[Abstract Title]. - Society for Neuroscience

Neurosurg., Univ. of New Mexico Sch. of Med., Albuquerque, NM; 3 Dept Mol Neurobio, Tokyo
Univ. Pharm., Hachioji, Tokyo, Japan
Abstract: Extra-synaptic NMDA receptor (NMDAR) -mediated plateau potential can be induced
either by synaptic stimulation in the presence of glutamate transporter antagonist TBOA or by
iontophoresis of glutamate in hippocampal CA1 pyramidal neurons. To investigate if the
NMDAR-mediated plateau potentials is accompanied by a rise in [Ca 2+ ]i, we performed wholecell
recordings and Ca 2+ imagings simultaneously from single CA1 pyramidal neurons in
hippocampal slices. Neurons were loaded with Ca 2+ indicator fluo-4 (100κM). NMDARmediated
plateau potentials were induced by repetitively stimulating Schaffer collaterals or by
applying glutamate iontophoretically in the presence of 10κM CNQX and 50κM DL-APV.
Substantial increase in [Ca 2+ ]i accompanying the plateau potential was detected both at the
dendrite and the soma. When TBOA was present, a slow rise in [Ca 2+ ]i was detected near the
soma after the end of the plateau potentials. After adding Cd 2+ and antagonists for metabotropic
glutamate receptors, most of the Ca 2+ rise was suppressed, leaving small but substantial Ca 2+ rise
in the dendrites. This Ca 2+ elevation was abolished by applying 30κM 5,7-dichlorokynurenic
acid, an antagonist for the glycine binding site of the NMDAR. Our results show that the
NMDAR-mediated plateau potential is accompanied by substantial Ca 2+ elevation mainly due to
Ca 2+ entry from voltage-gated Ca 2+ channels and partly due to Ca 2+ entry from NMDAR
channels.
Fig. Left, Fluorescence image of neuron filled with a Ca 2+ indicator fluo-4 (Scale bar, 10κm).
Right, Spatial distribution of iontophoretically-induced Ca 2+ elevation in the presence of 10κM
CNQX, 50κM DL-APV, 100κM Picrotoxin, 10κM MPEP, 50κM LY367385 and 1κM
Tetrodotoxin. Ca 2+ signals was recorded from areas of the square written on Left image, (1-7),
and whole-cell membrane potential was recorded from soma, (bottom).