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Dynamics of neuronal assemblies are modulated by anaesthetics but not analgesics

Published online by Cambridge University Press:  01 July 2007

T. F. T. Collins ,
E. O. Mann ,
M. R. H. Hill ,
E. J. Dommett  and
S. A. Greenfield
T. F. T. Collins
Affiliation:
Oxford University, Department of Pharmacology, Oxford, UK
E. O. Mann
Affiliation:
Oxford University, Department of Physiology, Oxford, UK
M. R. H. Hill
Affiliation:
Oxford University, Department of Pharmacology, Oxford, UK
E. J. Dommett
Affiliation:
Oxford University, Department of Pharmacology, Oxford, UK
S. A. Greenfield*
Affiliation:
Oxford University, Department of Pharmacology, Oxford, UK
*
Correspondence to: Susan A. Greenfield, Department of Pharmacology, Oxford University, Mansfield Road, Oxford, OX1 3QT, UK. E-mail: susan.greenfield@pharm.ox.ac.uk; Tel: +441865 271852; Fax: +441865 271853
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Summary

Background and objective

Analgesics and anaesthetics have diverse synaptic actions that nonetheless have a common net inhibitory action on neuronal discharge. It is puzzling, therefore, that these two classes of compounds have fundamentally different affects, one blocking pain and the other consciousness. Indeed, beyond the isolated synapse, little is known of the larger scale mechanisms that mediate actual function, for example, transient neuronal assemblies. It was hypothesized that the two classes of drugs might have, respectively, differential effects on transient activation of these assemblies of neurons working together.

Methods

Hippocampal tissue from juvenile Wistar rats was used for in vitro optical imaging with voltage-sensitive dyes and simultaneous field potential recordings. The response to paired pulse stimulation of the hippocampus was recorded in the presence and absence of two types of analgesic (morphine and gabapentin) and two types of anaesthetic (thiopental and propofol).

Results

Optical imaging and electrophysiology used in parallel yield quite different results. Most consistently, the imaging technique was able to detect an enhanced period of activation following anaesthetic, but not analgesic application. This effect was not readily seen from electrophysiology field potential recordings.

Conclusions

These findings suggest that, irrespective of the effects of the two drug classes at a synaptic level, the dynamics of transient neuronal assemblies are modified selectively by anaesthetics and not analgesics.

Keywords

ANAESTHETICS INTRAVENOUS, thiopental, propofolANALGESICS, morphine, gabapentinHIPPOCAMPUSPHARMACOLOGYRATS
Type
Original Article
Information
European Journal of Anaesthesiology , Volume 24 , Issue 7 , July 2007 , pp. 609 - 614
Copyright
Copyright © European Society of Anaesthesiology 2007

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