1,721,112 research outputs found
Aberrant Synaptic Function in Mouse Models of Disease-associated GRIN1 Genetic Variants of the NMDA Receptor
Full text linkN-methyl-D-aspartate receptors (NMDARs) are tetrameric ligand-gated ion channels that participate in excitatory synaptic transmission by allowing Na+, K+, and Ca2+ to permeate through their channel. NMDARs are composed of two obligatory GluN1 subunits and two GluN2 (A-D) subunits. Therefore, mutations in the obligate GluN1 subunit can manifest as a wide-range of neurodevelopmental phenotypes, emphasizing the importance to investigate the underlying pathophysiology. Genetic variants in GRIN1, the gene encoding the GluN1 subunit, have been identified in a considerable number of individuals affected with GRIN variants through whole exome sequencing. Two such de novo missense variants in GRIN1, c.1858G>C/A and 2479G>C/A, result in the substitution of a glycine to an arginine at amino acid positions 620th (G620R) and 827th (G827R) of GluN1, respectively. Although functional analysis using recombinant systems has demonstrated deficits in NMDAR function, the impact of both variants on synaptic function in a native physiological context remains unknown.
In this thesis, electrophysiological recordings – both extracellular field potential and whole-cell patch clamp – were made in acute hippocampal slices prepared from adult (8-12 weeks) transgenic mice mimicking the G620R and G827R missense variants found in patients in order to assess the physiological consequences of these Grin1 variants on NMDARs and synaptic functions. The Grin1-G620R variant significantly impaired NMDAR-mediated synaptic transmission and plasticity without affecting circuit formation or basal synaptic transmission in the CA1 hippocampus. Reduced NMDAR transmission caused by the Grin1-G620R variant was accompanied by reduced GluN2B activity and altered channel kinetics. However, Grin1-G620R did not affect NMDAR expression at the synapse or voltage-dependent magnesium block. The Grin1-G827R variant also significantly diminished NMDAR function. This phenotype was resulted from a reduced synaptic NMDAR expression, suggesting that GluN1-G827R containing NMDARs fail to assemble or traffic to the synapse. Interestingly, NMDAR dysfunction in Grin1-G827R variant mice was accompanied by an enhancement of presynaptic release probability.Ph.D
Native glycine receptor subtypes and their physiological roles
No full textThe glycine receptor chloride channel (GlyR), a member of the pentameric Cys-loop ion channel receptor family, mediates inhibitory neurotransmission in the spinal cord, brainstem and retina. They are also found presynaptically, where they modulate neurotransmitter release. Functional GlyRs are formed from a total of five subunits (alpha 1 -alpha 4, beta). Although alpha subunits efficiently form homomeric GlyRs in recombinant expression systems, homomeric alpha 1, alpha 3 and alpha 4 GlyRs are weakly expressed in adult neurons. in contrast, alpha 2 homomeric GlyRs are abundantly expressed in embryonic neurons, although their numbers decline sharply by adulthood. Numerous lines of biochemical, biophysical, pharmacological and genetic evidence suggest the majority of glycinergic neurotransmission in adults is mediated by heteromeric alpha 1 beta GlyRs. Immunocytochemical co-localisation experiments suggest the presence of alpha 2 beta, alpha 3 beta and alpha 4 beta GlyRs at synapses in the adult mouse retina. Immunocytochemical and electrophysiological evidence also implicates alpha 3 beta GlyRs as important mediators of glycinergic inhibitory neurotransmission in nociceptive sensory neuronal circuits in peripheral laminae of the spinal cord dorsal horn. It is yet to be determined why multiple Glyl? synaptic subtypes are differentially distributed in these and possibly other locations. The development of pharmacological agents that can discriminate strongly between different beta subunit-containing GlyR isoforms will help to address this issue, and thereby provide important insights into a variety of central nervous system functions including retinal signal processing and spinal pain mechanisms. Finally, agents that selectively potentiate different GlyR isoforms may be useful as therapeutic lead compounds for peripheral inflammatory pain and movement disorders such as spasticity. (C) 2008 Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Determining the Role of the Complement Cascade in Hippocampal Synaptic Physiology
