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Neurotransmitters: modulators, transporters and receptors; Excitatory amino acid receptors: structure, function and expression; NMDA receptor; Mg2+ block; Ca2+ influx; Transgenic mouse; Tet-System
Abstract:
High Ca2+ permeability and its control by voltage-dependent Mg2+ 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 small alpha, GreekCaMKII promoter to drive tTA-mediated tetracyclin 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 Ca2+ permeability and voltage-dependent Mg2+ 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.
