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Michalis Papadakis

Publications and source records attributed to Michalis Papadakis.

4 recordsLinked to original sources
PubMed2006

Improved regional cerebral blood flow is important for the protection seen in a mouse model of late phase ischemic preconditioning.

INTRODUCTION: Ischemic preconditioning (IPC) induces protection to cerebral ischemia. However, it was previously unclear whether this protection resulted from altered susceptibility to ischemia. The current study examines the effects of late phase ischemic preconditioning in a mouse model of middle cerebral artery occlusion (MCAO). Specific examination of the regional cerebral blood flow (rCBF) was conducted. EXPERIMENTAL PROCEDURE: Intra-abdominal radiofrequency probes were implanted in animals and core temperature was regulated. Mice were subjected to MCAO: (1) brief 15 min duration (preconditioning ischemia) and (2) 45 min MCAO (injurious ischemia). Naive (i.e. not preconditioned) animals were compared with preconditioned animals (preconditioning ischemia plus injurious ischemia at 72 h reperfusion). rCBF was measured using laser Doppler flowmetry (LDF) and magnetic resonance cerebral perfusion (MRP) arterial spin labeling. Percentage of brain infarcted was compared between groups. RESULTS: rCBF was significantly improved in the preconditioned cohorts of mice. Naive animals showed flow reductions to 16+/-3.59% (MCAO_45; injurious, unpreconditioned) and 17.1+/-8.6% (MCAO_15; preconditioning ischemia alone) of baseline, while preconditioned animals had flows 33.9+/-13.2% (IPC_45; preconditioned animals with injurious ischemia at 72 h reperfusion) of baseline (p=0.001). Percentage of brain infarcted was 17.2+/-6.2% in naive animals, while it was 5.1+/-4.6% in the preconditioned animals (p=0.003). MRP of the perfusion to the ischemic hemisphere, in a striatal coronal slice of the brain was 26.7+/-5.8% of the contralateral hemisphere in naive animals while preconditioned mice had flows of 38.7+/-6.8% of contralateral (p=0.04). CONCLUSIONS: Improved rCBF is an important factor in the protection of IPC, during injurious MCAO in the mouse. Stringent monitoring of rCBF is required in future studies of IPC.

Animals↗
PubMed2006

Prior deafferentation confers long term protection to CA1 against transient forebrain ischemia and sustains GluR2 expression.

Hippocampal CA1 pyramidal neurons undergo delayed neurodegeneration after transient forebrain ischemia, and the phenomenon is dependent upon hyperactivation of l-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) subtype of glutamate receptors, resulting in aberrant intracellular calcium influx. The GluR2 subunit of AMPA receptors is critical in limiting the influx of calcium. The CA1 pyramidal neurons are very sensitive to ischemic damage and attempts to achieve neuroprotection, mediated by drugs, have been unsuccessful. Moreover, receptor antagonism strategies in the past have failed to provide long-term protection against ischemic injury. Long-term protection against severe forebrain ischemia can be conferred by fimbria-fornix (FF) deafferentation, which interrupts the afferent input to CA1. Our study evaluated the long-term protective effect of FF deafferentation, 12 days prior to induction of ischemia, on vulnerable CA1 neurons. Our results indicate that at 7 and 28 days post-ischemia, prior FF deafferentation protected 60% of neurons against ischemic cell death. Furthermore, we sought to evaluate whether FF deafferentation also sustained GluR2 levels in these neurons. GluR2 protein and mRNA expression were sustained by deafferentation at 70% of control following ischemia. Correlation studies revealed a positive correlation between GluR2 protein and mRNA level. These results demonstrate that protection conferred by FF deafferentation was long-term and related to sustained GluR2 expression.

Afferent Pathways↗
PubMed2004

Appropriate NR1-NR1 disulfide-linked homodimer formation is requisite for efficient expression of functional, cell surface N-methyl-D-aspartate NR1/NR2 receptors.

A c-Myc epitope-tagged N-methyl-D-aspartate receptor NR1-2a subunit was generated, NR1-2a(c-Myc), where the tag was inserted after amino acid 81. NR1-2a(c-Myc) /NR2A receptors when expressed in mammalian cells are not trafficked to the cell surface nor do they yield cell cytotoxicity post-transfection. NR1-2a(c-Myc) was, however, shown to assemble with NR2A subunits by immunoprecipitation and [(3)H]MK801 radioligand binding assays. Immunoblots of cells co-transfected with wild-type NR1-2a/NR2A subunits yielded two NR1-2a immunoreactive species with molecular masses of 115 and 226 kDa. Two-dimensional electrophoresis under non-reducing and reducing conditions revealed that the 226-kDa band contained disulfide-linked NR1-2a subunits. Only the 115-kDa NR1-2a species was detected for NR1-2a(c-Myc)/NR2A. The c-Myc epitope is inserted adjacent to cysteine 79 of the NR1-2a subunit; therefore, it is possible that the tag may prevent the formation of NR1 disulfide bridges. A series of cysteine --> alanine NR1-2a mutants was generated, and the NR1-2a mutants were co-expressed with NR2A or NR2B subunits in mammalian cells and characterized with respect to cell surface expression, cell cytotoxicity post-transfection, co-association by immunoprecipitation, and immunoblotting following SDS-PAGE under both reducing and non-reducing conditions. When co-expressed with NR2A in mammalian cells, NR1-2a(C79A)/NR2A displayed similar properties to NR1-2a(c-Myc)/NR2A in that the 226-kDa NR1 immunoreactive species was not detectable, and trafficking to the cell surface was impaired compared with wild-type NR1/NR2 receptors. These results provide the first biochemical evidence for the formation of NR1-NR1 intersubunit disulfide-linked homodimers involving cysteine 79. They suggest that disulfide bridging and structural integrity within the NR1 N-terminal domain is requisite for cell surface N-methyl-D-aspartate receptor expression.

Animals↗