Cubic phases in hydrated 1:1 and 1:2 dipalmitoylphosphatidylcholine-dipalmitoylglycerol mixtures.

The structures of fully hydrated 1:1 and 1:2 (mol/mol) dipalmitoylphosphatidylcholine (DPPC)-dipalmitoylglycerol (DPG) mixtures were studied by means of small-angle x-ray diffraction. The x-ray diffraction pattern of the 1:1 (mol/mol) DPPC-DPG mixture at 65 degrees C contains three reflections with spacings in the ratio of 1:1/ square root of 2:1/ square root of 3 in addition to reflections of an inverted hexagonal (H11) phase. A possible interpretation of this result is that a cubic phase of the body-centered space group lm3m, with a lattice constant of 23.1 +/- 0.6 nm, is formed. This cubic phase appears at intermediate temperatures between the lamellar and the H11 phases. The 1:2 (mol/mol) DPPC-DPG mixture gives an x-ray diffraction pattern at temperatures higher than the lamellar-to-H11 transition containing a number of reflections that index a cubic phase structure. The space group of the cubic phase was assigned a face-centered group Fd3m with a lattice constant of 16.3 +/- 0.1 nm at 82 degrees C. The possible role of cubic phases in membrane phenomena such as transmembrane signal transduction and fusion is discussed.     

Abstracts: 1

Lead (Pb) is a known neurotoxic agent, however, mechanisms of its neurotoxicity are still an open question. The aim of the study was to assess the function of nerve endings and astroglia in regard to the relationships between GABA, glutamate and glutamine using the rodent model of Pb toxicity. Synaptosomal processes of radioactive neurotransmitter transport, both GABA and glutamate, were impaired. Moreover, the uptake of glutamine, involved in the neuronal recycling of the neurotransmitters GABA and glutamate, decreased. However, evidences of astroglial activation (enhanced uptake of glutamate and activation of glutamine synthetase) were observed, together with parallel existing weakness of glutamine transport. The results suggest that the disturbances in GABAergic and glutamateric neurotransmission may be partially the effect of impaired neuronal–astrocytic interaction, mainly in intercellular trafficking of glutamine.     

Symposium 6: 1

Endogenous neural stem cells have been identified in diverse areas of the adult mammalian central nervous system including the subventricular zone, cerebral cortex and hippocampus. These cells have been demonstrated to participate actively in postnatal neurogenesis in restricted territories within the adult brain. They have further been characterized as having a committed neural fate in vivo, capable of generating neurons, astroglia and oligodendroglia. Endogenous CNS stem cells, when cultured in vitro, have been shown to have a much broader potential, capable of differentiating into diverse tissues such as blood, muscle, bone and kidney. Conversely, stem cells taken from other organs and grown in vitro have been demonstrated to differentiate into neurons, and hematopoietic stem cells injected intravenously have been shown to migrate into mature CNS, and differentiate into neurons. We have previously reported the mobilization of endogenous neural stem cells in vivo. Further work to determine if the stem cells so mobilized may include hematopoietic stem cells is reported here. Using immunohistochemical localization of antigens known to be present on primitive hematopoietic stem cells, or antigens present on neural stem cells, we report the presence of cells closely resembling hematopoietic stem cells in the mature CNS whose response to a mobilization paradigm is similar to that of endogenous neural stem cells. We further propose a lineage relationship between primitive hematopoietic stem cells and neural stem cells.