Volatile anesthetic effects on isolated GABA synapses and extrasynaptic receptors
S K Ogawa1, E Tanaka, M C Shin
1Research Division for Life Science, Kumamoto Health Science University, Kumamoto, Japan. sogawa@kumamoto-hsu.ac.jp
Neuropharmacology
|November 30, 2010
Summary
Volatile anesthetics differentially affect GABAergic transmission. Isoflurane and enflurane reduce GABA release at nerve endings, while sevoflurane impacts synaptic current kinetics.
Area of Science:
- Neuroscience
- Pharmacology
- Anesthesiology
Background:
- Volatile anesthetics are known to enhance GABAergic inhibitory transmission.
- GABA(A) receptors are crucial for inhibitory neurotransmission in the central nervous system.
- Understanding the specific effects of different volatile anesthetics on synaptic and extrasynaptic GABA(A) receptors is important for anesthetic practice.
Purpose of the Study:
- To investigate the differential effects of isoflurane, enflurane, and sevoflurane on synaptic and extrasynaptic GABA(A) receptor responses.
- To determine the impact of these anesthetics on GABA release and postsynaptic currents in hippocampal neurons.
Main Methods:
- Mechanically dissociated rat hippocampal CA1 neurons with retained nerve endings were used.
- Extrasynaptic GABA(A) receptor responses were measured using exogenous GABA application.
- Synaptic responses were assessed via miniature inhibitory postsynaptic currents (mIPSCs) and evoked inhibitory postsynaptic currents (eIPSCs).
Main Results:
- All tested volatile anesthetics enhanced exogenous GABA-induced responses concentration-dependently.
- Isoflurane and enflurane increased mIPSC frequency, while sevoflurane did not.
- Sevoflurane prolonged mIPSC and eIPSC decay times at clinically relevant concentrations; isoflurane and enflurane did so only at high concentrations.
- Isoflurane and enflurane decreased eIPSC amplitude and increased failure rate, suggesting reduced GABA release.
- Sevoflurane decreased eIPSC amplitude without affecting the failure rate.
Conclusions:
- Isoflurane and enflurane, at clinically relevant concentrations, primarily act presynaptically to reduce action potential-dependent GABA release.
- The volatile anesthetics exhibit heterogeneous effects on synaptic and extrasynaptic GABA(A) receptors.
- These findings highlight distinct mechanisms of action for different volatile anesthetics on GABAergic neurotransmission.
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