Regulation of calcium-permeable AMPA receptors in glia

AMPA receptors (AMPARs) mediate majority of excitatory synaptic transmission, and are involved in fast neuronal glial signaling in the central nervous system (CNS). These receptors are tetrameric assemblies that function as homomeric or heteromeric combinations of four AMPAR subunits (GluA1-4). Many key AMPAR properties are determined by the GluA2 subunit, the absence of which renders the AMPAR calcium permeable. Calcium permeable AMPARs (CP-AMPARs) are relatively widespread in the CNS being present in certain neurons and many glia. The calcium permeability of neuronal AMPARs is known to be relatively plastic, changing during development and following high frequency synaptic activity. It is clear that calcium permeable AMPARs play an important role in normal functions of Bergmann glia and oligodendrocyte precursor cells, however factors that regulate the CP-AMPAR in glial cells are still poorly understood. Little is known about the transmembrane auxiliary AMPA subunit (TARPs) present in glial cells. In Chapter 3 of this thesis, I consider the role of transmembrane AMPAR regulatory proteins (TARPs) in controlling AMPAR channel properties and trafficking. In particular, these experiments identify γ-5 as a novel TARP that occurs mainly in glial cells, and is present at high levels in Bergmann glia. Functionally, this TARP appears selective for long form AMPAR subunits (predominantly calcium permeable). My experiments also demonstrate that γ-5 co-localizes with a late endosome protein. Uniquely, γ-5 appears selective for the trafficking of GluA2, and is dependent on the protein SAP97 for trafficking and/or localisation. Oligodendrocyte precursor cells (OPCs), which are responsible for the formation of myelinating cells in the CNS, form a large proportion of the glial cells present in developing brain. OPCs are vulnerable to cell death in conditions such as periventricular white matter damage (hypoxic-ischemic white matter injury) in newborns. In Chapter 4, I have investigated factors that regulate calcium permeable AMPARs in OPCs, including mGluRs and purinergic receptors. Surprisingly I find that these receptors regulate calcium permeable AMPARs. This chapter identifies key mechanisms underlying this switch in AMPAR subtype, including the TARP γ-2 (Stargazin) that is involved in mGluR-induced ‘plasticity’ of AMPARs in OPCs. The experiments described in the final chapter, investigates the transmembrane AMPAR regulatory protein cornichon-3 (CNIH3). In this thesis I identified that the AMPAR regulatory protein cornichon-3 (CNIH3) is expressed at the cell surface in OPCs and that when over-expressed can influence their AMPAR channel properties

Experimental Study of Subcooled Boiling Heat Transfer of Axial and Swirling Flows inside Mini Annular Gaps

An experimental study of the subcooled boiling heat transfer of axial and swirling upward flows inside vertical mini annular gaps was conducted using deionized water. The subcooled boiling heat transfer coefficients and the boiling curves of the flow inside mini annular gaps with different gap sizes have been investigated. The experimental results both for the single phase heat transfer and subcooled boiling heat transfer inside mini annular gaps showed very good agreement with correlations in the literature. The results showed that the subcooled boiling heat transfer coefficient for a given heat flux increases as the size of the annular gap is decreased. The maximum wall superheat is also influenced negligibly by mass flux. Furthermore, the effects of swirl flow by using spring insets inside the mini annuli on the single phase and subcooled boiling heat transfer have been studied. The results showed that the single phase and subcooled boiling heat transfer coefficients are increased by having swirl flow inside mini annuli using spring inserts. The obtained results also showed that the heat transfer enhancement by having swirl flow inside the annuli using spring inserts decreases as the applied heat flux is increased in the subcooled boiling heat transfer region

Acid-sensing ion channel 1a drives AMPA receptor plasticity following ischemia and acidosis in hippocampal CA1 neurons

