The role of NMDAR subtypes in synaptic plasticity is very controversial, partially caused by the lack of specific GluN2A containing NMDA receptor (GluN2AR) antagonists. Here we took a novel approach to selectively modulate NMDAR subtype activity and investigated its role in the induction of plasticity. Whole cell recording in both acutely isolated CA1 cells and hippocampal slices demonstrated that pituitary adenylate cyclase activating peptide 1 receptors (PAC1 receptors), which are Gαq coupled receptors, selectively recruited Src kinase and enhanced currents mediated by GluN2ARs. In addition, biochemical experiments showed that the activation of PAC1 receptors phosphorylated GluN2ARs specifically. In contrast, vasoactive intestinal peptide receptors (VPAC receptors), which are Gαs coupled receptors, selectively stimulated Fyn kinase, potentiated currents mediated by GluN2B containing NMDARs (GluN2BRs). Furthermore, dopamine D1 receptor activation (another Gαs coupled receptor) specifically phosphorylated GluN2BRs. Interestingly, field recording experiments showed that PAC1 receptor activation lowered the threshold for LTP whilst LTD was enhanced by dopamine D1 receptor activation. In conclusion, the activity of GPCRs can signal through different pathways to selectively modulate absolute contribution of GluN2ARs versus GluN2BRs in CA1 neurons via Src family kinases. Furthurmore, Epac, activated by some Gαs coupled receptors, also modulated NMDAR currents via a PKC/Src dependent pathway, but whether it selectively modulates NMDAR subtypes, and has capacity to change the induction of plasticity, requires further study. By this means, we can investigate the role of NMDAR subtypes in the direction of synaptic plasticity by selectively modulating the activity of GluN2ARs or GluN2BRs. In addition, based on my work, some interfering peptides and drugs can be designed and used to selectively inhibit the activity of GluN2BRs and GluN2ARs by interrupting Fyn- and Src - mediated signaling cascade respectively. It will provide new candidate drugs for the treatment of some neurological diseases such as Alzheimer disease (AD) and schizophrenia.

N-Methyl-D-aspartate receptors (NMDARs) are a principal subtype of excitatory ligandgated ion channel with prominent roles in physiology and disease in the mammalian central nervous system (CNS). Activation of NMDARs requires binding of both glutamate and glycine. Apart from its co-agonist action, glycine can also prime NMDARs for subsequent internalization upon binding of both glutamate and glycine. However, the molecular basis responsible for mediating and regulating glycine priming and NMDAR endocytosis is largely unknown. In my thesis, I discovered the principle that although NMDAR gating and priming share a common requirement for glycine binding, the molecular constraints for gating are distinct from those for priming through two mutations of the glycine binding site in GluN1 subunit of the NMDAR that, while maintaining gating of NMDARs, eliminate glycine priming of the receptors. One of the molecular signatures of glycine priming is recruitment of the endocytic adaptor protein AP-2. I have characterized the two regions in GluN2 subunits required for enhanced AP-2 association. This unexpected result suggests binding of glycine initiates a conformational change transmitted from GluN1 to GluN2 allowing for docking of endocytic machinery. Furthermore, I have discovered that naturally occurring splice variants of GluN1 subunit, containing a 21 amino acid sequence in the N-terminus domain (N1) cassette, abrogate glycine stimulated AP-2 recruitment and glycine-primed NMDAR internalization. These findings imply that there are distinct populations of native NMDARs in the CNS – those lacking N1 that show glycine-primed internalization and those containing N1 that are not primable. Collectively, my thesis work demonstrates a dramatic all-or-none priming effect with splice variants of NMDARs, a highly unexpected discovery providing novel insight into the molecular mechanisms and physiological role of glycine priming. Ultimately, elucidating principles and mechanisms of glycine priming lay the foundation for new types therapeutic approaches for CNS disorders, approaches without the deleterious consequences of directly blocking NMDARs.

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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.

Zebrafish, Danio rerio, have become an important model for developmental studies and have several advantages over other model systems. These advantages include (1) the easy accessibility of zebrafish embryos for direct observation of their development and (2) their suitability for systematic mutagenesis studies for the identification of genes regulating the development of various tissues and organs, including the skeletal system. Recently, it has been reported that glutamate receptors are expressed in many types of bone cells and regulate bone physiological functions. In the present study, we have examined the effects of a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist¡Xdextromethorphan¡Xon the development of the axial skeleton in zebrafish embryos by using calcein stain. Our results revealed that dextromethorphan significantly attenuates the formation of the axial skeleton and that it is inhibited on pretreatment with glutamate. Moreover, immunohistochemical analysis revealed protein level expression of the NMDA subunit NR1 in the axial region of zebrafish. Our results also indicate that attenuation of NMDA receptor activity-induced change in the axial skeleton may be related to heat-shock protein and extracellular signal-regulated kinase (ERK) signalings. In conclusion, we suggest that the NMDA receptor plays an important role in the development of the axial skeleton. However, further studies are required on the cellular mechanisms of glutamate regulated bone formation.

