynaptic PI3K activity also modifies the expression of the postsynaptic protein Discs large (Dlg). Remarkably, PI3K specifically overexpressed in the final larval stages is sufficient for the formation of NMJ synapses. No differences in the number of synapses and PSDs were detected when PI3K was selectively expressed in the postsynaptic compartment. Taken together, these results demonstrate that PI3K-dependent synaptogenesis plays an instructive role in PSD formation and growth from the presynaptic side.

The Nogo Receptor Family Restricts Synapse Number in the Developing Hippocampus

Neuronal development is characterized by a period of exuberant synaptic growth that is well studied. However, the mechanisms that restrict this process are less clear. Here we demonstrate that glycosylphosphatidylinositol-anchored cell-surface receptors of the Nogo Receptor family (NgR1, NgR2, and NgR3) restrict excitatory synapse formation. Loss of any one of the NgRs results in an increase in synapse number invitro, whereas loss of all three is necessary for abnormally elevated synaptogenesis invivo. We show that NgR1 inhibits the formation of new synapses in the postsynaptic neuron by signaling through the coreceptor TROY and RhoA. The NgR family is downregulated by neuronal activity, a response that may limit NgR function and facilitate activity-dependent synapse development. These findings suggest that NgR1, a receptor previously shown to restrict axon growth in the adult, also functions in the dendrite as a barrier that limits excitatory synapse number during brain development.

Presynaptic PI3K activity triggers the formation of glutamate receptors at neuromuscular terminals of Drosophila

Synapse transmission depends on the precise structural and functional assembly between pre- and postsynaptic elements. This tightly regulated interaction has been thoroughly characterised in vivo in the Drosophila glutamatergic larval neuromuscular junction (NMJ) synapse, a suitable model to explore synapse formation, dynamics and plasticity. Previous findings have demonstrated that presynaptic upregulation of phosphoinositide 3-kinase (PI3K) increases synapse number, generating new functional contacts and eliciting changes in behaviour. Here, we show that genetically driven overexpression of PI3K in the presynaptic element also leads to a correlated increase in the levels of glutamate receptor (GluRII) subunits and the number of postsynaptic densities (PSDs), without altering GluRII formation and assembly dynamics. In addition to GluRIIs, presynaptic PI3K activity also modifies the expression of the postsynaptic protein Discs large (Dlg). Remarkably, PI3K specifically overexpressed in the final larval stages is sufficient for the formation of NMJ synapses. No differences in the number of synapses and PSDs were detected when PI3K was selectively expressed in the postsynaptic compartment. Taken together, these results demonstrate that PI3K-dependent synaptogenesis plays an instructive role in PSD formation and growth from the presynaptic side.