The CA1 region of the hippocampus is particularly vulnerable to ischemic damage. While NMDA receptors play a major role in excitotoxicity, it is thought to be exacerbated in this region by two forms of post-ischemic AMPA receptor (AMPAR) plasticity - namely, anoxic long-term potentiation (a-LTP), and a delayed increase in the prevalence of Ca2+ -permeable GluA2-lacking AMPARs (CP-AMPARs). The acid-sensing ion channel 1a (ASIC1a) which is expressed in CA1 pyramidal neurons, is also known to contribute to post-ischemic neuronal death and to physiologically induced LTP. This raises the question - does ASIC1a activation drive the post-ischemic forms of AMPAR plasticity in CA1 pyramidal neurons? We have tested this by examining organotypic hippocampal slice cultures (OHSCs) exposed to oxygen glucose deprivation (OGD), and dissociated cultures of hippocampal pyramidal neurons (HPN) exposed to low pH (acidosis). We find that both a-LTP and the delayed increase in the prevalence of CP-AMPARs are dependent on ASIC1a activation during ischemia. Indeed, acidosis alone is sufficient to induce the increase in CP-AMPARs. We also find that inhibition of ASIC1a channels circumvents any potential neuroprotective benefit arising from block of CP-AMPARs. By demonstrating that ASIC1a activation contributes to post-ischemic AMPAR plasticity, our results identify a functional interaction between acidotoxicity and excitotoxicity in hippocampal CA1 cells, and provide insight into the role of ASIC1a and CP-AMPARs as potential drug targets for neuroprotection. We thus propose that ASIC1a activation can drive certain forms of CP-AMPAR plasticity, and that inhibiting ASIC1a affords neuroprotection

The Effect of Intracanal Irrigants on Push out Bond Strength of CEM, Root MTA and Angelus MTA Cements to the Dentin Wall

Background and Objective: To reduce microbial contamination in cases such as perforation treatment, it is necessary to use irrigants after cement placement. The aim of the present study is to investigate the effect of intracanal irrigants on the push out bond strength of CEM, Root MTA and Angelus MTA cements to the dentin wall. Methods: In this laboratory research, 150 cross-section samples from the mid-root region of single canal teeth without caries with a thickness of 1 mm, which were randomly divided into 3 groups of 50 and filled with CEM cement, Root MTA or Angelus MTA, were examined. After the cements were set, the samples of each group were divided into 5 subgroups of 10; 4 subgroups were cleaned with sodium hypochlorite, EDTA, normal saline, 2% chlorhexidine for 30 minutes, and one subgroup was not cleaned as a control group. Then, the push out bond strength of cement with the dentin wall (MPa) and the failure pattern of the samples were evaluated. Findings: Different cleaning methods did not show any significant effect on the bond strength of CEM, Root MTA and Angelus MTA cements. In the cleaning method with saline, the bond strength of Angelus MTA (6.3±1.98) was higher than Root MTA (2.1±3.61) (p=0.004). In the cleaning method with 2% chlorhexidine, the bond strength of Angelus MTA cement (8.72±3.13) was higher compared to CEM (3.87±1.35) and Root MTA (4.66±1.76) (respectively p<0.001 and p=0.001). The most common type of failure in the Angelus MTA group was of the adhesive type, and in the CEM cement and Root MTA groups, it was of the mixed type. Conclusion: The results of the study showed that different cleaning methods have no effect on the push-out bond strength of the examined cements

The Effect of Different Methods of Fluoride Administration at Different Concentrations on the Load-Deflection Properties of Rhodium-Coated Niti Archwires

Background and Objective: Fluoride compounds are widely used for the control of dental plaque. Considering the effect of different fluoride compounds on the mechanical properties of orthodontic wires, this study was conducted to analyze the effect of different methods of fluoride administration at different concentrations on the load-deflection properties of rhodium-coated NiTi orthodontic archwires. Methods: This clinical trial was conducted on 30 patients aged between 15 and 25 years referring to Babol University of Medical Sciences due to dental crowding and didn't have vertical skeletal defects. 0.016-inch Rhodium-Coated A-NiTi wire was placed on patients' maxillary brackets. Patients were randomly divided into three groups of ten: The control group used only fluoride toothpaste, the second group used fluoride toothpaste with sodium fluoride mouthwash (0.05%) and the third group used fluoride toothpaste with Acidulated Phosphate Fluoride gel (1.23% APF). After six weeks, the values of unloading force (N), yield strength (N/m2) and stiffness (N/m) of the wires were obtained using a three-point bending test. Findings: The mean unloading force and stiffness of the second group wires were higher than that of the other groups and in the first group, they were higher than the control group in all values, but no significant differences were found between the groups. There was a significant difference between the yield strengths of different groups (p=0.038). The mean yield strength in the second group was higher than the other groups (0.94±0.16 N/m2) and was significantly different from the control group (0.75±0.19 N/m2) (p=0.030). Conclusion: According to this study, method of fluoride administration does not affect the unloading force and stiffness but the yield strength of rhodium-coated NiTi archwires increases with an increase in the fluoride concentration

