No description available.

Glucose entry into the brain and its subsequent metabolism to L-lactate, regulated by astrocytes, plays a major role in synaptic plasticity and memory formation. A recent study has shown that L-lactate produced by the brain upon stimulation of glycolysis, and glycogen-derived L-lactate from astrocytes and its transport into neurons, is crucial for memory formation. A recent study revealed the molecular mechanisms that underlie the role of L-lactate in neuronal plasticity and long-term memory formation. L-lactate was shown to induce a cascade of molecular events via modulation of redox-sensitive N-Methyl-D-aspartate (NMDA) receptor activity that was mimicked by nicotinamide adenine dinucleotide hydride (NADH) co-enzyme. This indicated that changes in cellular redox state, following L-lactate transport inside the cells and its subsequent metabolism, production of NADH, and favouring a reduced state are the key effects of L-lactate. Therefore, we are investigating the role of L-lactate in modulating NMDA receptor function via redox modulatory sites. Accordingly, crucial redox-sensitive cysteine residues, Cys320 and Cys87, of the NR2A NMDA receptor subunit are mutated using site-directed mutation, transfected, and expressed in HEK293 cells. This cellular system will then be used to characterise and monitor its activity upon Llactate stimulation, compared to the wild type. This will be achieved by calcium imaging, using fluorescent microscopy. Our data shows that L-lactate potentiated NMDA receptor activity and increased intracellular calcium influx in NR1/NR2A wild type compared to the control condition (WT NR1/NR2A perfused with (1μM) glutamate and (1μM) glycine agonist only), showing faster response initiation and slower decay rate of the calcium signal to the baseline. Additionally, stimulating with L-lactate associated with greater numbers of cells having high fluorescent intensity (peak amplitude) compared to the control. Furthermore, L-lactate rescued the mutated NMDA NR1/NR2A C320A C87A receptor response that showed altered activity upon mutation up to the control level. Future experiments need to be carried out on different redox-sensitive residues of various NMDA receptor subunits to reveal the exact molecular mechanisms of L-lactate.

No description available.

NMDA receptor signaling is required for proper synapse formation, maintenance, plasticity and function. Dysregulation of the NMDA receptor has been implicated in pathophysiology of schizophrenia, which has an adult onset of symptoms. NMDA receptor deficient mice were utilized to assess the developmental consequences of NMDA receptor hypofunction. Locomotor activity was elevated throughout development; however, deficits in social interaction and working memory only manifest in adulthood and did not progress with age. Age-dependent deficits in neuron synapse biology were also detected; postsynaptic spine number was normal in juveniles, decreased post-adolescence, and progressively declined in adulthood. To investigate possible molecular mechanisms underlying the observed changes in spine number, protein levels of RhoGTPases and their downstream effectors were examined. Significant changes in Rac1 and downstream effectors were detected at different developmental stages. These studies provide clarification of the temporal sequence of events and mechanisms by which NMDA receptor dysfunction affects neurodevelopment.

NMDA receptor signaling is required for proper synapse formation, maintenance, plasticity and function. Dysregulation of the NMDA receptor has been implicated in pathophysiology of schizophrenia, which has an adult onset of symptoms. NMDA receptor deficient mice were utilized to assess the developmental consequences of NMDA receptor hypofunction. Locomotor activity was elevated throughout development; however, deficits in social interaction and working memory only manifest in adulthood and did not progress with age. Age-dependent deficits in neuron synapse biology were also detected; postsynaptic spine number was normal in juveniles, decreased post-adolescence, and progressively declined in adulthood. To investigate possible molecular mechanisms underlying the observed changes in spine number, protein levels of RhoGTPases and their downstream effectors were examined. Significant changes in Rac1 and downstream effectors were detected at different developmental stages. These studies provide clarification of the temporal sequence of events and mechanisms by which NMDA receptor dysfunction affects neurodevelopment.

