In vivo monoamine release during naloxone-precipitated morphine withdrawal.

There is much evidence from animal work suggesting that the release of noradrenaline (NA) in the brain increases during naloxone-precipitated morphine withdrawal, but the evidence in favour of changes in release of 5-hydroxytryptamine (5-HT) and dopamine (DA) is contradictory. Here we demonstrate, using in vivo microdialysis, that whilst there is a considerable increase (300%) in release of NA in hippocampus precipitated by naloxone in morphine-dependent rats, there is no change in the release of either 5-HT (in hippocampus) or DA (in nucleus accumbens). These results are consistent with suggestions that the symptoms of morphine withdrawal in rats are due primarily to an increase in central NA release.