Full text linkA key feature of brain development is the refinement of exuberant synapses, known as synapse pruning. This phenomenon is executed by microglia, the resident immune cells of the brain. Evidence that microglia prune retinal inputs via activation of the complement cascade in the dorsolateral geniculate nucleus has led to the principle that complement-dependent synapse pruning occurs ubiquitously in the brain. However, this principle has not been empirically validated. Here, I investigated this principle in the hippocampus, a critical region for learning and memory which is known to undergo developmental pruning by microglia. In the healthy brain, complement cascade proteins are enriched in VGLUT2+ regions of the hippocampus. Therefore, I hypothesized that in the developing hippocampus, microglia-mediated pruning of VGLUT2+ synapses is complement-dependent. To test this hypothesis, I used mice with a genetic deletion of the essential complement protein C3. Microglia pruning of VGLUT2+ synapses was not different between C3 -/- mice compared to WT during development in the hippocampus. Further, functional synapse properties and plasticity were not significantly altered in C3 -/- compared to WT mice. Thus, complement-dependent pruning by microglia is a not general mechanism in the brain under physiological conditions. I then tested whether a complement-dependent mechanism could be induced in the hippocampus by peripheral inflammation. I found that treating mice systemically with lipopolysaccharide (LPS) led to a neuroinflammatory microglia phenotype and VGLUT2+ synapse loss. Surprisingly, the neuroinflammatory microglia phenotype was exacerbated in LPS-treated C3 -/- mice compared to LPS-treated WT mice. As such, in an inflammatory context, complement C3 acts as a negative regulator of microglia reactivity in the hippocampus. Finally, I observed that under physiological conditions, an immature-like phagocytic state persists in adulthood specifically in the CA1 SLM, but not in adjacent CA1 SR and DGML hippocampal subregions. Together, my Thesis work has i) provided a counterexample to the principle of ubiquitous complement-dependent synapse pruning by microglia, ii) uncovered an unexpected role for C3 in neuroinflammation, and iii) revealed that phagocytic activity in the hippocampus is governed in a subregion-dependent manner. These findings refine our understanding of microglia function in the hippocampus.Ph.D.2024-11-13 00:00:0
A Novel Role of STAT3 in Synaptic Plasticity in Juvenile Mice
Full text linkThe dynamic and complex process by which neurons modulate their connections is termed synaptic plasticity. Synaptic connections between neurons can be strengthened or weakened in an activity-dependent manner, through long-term potentiation (LTP) or long-term depression (LTD), respectively. In recent years, the Janus Kinase (JAK) and Signal Transducer and Activator of Transcription (STAT) signaling pathway, traditionally involved in immune signaling, was implicated in synaptic plasticity. More specifically, STAT3 was required for N-methyl-D-aspartate receptor (NMDAR)-LTD in distinct hippocampal CA1 synapses in juvenile and adult rats. Studies in rats utilized pharmacological and knockdown approaches to evaluate STAT3 in LTD. This thesis aimed to further elucidate the role of STAT3 in LTD and in additional forms of plasticity through conditional genetic targeting and pharmacological inhibition in mice across development.Two brain-specific conditional STAT3 deletion mouse lines were generated through CaMKII- and Emx1-mediated Cre expression, allowing for investigations into hippocampal NMDAR-dependent synaptic plasticity in juvenile and adult mice. Conditional knockout (KO) and pharmacological inhibition of STAT3 did not impair basal synaptic transmission or synaptic facilitation in either age cohort studied. Furthermore, adult CaMKII-STAT3 KO mice, juvenile Emx1-STAT3 KO mice, and juvenile wildtype mice treated with pharmacological inhibitors of STAT3 displayed intact NMDAR-LTD. Two theta burst stimulation (TBS) protocols, either in a compressed (cTBS) or spaced (sTBS) pattern, were used to study STAT3 in LTP. These protocols trigger distinct forms of LTP reliant on different postsynaptic expression mechanisms. Juvenile Emx1-STAT3 KO mice displayed a significant reduction in LTP following a cTBS, but not an sTBS induction protocol. Adult CaMKII-STAT3 and adult Emx1-STAT3 KO mice displayed normal LTP following either protocol. This LTP deficit in juvenile KOs following cTBS was linked to protein kinase A (PKA) activity. Inhibition of PKA significantly increased LTP in Emx1-STAT3 KOs despite cTBS LTP being PKA-independent in Emx1-STAT3 controls. Taken together, I identified a novel developmental requirement for STAT3 in a specific form of LTP following cTBS. This work highlights the importance of comprehensive developmental studies and emphasizes the complexity of synaptic plasticity in the CA1 region in mice.
