| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2002: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2001: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
We have been studying the long-term potentiation (LTP) of synaptic transmission in visual cortical slices mainly by recording extracellular field potentials (FPs). However, the FPs can be potentiated when long-term depression (LTD) of inhibitory synaptic transmission takes place. In fact, we have found the LTD of IPSP induced by repetitive firing of postsynaptic neurons. The LTP of FPs we have investigated may results from the LTD of IPSP. Therefore, we investigated this LTD using whole cell recording techniques combined with an IR-DIC video mycroscopy. To test whether the LTD expression is postsynaptic or presynaptic, we conducted whole cell voltage clamp recordings in the present study. Visual cortical slices (300 μm thick) were obtained from the brain of Sprague-Dawley rats at postnatal 20-30 days. After a suppression of excitatory transmission by NMDA and non-NMDA receptor antagonists, IPSC evoked by layer 4 stimulation was recorded from layer 5 pyramidal neurons held at -70 mV. Thirty depolarizing voltage trains (+70 mV, 20ms, 20 Hz for 5 s) applied every 10 s induced LTD of IPSC in which the amplitude of IPSC decreased to 75% of that before the depolarization pulses. This reduction was due to a decrease in IPSC conductance while the reversal potential of IPSC demonstrated no change. Current responses evoked by iontophoretically applied GABA also reduced in amplitude after LTD induction. In the presence of tetrodotoxin, the depolarization pulses induced a reduction in the mean amplitude of miniature IPSCs. On the other hand, paired-pulse ratio did not change after the LTD induction. These results suggest that the expression site of LTD is, at least, partly postsynaptic.
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