Dynamics of neuronal assemblies are modulated by anaesthetics but not analgesics.
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.
Collins
T F T
TF
Oxford University, Department of Pharmacology, Oxford, UK.
Mann
E O
EO
Hill
M R H
MR
Dommett
E J
EJ
Greenfield
S A
SA
D000588:Amines / Q000494:pharmacology; D000700:Analgesics / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000818:Animals; D003509:Cyclohexanecarboxylic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004594:Electrophysiology / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005456:Fluorescent Dyes; D000077206:Gabapentin; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects*; D066298:In Vitro Techniques; D008856:Microscopy, Fluorescence / Q000379:methods; D009020:Morphine / Q000494:pharmacology; D009415:Nerve Net / Q000187:drug effects*; D015742:Propofol / Q000494:pharmacology; D011726:Pyridinium Compounds; D051381:Rats; D017208:Rats, Wistar; D009435:Synaptic Transmission / Q000187:drug effects*; D013874:Thiopental / Q000494:pharmacology; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D000588:Amines; D000700:Analgesics; D018686:Anesthetics, Intravenous; D003509:Cyclohexanecarboxylic Acids; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D005680:gamma-Aminobutyric Acid; D000077206:Gabapentin; D009020:Morphine; C050019:1-(3-sulfonatopropyl)-4-(beta)(2-(di-n-butylamino)-6-naphthylvinyl)pyridinium betaine; D013874:Thiopental; D015742:Propofol