The effects of general anaesthetics on carbachol-evoked gamma oscillations in the rat hippocampus in vitro.
The effects of general anaesthetics and temperature on carbachol-evoked gamma oscillations in the rat hippocampal brain slice preparation were investigated. The frequency of the oscillations was found to be dependent on temperature in the range 32-25 degrees C, with a linear reduction in frequency from 40-17 Hz over this temperature range. The volatile anaesthetics isoflurane and halothane, and the intravenous anaesthetics thiopental, propofol and R(+)-etomidate caused a reduction in the frequency of the oscillations, in a concentration-dependent manner, over a range of clinically relevant concentrations. On the other hand, the intravenous agent ketamine and the "inactive" S(-)-isomer of etomidate had no significant effect on the oscillation frequency. The oscillations were markedly asymmetric over one cycle with a relatively rapid "rising" phase followed by a slower "decaying" phase. The decrease in oscillation frequency was due to an increase in the time-course of the "decaying phase" of the oscillation with little effect on the "rising" phase, consistent with the idea that carbachol-evoked gamma oscillations are trains of GABAergic inhibitory postsynaptic potentials and that the anaesthetics are acting postsynaptically at the GABA(A) receptor.
Biophysics Group, Imperial College of Science, Technology & Medicine, Blackett Laboratory, Prince Consort Road, London SW7 2BW, UK. r.dickinson@ic.ac.uk
R
R
Dickinson
S
S
Awaiz
M A
MA
Whittington
W R
WR
Lieb
N P
NP
Franks
D018681:Anesthetics, General / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects*; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects*; D066298:In Vitro Techniques; D009415:Nerve Net / Q000187:drug effects; D010277:Parasympathomimetics / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D051381:Rats; D012996:Solutions; D013696:Temperature; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D018681:Anesthetics, General; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D010277:Parasympathomimetics; D012996:Solutions; D005680:gamma-Aminobutyric Acid; D002217:Carbachol