Effects of pethidine on central neurotransmitters: changes in the state of tolerance.

Cerebral concentrations of neurotransmitters: noradrenaline, dopamine, serotonin and GABA were assayed in male Wistar rats receiving either a single dose of pethidine, or a prolonged treatment with the drug (twice daily for 21 days, im), leading to tolerance development. In tolerant rats the GABA content in the cerebral tissue was increased, and the activity of serotonergic system (assessed from the changes in 5-hydroxyindoleacetic acid level and serotonin turnover rate) was augmented.