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NMDA receptor-dependent long-term synaptic depression in the entorhinal cortex in vitro
Saïd Kourrich1, C Andrew Chapman
1Center for Studies in Behavioral Neurobiology, Department of Psychology, Concordia University, Montreal, Quebec H3G 1M8, Canada.
Journal of Neurophysiology
|March 4, 2003
Summary
Long-term synaptic depression (LTD) in the entorhinal cortex requires intense, paired-pulse stimulation. NMDA receptor activation is crucial for LTD induction, but GABA(A) or mGluRs are not necessary.
Area of Science:
- Neuroscience
- Synaptic Plasticity
- Olfactory System
Background:
- The entorhinal cortex (EC) is vital for memory encoding, receiving olfactory input from the piriform cortex.
- Synaptic plasticity in the EC-hippocampal pathway influences olfactory information processing and memory.
- Previous in vivo studies showed long-term synaptic depression (LTD) induced by paired-pulse stimulation, not low-frequency stimulation.
Purpose of the Study:
- To investigate the specific stimulation parameters and neurotransmitter receptor requirements for inducing LTD in the rat EC in vitro.
- To compare the effectiveness of low-frequency versus paired-pulse stimulation for LTD induction.
- To determine the role of NMDA, GABA(A), and mGluRs in EC LTD.
Main Methods:
- Field potential recordings were used to measure synaptic responses in rat EC slices.
- Low-frequency (1 or 5 Hz) and repeated paired-pulse (30-ms interval) stimulation protocols were applied.
- Pharmacological agents, including NMDA, GABA(A), and mGluR antagonists, were used to assess receptor involvement.
Main Results:
- Only repeated paired-pulse stimulation induced lasting LTD in the EC.
- LTD induction was effective in vivo with low-intensity paired-pulse stimulation only when GABA(A) receptors were blocked.
- In vitro, LTD required increased stimulation intensity or pulse-pair number and was blocked by an NMDA receptor antagonist but not by GABA(A) or mGluR antagonists.
Conclusions:
- LTD induction in the rat EC in vitro is dependent on high-intensity, paired-pulse stimulation.
- NMDA receptor activation is essential for EC LTD.
- GABA(A) and mGluRs are not required for LTD induction in the EC under these experimental conditions.