Thesis deals with glutamate transport in rat brain nerve terminals and neuromodulatory effects of ferritin, apoferritin, physiological and unphysiological heavy metals, synthesized nanoparticles of magnetite and magemite coated with different substanses. At first, extracellular/intracellular L-[14C]glutamate exchange and conservativeness of the extracellular level of L-[14C]glutamate was analyzed in isolated rat brain nerve terminals. "Cold" nonradiolabelled L-glutamate, DL-threo- -hydroxyaspartate, D-aspartate extruded a quarter of radioactivity from L-[14C]glutamate-preloaded. The existence of the efficient extracellular/intracellular glutamate exchange, and so dynamic glutamate gradient across the plasma membrane of nerve terminals was demonstrated. The central role of glutamate transporters in permanent glutamate turnover in nerve terminals was suggested. Permanent glutamate turnover is responsible for maintenance of dynamic glutamatein/glutamateout gradient resulting in the establishment of flexible extracellular level of glutamate, which can be unique for each synapse because of dependence on individual presynaptic parameters. The authors suggest that there are two main relatively independent mechanisms at the presynaptic level, which can influence the extracellular glutamate concentration, and so signaling, and its regulation. These two mechanisms, i.e. exocytosis and transporter-mediated glutamate turnover, are both precisely regulated, but do not directly interfere with each other, because they have different intracellular sources of glutamate in nerve terminals for release purposes, i.e. glutamate pool of synaptic vesicles and the cytoplasm, respectively. This duality can set up a presynaptic base for memory consolidation and storage, maintenance of neural circuits, long-term potentiation, and plasticity. New neuromodulatory properties of heavy metals were demonstrated. It was shown that the preincubation of rat brain nerve terminals with Cd2+ or Pb2+ resulted in the attenuation of synaptic vesicles acidification, which was assessed by the steady state level of the fluorescence of pH-sensitive dye acridine orange. A decrease in L-[14C]glutamate accumulation in digitonin-permeabilized synaptosomes after the addition of the metals, which reflected lowered L-[14C]glutamate accumulation by synaptic vesicles inside of synaptosomes, may be considered in the support of the above data. Using isolated rat brain synaptic vesicles, it was found that cadmium and lead caused dissipation of their proton gradient, whereas the application of essential heavy metal manganese did not do it. Thus, synaptic malfunction associated with the influence of Cd2+ and Pb2+ may result from partial dissipation of the synaptic vesicle proton gradient that leads to: 1) a decrease in stimulated exocytosis, which is associated not only with the blockage of voltage-gated Ca2+ channels, but also with incomplete filling of synaptic vesicles; 2) an attenuation of Na+-dependent glutamate uptake. Exogenous ferritin significantly increased the ambient level of L-[14C]glutamate in the nerve terminals. This increase was not a result of augmentation of tonic release because the velocity of tonic release of L-[14C]glutamate was not changed significantly in ferritin-treated synaptosomes as compared to the control. Ferritin caused a decrease in synaptic vesicle acidification that was shown using fluorescent dye acridine orange. Iron-dependence of the effects of ferritin was analyzed with apoferritin. Apoferritin weakly affected the proton electrochemical gradient of synaptic vesicles but increased the ambient level and decreased the initial velocity of uptake of L-[14C]glutamate by synaptosomes, nevertheless these effects were lesser than those caused by ferritin. Exogenous ferritin can provoke the development of excitotoxicity increasing the ambient level of glutamate and lowering synaptic vesicle acidification and glutamate uptake in the nerve terminals, however these effects are not completely iron-dependent. Thus, in the CNS exogenous ferritin can act as modulator of glutamate homeostasis in iron-dependent and iron-independent manner. Using -Fe2O3 nanoparticles coated by D-mannose, and Fe3O4 nanoparticles coated by 3-aminopropil (dietoksi) metylsilane, we showed the possibility of manipulation of population of nerve terminals by the external magnetic field.