Neuronal activity disrupts myelinated axon integrity in the absence of NKCC1b

Through a genetic screen in zebrafish, we identified a mutant with disruption to myelin in both the CNS and PNS caused by a mutation in a previously uncharacterized gene, slc12a2b, predicted to encode a Na+, K+, and Cl− (NKCC) cotransporter, NKCC1b. slc12a2b/NKCC1b mutants exhibited a severe and progressive pathology in the PNS, characterized by dysmyelination and swelling of the periaxonal space at the axon–myelin interface. Cell-type–specific loss of slc12a2b/NKCC1b in either neurons or myelinating Schwann cells recapitulated these pathologies. Given that NKCC1 is critical for ion homeostasis, we asked whether the disruption to myelinated axons in slc12a2b/NKCC1b mutants is affected by neuronal activity. Strikingly, we found that blocking neuronal activity completely prevented and could even rescue the pathology in slc12a2b/NKCC1b mutants. Together, our data indicate that NKCC1b is required to maintain neuronal activity–related solute homeostasis at the axon–myelin interface, and the integrity of myelinated axons

GABAergic regulation of cerebellar NG2 cell development is altered in perinatal white matter injury.

Diffuse white matter injury (DWMI), a leading cause of neurodevelopmental disabilities in preterm infants, is characterized by reduced oligodendrocyte formation. NG2-expressing oligodendrocyte precursor cells (NG2 cells) are exposed to various extrinsic regulatory signals, including the neurotransmitter GABA. We investigated GABAergic signaling to cerebellar white matter NG2 cells in a mouse model of DWMI (chronic neonatal hypoxia). We found that hypoxia caused a loss of GABAA receptor-mediated synaptic input to NG2 cells, extensive proliferation of these cells and delayed oligodendrocyte maturation, leading to dysmyelination. Treatment of control mice with a GABAA receptor antagonist or deletion of the chloride-accumulating transporter NKCC1 mimicked the effects of hypoxia. Conversely, blockade of GABA catabolism or GABA uptake reduced NG2 cell numbers and increased the formation of mature oligodendrocytes both in control and hypoxic mice. Our results indicate that GABAergic signaling regulates NG2 cell differentiation and proliferation in vivo, and suggest that its perturbation is a key factor in DWMI

The Effect of Intracanal Irrigants on Push out Bond Strength of CEM, Root MTA and Angelus MTA Cements to the Dentin Wall

Background and Objective: To reduce microbial contamination in cases such as perforation treatment, it is necessary to use irrigants after cement placement. The aim of the present study is to investigate the effect of intracanal irrigants on the push out bond strength of CEM, Root MTA and Angelus MTA cements to the dentin wall. Methods: In this laboratory research, 150 cross-section samples from the mid-root region of single canal teeth without caries with a thickness of 1 mm, which were randomly divided into 3 groups of 50 and filled with CEM cement, Root MTA or Angelus MTA, were examined. After the cements were set, the samples of each group were divided into 5 subgroups of 10; 4 subgroups were cleaned with sodium hypochlorite, EDTA, normal saline, 2% chlorhexidine for 30 minutes, and one subgroup was not cleaned as a control group. Then, the push out bond strength of cement with the dentin wall (MPa) and the failure pattern of the samples were evaluated. Findings: Different cleaning methods did not show any significant effect on the bond strength of CEM, Root MTA and Angelus MTA cements. In the cleaning method with saline, the bond strength of Angelus MTA (6.3±1.98) was higher than Root MTA (2.1±3.61) (p=0.004). In the cleaning method with 2% chlorhexidine, the bond strength of Angelus MTA cement (8.72±3.13) was higher compared to CEM (3.87±1.35) and Root MTA (4.66±1.76) (respectively p<0.001 and p=0.001). The most common type of failure in the Angelus MTA group was of the adhesive type, and in the CEM cement and Root MTA groups, it was of the mixed type. Conclusion: The results of the study showed that different cleaning methods have no effect on the push-out bond strength of the examined cements