Establishment of a cross-European field site network in the ALARM project for assessing large-scale changes in biodiversity.

The field site network (FSN) plays a central role in conducting joint research within all Assessing Large-scale Risks for biodiversity with tested Methods (ALARM) modules and provides a mechanism for integrating research on different topics in ALARM on the same site for measuring multiple impacts on biodiversity. The network covers most European climates and biogeographic regions, from Mediterranean through central European and boreal to subarctic. The project links databases with the European-wide field site network FSN, including geographic information system (GIS)-based information to characterise the test location for ALARM researchers for joint on-site research. Maps are provided in a standardised way and merged with other site-specific information. The application of GIS for these field sites and the information management promotes the use of the FSN for research and to disseminate the results. We conclude that ALARM FSN sites together with other research sites in Europe jointly could be used as a future backbone for research proposals.

Impaired NMDA receptor function in mouse olfactory bulb neurons by tetracycline-sensitive NR1 (N598R) expression.

High Ca(2+) permeability and its control by voltage-dependent Mg(2+) block are defining features of NMDA receptors. These features are lost if the principal NR1 subunit carries an asparagine (N) to arginine (R) substitution in a critical channel site at NR1 position 598. NR1(R) expression from a single allele in gene-targeted NR1(+/R) mice is lethal soon after birth, precluding analysis of altered synaptic functions later in life. We therefore employed the forebrain specific alphaCaMKII promoter to drive tTA-mediated tetracycline sensitive transcription of transgenes for NR1(R) and for lacZ as reporter. Transgene expression was observed in cortex, striatum, hippocampus, amygdala and olfactory bulb and was mosaic in all these forebrain regions. It was highest in olfactory bulb granule cells, in most of which Ca(2+) permeability and voltage-dependent Mg(2+) block of NMDA receptors were reduced to different extents. This indicates significant impairment of NMDA receptor function by NR1(R) in presence of the wild-type NR1 complement. Indeed, even though NR1(R) mRNA constituted only 18% of the entire NR1 mRNA population in forebrain, the transgenic mice died during adolescence unless transgene expression was suppressed by doxycycline. Thus, glutamate receptor function can be altered in the mouse by regulated NR1(R) transgene expression.

Associative long-term depression in the hippocampus is dependent on postsynaptic N-type Ca2+ channels.

Long-term depression (LTD) is a form of synaptic plasticity that can be induced either by low-frequency stimulation of presynaptic fibers or in an associative manner by asynchronous pairing of presynaptic and postsynaptic activity. We investigated the induction mechanisms of associative LTD in CA1 pyramidal neurons of the hippocampus using whole-cell patch-clamp recordings and Ca(2+) imaging in acute brain slices. Asynchronous pairing of postsynaptic action potentials with EPSPs evoked with a delay of 20 msec induced a robust, long-lasting depression of the EPSP amplitude to 43%. Unlike LTD induced by low-frequency stimulation, associative LTD was resistant to the application of d-AP-5, indicating that it is independent of NMDA receptors. In contrast, associative LTD was inhibited by (S)-alpha-methyl-4-carboxyphenyl-glycine, indicating the involvement of metabotropic glutamate receptors. Furthermore, associative LTD is dependent on the activation of voltage-gated Ca(2+) channels by postsynaptic action potentials. Both nifedipine, an L-type Ca(2+) channel antagonist, and omega-conotoxin GVIA, a selective N-type channel blocker, abolished the induction of associative LTD. 8-hydroxy-2-dipropylaminotetralin (OH-DPAT), a 5-HT(1A) receptor agonist, inhibited postsynaptic Ca(2+) influx through N-type Ca(2+) channels, without affecting presynaptic transmitter release. OH-DPAT also inhibited the induction of associative LTD, suggesting that the involvement of N-type channels makes synaptic plasticity accessible to modulation by neurotransmitters. Thus, the modulation of N-type Ca(2+) channels provides a gain control for synaptic depression in hippocampal pyramidal neurons.

Effect of kainate on the membrane conductance of hilar glial precursor cells recorded in the perforated-patch configuration.

The effects of kainate on membrane current and membrane conductance were investigated in presumed hilar glial precursor cells of juvenile rats. The perforated-patch configuration was used also to reveal possible second-messenger effects. Kainate evoked an inward current that was accompanied by a biphasic change in membrane conductance in 69% of the cells. An initial conductance increase with a time course similar to that of the inward current was followed by a second delayed conductance increase. This second conductance was absent in whole-cell-clamp recordings, suggesting that it was mediated by a second messenger effect. Analysis of the reversal potentials of the membrane current during both phases of the kainate-induced conductance change revealed that the first conductance increase reflected the activation of AMPA receptors. Several lines of evidence suggest that the delayed second conductance increase was due to the indirect activation of Ca2+-dependent K+ channels via Ca2+-influx through AMPA receptors. (1) the delayed second conductance increase was blocked by Ba2+ and the reversal of its underlying current was significantly shifted towards EK+, suggesting that it is due to the activation of K+ channels. (2) The delayed second conductance increase disappeared in a Ca2+-free saline buffered with BAPTA, indicating that it depended on Ca2+-influx. (3) Co2+, Cd2+ and nimodipine failed to block the delayed second conductance increase excluding a major contribution of voltage-dependent Ca2+ channels. (4) The involvement of metabotropic glutamate receptors also appeared unlikely, because the kainate-induced delayed second conductance increase could not be blocked by a depletion of the intracellular Ca2+ stores with the Ca2+-ATPase inhibitor thapsigargin, and t-ACPD exerted no effect on membrane current and conductance. We conclude that kainate activates directly AMPA receptors in presumed hilar glial precursor cells. This results in a Ca2+ influx that could lead indirectly to the activation of Ca2+-dependent K+ channels.