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Presynaptic Depression at a Calyx Synapse: The Small Contribution of Metabotropic Glutamate Receptors
- Source :
- The Journal of Neuroscience. 17:8137-8146
- Publication Year :
- 1997
- Publisher :
- Society for Neuroscience, 1997.
-
Abstract
- Synaptic depression of evoked EPSCs was quantified with stimulation frequencies ranging from 0.2 to 100 Hz at the single CNS synapse formed by the calyx of Held in the rat brainstem. Half-maximal depression occurred at ≈1 Hz, with 10 and 100 Hz stimulation frequencies reducing EPSC amplitudes to ≈30% and ≈10% of their initial magnitude, respectively. The time constant of recovery from depression elicited by 10 Hz afferent fiber stimulation was 4.2 sec. AMPA and NMDA receptor-mediated EPSCs depressed in parallel at 1–5 Hz stimulation frequencies, suggesting that depression was induced by presynaptic mechanism(s) that reduced glutamate release. To determine the contribution of autoreceptors to depression, we studied the inhibitory effects of the metabotropic glutamate receptor (mGluR) agonists (1S, 3S)-ACPD andl-AP4 and found them to be reversed in a dose-dependent manner by (RS)-α-cyclopropyl-4-phosphonophenylglycine (CPPG), a novel and potent competitive antagonist of mGluRs. At 300 μm, CPPG completely reversed the effects ofl-AP4 and (1S, 3S)-ACPD, but reduced 5–10 Hz elicited depression by only ≈6%. CPPG-sensitive mGluRs, presumably activated by glutamate spillover during physiological synaptic transmission, thus contribute on the order of only 10% to short-term synaptic depression. We therefore suggest that the main mechanism contributing to the robust depression elicited by 5–10 Hz afferent fiber stimulation of the calyx of Held synapse is synaptic vesicle pool depletion.
- Subjects :
- Patch-Clamp Techniques
Glycine
Action Potentials
Glutamic Acid
Stimulation
AMPA receptor
Neurotransmission
Receptors, Metabotropic Glutamate
Inhibitory postsynaptic potential
Receptors, N-Methyl-D-Aspartate
Animals
Cycloleucine
Receptors, AMPA
Rats, Wistar
6-Cyano-7-nitroquinoxaline-2,3-dione
Afferent Pathways
Neuronal Plasticity
Chemistry
Aminobutyrates
General Neuroscience
Glutamate receptor
Articles
Electric Stimulation
Rats
Metabotropic glutamate receptor
Synapses
NMDA receptor
Neuroscience
Calyx of Held
Brain Stem
Subjects
Details
- ISSN :
- 15292401 and 02706474
- Volume :
- 17
- Database :
- OpenAIRE
- Journal :
- The Journal of Neuroscience
- Accession number :
- edsair.doi.dedup.....8eeb8b32cc4929b9d44d0bdb85029af7