Key words: STAT3, synaptic plasticity, CA1, long-term potentiation, long-term depression, protein kinase A, juvenile micePh.D.2025-11-13 00:00:0
Alterations in NMDARs and STEP in the Hippocampus of a Fragile X Syndrome Mouse Model
Full text linkFragile X Syndrome (FXS) is one of the most prevalent developmental disorders causing intellectual disability. The disorder has a high burden on society and no efficient treatment options exist. FXS typically stems from mutations that silence the Fragile X messenger ribonucleoprotein 1 (Fmr1) gene hindering the production of the protein, Fragile X Messenger Ribonucleoprotein (FMRP). According to a long-held theory, based on results from animal Fmr1 knock-out (KO) models, the absence of FMRP causes exaggerated metabotropic glutamate receptor (mGluR) signaling which in turn leads to impairments in the KO. Drugs blocking mGluRs are known to normalize synaptic deficits and reverse traits in the animal models, but in clinical trials the approach has failed to translate to FXS patients.
The failure of clinical trials has led to a search for new protein and signaling pathway targets that may offer a treatment for FXS. In this thesis, the role of the glutamatergic N-methyl-D-aspartate receptor (NMDAR), and the synaptic protein, Striatal-Enriched Protein Tyrosine Phosphatase (STEP)61, were examined in the hippocampus of Fmr1 KOs. NMDARs are required for some excitatory synaptic functions and are comprised of several subunits that change in expression with development. The Fmr1 KO mouse showed an age-dependent decrease of the NMDAR subunit GluN2A expression compared to wild-type (WT) littermates. The decreased GluN2A resulted in a delayed developmental switch in the GluN2A/GluN2B ratio, a switch that is important for the optimal development of synapses. Furthermore, the KO expression differences were accompanied by a developmental-dependent deficit in long-term potentiation (LTP). However, the developmental impact was only found in the CA1 area of the hippocampus, since the dentate gyrus (DG) showed a consistent decline in GluN2A expression and LTP impairment throughout development. Additionally, this thesis reports a contribution of an increased STEP61 activity accompanied by a decreased activity of the tyrosine kinase Src to the NMDAR-related deficits in the Fmr1 KO in both hippocampal areas. Taken together, this work shows the importance for developmental studies and distinguishing between hippocampal subregions in cellular, synaptic, and behavioural functions in the FXS model. Furthermore, it highlights STEP61 as a target for further investigation into FXS therapeutics.Ph.D
The Role of Endogenous Cellular Prion Protein in Brain Synaptic Function
No full textSynaptic plasticity is the ability of synapses to change their strength. Long term potentiation (LTP) is one of the neurophysiological correlates of synaptic plasticity. α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are heterotetrameric ionotropic receptors, composed of subunits GluA1-4, that are involved in LTP. Cellular prion protein (PrPC) is a ubiquitously expressed glycosylphosphatidylinositol (GPI)-anchored protein that is exposed to the extracellular compartment. PrPC interacts with GluA2 subunit of AMPARs, however, its role in synaptic plasticity and LTP is poorly understood. To explore the role of PrPC in brain synaptic function, I used a recently available strictly co-isogenic Prnp knockout (Prnp KO) mouse model (PrnpZH3/ZH3) to carry in vitro electrorheological recordings from CA1 synapses. I also used interfering peptides, short peptides derived from PrPC that included a trans activator of transcription (TAT) sequence to make it cell-permeant, to acutely disrupt PrPC-GluA2 interaction.
Prnp KO mice showed normal paired pulse facilitation (PPF), reduced basal synaptic function, normal LTP induced by strong induction protocol (75 pulses), but enhanced LTP induced by weak induction protocols (25 pulses and 10 pulses). The enhanced LTP in Prnp KO mice was sex and age independent. The enhanced LTP in Prnp KO mice was Protein Kinase A (PKA) and calcium-permeable AMPAR (CP-AMPAR) dependent, but N-methyl-D-aspartate receptor (NMDAR) independent. Furthermore, the active interfering peptide enhanced LTP in wild type (WT) mice, but not in Prnp KO mice, by acutely disrupting PrPC-GluA2 interaction. The enhanced LTP in WT mice caused by the active interfering peptide was protein synthesis independent but CP-AMPAR dependent. These findings demonstrated that in the absence of PrPC-GluA2 interaction, either deleting PrPC genetically (in Prnp KO mice) or acutely disrupting PrPC-GluA2 interaction using the active interfering peptide (in WT mice), a CP-AMPAR and PKA dependent form of LTP is expressed. This suggests that PrPC- GluA2 interaction plays a role in trafficking GluA2-containing AMPAR, calcium-impermeable AMPAR (CI-AMPAR), to synapses. Lack of PrPC modulates AMPAR composition/distribution and causes insertion of GluA2-lacking AMPAR, CP-AMPAR, to synapses which leads to increased calcium influx and subsequently expression of PKA dependent form of LTP. The research findings shed light on the physiological role of PrPC in brain synaptic function.Ph.D
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