Introduction and Objectives: The PDGFβ receptor and its ligand, PDGF-BB, are expressed throughout the central nervous system (CNS), including the hippocampas. Several reports confirm that PDGFβ receptors are neuroprotective against N-methyl-D-asparate (NMDA)-induced cell death in hippocampal neurons. NMDA receptor dysfunction is important for the expression of many symptoms of mental health disorders such as schizophrenia. The serotonin (5-HT) type 7 receptor was the most recent of the 5-HT receptor family to be identified and cloned. 5-HT receptors interact with several signaling systems in the CNS including receptors activated by the excitatory neurotransmitter glutamate such as the NMDA receptor. Although there is extensive interest in targeting the 5-HT7 receptor with novel therapeutic compounds, the function and signaling properties of 5-HT7 receptors in neurons remains poorly characterized. Methods: The SH-SY5Y neuroblastoma cell line, primary hippocampal cultures, and hippocampal slices were treated with 5-HT7 receptor agonists and antagonists. Western blotting was used to measure PDGFß receptor expression and phosphorylation as well as NMDA receptor subunit expression and phosphorylation levels. Real-time RT-PCR was used to measure mRNA level of PDGFß receptor in neuronal cultures. Cell death assays (MAP2, MTT) were used to measure the neuroprotective effects of 5-HT7 and PDGFß receptor activation. Results: My research involved elucidating the molecular mechanisms of neuroprotection after 5-HT7-induced PDGFß receptor upregulation. I demonstrated that 24 h treatment with the selective 5-HT7 receptor agonist, LP 12, increased not only the expression but also the activation of PDGFß receptors as measured by the phosphorylation of tyrosine 1021, the phospholipase Cγ binding site. Activation of the 5-HT7 receptor also selectively changed the expression and phosphorylation state of the NR2B subunit of the NMDA receptor. Activation of 5-HT7 receptors was neuroprotective against NMDA-induced toxicity in primary hippocampal neurons and this effect required PDGFß receptor kinase activity. Thus, long-term (24 h) activation of 5-HT7 receptors was neuroprotective via increasing the expression of a negative regulator of NMDA activity, the PDGFß receptor. In contrast, acute activation (5-30 min) of 5-HT7 receptor increased NMDA evoked current and altered NMDA receptor subunit phosphorylation in hippocampal neurons in a manner that was different from what we observed in our 24 h experiments. Conclusions: I identified two 5-HT7 receptor to NMDA receptor pathways: acute activation of the receptor increased NMDA-evoked currents whereas long-term 5-HT7 agonist treatment prevented NMDA-induced excitotoxicity in a PDGFß receptor-dependent manner. This research is significant in the ongoing advances for the treatment of mental heath disorders, such as schizophrenia and depression, that involve the 5-HT, glutamate, and neuronal growth factor systems.

No description available.

No description available.

Long-term depression (LTD) induced by low frequency stimulation (LFS; 900x1Hz) at medial perforant path (MPP) synapses in the rat dentate gyrus (DG) has been described as both developmentally regulated and N-methyl D-aspartate receptor (NMDAr) independent, yet sufficient evidence suggest that the processes is not entirely independent of NMDAr activity. In the present study, in vitro DG-LTD LFS was induced in hippocampal slices prepared from rats at postnatal day (PND) 14, 21 and 28 to investigate how the sensitivity of DG-LTD~LFS to the NMDAr antagonist amino-5-phosphonovaleric acid (AP5; 50µM) changes throughout the juvenile developmental period (jDP; PNDs 12-29) that occurs immediately after the period of peak neurogenesis. We further examined the acute effects of the partial NMDAr antagonist ethanol (EtOH) on DG-LTD LFS and NMDAr excitatory post synaptic currents (NMDAr-EPSCs) in dentate granule cells (DGCs) using 50 and 100mM concentrations (50mM ~0.2%BAC) of EtOH. The magnitude of LTD induced at all three time points was not statistically different between age groups, but the probability of successfully inducing LTD did decrease with age. We found that AP5 was insufficient to inhibit DG-LTD LFS at PND14, but significantly inhibited DG-LTD LFS at PND21 and PND28. We also found that 50mM EtOH, but not 100mM EtOH, significantly attenuated the mag-nitude of DG-LTD LFS induced at each time point. Acute effects of 50mM EtOH had relatively little effect on NMDAr-EPSCs at PND14, and showed a slight potentiation of the response at PND21. 50mM EtOH at PND28, and 100mM EtOH at all three developmental time points showed inhibition of the NMDAr-EPSC. These findings provide insight on how developmental changes to the DG network and dentate gran-ule cells (DGCs) influences mechanisms and processes involved in the induction and expression of synaptic plasticity in the DG. / Graduate

The sigma-1 receptor (σ-1R) is an endoplasmic reticulum (ER) protein that modulates a number of ion channels. It is hypothesized that σ-1Rs activated with agonist translocate to the plasma membrane. The σ-1R potentiates N-methyl-D-aspartate Receptors (NMDARs), important constituents of synaptic plasticity. NMDARs are anchored in the plasma membrane by Postsynaptic Density Protein-95 (PSD-95). The mechanism behind σ-1R modulation of NMDARs is not known. The results of my investigation confirm that σ-1Rs localize extrasomatically. Following σ-1R activation, σ-1R localization to dendrites and postsynaptic densities (PSDs) is upregulated. Unpublished work from our lab has shown that σ-1Rs associate with PSD-95 and NMDARs. Furthermore, immunocytochemistry (ICC) showed σ-1R colocalization with PSD-95 and NMDAR subunits. After σ-1R activation there was significantly increased colocalization between σ-1R, PSD-95, and GluN2B. Overall, this study may have provided insight into the molecular mechanism behind σ-1R modulation of NMDARs, which could have implications in the understanding of synaptic plasticity.