Impaired dopamine release and uptake in R6/1 Huntington's disease model mice

The aim of this study was to evaluate the intracellular cytosolic calcium concentration (Ca(2+)](i)) changes induced by activation of ionotropic glutamate receptors in cultured hippocampal neurons after repeated brief episodes of hypoxia. To investigate what kinds of ionotropic glutamate receptors are involved we used specific agonists for AMPA- and NMDA-type glutamate receptors. Measurements of Ca(2+)](i) in cultured hippocampal neurons were made by imaging Fura-2AM loaded hippocampal cells. In the rat hippocampal slice method, field potential measurements in CA1 pyramidal neurons were used. The main result of our study is that brief hypoxic episodes progressively depress the Ca(2+)](i) increases induced by agonists of AMPA and NMDA glutamate receptors in cultured hippocampal neurons. An effectiveness of this depression is increased from the first hypoxic episode to the third one. Hypoxic preconditioning effect is observed during 10-20 min after termination of hypoxic episode and depends on Ca(2+)](i) response amplitudes to agonists before hypoxia. In contrast to AMPA receptor activation, NMDA receptor activation before hypoxia induce the spontaneous Ca(2+)](i) increase about 3 min after each hypoxic episode. These spontaneous Ca(2+)](i) increases may be an indicator of the development of posthypoxic hyperexcitability in hippocampal neurons. Our results suggest that brief hypoxia-induced depression of the glutamate receptor-mediated Ca(2+)](i) responses contributes to the development of rapid hypoxic preconditioning in hippocampal CA1 neurons.