Despite intensive research on the neurobiological mechanisms of chronic pain, this therapeutic area remains one of the least satisfactorily covered by current drugs. Glutamate activates two major classes of receptors: ionotropic and metabotropic. Ionotropic receptors are classified into three major subclasses:a-amino-3- hydroxy-5-methyl-4- isoxazolepropionic acid (AMPA), kainate and N-methyl-D-aspartate (NMDA). NMDA receptor activation, at the level of the spinal cord and peripheral tissue has been shown to play an important role in the facilitation of nociption in several animal models. Although the efficacy of NMDA receptor antagonists in various experimental and clinical pain situations has been well documented, their use as analgesics is limited by serious side effects such as memory impairment, psychotomimetic effects, ataxia and motor incoordination. Two promising current approaches to obtain effective analgesia devoid of side effects are by subtype-selective NMDA receptor antagonism in central nervous system (CNS) or peripheral use of NMDA receptor antagonist that do not interfere with central glutamate processing. NR2B subunit of NMDA receptor was predominantly found in the superficial dorsal horn of spinal cord. Recent discoveries have revealed that the transfection of small interfering RNAs (siRNAs) into animal cells results in the potent, long-lasting post-transcriptional silencing of specific genes. Thus, two approaches of antagonizing NMDA receptor in CNS and peripheral nervous system (PNS) for pain relief using siRNAs or pharmacological agents are investigated in this study. The first approach involves intrathecal administration of NR2B-siRNA into subarachnoid space and transfection of siRNA into cell of spinal cord by transfection agent of polyethylenimine (PEI). Formalin test was used to induce inflammatory pain in the hind paw of rats. Behavior response to formalin test was observed and recorded on 3rd, 7th, 14th, and 21th day after injection of siRNA. The spinal cords were dissected immediately after formalin test and used for analysis of mRNA and protein. The results revealed that the use of siRNA targeting the NR2B subunit could abolish formalin induced pain behaviors and not impair motor coordination in rat model. The expression of NR2B mRNA and its associated protein as demonstrated by real time reverse transcription-polymerase chain reaction (RT-PCR) and western blotting were decreased. Significant reduction of NR2B immunoreactivity in dorsal horn of spinal cord were detected after 7 days treated by NR2B siRNA. The peak effect of gene knockdown occurred on day 3 for mRNA and day 7 for its protein, following intrathecal injection of 5 µg of siRNA targeting NR2B subunit. The inhibition of NR2B mRNA and protein lasted about 14 days and recovered on 21th days after injection of siRNA. The nociceptive response induced by formalin was decreased during the period of downregulation of NR2B protein. A novel intrathecal delivery of siRNA transfected with PEI into cell of dorsal horn reduced formalin-induced pain. The second approach involves subcutaneous injection of NMDA receptor antagonist and topical use of alpha2-adrenergic agonist for abolishing surgical pain. Additionally, we proved the upregulation of glutamate receptors in human inflamed skin. The study examined whether the peripheral ionotropic glutamate receptors (iGluRs) increased in inflamed human skin taken from patients having inflammatory pain over inflamed skin and surrounding area. Real time RT-PCR and western blot were used for quantitation of mRNA and protein of iGluR in normal and inflamed human skin. A significant increase in mRNA and protein for the subunits of NMDA, AMPA, and kainate receptor were detected in inflamed skin when compared to normal skin. The results demonstrate that mRNA and protein level of iGluRs are increasingly expressed during states of persistent inflammation, and that this increased activity may be involved in mediating clinical inflammatory pain in human skin. To examine the postoperative analgesic effect and adverse effect of local NMDA receptor antagonist (ketamine), ketamine (0.3%, 3 ml) or saline was subcutaneous infiltrated pre-incisionally in 26 patients equally assigned to two groups undergoing circumcision surgery. The saline-infiltrated subjects also received 9-mg intramuscular ketamine into the upper arm to control for any related systemic analgesic effects. The postoperative analgesic and adverse effects were followed for 24 hours. For ketamine infiltrated patients, the time interval until first analgesic demand was prolonged and the incidence of pain free (pain score = 0) during movement and erection was significant higher than saline infiltrated patients. No significant differences were noted in the incidence of adverse effects between the two groups. Pre-incisional subcutaneous infiltration of ketamine acting via a peripheral mechanism can suppression postoperative pain after circumcision surgery. Apraclonidine hydrochloride (AH) is a topical, relatively selective alpha2-adrenergic agonist that has limited access to the CNS and exhibits fewer systemic (adverse) effects such as dizziness and hypotension. Eighty patients scheduled for arthroscopic knee surgery received either intraarticular (IA) normal saline, 50 ug IA AH, 150 ug IA AH, or 150 ug IA clonidine subsequent to surgery. The IA application of 150 ug apraclonidine and 150 ug clonidine provide similar degree of postoperative analgesia and similar incidence of adverse effect. The promise is that both approaches attenuating nociception state devoid of CNS adverse effects provide novel approach for the management of chronic pain.

Chronic intermittent ethanol exposure (CIE) is associated with degeneration of hippocampal neurons. The present study used hippocampal cultures to examine the loss of NeuN immunoreactivity, a relaible marker or neuronal density, after 1, 2, or 3 cycles of 5 days EtOH exposure (50 mM), followed by a 24-hour period of EWD or continuous EtOH exposure. NeuN immunoreactivity was decreased by 13%, 19%, and 16% in the CA1, CA3, and dentate gyrus after 3 cycles of CIE respectively; thionine staining confirmed significant cellular losses within each hippocampal subregion. Two cycles of CIE in aged tissue cultures resulted in significant decreases in NeuN immunoreactivity in all hippocampal subregions; however continuous ethanol exposure or exposure to one cycle of CIE did not. Further, exposure to the N-Methyl-D-aspartate receptor (NMDAR) antagonist 2-amino-7-phosphonvaleric acid (APV) (30 uM) during periods of EWD attenuated the loss of NeuN in all hippocampal subregions, while exposure to APV (40 uM) prevented the loss of NeuN in the CA1 and dentate gyrus. These results suggest that the loss of mature neurons after CIE is associated with the overactivation on the NMDAR.

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.