Showing papers by "Robin A. de Graaf published in 2004"
TL;DR: Results indicate that neuronal glucose oxidation and not total glucose utilization is coupled to the glutamate/glutamine cycle during intense cortical activation.
Abstract: 13C nuclear magnetic resonance (NMR) experiments have previously shown that glutamatergic neurotransmitter flux (Vcycle(Glu/Gln)) changes proportionately with neuronal glucose oxidation (CMRglc(ox)N) in the nonactivated cortex of anesthetized rats. Positron Emission Tomography measurements of glucose and oxygen uptake during sensory stimulation had shown that the incremental glucose utilization is greater than oxygen leading to the suggestion that the energy required for stimulated neuronal activity arises from nonoxidative glucose metabolism. In this study, the authors used spatially localized 1H-observed, 13C-edited NMR spectroscopy during an infusion of [1,6–13C2]glucose to assess the relationship between changes in Vcycle(Glu/Gln) and glucose utilization (CMRglc(ox)N and CMRglc(nonox)) during the intense cortical activity associated with bicuculline-induced seizures. Metabolic fluxes were determined by model-based analysis of the 13C-enrichment time courses of glutamate-C4 and glutamine-C4 (CMRglc(ox)...
153 citations
TL;DR: The exchange rate between the mitochondrial and cytosolic metabolite pools was fast relative to the neuronal tricarboxylic acid cycle flux for all cerebral tissue types.
Abstract: Multivolume 1H-[13C] NMR spectroscopy in combination with i.v. [1,6-13C2]glucose infusion was used to detect regional glucose metabolism and glutamatergic neurotransmission in the halothane-anesthetized rat brain at 7 T. The regional information was decomposed into pure cerebral gray matter, white matter, and subcortical structures by means of tissue segmentation based on quantitative T1 relaxation mapping. The 13C turnover curves of [4-13C]glutamate, [4-13C]glutamine, and [3-13C]glutamate + glutamine were fitted with a two-compartment neuronal-astroglial metabolic model. The neuronal tricarboxylic acid cycle fluxes in cerebral gray matter, white matter, and subcortex were 0.79 ± 0.15, 0.20 ± 0.11, and 0.42 ± 0.09 μmol/min per g, respectively. The glutamate-glutamine neurotransmitter cycle fluxes in cerebral gray matter, white matter, and subcortex were 0.31 ± 0.07, 0.02 ± 0.04, and 0.18 ± 0.12 μmol/min per g, respectively. The exchange rate between the mitochondrial and cytosolic metabolite pools was fast relative to the neuronal tricarboxylic acid cycle flux for all cerebral tissue types.
93 citations
TL;DR: The measured encapsulation efficiencies for the liposomal dispersions prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) through extrusion using 50, 200 and 1000 nm polycarbonate membranes were found to be identical using the two different experimental approaches.
47 citations