British Journal of Anaesthesia, Vol 82, Issue 4 603-608, Copyright © 1999 by The Board of Management and Trustees of the British Journal of Anaesthesia
P. J. Hancock and J. A. Stamford
In addition to being a general anaesthetic, ketamine is a recognized drug
of abuse. Many, if not all, drugs of abuse have been shown to increase
dopamine efflux in the nucleus accumbens (NAc). As ketamine is optically
active, we examined if its actions on dopamine efflux in the NAc were
stereoselective. Slices of rat NAc were superfused with artificial CSF at
32 degrees C. Dopamine efflux was evoked by electrical stimulation (1 or 20
pulses, 100 Hz) and measured using fast cyclic voltammetry. (+/-)-Ketamine
100 microgramsmol litre-1 increased dopamine efflux (to mean 174 (SEM 17)%
of control, P < 0.05) and slowed dopamine uptake half-time (T1/2) to 164
(17)% of control, as did (+)-ketamine 100 microgramsmol litre-1 (efflux 236
(16)% (P < 0.001); uptake T1/2 177 (25)% (P < 0.05)). The (-)-isomer
was inactive. The effect of (+)-ketamine on dopamine efflux did not
correlate with its action on dopamine uptake. (+)-Ketamine increased
dopamine efflux on single pulse stimulation but to a lesser extent than on
20 pulse trains (P < 0.05). (+)-Ketamine was unable to block the
inhibitory effect of quinpirole on single pulse dopamine efflux. Neither MK
801 10 microgramsmol litre-1 nor metoclopramide 1 microgramsmol litre-1 had
any effect on dopamine release after short train stimuli (20 pulses, 100
Hz). We conclude that the (+)-isomer is the active form of ketamine and
increases NAc dopamine efflux not by block of dopamine uptake;
autoreceptors or NMDA receptors, but by mobilization of the dopamine
storage pool to releasable sites.
LABORATORY INVESTIGATIONS
Stereospecific effects of ketamine on dopamine efflux and uptake in the rat nucleus accumbens
Neurotransmission Laboratory, Academic Department of Anaesthesia and Intensive Care, St Bartholomew's and the Royal London School of Medicine and Dentistry, Alexandra Wing, Royal London Hospital, Whitechapel, London E1 1BB, UK
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