TOLERANCE TO DIACETYL MORPHINE ANTINOCICEPTION - EFFECTS ON BRAIN-SEROTONIN

THE effects of 5 mg kg(-1) diacetyl morphine (DAM) on brain serotonin metabolism of rats were investigated following tolerance to the antino ciceptive effects of 2.5 mg kg(-1) DAM. Brain levels of tryptophan and 5-hydroxy indoleacetic acid (5-HIAA) were higher in the DAM-tolerant rats killed 24h after last daily administration of 2.5 mg kg(-1) DAM. Administration of 5 mg kg(-1) DAM produced less antinociception in DAM -tolerant than DAM-naive rats and increased brain tryptophan concentra tion in both tolerant and naive rats, 5-HIAA concentrations increased only in naive rats. Combined use of drugs interfering with brain 5-HT turnover along with opiates may be of future benefit for the treatment of chronic pain.